Jag Diff Toe-In Measurements

jcraigau · #1 (**permalink**) 02-15-2011, 02:03 AM

Hey Guys,

I'm in the process of getting the diff sorted out and in my excitement to pull it all apart and make it look pretty I can't remember if there were any shims to achieve the correct toe-in.

Now it's all back together I've heard all sorts of stories from 0 degree toe-in to lots of toe-in. But I can't find any measurements.

The manual I have says 9-1/8" is where it should be as this is where the G-Force chassis runs the bolts through it for mounting.

Mine measures 9.128" at the front and 9.118" at the rear, so at the moment it toes-out.

What is everybody running?

The following picture shows the measurements I took...

--Jamie

Rebel1 · #2 (**permalink**) 02-15-2011, 03:12 AM

Jamie, looks like you need shims under the pivot bracket rear bolts.
Keep in mind, shims under the back bolts will reduce the front dimension.

However, even if you shim the pivot brackets to give no toe at all is no guarantee that will translate out to the wheel when you fit the lower wishbone.

The reason for this is the accuracy of how the lower wishbones were shortened (if they were) or the accuracy of the original wishbones.

I found my shortened wishbones were not as accurate as I'd like. In fact, testing some unaltered original wishbones also indicated them to be not accurate. Testing involved running shafts thru both ends of the wishbone and measuring if they were parallel.

So that means even if you shimmed your inner pivot brackets to give zero toe you may not get that after fitting the lower wishbone. You would then have to start the shimming process all over again just to get the alignment correct.

You could assemble the whole diff out of the car and play with the shims until you get zero toe on the outboard end but then the diff may be slightly out of square in the chassis and that stuffs up all your work.

The best way to handle this is to shim your inner brackets parallel and have the toe adjustable at the outboard end of the wishbone.

If you contact Scotty at venom and arrange to send him your wishbones. He has the jigs etc. to make the modification. http://www.venomcobras.com/

If you have trouble following the above I can send you an email with a phone number and we can chat.

OZVENOM · #3 (**permalink**) 02-15-2011, 04:20 AM

Hi if you want to get it right it has to be all mounted in chassis . when on the ground at ride height you need 1- 1.5 mm of toe across the rim. Each side it will make the cobra drive stable in corners and on roundabouts. its is a lot of work to pull the arms in and out so put say .010" of shim under the rear bolt of the pivot block when you assemble it a good place to start.
Thanks for the mention Rebel.
I dont like to pedal my wares on here. as i am not an advertiser on cc.
Regards oz.

RICK LAKE · #4 (**permalink**) 02-15-2011, 04:23 AM

jcraigau Craig you need to get old style GM shims with slots. For setting camber you add or remove from the drive shaft between the rotor and the outputshaft. put car in the air and remove the 4 nuts. let top of assembly fall out, EASY and installed or remove shims. You have to be 100% correct on the end play for the outter driveshafts into the hubs, you really want no play when the hub is warm. As far as the toe, you loosen the bottom to bolts that mount the lower arm to the bracket on the carrier, add or remove to get to spec and tighten. Wiretie both bolts and the 4 nuts for the out put shafts. My specs are +3/4 camber and toe is 1/16" in on both wheels. This is with my weight in the drivers seat. If the car weights for the corners are not done, than you need to start there. Do all suspension work with your weight in the drivers seat. Also make sure the THRUST angle is "0" or +/- 1, no higher. Check all mounts for tightness and rubber for good condition. If the car drift out to one side, start with a tire pressure adjustment, if more than 3-4 psi, there is something wrong with alignment or loose part. car should track straight. Rick L. Ps ask the alignment shop when was the last time it was serviced and setup for trueness. The printout could read perfect and the machine could be 3/8" off and cause all kinds of problems.

Rebel1 · #5 (**permalink**) 02-15-2011, 04:31 AM

Quote:

Originally Posted by OZVENOM

I dont like to pedal my wares on here. as i am not an advertiser on cc.
Regards oz.

You may not like to pedal your wares here Scotty but your lower arm toe mod is recognized as the best and easiest way to ensure that the rear alignment will be correct. Not only correct but easily adjustable at some later stage if one wants to play with it.

Modest bugga you are.

jcraigau · #6 (**permalink**) 02-15-2011, 06:17 AM

Sounds like a case of assemble it all and get it on an alignment machine.
The last thing you want to have to be doing is dropping the driveshafts and bottom wishbones out to keep fiddling.

Thanks for the quick replies and info. I'll keep you all updated as the build gets closer to rolling...

jcraigau · #7 (**permalink**) 02-15-2011, 06:29 AM

Oh, also forgot to mention that I already have the cutdown wishbones supplied from G-Force. Apparently the cut-and-shut was performed by an aircraft mechanic. I haven't measured them but I can only assume that they are square.

Rebel1 · #8 (**permalink**) 02-15-2011, 06:42 AM

Jamie, My wishbones were supplied by RMC and I also assumed they would be square. They were only out a few thou but when you hang a 15" wheel fitted with a 26.5" tyre off the end they end up all over the place and it was damn near impossible to get both rear wheels aligned correctly. Cross fingers yours are better than mine.

But it is worth the effort to get them right as they are a proper bugger to do anything with once the car is built.

jcraigau · #9 (**permalink**) 02-15-2011, 07:20 AM

Yea, last thing you want after spending all that time under it is to not enjoy it when you finally get it on the road. The Cobra club here has "a guy" that is meant to be a gun on suspension - specifically jag rear ended Cobras. Looks like I might give him a heads up!

glenview289 · #10 (**permalink**) 02-15-2011, 08:03 AM

This is a reply I did on the same topic over on the "Unique Cobra" site:

Rod,
That is how Brian and I measured the toe in when we did our car. I can't remember the source, but probably did a search on the site. We put straight edges against the center of the tire and parallel to the floor. We then measured the outside edges of the straight edge in the front and rear of the tire. The difference should be 1/16" total (smaller number in front-very important). If I remember correctly, we had a .005" shim under the front screw and a .012" shim under the rear screw that holds the bracket that mounts the lower hub carrier arm to the rear end. If you do the math, the .007" difference in shim thickness between the 2 screws that are approximately 7-8" apart would carry out to .030" on a 32" tire, or about 1/32" per side (1/16" overall). Be careful not to have the straight edge on an raised lettering you may have on the tire. You will have the same advantage that Brian and I had in that the body is not on the chassis. It will be much easier this way. Be sure to get the rear end lined up and locked down exactly parallel to the centerline of the chassis before setting the toe. I remember how great a freshly powder coated chassis looks. I'm sure Rick will remind you that this is the perfect time to put that first coat of wax on the chassis. If you need more info I can measure anything you may need on the car this weekend. Its over in Brians garage up on stands getting ready for a track day next week at Hallet Raceway in Tulsa.

Bill