MG Midget and Sprite Technical Diff rebuild 2023. Chapter 2. BBS discussion at MG-Cars.net

MG Midget and Sprite Technical - Diff rebuild 2023. Chapter 2.

This continues the rebuild of my two 3.9 diffs. Both diffs, DIFF 1 and DIFF2, have new bearings. Diff1 needs the pinion preload setting, and possibly the pinion height reducing a tad (but may not when the oreload is correct). It also needs the cage (side bearings) preload increasing. Diff 2 needs crownwheel runout correcting, and pinion preload setting. Previously--, I wrote that my pinion rear bearing was a very tight fit. How tight should it be on the pinion shaft? The shaft is smooth, no score marks. Should I relieve either the shaft or the bore of the inner race? Willy replied--, That bearing is usually a tap on fit and to get it out again just gentle taps with the end of a hammer handle on the threaded end of the pinion and it should tap through ok. Just drop it in a bucket of hot water for a while or sit it out in the sun(if there is any there) and it'll drop straight on----If you think it's too tight you can polish the pinion shaft a bit to get the fit you need, it'll only be less than half a thou.-takes no time at all- don't overdo it-.

anamnesis

And this is where I'm at now. Oil seal removed from Diff1. I'm going to confirm this again, but having loosened the pinion nut, I found 1 lbins of turning torque, just to turn the flange through the oil seal. Which suggests I only had barely much more than that on the pinion bearings for preload. And interestingly (different numbers but same principle using a crush sleeve), reading my FORD official workshop manual for English diffs, -- -- it says this about pinion preload and the oil seal -- See picture. Sun's out. Going for breakfast in town.

anamnesis

And this is where I'm at now. Oil seal removed from Diff1. I'm going to confirm this again, but having loosened the pinion nut, I found 1 lbins of turning torque, just to turn the flange through the oil seal. Which suggests I only had barely much more than that on the pinion bearings for preload. And interestingly (different numbers but same principle using a crush sleeve), reading my FORD official workshop manual for English diffs, -- -- it says this about pinion preload and the oil seal -- See picture. Sun's out. Going for breakfast in town.

anamnesis

Good question Richard. The crush spacers feel pretty hard. I've found some suitably sized tubing on ebay (although I'd need to shorten it accurately), but it's described as drawn mild steel. As you ask, does that matter? If applying as much as 140lbft torque to it, perhaps it does. The other thing I notice is, the ends of the spacer are different id/od. Bigger o/d at the pinion gear end where is sits on a shoulder on the shaft. Smaller at the flange bearing end, where it must sit snugly against the inner race of the tail bearing. I wonder though if that's something to do with making it collapsible. Whereas a stright sided tube isn't designed to collapse. Anybody got a picture of a Spridget solid spacer? Willy? These are for a Triumph Stag.

anamnesis

14 pieces, 30 quid, including postage. I was a bit doubtful that such a 'cheap' set would be up to the job. But actually, it's excellent, and does the job easily. This is my old 4.2 pinion and bearing. I didn't want to chance my arm on my good 3.9s, until I knew what to expect. https://www.ebay.co.uk/itm/285130689861

anamnesis

Good question Richard. The crush spacers feel pretty hard. I've found some suitably sized tubing on ebay (although I'd need to shorten it accurately), but it's described as drawn mild steel. As you ask, does that matter? If applying as much as 140lbft torque to it, perhaps it does. The other thing I notice is, the ends of the spacer are different id/od. Bigger o/d at the pinion gear end where is sits on a shoulder on the shaft. Smaller at the flange bearing end, where it must sit snugly against the inner race of the tail bearing. I wonder though if that's something to do with making it collapsible. Whereas a stright sided tube isn't designed to collapse. Anybody got a picture of a Spridget solid spacer? Willy? These are for a Triumph Stag.

anamnesis

14 pieces, 30 quid, including postage. I was a bit doubtful that such a 'cheap' set would be up to the job. But actually, it's excellent, and does the job easily. This is my old 4.2 pinion and bearing. I didn't want to chance my arm on my good 3.9s, until I knew what to expect. https://www.ebay.co.uk/itm/285130689861

anamnesis

Yep, your word "unless", qualifies it. The collapsible spacer, when new, doesn't collapse until the torque is great enough to secure the nut, and the spacer is designed such as that torque tightness, occurs at circa 140lbft. You stop torquing it when bearing preload reaches the desired amount. With the solid, you vary the length of the spqcer with shims, until the preload is correct, and then tighten the nut to circa '140' lbft. Though from what I've now read, anything in excess of 120lbft is enough.

anamnesis

Interestingly satisfying/enjoyable, pulling old bearings off diff' cages, to recover shims. Lol.

