Lotus Elan

Solid Suspension

PostPost by: GeoffKing » Wed Jun 23, 2004 11:38 am

Would others share their experience, please? I have just fitted some high density poly suspension bushes to the front of my S4. When driving the car the suspension goes up but doesn't come down! The reason is because the bushes are clamped in positon by washers and the spring rate is not enough to overcome the resistance created by the sides of the bushes and washers. Ignoring the manufacturers torque settings eases the problem but it is still not ideal. Needless to say the handling is a nightmare and what I thought would be a good idea has gone the wrong way.
Has anyone got any suggestions, please?
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PostPost by: ngs » Wed Jun 23, 2004 12:14 pm

I have purchased some poly bushes for my Elan, although I haven't fitted them yet.
The manufacturer has supplied sachets of special grease which is to applied to the crush tube and between the end faces of the bush and the washers during assembly.
Perhaps this type of lubrication on the faces of your bushes would help with your problem.
Have you discussed your problem with the manufacturer of the bushes ?

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PostPost by: steveww » Wed Jun 23, 2004 8:42 pm

My S4 SE has polybushes installed. I noticed the same problem when I re-assembled the front suspension after fitting new dampers. After doing up the nuts to the specified torque I could not move the suspension arms by hand, even with my full weight behind it. I had made sure that all was well greased. I backed off the torque and all appears OK so far. I will run the car for a while and then re-check the fixings to make sure nothing has worked loose.

I would be interested to hear what the supplier has to say on this matter. The bushes were fitted by the DPO so I do not have any instructions etc.
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PostPost by: rgh0 » Thu Jun 24, 2004 11:47 am

The nuts and washers on the suspension spindle should only be clamping the inner metal tube of the bushes in place so they dont move on the spindles. The poly bushes should then rotate on their inner metal tube with moderate hand force on the suspension arm.

If you have to back off the nuts it suggests you are also clamping the poly bush and that the inner metal tube is not long enough.

Alternatively you can also have problems if your suspension or chassis is not perfectly straight and the suspension is causing the bushes to bind when the nuts on the spindles are all tightened. The lack of compliance on the poly bushes means they will not accept misalignment like the orginal rubber bushes would.

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PostPost by: GeoffKing » Thu Jun 24, 2004 12:47 pm

Gents, Thanks for your comments. You have confirmed my belief that the inner tube of the bush is not long enough as there is no clearance between the (flat) washer and bush when assembled. This is something I'll be taking up with the supplier. Meanwhile, anyone else looking to fit these bushes please take care as they came from a respected supplier. Thanks again.
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PostPost by: steveww » Thu Jun 24, 2004 2:50 pm

When I had the suspension in bits fitting the new dampers I did notice that the face of the inner metal tube was just below flush with the face of the plastic bushing. Thus when fully clamped up the plastic will be clamped between the washer and suspension, thus the extra friction.

Hmm looks like something else on the shopping list :angry:

Please keep me updated on your communications with the suppliers.
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PostPost by: steveww » Thu Jun 24, 2004 6:02 pm

I think I might have a solution here :huh:

The original bushes are just cylinders but the poly bushes are H shaped. A common hack for the original bushes was to put big washers on to stop the wishbones dislocating should the bush fail. This was fine with the original type as they were cylindrical as there is nothing for the washer to rub against. According to the original parts diagram and pictures Lotus did not have washers against the bushes just the lock nuts.

The poly bushes being H section have a large area of bush to rub against the large washer causing extra friction. Not being too happy with my current fix of less torque I am going to remove the big washers and go for specified torque. I figure that with the poly bushes being new and longer lasting, not to mention the low mileage done by my Elan this should be safe. It will also save some weight ;)

I hope to have this done for the weekend and I will post the results.
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PostPost by: type26owner » Thu Jun 24, 2004 7:52 pm

Has anyone got any suggestions, please?

