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MG Midget and Sprite Technical - Diff Pinion Seal
|Before I put my back axle onto the car I added some oil to check for leaks and I see a slight leak from the diff pinion seal. It would make sense to change it while the axle is on the bench I guess. I assume these don't normally weep in use?|
Can anyone tell me the seal size as I would rather source it from a local bearing supplier?
Also, what is of concern is that the nut is going to be tight (this IS the 140 ftlb torqued nut, according to the manual). Suggestions on how to stop the flange turning would be welcome. I'm currently thinking of putting a couple of bolts in the flange and trying to clamp them in some way or putting a bar between them.
I've not worked on a diff before but I am aware there are all sorts of preloadings. Undoing the pinion nut to change the seal doesn't upset anything does it?
|midgetef 140 :)|
Nope seal shouldn't weep.
Seal is easy, and doesn't affect pre loading when you replace it as far as I'm aware -- as long as you don't also replace the crush spacers. But the man to tell you is Norm Kerr.
Don't know the seal size, but Sussex sell them
|It could do - the preload on the pinion is via a collapsible spacer between the two bearings. However, its coverage of changing the oil seal is more in line with that for early A series diffs which had a solid spacer and shims as it doen't comment on the importance of not collapsing the spacer any further and how to avoid that. |
So to paraphrase the MGB manual on this:
1. Remove brake drums (to eliminate drag for step 2)
2. Record the torque required to rotate the pinion
3. Remove and refit seal much as you would expect to do
4. Tighten the nut gradually until resistance is felt
5. Rotate the pinion a few times to settle the bearings
6. Measure the torque needed to rotate the pinion
7. Tighten a little more if required
8. Repeat 5,6,7 until a torque reading is achieved which is the GREATER of
(i) what you measured in step 2 OR
The manual further notes in bold type:
CAUTION: Preload build-up is rapid, tighten the nut with extreme care. If you exceed the target figure the diff must be dismantled and a new spacer fitted.
(But this is the same MGB manual which DOES list 135-140 lb-ft for the banjo wheel bearing nut!)
To stop the flange from turning I made s simple tool from a length of flatbar, with 2 holes to match 2 in the flange. It is necessary to nibble one side between the holes to get clearance for socket access to the pinion nut.
Not sure of the seal size off-hand sorry. I presume the local bearing supplier is very handy?
|I have a piece of angle iron with two holes drilled in it. I bolt it to the flange to stop it turning.|
What I would do is mark the pinion and the nut, so that when you tighten the nut, it is in the same relative position to the pinion. That way, you shouldn't upset anything.
|Mine was very simple - I obtained a long 3ft ? piece of steel flat about 60x10thick can't quite remember (or where it is now !), drilled two holes towards the edge and bolted to flange, marked the steel around the pinnion nut to give clearance for the socket - removed it and roughly ground the bar out and bolted it back up.|
Mounted bar in vice with diff attached, end of bar resting on bench to stop in rotating and removed nut, replaced seal - tap it in nice and square/ level and refit plates/ nut.
The one in the link is nice - just a bit more complicated.
|must learn to type faster !|
|I replaced a diff seal recently on my Midget. I did it with the diff in situ as I foresaw a difficulty in holding the diff steady on the bench whilst trying to undo the NUT. |
1 Jacked the car up.
2 I marked the position of the propshaft flange and diff flange so as to ensure they were reconnected in the same position.
3 Undid the prop and moved it out of the way.
4 Put some ramps under the rear wheels and dropped the jack to place the weight of the car on the wheels thereby preventing the wheels turning.
5. Marked the position of the NUT in relation to the diff casing.
5 Used a socket and a long breaker bar to turn the NUT. It was tough. Once it was loosened you need to count the number of turns of the nut.
6 Once the NUT is off, remove the diff flange and cover
7 Pick out the oil seal and replace with new one
8 Replace the diff flange and cover
9 Tighten the NUT back up the same number of rotations to the marked position.
Reconnect the propshaft.
10 Job done
Has been fine since.
|There seems to be conflicting written information about this one:|
Terry Horler ("Your Expert Guide") says replacing seal can affect preload. See your manual.
