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Is my chassis right? Rear radius arm mount shims - Suspension/Brakes/Wheels/Hubs/Steering/Geo - The Lotus Forums Jump to content
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Is my chassis right? Rear radius arm mount shims

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I have a bare chassis now and I'm worried it's out of whack, which wouldn't be a surprise given how abused it is. The crux of the matter is the two large shims I found between the the nearside radius arm mount [N/S on a domestic market car] and the chassis [pic].

There aren't corresponding shims on the offside. That can't be good can it? So scratching my head I wondered whether, given the engine mounting plates are integral to the radius arm ones, perhaps this part of the chassis is a-symmetrical and the two odd shims are by design. Sure enough the gap between the radius arm mounting plate and the engine mounting plate seems* different offside to nearside. I didn't do anything more than a quick and very rough measurement so I could be wrong.

Both sides did have four small shims each [washers] between the radius arm and it's mount.

Do you know what I'm talking about, and if you're with me, do you know what's going on?

 

Radius Arm Shims.jpg

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Think George is saying he also has a significant number of adjusment shims (washers) on the bolt between the radius arm and the mount - seems a lot in total.    Maybe just get a tape measure out and start measuring various fixed points on the chassis to make sure its symetrical

 

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The flat spacers are for toe-in adjust. They are available in 3 different sizes 0.9mm, 1.5mm and 6.0mm. I guess that means there could be quite a difference between the sides.

:) 

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Hi George. 

Both the small spacer washers and the square shim plates are for toe In/out geo adjustments, there may be varied amounts of each on either side, but there should be a maximum of three washers, any further adjustment must be made using shim plates.

Both should also be mounted between the chassis and trailing arm, so won't adjust engine mounts.

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Thanks lads. Knew they were for toe in, was hoping it wasn't uncommon to find the big ones on one side only. Well it looks like they are a pair of 1.5mm ones. There are four small washer shims on both sides too. So all in all not sounding good if I've an extra small on both sides, and the two large on one side.

Btw, before I stripped the car the rear wheels were visibly toed in. Well that's how they looked in relation to the body anyway.

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Hello George,

You have reason to be concerned as the asymmetry of the adjusting shims does imply something out of true. I went through an interesting exercise in sorting out a Spydersport tube-frame chassis for my Elan years ago when it was observed to be crabbing its way down the motorway. In that case it was due to the aft pair of the rear A-arm chassis pivots having shifted off-center during production. In your case one would want to consider how toe could become asymmetric at the aft end of an early Esprit by way of failed mounts in the powertrain as well as the rear links. If the car has been abused, or has high mileage you should also examine the u-joints and look for axial play (plunge) in the output (1/4) shafts at the transaxle where none should exist. Also look for play in the outboard axle bearings, again none should be found there.

Good hunting!

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I don't think it's a problem, in fact I had the same concerns when I did mine (3 spacers, 4 plates on the left, 2 spacers 2 plates on the right). It looks as though that's how my car left the factory.

Having never owned a car with such finite geometry adjustments it's a a bit of a learning curve, but I've found it a quite interesting topic.

IMO, I wouldn't worry too much, the whole thing will require re-setting up once the suspension is rebuilt.

Also there maybe something worth looking into, on the V8 it's not possible to access the head of the trailing arm pivot bolts with the engine in, so the spacer plates were redesigned in halves so they could be slid in behind the bush plate without loosening the bolts and without having to remove the trailing arm, the manual states that these will also fit 4 cylinder cars, if they're the same size on the S2 it would be a good upgrade.

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If in doubt why not get a 4 wheel laser alignment check.

The chassis were sometimes quite a way out from the factory. The galvanisation process made this worse. There is an article somewhere by a Lotus engineer who confirmed this was a problem right through the Esprit to Elan M100 until it was finally overcome by adopting aluminium for the Elise.

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I'd love to rock up to a laser alignment place with a bare chassis slung on my shoulder and ask them to align the wheels, dead pan 😂

Been searching for said article, no joy yet but other interesting things thrown up. I suppose whatever the case I just need to get it as close to symmetrical as I can. No pressure then.

 

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It's not only the chassis that causes the need for the shims, the arms are just as relevant. If the tube in the arm is slightly short/ off-set then that alters the shimming requirements. At an extreme, where shimming isn't enough then the mounting plate can even be moved to the other side of the chassis plate to get close to the desired setting.

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1 hour ago, GTK said:

I'd love to rock up to a laser alignment place with a bare chassis slung on my shoulder and ask them to align the wheels, dead pan 😂

Been searching for said article, no joy yet but other interesting things thrown up. I suppose whatever the case I just need to get it as close to symmetrical as I can. No pressure then.

