4CV rear suspension foibles

4cvgordini

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??? I suggest that R8/R10 style diagonal trailing arms do have a significant role in controlling toe changes. What makes you suggest otherwise?
 

4cvgordini

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Bloody editing time limit! Try this:

To John:
??? I suggest that R8/R10 style diagonal trailing arms do have a significant role in controlling toe changes. Even though the front mounts of the arms are rubber, that doesn't stop them having a constraining effect on toe movements & also, as Jahn claims, relieving stress loads on the trunnion bearings at the wrong end of a longish lever (thereby lessening wear & extending trunnion bearing resistance to toe changes).
What makes you suggest otherwise?
To Jahn:
The first thing I did to my first 4CV was lop a turn from the rear coils. The handling merits of the -ve camber thereby achieved outweighed the handling demerits of the increase in rear spring rate.
The second thing was to add toe control arms. In my case, the system used was pure leading arms &, as you note, this involves some geometric fight which was accommodated by rubber bushes at each end. Didn't stop them being notably effective though.
The only way of avoiding such compromise is to have a diagonal arm from a point directly in line with the trunnion with the pivot axis on the same line. In effect, such a set-up forms a wishbone together with the axle tube & has no geometric "fight" at all. Given how satisfactorily the crude pure leading arms work, such sophistication strikes me as over-thinking the problem.
 

JohnW

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1. I agree with Jaahn re early trunnions. The early ones chopped out, nylon or graphite-impregnated bushes were a very short term fix (the materials don't have enough compressive strength for the loads). I've been there. My bronze bushes have worked perfectly, with Molygrease, since 1991 (perhaps 8-10,000 km though, at most).

2. Regarding toe control.... If the trunnions are OK, the toe cannot change other than if the whole power pack rotates. They are rigid bearings, only allowing simple rotation in one (vertical) plane. A slight change of toe with suspension movement of course would result if the trunnion axis orientation isn't horizontal, but the trailing arms cannot shift one axle independently of the other - so more toe-in on one side would have equal toe-out rotation on the other side.

3. I'm not persuaded that the trailing arms do much to reduce wear. I've not heard of, or found on two sets of swing axles in my cupboard, wear on trunnion bearings from Dauphines. The Dauphine has pretty much the same engine/gearbox mount system as the R8/10, but the Dauphines don't have trailing arms. That isn't to say that the trailing arms aren't a good design but I really cannot see either that they are responsible for good trunnion bearing performance or how they can affect toe (in or out) on one side or the other given the constraint of unworn trunnion bearings.

4. The leading arm solution, with compliant rubber bushes to allow for the incorrect geometry, can only control slop in a badly worn trunnion as far as I can see. If the trunnion bearing is perfect, it can only allow movement at right angles to the axis of the trunnions and you'll just get compression on those trailing rubber bushes as the suspension works with two arcs of movement at right angles to each other. If they improve things on a 4CV (and I have no relevant experience) maybe they stop movement of the whole power pack, but I'd have thought the pretty firm bushes in the 4CV mounts would prevent this anyway, at least for normal driving. If you reckon they've improved handling Peter, I wouldn't argue with your direct experience, but I'd love to know how.

Always an interesting discussion. :)
 

jaahn

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Hmm 4CVG and John,
The times when I had my first 750s was when I was an apprentice and had no money, living away from home too. My only engineering was done at work by smuggling stuff in/out in my bag, and on the street or down at the servo car park where we hung out. So replacing a couple of trunion bushes was easy enough every now and again and cheap. Possibly bronze bushes would have been better but then I was not aware they were available. I did lop a coil or two off the rear springs at work.

But us Renault owners did look at the leading arms and with the benefit of a short education so far and observations realised that they were second best, at best, but you could get them at the wreckers. One person made up some leading arms that angled in onto the rear cross member but the details escape me now. I think there were relocations required. He always pointed out how much better it was but who knows ?? The 750s would leave a side valve Morrie or Hillman for dead in all respects, a Standard 10. Even a Berkley and a Gogo Dart which apprentices had as cheap cars then. Possibly equal to a VW. :rolleyes: I also had a motor cycle for cheap transport home. I walked to work.