THe manual says (paraphrased) undo the nut, whip out the seal, bung in another , tighten it to 140. No "careful!" warnings.
Haynes: similar to official manual.
Bristow ("Restoring S&M"): again no warnings about preload but a very strong emphasis on "tight!".
Paul: wow that sounds complex! I'm not sure I am fully understanding that. Isn't the pinion always going to turn freely? I don't know whather there are fundamental differences between the two diff set ups but the s&M manual doesn't go to that level.
Neil: I can see that idea. This presumably makes sure that the compression length (is that about collapsing spacers?) is the same after as it was before. All ok unless the nut gets to that position without having to torque it up to the level suggested.
I hope when I look in the morning the oil drip may have stopped and the problem gone away!
Would be nice to know the seal size though!
|From my personal experience, re-tightening to 140 ft lbs on a used crush spacer can lead to over tightened pinion bearings (mine wore out and got noisy in about 10k miles, after very carefully torquing to 140).|
All of the other diff rebuild materials that I could find (Ford, Morris, GM), they all said, "never re-use a crush spacer, they are one time use only", so when my diff got noisy I took it back apart and realized they were right.
The only difficult part about replacing the pinion seal properly (with a new crush spacer) is getting your hands on a torque wrench that reads between 6 in-lb and 15 in-lb, but if you've got one of them it is super easy to get the pre-load right.
While you are in there, it is a good idea to replace the thrust washers on the sun/planet gears, and the pin, too, if it is worn (these do wear, leading to excess freeplay). Then your diff will be like new.
Some folks have had good luck by marking the nut position and then simply turning it back to the same spot. It might work, but if you've already got the diff out of the car, it is probably easier to do it right, than to risk having to do it again later, if it doesn't turn out.
The Midget manual instructions are the same as those for the B which had the solid spacer and shims. I have always assumed that this is one aspect they overlooked updating when the collabsible spacer was introduced. Certainly the B manual is referring to an identical set-up to the Midget when it issues the caution note, so it pays to take notice of it.
Following the procedure for the solid spacer - which is that outlined in the Midget manual - is likely to result in further crushing of the collapsible spacer and excessive pre-load on the bearings and thence premature bearing failure as per Norm's experience above.
Regarding the pinion turning freely, it doesn't (or rather shouldn't) The preloading of the bearings results in drag on them when you turn the pinion flange. This is the 4-6 lb-in torque referred to. I have fashined my flange retaining bar so that its weight provides the required torque. However another way of measuring it without the official tools is to wrap a piece of string round the flange and pull on it with a spring balance ... at a radius of about 1.5" 4-6 lb-in translates to 3-4lb pull on the string to get the pinion to move.
The prupose of the pre-load is simple: it better braces the pinion in place against the side thrust from its contact with the crown wheel. With no (or inadequate) preload the pinion would flop about a bit and result in wear and noise.
The MGB manual procedure is quite simple: Measure the torque needed to move the pinion (string and spring balance) before undoing anything, then when replacing do tighten a little at a time until the original trque is reached, or bit more if it was less than 4-6 in-lb.
However, the mark-the-pinion methods others have outline is a simple means of restoring it to its setting before the seal was replaced. What it missed compared with the B manual procedure is checking whether the required minimum preload has been reached. It's worth doing while you are there as over time the preload can reduce due to gradual wear in the bearings.
|I'd completely forgotten this. About a year ago I had a conversation with Moss about re-conning one of my spare diffs. I got great advice from the guy that does the rebuilds for Moss.|
He will definitely know the right way to do this.
Call him, he's very helpful, and Moss can supply everything you need.
Mick Pratt. Technical Support Moss Europe Ltd,
Tel: 020 8867 2083
|Norm/Paul: looked back at manual and as you say, it is a solid spacer that's shown. When was the solid replaced by the crush spacer? It is obvious when looking at an assembled diff which is fitted? If it were a solid spacer then retorquing would be fine but I can see the risks using an existing collapsible spacer.|
What would happen if, with te collapsing spacer, you deliberately kept below the 140 torque - say 100 ft lbs? In theory the spacer would stay as the existing length wouldn't it?
|That could work. 100 ft-lb is usually safe enough to not collapse the spacer further whereas 140ft-lb usually will.|
As far as I know at least all 1275's had the collabsible spacer.
