Wheel wobble under breaking

[samco]

My wedge is fitted with the disk brake conversion with Capri discs and calipers. Under light breaking I get a wobble through the steering wheel and suspect it may be a disk (rotor) out of alignment. They are new discs with grooves and cross drilled but as I never drove the car before they were fitted I have no comparason with the old ones. There are new wheel bearings and they are correctly adjusted, I have stripped the calipers to ensure the pistons are free to move so this leaves me wondering if the hubs are badly machined to accept the capri discs, or are the new discs warped. There is no wobble under any other conditions just under light breaking. Any ideas!

If it doesn't fit you obviously need a bigger hammer.

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1980 Californian import converted to right hand drive V8. Under construction.

[andyf]

It does sound like warped discs to me as well. The only other thing that springs to mind is something to do with the calipers, but I really can`t think of anything that would cause that. Anyone any ideas?


1980 persian aqua DHC

[Hasbeen]

Samco, a couple of things.

Is it only with light braking, & nothing with hard braking?

Is there any pulsing in the brake pedal?

I would check the run out, [wobble from side to side] of your discs.
Jack the car up, & remove the wheels. Use some spacers, [a bit of
pipe] between the disc, & the nuts, & do up the nuts, so you can get
the discs clamped up tight, as with the wheel on.

Set up a dial gauge against the face of the disc, & rotate it, &
check the run out.
It should be less than 4 thou, but I have seen many road cars with
up to 10 thou, not exhibiting any problems for the driver.

If you don't want to get a dial gauge, you can set up a bit of
steel, clamped to an axle stand, with one end very close [a couple
of thou] to the disc. Now use feeler gauges to check the clearance
at 8 points around the disc. Don't be too amazed if your new discs
are not true. & yes, it is possable that your hub face is not true.

If all looks OK there, just check your castor. Over about 5
degrees "CAN" vive you wheel wobble, under brakes, & if it was going
to happen on any road car, our Triumphs are most likely to suffer
from it.

There are a dozen other, more obscure, possable causes, but much
less likely.

Hasbeen

[FI Spyder]

I would vote for disc warp. My Tercel had that for years and they were known for disc warp. When I did the brakes a few years ago I replaced the rotors as that was the same price as getting them machined ($17/ea.). Steering wobble went away.

TR7 Spider - 1978 Spifire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra

[humanoid]

Another one for rotors being warped. Also, were the lug nuts torqued correctly? Over torquing the lugs will cause the rotors to warp pretty quickly. I'm not sure how tight the 7's lugs need to be, but on my Toyota Tacoma, they need to be a 85 ft/lbs., I'm pretty sure it should be similar for the 7's.

_____________________________________________
<h3><b><font color="orange">1980 Inca Yellow TR7 Convertible</font id="orange"></b></h3>

[bmcecosse]

Could be worn steering joints/rubber bushes.

[John Clancy]

Just give it some hard braking for the first few thousand miles and see if it settles down. Seems to have worked with mine (which has the same brake kit).

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[Underdog]

I've had this problem with mine since I've owned it. Did it with the original brakes and now has the Rimmer kit. At first, with the new Rimmer kit, it seemed much better. But after geting some miles on it, the shakes are back. Doesn't do it all the time. As you state, more under initial application. I plan to check the rotors but I've always thought it was more to do with play in the frt suspension points. I have the uprated rubber bushes but plan on going to urethane and eventually a larger frt anti sway bar. If you look at how the frt suspension is located on these cars, it really isn't!

72 MGB BRG
80 TR8 Persian Aqua
If women don't find you handsome, they should at least find you handy.

[bmcecosse]

The 'anti-dive' modification to the roll bar mounts tightens up the front suspension nicely, and helped 'turn in' on my car - but does absolutely nothing to lessen the 'dive'! It's easy to do - certainly worth a go.

[Underdog]

Just as a follow up to this problem. Again, this is with the Rimmer Brake kit. I had the rotors trimmed and redid the frt wheel brgs with new outers. I set the brgs a little tighter than what I had before so that they are somewhat preloaded. Car now brakes smooth as glass and the shimmy I had between 60 & 65 mph seems to be gone. I have a TR7 manual rack and combined with the 205/60/14 tires, it seems to be really sensitive to any slight defect in the rotors/wheel brgs.

Should mention that the brake kit had a little short of 1,000mi when this shudder became very noticeable and somewhat severe. I'm hoping that the rotors hold true now that they have been heat cycled and cut.

72 MGB BRG
80 TR8 Persian Aqua
If women don't find you handsome, they should at least find you handy.

[omichaelshar]

Samco,

Obviously you just need to remove this bad habit of light braking from your driving style and this problem will go away.

Seriously though, I have this symptom periodically on my wedge with Volvo front calipers and find that cleaning and reseating the front wheel bearings and rebalancing the wheels has fixed the problem.

YMMV
Owen

[Hasbeen]

That makes sense to me Owen. I posted some time back how the Brabham
Repco F1 nearly shook the wheel out of my hands, under brakes, when
it was accidently given 7 degrees of castor.

With 3 Degrees, +/- 1/2, our cars have very high castor, & are more
porne to wheel wobble, if the wheel balance is not well done. They
are also closser to it, under brakes. Anything which allowes a
little slop, which would be no problem on most cars, will cause us
problems, by letting the wobble get started.

Just another good reason to keep aur cars in good trim.

Hasbeen