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MG Midget and Sprite Technical - Front suspension bits
|Nearside front shock absorber now leaking. The standard bounce test now gives a slight extra bounce after bounce one. Its certainly not as good on the bounce test as the off side. No other play that can be detected in the nearside suspension so going with straight forward replacement with standard shock. Any advice as to who's or who's not to get much appreciated.|
Offside top trunion moves as compared to the king pin. (not play in the bush). Read up on archive and advice is shims. Looked up shims and not sure why there are shims apart from 'washer' effect for pivoting of kingpin. Some threads in the archive say simply to tighten up top kingpin nut until steering 'feels right' with joint tight. Is this a good approach or is it likely the shim could be gone and I get wear on the pin or trunion? Your contributions and descriptions of how the shims help and or what to look for in more detail for worn parts in this area would be much appreciated.
Looking at it I suspect that the grease I am now forcing in the front suspension probably forced all the crud out and shows up the wear in the joint.
|Dave Squire (1500)|
|Re-con shocks are very hit and miss, I find.|
If you want one reconditioned properly, you could try somewhere like Stevson Motors
Re top trunion.
When you tighten the nut on the kingpin, you basically clamp the kingpin between the bottom of the lower stub axle brass lined bush -- which should sit just proud of the stub axle, and the "thick" oilite washer, which should sit on top of the top of the top brass lined bush, which itself should sit flush with the top of the stub axle. The shims that sit on the shoulder of the kingpin, prevent you from making this clamping too tight. Without the shims, you would, and should, lock the kingpin, unless you left the nut loose.
As the kingpin wears into the lower bush, and the kingpin itself wears, play developes. You selectively remove the correct thickness of shims to compensate.
There shouldn't be room for an opinion on this. It's much the same as the front wheel bearings. The nut should be tight, and the shims set the pre-load.
You said. "Offside top trunion moves as compared to the king pin."
If your top trunion is moving and the king pin isn't, then the nut is loose. The trunion should be clamped hard onto the shoulder of the kingpin, with the shims ensuring the kingpin and oilite washer aren't clamped too tight.
1st thing to do is check that the nut is tight. I haven't got my book to hand, but do it up to circa 25/30lbs. If the stub axle moves vertically with reference to the trunion and kingpin, then remove shims until it doesn't, and there is a slight drag as you rotate the stubaxle. If removing all the shims still results in play, then you need a new kpin and or bushes. However, there is a way around this too. But that's another tale, and a bit tricky -- although not that tricky, but I bet controversial, for most folks around here. :).
|Following from my last post.|
Trunion nut 40lbs. Actually just do it tight. Have you got a castle or a nyloc? If a castle, circa 40lbs and nearest hole for the pin will do.
Check the oilite washer, how does that look? The thinner it gets through wear, the more you'll need to de-shim. But these don't wear that much, if the system is greased regularly.
|Not sure that the answers I have read actually match your statement about the wear: |
"Offside top trunion moves as compared to the king pin"
The shim / oolite bush arrangement controls vertical play between the kingpin and the swivel hub. They should have no bearing (sic) on movement between kingpin and trunnion.
The Kingpin should be a close fit into the trunnion, held in place by the castellated (or nyloc) nut. This clamps the trunnion down tightly against the shim and the top step in the kingpin and this vertical clamping effect never wears as there is no relative movement between the parts. Similarly there should be no lateral movement between the two parts, so that bit doesn't wear either. Once assembled, the kingpin and the top trunnion should in effect act as one part, with no movement between them.
So, either the nut at the top of the kingpin is loose and just needs tightening, or you have wrongly identified where the movement is occurring. If tightening the nut restricts the hub carrier from swivelling, then the shims and/or oolite washer needs attention.
But maybe your problem is excessive movement between the kingpin and the swivel hub carrier, not the trunnion?
|So, looking at the parts on Moss, its probably not the kingpin I can feel movement against, its likely the swivel stub axel. Or I got it completely wrong (I will look again with new insight).|
Right I now know it works like this:
The kingpin does not rotate, it acts as a fixed shaft on which the hub carried rotates when the steering moves from side to side. It can't rotate because of the bottom end of the pin's design. (doh). (Unlike a moggie one that does rotate in threads and wears the threads at the top and bottom).
It could be loose nut of course, all my previously accepted OK assembly by PO has been woefully wrong.
OK so now the pre conceptions are out of the bone dome maybe I can diagnose it objectively this time.
Thanks guys, probably back tomorrow with better analysis.
|Dave Squire (1500)|
|The wear that you are likely to find is either:|
Vertical movement of the swivel hub carrier. Jack the car up under the chassis rail so that the wheel is off the ground and the suspension is not loaded. Then check for vertical movement in the hub. A lever at the base of the kingpin between the hub carrier and the lower A frame may help. Movement means attend to shims and/or oolite washer
Lateral movement between swivel hub and kingpin (check with suspension as before) If there is sideways movement then the only real solution is a new kingpin and swivel hub bushes.(press fit and ream) Slight wear here can sometimes be compensated for by removing one of the little shims on the kingpin, but its a bit of a dodge.