It is worth checking the pre-load though. We had an issue last year with our K diff that took some while to track down as the symptoms were propshaft out of balance. It was diabolical to the point of scary. Three propshafts erbuilds and re-balances later and no improvement we were still scratching our heads when Arie gave us a tip-off that he'd heard a simliar thing that turned out to be the diff.
And yes, it was pinion bearing preload gone. It appears what happens is the spacer collapsed further under extreme load (in this case a decade of autotesting behind a K engine) which means that the flange nut has nothing firm to grip against any more. So inevitably it loosens off, which if bad enough gives that gross out of balance feel.
We chucked out the collapsible spacer and set it up with a solid one and shims to give better control in this respect. More work but problem solved.
I have come across other hard working diffs where the pinion had loosened off, but the symptoms had always been a sudden development of diff whine rather than no whine and severe vibration.
|Paul: I understand your advice now. I hadn't realised (doh!) that the preload talked about is actually a resistance in the pinion shaft rotating. I had expected it to be freely rotating!|
As you will have gathered, this is new to me, never having worked on diffs before. I am very reluctant to start poking about with the internals but the string trechnique to measure preload perhaps combined with marking the position of the nut, perhaps all combined with a bit of luck, might let me do it without stripping anything out!
|Good luck! It's reasonably straight forward once you understand it, but don't forget to remove the brake drums or they might contribute to the drag.|
|This doesn't help with the Pinion bearing, but it's good for replacing the thrust washers. I assume it's the same on a Spridget as for a B.|
Watch from 5min 15sec in, ignore the bad jokes, and it's not half bad. :)
|Interesting reading this as went through a crown wheel and pinion rebuild on my neighbours Morgan earlier in the year. I had to keep reminding him of the difference between the pinion rotation torque measurement and the torque to crush the pre-load spacer. The pinion rotation torque is very low and he made a tool based on a Ford tool which used a lever arm and adjustable weights but was checked with a spring balance of mine. The torque to crush the spacer is quite high, 140 ft lbs might be in the ball park, to achieve the intended low rotational torque of the pinion. Once you get close to the required pinion pre-load you have to go carefully as very little angular adjustment can produce quite an increase in pre-load. A number of good videos of the subject on youtube for those who look. Advice would be to do the diff rebuild out of the axle although in the Morgan case information was available about the pinion torque with the diff out of the axle and in including the half shaft bearing drag.|
|Differential Ring and Pinion Gear Setup for "just about any car out there" the guy says in the video.|
|Because the pretension is a relatively low figure, I can imagine half-shafts in or out has a significant effect. I think the MGB manual refers to the seal contributing 3 lbs in.|
THere is mention in the responses above to removing the brake drums. Does that assume the halfshafts are fitted? Is there a figure for measurement without half shafts does anyone know?
|I should think you would need to pull the halfshafts, too.|
|Very very interesting this thread.|
The text in the picture below is from Moss. In the text it refers to 11-13lbs of preload, WITHOUT the oil seal. This must be the same figure Norm refers to of 12lbs.
However, Paul refers to 4-6 lb-in. Am I right in thinking that the 4-6lbs, is an empty diff casing, with only the pinion gear installed?
If so, is the 12lbs figure, a diff with the ring gear assembly in place too, in which the additional resistance of the preload on the ring gear bearings, contributes to the overall the preload figure?
|I've just taken some measurements and find the the diff, with seal but without halfshafts (and with some oil, but not full by any means) takes about 1_1/2 lb in to turn it!|
That's very low by all standards so, what's the view on tightening the nut? My plan would be to gradually tighten and keep checking the rotational torque until I can get somewhere near the right value (6 or 7?).
There is no sideways or axial movement in the pinion shaft. The diff is in the axle casing at the moment so I can't see what's going on inside. When it was out a few days ago, before I had any issues, a cursory glance suggested it was ok and nothing on the road indicated otherwise.