:cool: So what was the point again ? Ahh the rubber bushes on the leading arms covered 'a multitude of sins' as they say. In this case allowing some give and take. But it was the sixties and generally cheap easy to fix cars to get around in were the norm. Racing or hooning was frowned upon by decent people !! But who had the money anyway. I joined a car club and had a bit of fun and learned a bit, met Murray Bingham and learned a bit more about Renaults and going faster too. He was the guru around here then.

But we all moved on with more knowledge and books and learning. But the R8 was a revelation, showing the direction to go. I had possibly destroyed all my 750s by then, but continuous repair did teach me a lot of manual skills. As I said I had met some slightly older guys who lived nearby and had served their apprenticeship with the local Renault, Citroen ++ dealer. They were helpful and offered advice and ideas and even parts to help. Particularly when I bought a Traction B15 that was cheap too !! Another story. :cautious:
Jaahn
PS the short 10 mins for editing is annoying. I always now do the editing before i send !!
 
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JohnW

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Hmm 4CVG and John,
The times when I had my first 750s was when I was an apprentice and had no money, living away from home too. My only engineering was done at work by smuggling stuff in/out in my bag, and on the street or down at the servo car park where we hung out. So replacing a couple of trunion bushes was easy enough every now and again and cheap. Possibly bronze bushes would have been better but then I was not aware they were available. I did lop a coil or two off the rear springs at work.

But us Renault owners did look at the leading arms and with the benefit of a short education so far and observations realised that they were second best, at best, but you could get them at the wreckers. One person made up some leading arms that angled in onto the rear cross member but the details escape me now. I think there were relocations required. He always pointed out how much better it was but who knows ?? The 750s would leave a side valve Morrie or Hillman for dead in all respects, a Standard 10. Even a Berkley and a Gogo Dart which apprentices had as cheap cars then. Possibly equal to a VW. :rolleyes: I also had a motor cycle for cheap transport home. I walked to work.

:cool: So what was the point again ? Ahh the rubber bushes on the leading arms covered 'a multitude of sins' as they say. In this case allowing some give and take. But it was the sixties and generally cheap easy to fix cars to get around in were the norm. Racing or hooning was frowned upon by decent people !! But who had the money anyway. I joined a car club and had a bit of fun and learned a bit, met Murray Bingham and learned a bit more about Renaults and going faster too. He was the guru around here then.

But we all moved on with more knowledge and books and learning. But the R8 was a revelation, showing the direction to go. I had possibly destroyed all my 750s by then, but continuous repair did teach me a lot of manual skills. As I said I had met some slightly older guys who lived nearby and had served their apprenticeship with the local Renault, Citroen ++ dealer. They were helpful and offered advice and ideas and even parts to help. Particularly when I bought a Traction B15 that was cheap too !! Another story. :cautious:
Jaahn
PS the short 10 mins for editing is annoying. I always now do the editing before i send !!
I still remember my first ride in a friend's R8. And then when we bought our own, just what a capable vehicle I realised it was (and is, come to think of it, albeit a bit dated now). I still enjoy it several times every week.
Possibly interestingly, the original Silentbloc bushes are still in the trailing arms after 57 years and 360,000 km. They locate the arms longitudinally and aren't very big. I doubt they are much stressed....

Yes re editing time! Still, I'm grateful we still HAVE Aussiefrogs.
 
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schlitzaugen

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Well, here's your data. Compare wear in the trunion bushings/bearings in the R8 after 360kkm to the ones in the 4CV after 10kkm. Would be interesting. I am sure the OEM design of the 4CV was "good enough" but I also have a suspicion it was not done with longevity in mind. Or not with the longevity we expected in the sixties at least, let alone today. The R8/10 and others have no such problems. As for toe changes and relative movement of the rear axle to the front (geometry) alignment changes, I think the car was light enough and had too little power to suffer from the side effects. Whatever little movement there may have been, could have been absorbed by the entire system (rubber mounts, etc) before the tubes moved in the trunions. Either way, something has to give and I guess the trunion bushings will eventually wear faster than the ones on a car with control arms.

Also keep in mind, a .1mm play at the trunion becomes a few mm at the wheel, which translates in a serious toe change. Probably not important as said above in the overall context of the car (mass, grip, power, etc.) but significant if you are used with modern handling (I include here the R10 and similar cars, not much younger than the 4CV).
 