Check that top kingpin nut is tight first though!
|I thought that's what I said, but in slightly different words Guy?|
And since nobody asked, I'll tell you anyway.
If the oilite isn't worn, and the bottom radius on the kinping looks good, the shims are all out, the nut is tight, and you still have vertical movement of the stubaxle relative to the trunion/kingpin --
This can be resolved by pushing the lower bush down a thou or so in the stubaxle. They are often pushed in too far to begin with.
|Yes Lawrence, you probably did. But you forgot to copyright it ;-)|
Actually, like you, I was trying to get Dave to focus closer to determine where the actual movement was taking place, as between king pin and trunnion is not the most likely place for wear.
They don't normally wear at the base between the bottom of the lower bush and the kingpin radius as in normal use this contact isn't loaded. But certainly if the bush were pushed too far in then there would be too much vertical play. There is a round section O ring at the bottom as well, isn't there?
|Nope, no copywright Guy. LOL.|
Yup there is an o-ring there too, and quite a thick one at that. I've always assumed it's to retain(attempt) the grease.
I agree the loading is not often at the bottom. Mostly the thrust from the wheels pushes the swivel upwards onto the oilite, and the lower bush/kinping pin radius doesn't wear much. But it does wear to some extent. When the suspension unloads, there must be some reverse thrust, and with the state of our roads, that must be quite often.
If you take an assembley with vertical play, and insert a new kinpin, it often reduces or even eliminates the vertical play entirely. Assuming the pins are all made to the same spec (dangerous assumption these days perhaps), that must then be due to wear on the radius.
And then, re-using the older kinpin again, if the lower bush is pulled back out of the swivel a thou or so, the vertical play is also elliminated, so this must be due to wear in the lower bush. I've done this a lot over the years, and I've just done it to the midget.
|It's worth measuring the thickness of the oilite too. |
Any deep grooves will cause vertical play, so a new oilite can fix it too. I've got a new one (QH NOS kit), I'll measure the oilite thickness, and post it here.
Thinking on. I suppose an additional -- very thin -- oilite could take up play too. But a steel washer would be a bad idea, as it would grind away at the insides of the trunion, - unless it was fixed in place.
|Yes, I like the idea of pulling the lower bush out a bit. Although when I renewed mine they were very tight - I am not sure I could have shifted the bottom one without damaging the edges.|
I have an unused oolight washer here: 3.82mm / 0.152"
|You have both made significant enhancements to my understanding of the workings of the suspension and its component parts of a Spridget fellers. (Phew, thought I had a scrap on me ands then). And I am grateful for that.|
Interesting how the suspension is sort of in reverse to what seems logical. (that is its hanging from the road wheel rather than resting on it, ie the bottom of the pin is the fulcrum that is loaded with the cars weight). Therefore the top of the pin fittings (like the shim etc) tend to wear more than the bottom if maintained properly with grease. Now that's the sort of interaction I find helpful, sets the brain straight. Helps me understand and picture it better and therefore work out how to check and maintain it.
So: ;-) it reminds me of the discussion about wire wheel centres, do they hang from the top rim, or sit on the lower rim of the wheel?
This is where I exit left before you throw things at me.
PS as I have most of the bits for 2 cars I reckon I have some suspension bits in a box somewhere, so sort of no worries, just need to diagnose it right.
|Dave Squire (1500)|
|Shockers: usual advice is avoid reconditioned! Reputed to be unreliable. Moss (and others) sell new. I had two from them - they were so different that I had to take them back and find out which was ok and which was cr*p. They then provided me with one which matched the good one!|
Peter Caldwell in the States has the best reputation for rebuilds although they are exchange and it isn't really feasible to send the old ones back because of cost.
BTW you are supposed to change both (just to make it even more costly presumably).
|G Williams (Graeme)|
|best to change both sides so that both sides are balanced to each other as much as possible (within reason for these cars of course) and the steering and a lot of the braking is at the front|
there's a John Twist video on testing the lever arm dampers
I always wonder how many times has a unit been reconditioned in its life and how worn was it before each reconditioning and how much work was required and actually done at each reconditioning
just looking at one supplier - recon front damper £14.58 (exc. VAT), take off their mark up and it doesn't leave a lot of money to do the work and that without counting the fix and transport costs - true you can buy new dampers for that cost but not lever arm, same supplier charges £74.96 (exc. VAT)
|"Therefore the top of the pin fittings (like the shim etc) tend to wear more than the bottom if maintained properly with grease. "|
Dave, still not right I'm afraid. The shims don't, or shouldn't wear at all. They don't move because they are clamped tight on the king pin. At the top end, the only wear re vertical play, would be the oilite and possibly trunion recess that the oilite runs in. If there isn't much grease under the trunion, particles of metal from the trunion can embed in the oilite and wear the trunion. But my trunions are original and I don't have vertical play.
Guy. I've cut down an old king pin, and ground off the radius. I use it to drift the lower bush down. That prevents the bush edges getting damaged.
This thread was discussed between 19/05/2013 and 20/05/2013
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.