I think that Moss info must pertain to a shimmed solid spacer rather than a collapsible one as you can hardly leave the oil seal out when doing up a collapsible one as you're supposed to bin it after one use so you can hardly do it up the take it apart to fit the oil seal.
|...... and the nut is TIGHT! With a socket and 300mm bar I can't move it to undo it. Now I know there is an ancient quote about levers and the world - but I only want to move a nut!|
|David: as it reads, it would seem to apply to the collapsible spacer. Once the spacer is collapsed to the right amount would backing the nut off fitting the seal and then CAREFULLY retightening it ensuring the previous torque is not exceeded, actually change things?|
|Graeme, yes but it's a big tight bugger of a nut and unless you are v strong you will need a 600mm to 900mm bar to move a 140lb nut comfortably. I use a 600mm but a 900mm breaker bar is a good choice if you are body mass challenged (eg whimp :0).|
|M McAndrew: you've been looking! I'm going to get the wife to have a go once she's back from the Foundry.|
|When I tried it with and without the seal (oiled), the difference was so small that I could see that it was easily ignored when checking the preload (and, as pointed out, it doesn't make any sense to have to take it back apart again, once the spacer is correctly compressed, just to install the seal after!).|
The reason why I tried it both ways was because it was so difficult to get the preload right, the collapsible spacers that I was getting were reaching the target preload at around 120 ft lbs, so I had to do it over again, a few times (with a new spacer each time, good thing they are cheap).
|Norm: just to help my understanding of all this:|
THe spacers collapsed at 120 - so did you find yourself overshooting the torque or was it a case of "its only 120; it should be 140, so I need to do it again"?
|So, ignoring any effect from the oil seal then, what's the correct loading figure?|
4-6lbs as per Paul, 12lb as per Norm/Moss, or the 6-7lb Graeme is going for?
|My 6-7 is based on the 4-6 ...... plus a bit since the 12 lbs in figure is somewhat higher so decided to err on the high side of the low figure. If I overcooked it I should still hopefully stop before I exceeded the 12. Scientific...nah, just erring on the hope of getting somewhere in between. As long as I can still turn it!|
(Measuring it is a bit hit and miss anyway what with stiction making a contribution. I went for the string round the pulley with a weight on then end. The good thing about this is that it always works in the right direction whereas an arm with a weight will have a reducing moment as the arm turns. I just put a collection of sockets in a dog poo-bag tied to the string. Unused of course!)
|Graeme, you asked "Once the spacer is collapsed to the right amount would backing the nut off fitting the seal and then CAREFULLY retightening it ensuring the previous torque is not exceeded, actually change things?"|
Once the crush spacer is under the right torque, it's shortened to a set length. If you then back off the nut, and then retighten it, in order to achieve the same torque, won't that compress the spacer even more? After all, it's designed to crush at a set torque.
But if you torque it, and mark the shaft and nut, then tighten back to the same mark, that should be the correct pre-loading, but wouldn't that be at a much reduced torque on the nut? And does that matter?.
|Lawrence: If it compresses at 140, then stopping at 130 ought to do the trick (easily said, of course).|
I also wonder whether it is "all or nothing". Once you have gone beyond the elastic limit and hit plastic flow then the compression is set in. But more stress will still cause progressive compression. It wouldn't be a case of:
no load (say) 75mm long
138 ft lbs 74.5mm
139 ft lbs 74mm
140 ft lbs 65mm
141 ft lbs 25mm
Once it has been compressed at say 140 then backing off and applying the 140 again wont change the length! Just don't overdo it!
That's my theory but it would be nice to hear from someone who has tried that. Perhaps the seals never fail - other than mine!
|The seals are notorious for failing. I have a big bag of them!|
|Text from the Bentley manual:|
"The pinion bearing distance piece is of the collapsible type. That is to say, when the pinion nut is tightened to the correct torque spanner reading of 135 to 140 lb.ft. the distance piece collapses to give the correct bearing preload of 11 to 13 lb. in. It will only perform this function once. Thus, when the pinion is reassembled a new distance piece must be fitted."
