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TR 4 and 6 racers--tech help needed

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STUinAZ

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Greetings from sunny Arizona. I'm the guy who's upper A-arm was sliding out over the bushing/washer/nut. Well, the washers used were WAY too small, and I guess too much hard driving caused the problem (although after 35000+ miles). A new bushing and several new(larger) washers and that's no longer a problem.
However, as I had mentioned earlier, I'm planning to modify the front suspension somewhat to improve it's road-holding for autocross and fast road use. In an article in Classic Motorsports magazine a couple of years ago Tim Suddard described several ways that the TR3 set-up can be modernized/improved to better make use of modern radials, as well as adding a little adjust-ability to the TR3's non-adjustable suspension i.e. caster and camber.
With that in mind, I acquired a late TR6 front suspension set-up, complete except for springs. For now, I'm just looking to use the upper A-arms with the newer style ball joint. If you've read the article you know what I mean... I may even go with the Jag XJ6 ball joint with shims, but that depends on just how far I need to go.
This leads me (finally!) to my question for you racer-types out there. I can see that the TR6 A-arms are distinctly "sided" compared to the TR3 units, which I presume will result in some positive caster. What is the amount of caster and camber in the stock TR6 configuration? How far can I or should I go with regard to camber and caster?
I presume someone out there has already done the math. I need to know the formula to determine how much camber change results from "slotting" or otherwise bringing the ball joint inward? Like, you know, .5" at the A-arm equals 1.75 degrees negative camber. I suppose I could get some exact measurements of the length of the A-arms and the height of the kingpin, and apply trigonometric formulas to come up with the relationship of the length of the hypotenuse to the degrees of the opposite angle, but as I said, someone out there must already know answers (and my high school math is a little rusty). Can anyone help??? Thanks
 
I modified my upper A arms some years ago to get some neg. camber on my TR4. My TR had the later 3 degree trunnion so I was all set there. I don't think you will be able to use the narrower XJ6 upper with shims. Unlike the TR6, the lower inner A arm mounts are not adjustable. Using the shims will excessively wear the bushing. If you look carefully at the pictures and compare them to your A arms, you can see where I added to the "pocket" on the inner side of the ball joint mounting area. I am running about .5 degree negative camber. I moved the ball joint in the slots back and forth kinda trial and error. I then tack welded the washers to the arm. Works for me, I think the front sticks much better. You may have to trim a little metal from the end of the arms to clear the wheels, I am using 5.5 inch TR6 steel.

4080950429_0098af6798.jpg


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I'm installing an upper fulcrum kit I bought from Revington this weekend.
According to Revington, it's made primarily for early TR4's (or 3's) with little or no camber adjustment options. However, it can also be used on later TR4's, TR4A's and I suppose TR6's to gain a little more room for camber adjustments, even with the 3 degree trunnion. What's cool about it is that you can install it 2 ways, with the fulcrum pin up or down. Supposedly, installing it with the fulcrum pin up is more for fast road or rally, and with it down for hill climb. I opted for up mainly due to the lack of large hills in south Louisiana. It's ashamed they don't have a mud buggy setting for swamp use.

The kit appears to be solidly made and has a very nice yellow cad finish, just lose the cheap nuts and bolts supplied and get yourself some grade 8 with a matching finish.

PRTR3112K1085_m.jpg
 
Thanks for all the info. That link to the tjwakeman site provided lots of insight. Thanks for the pictures, Mark. I guess I hadn't really thought it through, what with the TR3 suspension not really being set up for changes to the caster... I guess I can't use the TR6 A-arms unless I also use the trunnions and vertical links as well. I didn't know about the change to 3 degree caster during TR4 production. By the way, Tab, what did that fancy fulcrum kit set you back? Let us know how the fitment works out!
 
Stu-

If you just want the caster change, you can use the TR6 upper a arms/ball joints, but you need later TR4 trunnions on the bottom which are LH/RH and have the 3 degrees built in as well. Vertical links remain the same, lower arms stay the same, etc. You might need to change out to TR4 steering arms, and maybe worry over the brake caliper mounts, but I'm not sure if that is necessary and suspect it may not be. The TR4 started with the same 0 degree arms as a TR3, then went to 3 degree version so parts can be pretty easily changed out.

Randy
 
Looking at the suspension chapter of my TR4 workshop manual. The tie rod lever is different between the 0 and 3 degree castor suspensions. The 3 degree has .22 inch more "drop".
 
I've got all the components from the TR6 front suspension assembly, so I could go ahead and just swap out the 3 degree trunnions, if they are indeed the same as the late TR4 pieces. Then I can go ahead and modify the A-arms for camber. The TR3 already has R & P steering (basically a narrowed TR4 set-up). Still, if I go ahead and take apart and rebuild the front suspension I suppose I could just as well freshen up the whole TR6 assembly. If I'm not mistaken they have the stub axle coming off the vertical link 1" higher, lowering the front of the car an inch. Then I'd have to use the late TR6 brakes, but they have larger pad surface area anyway, and better selection of after-market performance pads. Then the next logical step would be the swap to Toyota 4-pot calipers... and uncle jack's heavy duty, shimmed stub axles. More money again. I guess it never ends!
 
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