 

Er, yeah might need to put it together first :)

I just remembered the galvanising distortion was mentioned by Oliver Winterbottom in his book "A life in car design".

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I swapped my S3 chassis after my crash to a new old stock and the shims required were completely different. 

I guess the only way to check if your chassis will be OK before you rebuild would be to check its geo by measuring against some standard - not sure that the workshop manual has this though?

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deadly conversation lads, has really helped. Steve was saying there should be a mx of three shim washers on the radius mount bolt, so if mine has four and still needed the two large 1.5mm shims to correct it then somehow the chassis is narrow, where toe in is concerned. I just remembered that the rear of the radius arm mount has been digging into the back of the engine mount plate, so perhaps the two big shims were partly to give the mount enough clearance?

Regardless I'm going to have to get some careful measurements, maybe try and find someone with a frame jig to put it on for reference. It's not like I'll be finding another one, so it has to be put right by hook or by crook.

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2 hours ago, GTK said:

Steve was saying there should be a mx of three shim washers on the radius mount bolt, 

There should be a reference to rear suspension setup in your scorched service notes, G-cars have the same set up but the max number of usable shim washers may vary on your S2.

Either way, I think you're worrying too much, as long as you can get it shimmed and plated to the required setting the jobs a goodun, Lotus didn't seem to care as long as the rear wheels ended up in the right place eventually 😀

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Yeah I've gradually started to suspect that attitude although I still don't want to believe it. I'd love to think I could get the setup symmetrical, I mean being pragmatic in the light of things that's probably far fetched, but let's see what I can uncover. 

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Agree with above except Olly Winterbottom should know what he is talking about as he worked at Lotus at the time dealing with the issue.

Its very likely that this problem is lessened these days with more modern methods and knowledge.  

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I'll do an interview with a [good] galv specialist, but I've already had a lengthy conversation with one when I was daydreaming about a spec for my two door Range Rover. Basically the potential for distortion when something is galvanised is down to how conscientiously it's done. The preheat time before the dip, and the cool down time after the dip are crucial, and made more difficult in the case of the cool down because on the one hand you ideally want to let it cool very gradually, but you have to wash it in certain chemicals soon after it emerges to finish the galv process. Not good for gradual cooling. So I could imagine Lotus [Winterbottom] would have experienced some distortion because they were dealing in a production run of chassis, and so less time would have been given each one. Whereas Dave you're chassis was a once time deal for the specialist, and you obviously had a good one.

So here's a video of my chassis strip and some detailed shots of the shims, and holes that have been cut in it. Unfortunately I'd already recorded the voice over before we had this chat so I couldn't include the tasty info, and I may have gotten the point about shims ideally being used like for like side to side wrong.

 

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12 minutes ago, GTK said:

 they were dealing in a production run of chassis, and so less time would have been given each one.

 

Exactly the problem.

It is a fact that the cars were coming out of the factory with incorrect alignment. I remember speaking to pat Thomas at Kelvedon Motors in around 1984 and he was checking new cars on a laser alignment gauge and finding they were out. The factory had tried to re-jig the chassis and also used shimming to the max to correct things but some adjustments could not be corrected with shims especially rear camber.

Pat had some adjustable upper rear links made to correct this. My car has one of these on the rear left. 

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We’re I to buy another Esprit, I would insist on a geometry check from a decent machine. Most KwikFit has a Hunter, and they charge about £50.

Might be the best money ever spent.

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I wouldn't be completely shocked if it turned out your chassis wasn't entirely true. The chunks that the previous owner has hacked out of the spine chasing those water leaks won't have exactly added any strength! It may well have twisted slightly.  It would only take the smallest of twists to require an extra shim or two to bring the suspension back into alignment.

Screengrabs for those who haven't seen the video:

soupchassisihole1.jpg.d88d6866a698a7ea7adbd4f3936d1f09.jpg

soupchassisihole2.jpg.fa5b04bc2cde258e0b5fd9d19ad4f5e9.jpg

 

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Structural pop rivets :blink:

 

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the structuraliest 😄

Ferk me about sums it up yeah. I won't be surprised if it's twisted either. I fancied I could see a twist standing at the front looking aft, but there was so much visual interference from pipes and wires and flat tyres, and not least that dent in the aft section, that it was difficult to be sure.

I foresee a proper chassis jig, and geo alignments in the not so distant future. Actually that plan has always been to bring a chassis builder into the picture at some point, but the guy I had in mind is a reclusive type and I doubt seriously he'd be interested. I'd love to have a chat with Matt Becker too, that'd be the ultimate.

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