In my case, I was getting well over 15+ lb. in. from the pinion bearings before I got to 140 lb. ft. on the nut. I chose to go by the pinion pre-load, rather than by what the nut was saying. Maybe the distance pieces sold today are not exactly the same as the ones from back in the day?
So, I re-did it, creeping up slowly, and still over-shot it the second time, but the third time it came out spot on, because I had been warned about where to expect it.
The difference between 0 lb. in, and over 20, was just a few degrees. A real small margin, at least in my case.
|Does the preload actually reduce as the spacer collapses?|
|If the preload is that critical, then I would imagine it has to be accurately measured.|
How accurate is the torque wrench you are using to tigthen the nut? Has it been calibrated recently?
How accurate is the bar and weight method of measuring the preload?
Norm says, "Note that the force applied to the pinion should be measured when the pinion is already rotating (to eliminate any sticktion, or initial resistance to movement)."
So do you turn the pinion, and see if there is sufficient weight to keep it moving?
As I understand it, the preload only affects the bearings, and there are 2 shims to set the pinion gear against the ring gear. So if there was a little less preload than specified, how much would that matter?
Better a little less preload, than a little too much?
|Norm: you could almost manage without a torque wrench if you use pre-load as the criteria for the set up. In fact, if spacers are so variable then working to a tightening torque could be misleading because the torque is not the issue and could take your eye of the ball ie not watch the pre-tension closely enough.|
That's a good concept for me as my wrench stops at 100 lbs ft!
So, reading between the lines if I were to re-use the existing spacer and not disturb the setup other than replace the seal:
1) with the nut loose I will have no pre-load as it's all slack.
2) once the clearances are closed up (between spacer and bearings) the nut will tighten in a relatively small movement and pre-load will build. Because I am not "squashing" the spacer pre-load will build up more quickly than usual.
3) I will reach the point at which the torque equates to the original set-up torque (value not known) and any more tightening will restart the "squashing".
One thing which might be in my favour is the very low pre-load that I have (about 1.5lb in). I need to squash the spacer a bit more anyway.
That's the theory anyway.
Dave: so what did you do when you replaced the seals?
Dave: my understanding from what i have picked up in the post is that preload increases as the nut tightens. That is right....... isn't it?
|When I replace the seals, I just mark the nut and the pinion and then retighten to the same relative position.|
Yes, the preload will increase as the nut tightens, but I was wondering what happens to the preload as the spacer begins to collapse.
as the spacer is crushed, the bearings are pressed further and further into each other by the pinion nut, so the preload will continue to increase the more you crush it
|Norm: I wasn't sure whether the pretension was between the bearings or between the pinion gear and the ring gear (although had it been the latter I couldn't understand how the collapsing spcer make it tighter rather than looser).|
Would lower side forces on the bearings be seriously detrimental to their life? (Presuambly at least one in the pair is an angular contact roller bearing?)
|The pinion bearings are tapered roller type.|
Graeme, in attempt to answer your question: from the wording of the Bentley manual (quoted above), which substantially agrees with the other manuals that I've seen from other makers, the bearing pre-load is essential to differential life (gears and bearings). I can't say what life you'll get from a set that are installed too loosely, but I know from personal experience that too high will quickly ruin them.
|The pinion pre-loading, only refers to the pinion bearings, not the ring(crown) gear.|
I removed the diff cage from a spare diff today.
Prior to removing it, I was able to move the pinion gear teeth(rotate), a small amount between the teeth of the crown gear. (The backlash). Further rotation obviously also turned the crown gear and cage.
The bearings in the diff cage, are also pre-loaded. So if you're rotating the pinion shaft with the diff cage still in the diff case, then not only are you feeling the pre-load of the pinion bearings, you are also rotating the pinion shaft against the pre-loading of the diff cage bearings. The two pre-loads must be additive when you measure them this way.
Once the diff cage was removed, I could feel the resistance of only the pre-load on the pinion bearings. It definitely felt less, even though I haven't measured it.
So again I ask.
Is the 11/13 lbs figure for a fully assembled diff, and is the 4-6lbs figure, for the pinion bearings alone?