JohnW

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Well, here's your data. Compare wear in the trunion bushings/bearings in the R8 after 360kkm to the ones in the 4CV after 10kkm. Would be interesting. I am sure the OEM design of the 4CV was "good enough" but I also have a suspicion it was not done with longevity in mind. Or not with the longevity we expected in the sixties at least, let alone today. The R8/10 and others have no such problems. As for toe changes and relative movement of the rear axle to the front (geometry) alignment changes, I think the car was light enough and had too little power to suffer from the side effects. Whatever little movement there may have been, could have been absorbed by the entire system (rubber mounts, etc) before the tubes moved in the trunions. Either way, something has to give and I guess the trunion bushings will eventually wear faster than the ones on a car with control arms.

Also keep in mind, a .1mm play at the trunion becomes a few mm at the wheel, which translates in a serious toe change. Probably not important as said above in the overall context of the car (mass, grip, power, etc.) but significant if you are used with modern handling (I include here the R10 and similar cars, not much younger than the 4CV).
Yes, that's pretty much what I was saying, and Jaahn. The early ones were poor regarding longevity, and I suspect mostly due to the materials available/used for the pins. The later ones are larger but probably a better grade of steel. My bronze bushes rotate only on the outside, so are bigger again.

But I will repeat, unless they are worn, they simply don't move in the trunnions. I am presuming that the swing axle themselves are perfectly rigid within the envelope of forces acting on them.
 

jaahn

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===

Also keep in mind, a .1mm play at the trunion becomes a few mm at the wheel, which translates in a serious toe change. Probably not important as said above in the overall context of the car (mass, grip, power, etc.) but significant if you are used with modern handling (I include here the R10 and similar cars, not much younger than the 4CV).
Hmm quite some years back 12-15 perhaps I drove a 750 'barn find' unrestored. It went OK but slow, however the wandering in a straight line scared me. Even in the back streets at 50Km it scared me and I declined to go faster on to the by-pass. I knew what the problem was and how easy it was to fix but nah not for me even then. I have driven newer better cars for too long to go back to that. As you say an R10 seems like a new car compared to that.
In the same vein from 30 years before I was offered a good EH Holden and test drove that, and was singularly unimpressed by everything about it and just walked away. I was driving R12s at that time.:rolleyes:
Jaahn
 

JohnW

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Hmm quite some years back 12-15 perhaps I drove a 750 'barn find' unrestored. It went OK but slow, however the wandering in a straight line scared me. Even in the back streets at 50Km it scared me and I declined to go faster on to the by-pass. I knew what the problem was and how easy it was to fix but nah not for me even then. I have driven newer better cars for too long to go back to that. As you say an R10 seems like a new car compared to that.
In the same vein from 30 years before I was offered a good EH Holden and test drove that, and was singularly unimpressed by everything about it and just walked away. I was driving R12s at that time.:rolleyes:
Jaahn
Yes, unless it is a late 750, you'd be very lucky to have acceptable trunnions. I have several sets of later swing axles and they are all unmarked on the pins or quite free of side play. I reckon they just got the steel right on the later ones, although the greater diameter can hardly hurt. The caps are too hard to drill with anything I've found!

The best solution to the old ones (now, that is) is to purchase from France a new set of needle rollers, which come in their new cap and with a seal on the outside, and get a hard steel bush machined up to press over the old pin and EXACTLY the right OD for the new needle roller set. If I'm ever unfortunate enough to need to address this again, that's what I'll do. Hope never though!
 

schlitzaugen

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Why do you need to drill the cap?

Carbide will go through any kind of steel you are likely to encounter including fully hardened tool steel. Not cheap, but if you need the job done, that's the way.
 

JohnW

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Why do you need to drill the cap?

Carbide will go through any kind of steel you are likely to encounter including fully hardened tool steel. Not cheap, but if you need the job done, that's the way.
Good question! Years ago, I had an idea of fitting grease nipples to the trunnion bearings but actually with their end seal, the caps seem to keep the needles clean and the light grease stays in place. I've just pulled a 60-year old one apart and it was perfectly clean, unworn and greased. I'm pretty sure it had never been touched from new.

