Got a bit of a issue here. Due to more than normal attention needed to keep my car in a straight line on the highway, I discovered I have 1/2" toe-in at the rear. I took it to my favorite alignment specialist whose fancy machine confirmed my findings and also confirmed all other variables involved, such as frame straightness, camber, castor (for front and rear), cross corner alignments, etc, are all in order. All the holes in the hubs are in good shape with no wallowing out.
So, the only real unknown are the bushes, which are quite old. Is it possible to make up a 1/2" with new bushes? If not, what further measures can I take to get proper toe? I saw TTR’s adjustable arms are quite expensive but wondered if anyone’s done a DIY job for adjustable rear arms?
It was suggested by the alignment shop and others I know, that the best route might be to slot the front mounting flanges on the frame to get the arm to move outward a bit. I’m not sure if the clamping force of the bolt will hold it though but I thought about welding a washer over the hole for the new location.
Any ideas out there, or should I report back after new bushes?
I have seen other cars with the rear toe out of spec, and these cars had undamaged frames. Personally, I do not think that bushes would make up the difference.
I would be wary of slotting frame holes, especially on a good, unmarred chassis. The TTR arms may be pricey, but they will definitely cure the problem without any “reengineering”
I fitted the TTR arms when I installed my new chassis, and was able to get all alinement specs right on the money. You cannot put a price on peace of mind.
I would remove the frame - and check frame dimensions if not correct replace frame. Also check location of holes in chassis mounting lugs. Also check bushes not distorted and replace if needed- if all OK then reassemble and recheck alignment.
1/2" toe measured at tyre tread, side-to-side (not side-to-centreline) is possible if each of the outboard wishbone bushes allows 0.8mm movement off centre, so I think worn bushes could quite easily account for this.
Also, given the way the bush, upright and wishbone are connected, I think loose wishbone bolts, and possibly also elongated holes in the uprights, could probably also account for it.
Since the spring/damper are pretty much in line with the rear bush, won’t the force of the spring tend to push out on the rear bush more than the front, giving toe-in?
Is there any perceptible movement if you try turning the wheel side to side? Have you tried measuring with the handbrake on and off? Is the toe-in on both sides equally?
seems to me that the validating and replacing the bushings is the expedient/low cost route assuming you are reasonablely sure the metal is straight.
the sure fire methods as Mike points out is to buy somebodies adjustable arms, but it will be costly bu the time you fit rod ends , spherical bearings and making spacers ( not a fan of stacked washers) .
My fall back on the current project if the stock a-arms with TTR bushings don’t put the wheels were I need them is to convert an inboard mounting to a rod end, untried at this point , if that won’t do it , then I buy the adjustables.
Thanks guys. Paddy, there is no perceptable movement of the wheels when applying force in all directions. The wheels are sitting on two sheets of wax paper, also; easier to pick up on any discernable movement that way. Handbrake is off and toe-in is 1/2" on drivers’ side (lh) and 1/4" on passenger side (rh)
Russ, what’s different about the TTR bushes from stock? Poly? But I assume the measurements will be the same as stock. Let me know if you happen to follow through on your mounting point conversion.
Greg
Rear toe in alone will not make your car drive to one side. Total toe in is not the problem it must be unequal rear toe in. Unlike front toe in settings where the steering wheel just runs off center if you are unequal on right and left.
You can determine which side has more tow in with a helper, a piece of string and a tape measure. With the string held at the center (top to bottom) of the rear of the rear tire. Hold the string so that it does not touch the front of the tire while stretching the string near the front wheel hub. Move the string inward until the string just touches the front of the rear tire and measure distance from the front hub to the string. Repeat on the opposite side. Any rear toe in differences are greatly amplified by the wheelbase. Race teams use to do this before they got all their electronics.
As an alternate to expensive rear wishbones I had offset bushings made out of reinforced Teflon for the front inner bushing on the wishbone. This gave me just enough adjustment to meet spec.
Ken
If you’re saying you’ve a total of 3/4" toe-in (it should be 0 to 3/16") there must by somthing seriously wrong. If its the result of damage to the chassis or a bent wishbone this should be obvious with a visual inspection.
I’d tend to side with Paddy and would suggest wear in the pivots or soft bushes. You’ll not spot this by movement of the wheel though as the spring will be pushing too hard against you. What you could try is clamping the springs up to take the load off the upright, then trying to find some movement.
Ken, yes, there is a toe difference, verified with the string test. LH side is toe’d in by almost a 1/2" more than the RH side.
LH side is toe’d in 1/2" and RH side is about 1/8" (although in a previous post I said it was a 1/4", I’m sure it’s only an 1/8")
I like the offset bushing fix, since I’m going to rebush the arms anyway. Do you remember who did the job?
Andy, before I pull the arm off, I’ll clamp the spring and double check for any unnecessary movement.
The rear toe in specification is per individual side compared to the front toe in spec which is total. The reason Lotus did it this way according to their current technical manual writer is that the front is not individually adjustable while the rear is.
I dont have the manual in front of me at work but ifl the manual says 0-3/16 inch toe in specification then this is for each side so 1/4 inch and 1/2 inch suggests the bushes have deformed rather than anything else if the arms were made right in the first place - which they may not have been.
Interesting statement here Rohan. I had planned to rebush a spare arm I have but that would be changing two variables here. So before I do that I will measure both arms to be sure they are exactly the same.
I would suggest that all you need to do with the replacement arms is check that the inner and outer pivots are parallel (For the Plus 2 they should be and I assume it’s the same for the Elan).
If I were doing this I’d make some bushes out of aluminium, which I knew were concentric, and then check with a couple of long stright bars. I’d then re-check with the actual rubber bushs in place just to be sure pressing them in hadn’t introduced any errors. If you do this and everything’s ok but you still a problem with the toe-in, then the errors got to be with the chassis
Greg
I had a local machine shop drill the bushing with the maximum offset we were both safe with. I do not think Cadillac Plastic still exists in the US but there are similar places to buy rods of various plastics including reinforced Teflon. On a race Super 7 I did similar offset bushes on the upper control arm but in oil-filled bronze. You do not want that on a street car!
Ken
Just remember that the way the rear suspension is designed ( and the front for that matter) all the movement is taken by the flexing of the rubber bushes. The bolts must be tight and clamped hard against somthing which normally is the inner sleeve of the rubber bush. If modifications are made which don’t allow the bolts to be pulled up tight, relative movement will wear the holes in the chassis or upright in no time at all.