Assuming the original crush spacers were made to a tight tolerance, and are still made the same way, then presumabley, using a torque of 140lbs(ish) achieves the correct pre-load. However, Norm has already found that the spacers crush too much, at a lower torque than this. Hence, you have to set this as Graeme says, using only the measure of pre-load. Then, whatever that results in, is the accurate torque, which is not really worth knowing, because you don't know it in advance of crushing the spacer.
|Lawrence: no-one has made reference to taking measurements with the diff partially stripped down. There was a comment about the lower figure resulting from the whole unit "settling in" (my wording). Perhaps it's a bit like a pair of shoes - tight to start with but ease off with use!|
The pre-loading is easy to meaure using the string technique as suggested by Paul. The pinion body is 2" diameter so at 1" radius the maths is easy too!
|Graeme, I agree, no they didn't.|
I was trying to understand why there is a difference in the 4-6lbs quoted by Paul, and the 11/13 lbs quoted by Norm for the bearing pre-load.
If the lower figure is for a disassembled diff -- pinion shaft only, maybe that makes sense?
PS, I haven't got a spring balance.
|Just hang a few suitably weighted items in a small plastic bag on the end of the string until with a slight nudge the string unwinds. Weigh items on kitchen scale!|
|THe reference to 4-6 lb in is here (post by FRM):|
(suggests that with used components rather than new this would be the best you can get)
|Thanks Graeme, good thread that.|
Yup what FRM says makes good sense, so the 140ish torque figure is a bit meaningless if not replacing the bearings.
Also, Paul in that thread says the same as I did, about the extra rotational torque needed if turning the diff cage as well, in a completely assembled diff.
If the preload on the pinion bearings is required to keep the pinion shaft from moving back and forth in the diff casing, and it more than halves over time with wear, then -- if loose bearings add up to worn gears --- shouldn't you try to re-instate the correct preload on the existing bearings? Since they're are tapers, they must be adjustasble.
Or once the pre-load has been lost to that extent, are new bearings the only solution to avoid future wear on the CW and P?
|Sorry, I am out of town with intermittent internet access. (But though the access is poor, the back country roads are great!! And free of other traffic ... )|
The difference in pre-load figures:
The 12-ish lb-in figure applies when setting a diff up with new bearings etc. It is measure with only the pinion installed - no crown wheel or cage in place. Once the set-up is installed and gets a bit of mileage on, the pre-load gradually reduces. Hence:
The 4-6lb-in figure is what the (MGB) manual lists as a MINIMUM figure if replacing the pinion seal without stripping the diff and replacing bearings etc. From the manual method, this figure includes the seal and the diff cage, as it is referring to an assembled diff in the car.
What the manual actually says is to tighten to the existing preload (that's the mark-the-nut method) but if that pre-load is less than 4-6 in-pb then tighten it till that figure (4-6) is achieved.
On tightening the nut:
The feeling I have (though I hyave never taken measurements to investigate this) is the the highest load to collaps the spacer is that needed to collaps it initially. It feels that way, and it also seems logical as the straighter the side-walls the greater the resistance to buckling, more-or-less.
The spacer starts to buckle before the bearings are in contact. Once the bearing clearnce is taken up and some pre-load sets in, this will account for some of the effort going into the torque wrench. In an extreme case, if there is no spacer at all you can still tighten the nut to 140 lb-ft eventually. Poor bearings. (Don't ask how I know this bit! I plead old age and memory loss, I'm sure I put that bloody spacer in ... )
So yes, the spacer collapses before 140 lb-ft, but once there is also a bit of resistance from the bearings nipping together then the torque needed to further compress the assembly gets larger. usually, but not always, 140 lb-ft and the requisite torque figure on new bearings come up about together. But not always, as Norm pointed out, so I always do what he said - a bit at a time until the pre-load figure comes right. So yes, you could do that bit without a torque wrench.
On occasion, when in a hurry (imminent event) and being out of stock of the spacer and not having time for another to wing its way halfway round the world, I have recycled the spacer with a thick-ish shim (20 thou-ish) between it and the bearing. While this has proved perfectly OK in practice, my preference would be to fit another spacer if I possibly could. But it's a handy thing to know if you are desparate. (But not to save a few pence!!)