It is engineering shop territory for me - drillling and threading. I think one pump from a grease gun every 5-10 years would do it.
 

schlitzaugen

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Not that hard to drill and tap. My suspicion (based on other similar car components) is that the outer layer is hardened but the inside is soft so once you're in, it should be easy. Carbide drill bit to punch through, chamfer hole and follow with threading size drill and finally tap. Carbide drill bits are expensive but they last and are the only thing that will cut through. Only needs steady hand so you don't break it. Sure, it's much easier on a lathe but for such a simple job not absolutely necessary.
 

JohnW

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Not that hard to drill and tap. My suspicion (based on other similar car components) is that the outer layer is hardened but the inside is soft so once you're in, it should be easy. Carbide drill bit to punch through, chamfer hole and follow with threading size drill and finally tap. Carbide drill bits are expensive but they last and are the only thing that will cut through. Only needs steady hand so you don't break it. Sure, it's much easier on a lathe but for such a simple job not absolutely necessary.
Thanks. Learn something every day. This time "threading size drill"!!
 

AlexB

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Thanks. Learn something every day. This time "threading size drill"!!

To save yourself from having to look up the correct size drill you can get a good quality tap&drill kit from Hare&Forbes
Put yourself on the mailing list and buy when they have their sale catalogue.

T019 - Metric HSS Hand Tap & Drill Set - 29 Piece​

HSS tapping drill bit : 2.5, 3.3, 4.2, 5.0, 6.8, 8.5, 10.2mm
HSS taps: (M3x0.5, M4x0.7, M5x0.8, M6x1.0, M8x1.25, M10x1.5, M12x1.75)

 

schlitzaugen

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Finding the right drill size for whatever thread is not hard. In fact el cheapo sets like that one is actually recycling imperial size drills as specialised sizes (for tapping etc) when a metric size is not in their suppliers' list.

And it works. I do that all the time.

But if you want to drill hard materials you need to know that those drills you buy are M2 tool steel (as opposed to carbide or other high grades tool steel). Which means it may not actually go through the hardened surface. I would actually guarantee it won't. M42 might go but M42 drills are more expensive than carbide (not because they are better but because they are are more difficult to make and less frequently used). The taps also come in various hardness and materials from carbon steel, tungsten steel and HSS, HSS Co and so on. I think you need to know what the material is before you decide which tap will work otherwise you might have surprises.

Another problem I have come against is that not all taps are created equal. Same material on paper but some cut, some break. Sutton is my go to company most of the time (mainly for local availability, but they also have decent machine taps).
 

pugwash

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would be interesting to know if the early trunnions had larger and fewer rollers i recall mine had quite substantial grooves in them were the roller had been hammering when hitting pot holes etc ,a larger number of smaller diameter rollers is going to spread the load ,and possibly have less tendency to branell [put dings in] the pivot PUGS
 

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would be interesting to know if the early trunnions had larger and fewer rollers i recall mine had quite substantial grooves in them were the roller had been hammering when hitting pot holes etc ,a larger number of smaller diameter rollers is going to spread the load ,and possibly have less tendency to branell [put dings in] the pivot PUGS
Dunno exactly, don't have any early ones with rollers. Substantial grooves is right!

Like the rear suspension tapered roller bearings on Citroen BX, Xantia and CX (?C5) it might be that they are too large to rotate sufficiently for the small angular movement of the swing axle. If they don't roll enough they may not lubricate properly. I forgot that. Not sure that the number of them would make much difference really but I guess it might.

It is a point load more or less, per roller and I don't think there could be a factor of as much as 2 different from small to largest pin diameter. The larger diameter pins would be likely to have more rollers even if their sizes were the same. The caps have the same OD for all the pin diameters.
 

pugwash

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more rollers off lesser diameter ,larger pin, same size outside diameter, was what i was thinking ,similar problem with rollers on rear suspension arms on Peugeot 205 306 405 limited movement of arm and shock loads ,
 

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Peugeot acquired Citroen in CX times. I wonder which rear suspension bearing design was the egg. Pleiades in Qld (hydraulic repair guru) told me some years ago that they fixed it with Citroen BX suspension by fitting good seals and installing a screwed plug and filling the bearing cavity with heavy oil. He reckoned that fixed the problem completely - lubrication assured. Suggests that shock loads maybe not the issue too, come to think of it. Interesting.
 

pugwash

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I drilled the trailing arms and fitted grease nipples on my 405 SRDT ,similar principal although it took a lot of grease to fill that cavity ,prose you only have to do it once ,
 
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