Reinstall the rubber ones. The urethane ones are a sales gimmick that won't die off. As far as I know not a single automotive manufacturer supplies them on their cars. If it were such a good idea one would normally assume they would use this technology. The hassle they cause by requiring a precision fit (which you'll probably have to modify to get it right) and occasional lubrication (without grease fittings you'll have to disassemble to do it) does not justify the claimed miniscule reduction in suspension misalignment under loading. I'd be flabbergasted if in a true blind test anyone could actually tell a difference in the suspension misalignment degrading the traction assuming the binding effect of both bushing types was identical.
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PostPost by: rgh0 » Fri Jun 25, 2004 8:48 am

Keith

When I fitted poly bushes to my elan I thought I noticed two differences

1. Better stability under braking ( less toe out under brake loads)

2. Better stability in fast sweeping corners with the back end less "nervous" and not moving around as much.

Both of these effects relatively small and only really noticeable at race speeds and suspension loadings, not a real difference for road use.


In a plus 2 I think you may see more difference given the longer suspension arms. But I have not installed on my plus 2 so dont really know.


Steve
I would be cautious about removing the washers. The inner tubes on my bushes are the same diameter as the larger diameter section of the suspension spindle that sticks out about 15mm from the front towers. If you remove the washers you could get the wishbone moving back or forward by about 15mm as the bush slid over this section of spindle and the nut chews a hole in the bush at the opposite end. Ideally with the washers in place and the nuts torqued up on the inner tubes you should have a small clearance between the poly bush and the washer at each end and the bushes riding on the metal tube not the spindle near the towers if your suspension components and chassis are all dimensionally correct. The washers on the outboard ends stop each wishbone moving forward or backward under torque reaction and braking loads.


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PostPost by: steveww » Fri Jun 25, 2004 9:54 am

I have not found any mention of washers in the parts or workshop manual. Pictures I have seen of old (unrestored) front suspensions have not shown washers. However I know what you are saying. I am not sure how every stayed in place with out big washers but that appears how it was designed :huh:

I might try adding a regular plain washer between the bush and the big washer to stand off the poly from the big washer reducing friction. I will be rolling around under the car this weekend and will post updates as I go.
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PostPost by: mgb2010 » Fri Jun 25, 2004 11:29 am

My +2s did not have any washers fitted by lotus. I have just rebuilt the suspension (as part of a full rebuild), is it generally agreed that it is prudent to retro-fit washers when using rubber bushes? After talking to the guys at Kelvedon Lotus I replaced all the bushes with rubber, except the inner rear wishbones where I fitted poly ones.

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PostPost by: berni29 » Fri Jun 25, 2004 6:42 pm

Hi

I used polybushes on my +2 for the rear A frames, front arms and roll bar lower bushes. The reason that the big carmakers do not use them is probably because they increase the NVH (noise vibration harshness) for the vehicle. I found them to be very good, and if you use nylocs you can safely slacken them off a bit to get things moving. I also used copperslip as a lubricant.

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PostPost by: elansprint71 » Sun Jun 27, 2004 6:30 pm

Since changing my chassis a couple of months ago I have noticed that the front suspension, particularly on the left side does not want to move too much. I refitted the (Spyder) wishbones, which the PO had put some sort of plastic bushes in- they are white rather than the usual more colourful poly bushes. I have convinced myself that these bushes are not rotating on the tube through them, the ends appear to be flush, hence the clamping up effect.
I have a set of spare brand new Spyder top wishbones fitted with standard rubber bushes, I think that I'll give them a try.
Presumably the only way that the suspension was working previously was that the nuts were not tightened correctly thus the bush tubing may have been rotating on the bolts- not a good bearing interface!

Cheers,

Pete
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PostPost by: elansprint71 » Tue Jun 29, 2004 8:46 pm

Well I fixed it! I fitted the "spare" Spyder top wishbones with the rubber bushes and now have working front suspension again- what a difference.

The orignal wishbones with the poly bushes were evidently faulty- the inner steel bush was shorter than the poly bush so the whole thing was clamping tight when I torqued it up.

If you want a photo of the faulty parts e-mail me off list at

[email protected]

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PostPost by: steveww » Thu Jul 01, 2004 4:32 pm

Tried with some normal plain washers rather than the big penny washers and only slightly better. Decidied to save weight ;) and fit with some new nyloc nuts and no washers :o

Torqued up suspension to recommened figures IIRC 75Nm and I can now move suspension arms by hand :D

I am going to run it like this and keep an eye on the bushes to see how it goes.
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