Update on my tire balancing

Tom Howland · #1 (**permalink**) 05-05-2006, 11:47 AM

Working on the rear tires this time. I have 295-50-15 BFG. Quite a bit of seat shake at 65 to 75 mph. Not a solid shake but a on and off one. Had the tires shaved (made round.) Then balanced on a Hunter 9700 machine. Road force was measured at 25 and 29 #’s. This shop won’t do tires over 30 #’s. My numbers were quite a disappointment after the effort of getting them shaved. Drove on them yesterday. The shake is now around 70 mph and is constant. About 1/2 of the before shake. Conclusion is there is an improvement. I was hoping to eliminate the entire shake but it is better. I’ve looked at all the other tire brands and not come up with tires that meet my requirements. I’ll keep checking the tire companies every 6 months.

clayfoushee · #2 (**permalink**) 05-06-2006, 10:17 AM

A rather large percentage of BFG Radial TAs seem to be notoriously "unround", and the condition is exacerbated on a light car like Cobras. I could never completely get rid of the "shakes" even though I did most of the things you mentioned above. I switched to Yoko Avid STs and the problem disappeared.

There are many similar reported experiences here and on other Cobra forums.

Jerry Clayton · #3 (**permalink**) 05-06-2006, 02:24 PM

I noticed you have a Jag IRS rear end---have you got modified hubs, pin drive adapters, custom wheels, etc?????
The stack up of tolerances could give you a resulting almost uncurable shake---
Start at the u-joints and verify there condition--then hub wobble and runout--verify the wheel mounting face is parallel to the mass of the wheel(lip run out) Bolt or pin drive circle could be off in either the hub or wheel

When you verify every thing is zeroed out then mount some tires

Put wheels on the same stud or pin every time.

Jerry

Bob In Ct · #4 (**permalink**) 05-06-2006, 04:27 PM

I finally gave up on the BFGs. The S/Ts are in the garage!

Bob

Tom Howland · #5 (**permalink**) 05-07-2006, 10:11 PM

Clay,
My big issue with size is the front tires. I have the old 265-50-15 BFG. They are 25.25” diameter. I have moved the front suspension 1 1/2” forward so the left tire wouldn’t rub the rear of the wheel well when turning left. Right now everything works great. The Yokos 255-60-TR15 are 27” in diameter. That wouldn’t work. I’d be rubbing again. Last night I found Dunlop 265-50-TR15 at 25.5”. The rears seem to be the same with all manufactures at 26.7”. I think I’ll go with the Dunlop’s.

Jerry,
I had the rear totally rebuilt 2 years ago. Even new driveshaft u-joints. Hadn’t thought about hub wobble or lip runout. I have bolt on’s. They are U.S. Indy slot mags, 8.5” in front, 10” in back. That’s a good idea to align with the same stud each install. I had the car on a dyno last month and specifically watched the rear wheels for any hop. Didn’t see any. But now I remember the operator only went to 60 mph. Thanks for the tips.

Fred Douglass · #6 (**permalink**) 05-21-2006, 07:22 PM

Tom,

Speaking of rebuilding the Butler JAG rears---it might be time to get mine up to spec. Do you have any leads on good Jag-rear rebuilders--nationally? I heard there's some outfit in Tennessee. If you don't know of any east of the Mississippi, maybe you know someone who does. Also, what did you have your guys do/replace? I suspect that my rearend is not "locked" and don't know the health of the gears and guts.

E-mail me if you want: douglassf@aol.com

Tom Howland · #7 (**permalink**) 05-22-2006, 09:16 AM

Hi Fred,

I had a local shop in town do the work. The left wheel had a pretty good wobble in it and there was a scraping noise coming from the differential. The first thought was to replace the hub bearings and shims, and the pinion bearing. They couldn’t get the stub axel out of one side of the diff. The one that did come out had a slight twist in the splines and was really hard to get out. That made us think the one we couldn’t get out would be very bad and possibly have damaged the diff. splines. So I went with a new diff., new stub axels, and new u-joints. Did new driveshaft u-joints while apart. I upgraded the brake calipers from type 1 to type 2 then also. That was expensive because of hand grinding to adapt them. Plus new rotors. As you can see it just keeps going. The type 2 calipers give you about 2 times the pad area. Thought that would be good but haven’t noticed any difference. It has a posi type gear set up. You can tell by jacking up the rear and turning a tire. If the other one turns the same way it’s posi. It all cost around $6,600. They did a great job. Cleaned and painted everything, including the frame in the rear. Did a 4 wheel alignment. I am very pleased with the work.

Fred Douglass · #8 (**permalink**) 05-22-2006, 10:20 AM

....you're a true blue! Thanks for the info.........

Yetiman · #9 (**permalink**) 05-22-2006, 11:51 AM

Quote:

Originally Posted by Tom Howland

They couldn’t get the stub axel out of one side of the diff. The one that did come out had a slight twist in the splines and was really hard to get out. That made us think the one we couldn’t get out would be very bad and possibly have damaged the diff. splines.

I don't want to tell you how long it took to get this piece dis-lodged !

Tom Howland · #10 (**permalink**) 05-22-2006, 01:34 PM

Yetiman,
Wow, mine wasn't nearly that bad. What was the condition of the receiving part in the diff.? Did you have to rebuild any of the diff.?