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martx-5
09-11-2006, 06:37 PM
I just got my copy of Classic Motorsports magazine, and there is an article on improving the handling of the TR3. They talk about camber and caster changes. The part on the camber change is easy enough to visualize. They use TR6 upper A-Arms and slot the holes for the ball joint mounting so that the verticle link can tilt inward for negative camber. But, then they talk about giving the suspension some caster. They don't mention the TR4 3 deg. caster trunnions. They use the Jag XJ-6 ball joint as it is .150" narrower then the TR6 joint. They put shims between the Jag joint and the front of the upper A-Arm to move the joint rearward. I understand this. What I don't understand is how is the vertical link going to tilt backwards when the pins on the trunnion that go through the lower A-Arms are fixed. How is that whole trunnion and vertical link are able to tilt backwards??? Am I missing something here?? They said that they were able to get 7.5 deg of positive caster by doing this.

jsneddon
09-11-2006, 10:24 PM
You should go to www.kaskastner.com (https://www.kaskastner.com) and post this on his forum. I'd love to hear what the master says about something like this.

Alan_Myers
09-12-2006, 05:36 PM
Hi,

Yeah, I'd question that too! I'll have to look for that magazine article. (Is it online anywhere?)

For one thing, I can't imagine why anyone would want to go to that much caster. 3 deg is more like it. And, if they DIDN'T change to the later, 3 deg caster vertical links (or possibly heat & bend the 0 deg v-links they had), I think it very likely they'll break something before very long.

If they changed to the Jag ball joints with a lot of shimming AND changed to the upper arms off later cars, that might allow for 7.5 deg. of caster... But why? I would imagine the car handles somewhat like a shopping cart with that much caster.

Just changing to the later upper a-arms and v-links gives about 3 deg, which IMHO is much more sensible (Triumph got that about right, IMHO, on the later cars with R&P steering). The reason to use the Jag Mk IV ball joints is to allow fine tuning to 3 degrees of caster, not to increase caster radically to the point where the car will be downright dangerous in high speed corners!

Slotting the upper arms IS a common way to change camber This can be done with parts taken from TR4 after approx. CT6500 or any later 4A/250/5/6... They all use the same unequal length upper control arms. The problem with doing this is that shortening those arms (which slotting effectively does) can also easily induce (or increase) some nasty bump steer problems. There are other ways to effect a change in camber that are more likely to avoid the problems:
1. Install adjustable upper/inner pivots, either homemade or such as Revington TR sells (not allowed in some race classes).
2. Heat up and bend the vertical links (rude & crude, but generally race legal).
3. Shorten the cross tube in the engine compartment and pull the entire spring tower inward slightly (sneaky enough that it might get by a tech inspection).
4. Change to reinforced versions of TR4A/TR6 lower/inner suspension mounting brackets and use positioning of the new brackets along with shims to push the lower arms outward (also might not pass tech inspection in some classes).

All these methods avoid changing the length of the upper or lower suspension arms, and so are less likely to induce bump steer or other hard-to-correct handling problems.

Personally, my preferred overall solution would be to build a "Beta". In other words, put a modified TR4 frame under the TR3. That will still need some changes for camber, but this way you'll also get the wider track front & rear, plus convert to rack & pinion pinion steering and 3 degrees of caster, all at the same time! Modifications necessary to fit the frame include shortened outriggers and changed front and rear body mounts. Oh, and the TR3 body itself will need "Beta" fenders front and rear to allow room for the extra track width and some nasty-wide tires.