anamnesis

Yep. UK. Ordered 09:01 Saturday 18th, got it 11:01 Monday 20th. Pretty good I reckon. Actually that previous link wasn't the supplier. I was lazy, and just posted the earlier link an example, as so many sell it. This is who I bought it from. https://tinyurl.com/bddubfea 3bay Item number 314268185235 Interesting also Dunstable. Suspicious that all the ad's for this set, appear identical too. But, fast delivery, and a good kit at a cheap price. No complaints here.

anamnesis

Fun putting a pinion bearing on. Good job when the wife's at work, I master in me own kitchen. 😄😄

anamnesis

I put the pinion in the freezer for about an hour. Bearing on the hob for about a minute. It dropped right on with a nice solid click/donk, as it hit the bottom. 😁 It was as easy as making tea. Lol

anamnesis

Anam, Out of intere and the spacer is designed such as that torque tightness, occurs at circa 140lbft. You stop torquing it when bearing preload reaches the desired amount. With the solid, you vary the length of the spqcer with shims, until the preload is correct, and then tighten the nut to circa '140' lbft. Though from what I've now read, anything in excess of 120lbft is enough.

David Billington

Yep the price is great Grey, but I can only say that now I've proved it. An equivalent branded kit is at least double (for an unknown brand), and 4 times for a well known brand. Even a single branded clamshell/knife puller is more than this kit. So I did wonder myself. However ebay is great for buyers, if you are careful what you buy, who from, and if you select items with a good catch all description. This is described as heavy duty. If it broke when I used it, I could have sent it back for a full refund, under not as described. But as soon as I opened the box, you could tell it is solid kit. Certainly *easily* good enough for 'home use'. David. Pinion tail bearing is NTN 4T M84548 Pinion head bearing is KOYO HI CAP M88010-N. What's hi cap? My guess is hi capacity. I was expecting matching brands. But I assume/hope it doesn't matter. And my pinion head shim is 0.122

anamnesis

'Heavy duty' is applied so often these days to things that aren't it's lost any real meaning in most cases IMO. The image is of an old 8" Lion brand G clamp I have which was made when things were more honest. Hard to read clearly but the text says 'light service clamp', I wonder what their heavy duty ones look like, the other side says drop forged steel.

David Billington

Yep, I agree Martin. This is interesting (to me at any rate). The topic of locktabs/washers and threadlock has been raised before. One picture is one of the bolts securing the crownwheel on my Capri diff. The other picture is of one of the bolts that fixes the disc to Spridget hubs. Reading the Ford manual, I discovered that these bolts are self locking. They are called 'place bolts' after the bloke that invented them. "AA Place bolt — The original Place bolt design invented by Charles Place in the 1950s. It features a symmetrical six-slot head with an undercut." https://wilsongarner.com/what-is-a-self-locking-bolt-and-how-does-it-work/ https://www.earnestmachine.com/blog/2018/02/02/locked-and-loaded I wonder why bmc didn't use them on the diff's as well as the discs.

anamnesis

Nice picture explaining it.

anamnesis

I think this has been posted before, but maybe some haven’t seen it! 🙂 Simon

S Holt

Answering my own question, this is the puller needed to remove diff cage bearings. You can buy it in Australia, and the US. But not here. Very useful. So in order to correct the backlash and preload, either I trash a set of new bearings, or I make a tool myself; assuming I can.

anamnesis

That doesn't look the same Martin. Needs to be a bearing puller, not a gear puller. Bearing pullers have longer feet. THE one in the small picture is in Oz, on ebay. https://www.ebay.co.uk/itm/252831917611 This one's in the US. A company called OTC. https://www.otctools.com/products/differential-bearing-puller

anamnesis

This *might* do it. But not as good as the 'foreigners'. On Ebay uk. Circa 20 quid inc postage. https://www.ebay.co.uk/itm/403709312105

anamnesis

How about an Ak47? Now that's a different approach. 😅 David, that sealey is the same, but branded version, of the one I listed for 20 quid. But as well as being branded, it's a good bit cheaper on ebay too. 16 quid inc postage. It might do, but it's the length of the claws/feet that decides it. https://www.ebay.co.uk/sch/i.html?_nkw=sealey+ak46080 I've got a grinder, drills, and a welder. I'm thinking, drill into the legs just above the feet. Insert and weld in a plain rod to sit on the feet, but longer than the feet. Then grind to shape to fit the notches in the cage.