Lawrence - that last question is a good one, I've never been brave enough to find out as it's so much effort to do it all again I experiment only when I have no other option!
|Thanks Paul, that explains a lot, for me at least. :)|
|Just discussing this off the BBS. But I'd like the views of those here too.|
The 140Lbs quoted torque must be important other than just for crushing the spacer. It must also be about ensuring that the pinion flange doesn't fall off. It has no locking washer behind the nut, it has a spring washer, and isn't a LH thread. So isn't the crush spacer that tough, in order to allow you to get a very high torque on that nut, as well as controlling the application of pinion bearing pre-load?
If using a solid spacer, it's still 140lbs isn't it, not for the pre-load, as that's set by the length of the spacer, -- as in the front hubs -- but to ensure the nut stays done up?
|Paul: thanks mate for that clear explanation. I have found a long enough lever so now I can have ago. I can't ignore it unfortunately as the seal is leaking like a seive.|
I'm going to remove nut, replace seal and nip up nut to wahetever torque is required to get the 6 unit resistance on turning the pinion. Well that's the theory!
|Lawrence - Yes, it needs the torque for tightening purposes too. You may have seen in my comments above that after a decade of autotesting behind the K engine we had a collapsible spacer fail, and that led to the nut starting to unwind itself.|
The 140 lb-ft derives from the earlier solid spacer version, and is the same figure on the B series.
As per the discussion above, the figure when using a collabsible spacer is "about" 140 lb-ft ... the key thing is to have the right pre-load. Too much pre-load and you'll get failure as per Norm's experience (Norm: was that just the bearings that failed, or the whole lot?)
Too little and you'll end up with unwanted deflection between crown wheel and pinion.
If you get the pre-load below 140 lb-ft, then don't fret about it coming loose unless it's under the 100 lb-ft mark. If less than 100, I would renew the spacer. A bit more work, but ultimately less and cheaper than renewing the bearings and possibly the CW&P as well if the nut undoes itself.
Though having said that, due to the usual time constraints of an imminent event, when we found the K's little problem we ignored the bruised-looking wear pattern on the crown wheel & pinion (none in stock) and just fitted a new spacer with the gears set up to give the best contact pattern we could -promising to do it properly later. It turned out that (amazingly) it ran almost quietly - just a faint murmur. A year later it is still as quiet and this discussion has reminded me we have yet to do that!
|I have replaced the oil seal! But.......|
I have just heard that the seal should not be pushed right home into the recess as it can miss the end of the shaft..... and leak like a seive. If this is true then it is going to be another battle with THAT nut and 140 ft lbs again!
Advice and experience welcome!
|I just push the seal in till its flush with the outside of the casing, so can't confirm or otherwise whether further in is a problem.|
|It is capable of being pushed in another couple of mm. You would hope that it would be designed so the seal pushed against the stop (not unreasonable as a way of assembly) would still be in an acceptable position.|
A few years ago there was a posting here which points out this as a cause of leaks although no-one else has confirmed it. Having discovered this late in the day I am hoping to get confirmation one way or the other.
|I have stripped out the seal again and taken some measurements. Conclusion: the seal face must be flush with the diff face, not pushed into the housing. The latter would cause the seal to sit on the chamfer on the shaft and cause a major leak.|
We found the pre-load in the bearings could be reset using the old collapsible spacer if care is taken and provided it wasn't high in the first place (because there is no opportunity to reduce the pre-load once the spacer is "set").
We achieved this by repeatedly measuring the torque on the pinion shaft as the nut was tightened. There was no noticeable shaft torque until what must have been the original nut-torque was reached. At that point shaft torque increased quickly for very small movements in the nut position and the nut was taken about 30 degrees passed its original alignment to achieve 6 lb in pre-load torque. The original setting was low to start with so I guess there was a small further collapse of the spacer.
But it was TIGHT! Two people and a scaffold bar extention on the breaker bar needed to hold everything down and still deliver sufficient grunt on the nut. The diff was also installed in the axle casing which provided usefull handles to hold it all down!
I just hope, having taken it down again to check the seal, that retightening goes as well for a second time!
This thread was discussed between 20/10/2012 and 28/10/2012
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.