#460002 - Restoration

[jbcollier]

I am NOT a suspension design expert but I do recall reading that the large rubber mount was used to cure some wicked high-speed handling traits.  There are HD versions of the mount available.  Why not ask Richard?  Just don't want your obit reading "Exited stage left, pursued by a Europa."

[Serge]

One thing that they changed from the early cars to the later cars was mounting the rubber to the inside of the chassis in stead of on the outside face. They did this because this changed the toe of the rear suspension and this cured some high speed handling issues. I've accounted for this change and the toe is easily set by adding or subtracting washers in this new setup.

Richard at Banks sells his own version of these spherical bearing mounts, so the inherent design is OK I think.


Serge

[jbcollier]

Richard's the man.  Just wanted to make sure.

[BDA]

Richard IS the man!

Jensen Motors used the same idea but a different implementation in their TCS race car for SCCA C Production. They added a bracket to the frame for the trailing arm attachment to give it double shear and modified the trailing arm to take a rod end at the leading end.

[EuropaTC]

Yes, now you mention it I remember the Jensen Motor's conversion. The disadvantage with their method is that it's a major mod on the arm and not so easy to go backwards should you decide you didn't like it.   I think it's ok for race or  track but not something I'd consider for a road car.  At least with Serge's idea it's just a case of bolting in the standard or polyurethane bush.

I suspect the reason there's so much rubber in the mounts is to reduce noise and vibration, I can't see any other reason why they'd use such a large bush when they'd know the amount of movement they'd get on the suspension arm. I guess it's all down to what you want the car for and how you drive it ?

Brian

[BDA]

Could be. My thought was that it was they got a good deal on a lot of them!  I never understood how they devised that. The bush in the trailing arm is oversized for the bolt that fits the rubber bush. 

The Jensen solution is technically better because that bolt is in double shear rather than single, but from the pictures, it looks like the range of toe adjustment is a lot smaller. I think Richard's/Serge's solution is better for a car that would be driven on the street for that reason as well as it it could be brought back to the stock configuration easier (except that Serge said he's going to drill out the bush in the trailing arm). I also don't think there is a serious problem with the bold bending so the practical difference is negligible.

[Serge]

There are some things that were brought to my attention that I will have to look into once it's all finished.

Firstly the reason for the big bush: When tightening the big bolt holding the trailing arm on, the rubber will expand a bit and grip the circumference of the big hole in the chassis. Apparently this will help to fix the bush to the chassis, because the two bolts holding the mount in wouldn't be strong enough on their own.

- Now, I'm not so sure of this, but it looks to be a reasonable explanation, anyone has any views on this?

The second thing that I need to be careful of, is that there are some shear strengths that will be going towards the circlip holding the bearing in. I'm not sure how much strength there will be applied in this direction, or how much this circlip can take.

- This we'll only be able to find out once the car is driving, and it could be an issue.


This is one of those times that I'm quite glad that all the modifications that I make are easily reversable. There are a lot of experimental pieces on this car and there will be some that will not work as well as intended.

Serge

[BDA]

I just checked the documentation on my old Lola T492 S2000 race car and the spherical ball joints on the upper and lower front A-arms were, as I thought, retained by circlips. A wide washer that allows enough misalignment in the ball joint on your set up, Serge, might be a good safety feature.

[EuropaTC]

  (edited/part quote)
Firstly the reason for the big bush: When tightening the big bolt holding the trailing arm on, the rubber will expand a bit and grip the circumference of the big hole in the chassis. Apparently this will help to fix the bush to the chassis, because the two bolts holding the mount in wouldn't be strong enough on their own.

- Now, I'm not so sure of this, but it looks to be a reasonable explanation, anyone has any views on this?

The second thing that I need to be careful of, is that there are some shear strengths that will be going towards the circlip holding the bearing in. I'm not sure how much strength there will be applied in this direction, or how much this circlip can take.

Hi Serge,

I'm not sure on the expansion theory because the bush has a steel insert which will limit the amount of compression on the rubber -  the big washers will nip it and then stop further compression/expansion.  My assumption why Lotus stipulate the thick large diameter washers either side of the rubber is to hold everything together should the steel insert disbond or pull free ?

I've never really thought too much about the loads in that area, my first guess is that it's mainly fore & aft during acceleration & braking along the axis of the car, which would place the two smaller bolts almost in shear.  A slight bending moment on the chassis given the angle, but I wouldn't have thought it enough to break the bolts, more likely to distort the thinner chassis section if anything.

I think your mod will be fine, your work is excellent and it all looks well engineered.  I have no idea about the security of the circlip, my thoughts would be to sandwich the joint either side with large washers, not enough to limit movement/adjustment, but large enough that should the joint fail, it won't all fall apart in similar vein to Lotus and the OEM rubber bushes.  (that would be rather upsetting if you were driving at the time     )

Brian

[EuropaTC]

I just checked the documentation on my old Lola T492 S2000 race car and the spherical ball joints on the upper and lower front A-arms were, as I thought, retained by circlips. A wide washer that allows enough misalignment in the ball joint on your set up, Serge, might be a good safety feature.

 

great minds think alike !  You must have posted that last comment while I was still struggling with the spil-chucker.....

[BDA]

  You didn't have a T492 also, did you?

[Serge]

And while you were all posting this, I was adding big penny washers to the mount! Great minds think alike?! If the circlip will break now (which doesn't look like it would happen, there isn't any flex), the radius arm won't fall off.

Thank you all for your thoughts on this subject, I'm hoping everything will work out fine, if not, time will tell.

Serge

Edit: BDA, the owner of #460040 (going to be restored soon) here in Belgium does have a T492! As well as a Lotus Eleven, Elise S1, R340 and some other cool stuff! I'll try to make some more pictures and video next time I visit him or he comes to see me.

[BDA]

Thanks, Serge! I'd love to see them. He sounds like a lot of fun to visit! It's been a long time since I had my T492 and I'm amazed at the prices they get for S2000 cars now - but in actuality, when you consider inflation, the prices aren't that bad.

[Serge]

I've edited my footage of the fabrication of the 'competition' radius arm mounts and made this short video:


https://www.youtube.com/watch?v=0Os40ns8NiI

Serge

[BDA]

Well done, Serge!! You're going to have a really sweet car when you're done!