anamnesis

This *might* do it. But not as good as the 'foreigners'. On Ebay uk. Circa 20 quid inc postage. https://www.ebay.co.uk/itm/403709312105

anamnesis

Have to ask Admin if he can sort it out. Meanwhile, on a visit to ESM Morris Minor workshop in Ticehurst, I asked how they remove the diff cage bearings. Previously, as I already knew, if changing them for new, the outer race is prised off, which gives access to the inner race, and then a simple 2 leg puller will do. Unfortunately (I happen to know) that same method is used by others, on new bearings to adjust the shims. The outer race is pressed back on after. Actually, if the balls are significantly harder than the race way (are they?), then it works ok, because the running surface if the outer race is unaffected. BUT, there's a better way. John at ESM showed me how he removes cage bearings. He's made a version of what I was thinking for a home made puller, that reaches the inner race and notches, without pulling on or damaging the outer race. He modified a knife/clam/splitter instead of a 2 leg puller, by welding strong teeth/feet to the bottom of two halves. It's neat and strong, and the two horizontal bolts keep the legs engaged. So if altering a leg puller instead, it would need a clamp around the legs to stop them spreading, and disengaging the teeth/feet.

anamnesis

Doh... cross post! For clarity I was referring to this type...

Malcolm

Thanks Willy, I'll try that. David, that definitely sounds like it would be the best way, and looking at the original bmc tool, would be essentially, much the same thing I think. Yes shame I don't have the means to do that. If you do it, patent it. Lol. But seriously, like Alan Anstead did with his roller clutch releases, it would create a demand, and you could make a few/a batch, and sell them on to people who need them if you were so minded. Meanwhile, this cheapy, with a bit of welding to strengthen and extend the feet inwards, might do it. Only circa 8 quid inc post on ebay. It has leg clamps already, and is described as use for bearing removal. If crap, cheap enough to not worry. https://www.ebay.co.uk/itm/284879013132 Meanwhile meanwhile, I only potentially need to remove one set of cage bearings, to shim them, because they have no preload. But I've just bought some 2 thou shim steel sheet. 6"×3". Enough for two external shims, and if careful two internal as well. Only £3.25. It cuts with scissors or a craft knife. So I'm going to make an extetnal 2 thou shim, and see what happens to the gear pattern. https://www.ebay.co.uk/itm/264292078489

anamnesis

Ah I think I understand now David. Mask the steel sheet, and disolve away the 'unwanted' stuff, to reveal the shim. Yep, as per pcb's. But as Willy says, decent scissors. You may laugh, but pilchards is what I say. Lol. The tin is coated with a white 'paint' on the inside. Open it up, strip off the external paper wrapper, and the white paint. It's about 5 thou thick. Enough for two external shims. And it cuts nicely with scissors. I made one shim. Too thick of course for my immediate needs. But I happen to like pichards too. 😅. Willy, I thought the benefit came from the GL *5*. And yep the 140 aspect also put me off, but you say in an 85/140, it isn't as thick. My understanding, which may be wrong, is that as these multigrades heat up, they do become thicker. Hence an 85/140, due to the added chemicals/polymers, when it gets hot, does become thick like a single 140 - which thins a bit as it gets hot. I thought that was the point. Btw. I should have said, I sorted my diff myself, with a fair amount of help on here, not least from Willy. 😁

anamnesis

VERY clever Willy. It works. What made you think of using spanners this way? It's GENIUS. So simple. So quick. You need to remove the two adjacent bolts to get the spanner jaws in. I happen to have the crownwheel off, but just those two bolts out would do. I used a couple of 13/16 spanners, but anything close will do, as long as they don't apply pressure to the outer race. I needed a bit of extra leverage and used rings. Who needs pullers anyway? I've said it before though, we all need a Willy. 🤣🤣.

anamnesis

Ok thanks Willy. think I get it now. I did find that once up to temp', the straight 140 was ok-ish, as it was thinner, and the drag more or less ceased. So if a hot multi 140, is like a hot straight 140, it won't be a problem. Right? And I can comfirm the spanners will work on the long side of the Diff too, without needing the clam puller as a base. Although it might be easier/better. I'll experiment and confirm. Beer cans here may all be ally now. I'll take a magnet to the supermarket and check. 😁

anamnesis

Thanks Willy. Great, ok for ally. I just wondered if it could be squashed, because it might be too soft, but glad to hear not. It's free shims all round then. I don't even have to buy the beers. The vagrant wino's and special brew drinkers round here, chuck their empties in the street. I'll collect a couple. 🤣🤣. Yep, that's what clued me in about the bearing not being fully seated. Dull sound with the hammer on the bearings until they seated. I use old bearings too, for the same reasons you describe. Yep, noted about not removing/reffiting the bearings too often. Making shims. Even with my old cheap ones, shims are easy to cut with scissors. You're right though David, it does leave a slightly ragged edge, but it's easily hammered flat, and a 2 thou shim feels almost as flimsy as tissue paper; as I've now discovered, so it's not going to damage the casing. Having fully seated my bearings, I need 2 thou each side to keep the same backlash and tooth pattern. Got one in one side, 'fairly' easily, but it stretched a bit, and I had to slice a bit of spare out at the top. And, as I think Willy or someone else said before, 2 thou crumples easily, once you've taken up the space and start compressing the bearings. The real 'crunch' came, when trying to fit the caps with a shim in both sides. They just kept crumpling more. I'll have another go tommorow using a g-clamp, to see if I can move the cage over a tad, enough to get the 2nd 2thou shim in. If not, then bearings off, and I'll cut a pair of internal 2 thou shims. It was worth the experiment with 2 thou externals though.

anamnesis

Lol Willy. I'm a regular Edward Scissor hands me. 😅😅😅. Ah yeah, so it was you. I was searching for what you wrote before about the difficulty with thin external shims. I remember now, the thin one needs to be behind a thick one, hence remove all the internals. Think I'll follow the advice. I'll just go straight to an additional 2 thou internal on each side. Much easier than faffing around trying to do the external, just for the sake of it. I've only had one of the outer pinion races out, in Diff 1, fortunately no burrs, and the other looks properly seated. This must have been interesting. "-- I can remember doing a diff in an ambulance --" Blimey Willy don't you even stop work when your sick? 😉

anamnesis

Long side. Nice an easy does it ---- 😁 2 versions. https://youtu.be/I6_ivUkCHWY And https://youtu.be/MZ9jbG9b3kw 😉😉

anamnesis

Thar she blows. Finish off with a couple of screwdrivers. 😅 https://www.socialandcocktail.co.uk/cocktails/screwdriver/

anamnesis

Not the prettiest internal shims you'll see, but not a beauty contest, and does the job. 😁 Both sides done, and the bearings back on. Pinion in with no spacer or oil seal. Tooth pattern for Diff1, much as it was when Willy said ok, but pinion a tad high. Runout less than 1.5 thou all round. Backlash for the cw/p on this diff is marked as 7 thou. It measures 6-7 all round. Maybe I'll see if I can drop the pinion height a little. Turns out, I quite like fiddling with diff's; now I understand it, and have the means to take them apart and put them back together again easily. Can't believe I'm saying this, but it's fun. Lol.

anamnesis

Spoke with esm morris again. They sell the shims to go with the solid spacer. https://www.morrisminorspares.com/rear-suspension-axle-propshaft-c87/rear-axle-propshaft-rear-suspension-c88/shim-outer-bearing-003-0-076mm-1g7261-p831303 But they don't sell the solid spacer; -- ATA-7046. Either you already have one, or you make one.

anamnesis

Hi Willy. My mistake. I meant to write 85/140 GL5 oil on order. The only 85/140 castrol I can find here is Castrol TRANSMAX Axle EPX 85W-140. It's sold in 5 litres. Circa 38 quid. Less than 8 quid a litre, but not sure I want 5 litres until I try it. So I bought Comma oil instead, as it was on special offer 8 quid for 1 litre It's a mineral not synthetic, so I guess from what you say it'll be a little 'thicker' than the Castrol, but not as gloopy as a monograde ep90. If I'll use it as a try it and see, and to flush out all the other used stuff. Then maybe buy the Castrol. And forgot to say, yep I did spend an hour or so to get sore fingers, lol, and take about 2.5 thou off the pinion washer. This is the pattern I got. Is it still a bit high? Anyway, it sounds good in the car. I'll run it for 6 months or so and see if the bearings are still good. With all the mucking about they've had, and having to guess a bit with the pinion preload new/used bearings, I'm half expecting them to start making noises. Hope not though. Diff 1 is set about 6 inslb. Time will tell. Yep, once you get your head around how they work, and even more when you actually do the job, it all becomes clear and way less complicated. But what also becomes clear is you need to be a bit patient and be preoared to do some things more than once, to get it right. It is indeed satisfying. I had a 1/2 bottle of Chianti last night to celebrate. 😆. I must be a glutton for punishment. My Capri Diff is a bit noisey. I paid someone 250 quid 7 years ago to rebuild it. It wasn't great, but I can live with it. Untill now. I just picked this up cheap, -- an additional 3.9 english diff. Out of an unfinished kit car project. No visible damage and turns freely. But no idea if the bearings are great or poor. I'll measure the preload and mark the teeth, and then bung it in the Capri to test it. Worst case, I now know how to fix it, and it's got adjusters, so even easier. Plus, the Ford workshop manual is brilliant, with good clear photographs, not drawings; and excellent descriptions. 😁. So indeed, a good result. Thanks Willy.

anamnesis

This thread was discussed between 19/03/2023 and 13/09/2023

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