Brake Problem

[gwr]

Had a great day at Prescott, but all day my brakes were pulling the car to the right. Ideal for the Ettore Hairpin, but not so clever for the run back home.

 

I've checked the tyre pressures, I've checked for leaks and I've checked for any debris in the calipers - all OK. So I bled the left hand side, still pulls to the right. All the steering linkages etc appear normal.

 

On my last check run this evening I've now lost all braking - the pedal will travel all the way to the floor, but returns to normal after a couple of pumps. Rotation of the front right wheel is now accompanied by a 'graunching' sound. I cleaned the right hand caliper, in case it was sticking and bled that side too. But still no brakes unless I pump the pedal. don't know if it still pulls to the right, because I'm too chicken to take it out.

 

I think I've got a couple of problems here, can anyone give me any pointers? Why would the single, common hydraulic system allow differential braking?

 

As ever, thanks in anticipation.

[Rhodri]

If you are getting a graunching sound then the first thought would be that the pads have worn out and are down to the metal backing- but you would have seen that. The other possibility is that a wheel bearing has gone thus knocking back the pads and needing a pump to set the pads again, but this would not give you pulling to one side as the pressure in each caliper would be the same. This would cause a noise, but easily checked by rocking the wheel. The third reason, and the one I think most likely, is that a piston in the caliper has seized- although it seems that you have checked for movement by removing each piston?

I can not think of any other reason to cause one brake to start misbehaving- very low pressure in that tyre, brake hose breaking down internally?

Edited May 19, 2008 by Rhodri

[gwr]

Make that a rhythmic knocking sound rather than graunching. My limited knowledge suggests that's the wheel bearing going. Could its incipient failure have caused the pull towards it under braking?

[BrianC]

Make that a rhythmic knocking sound rather than graunching. My limited knowledge suggests that's the wheel bearing going. Could its incipient failure have caused the pull towards it under braking?

I'm no expert (understatment), but if the left-hand wheel bearing were badly worn or loose, then I think you would get pad knock-back on that side and the right brake would therefore take effect slightly earlier, so this could perhaps cause a pull to the right.

[gwr]

The knocking sound is coming from the right hand side. My thinking was that the breakdown of the bearing was causing additional friction under braking, making the car pull to the right. Only one way to find out I suppose...

[Rhodri]

Gordon, if the wheel bearing has gone the wheel will lean complete with the disc. The caliper is held stationary by the vertical link so the disc will be at an angle inside the jaws of the caliper. When you brake there will be excessive movement of the pads to push the disc upright again requiring you to pump the brakes. Put a jack underneath the wishbone and jack up enough to get the wheel off the ground, then, holding the wheel at the top and at the bottom try to rock it. It should only move a fraction at the rim but that is all, also spin the wheel to listen for a noise. you could try rocking it whilst it is on the ground . Caliper tight, wheel nuts tight?

[gwr]

Oops!

Edited May 20, 2008 by gwr

[gwr]

Rhodri, what you say confirms my diagnosis, I think. When the car is stationary the brake pedal is firm. When I drive(slowly) the pedal will press all the way to the floor, unless I pump it. As the wheel rotates when I drive it makes a regular knocking sound. When I've jacked the wheel up and spun it, there is an obvious resistance at a regular point in its rotation. I think I'm on the right track suspecting the bearing, I'll pull the hub tomorrow and have a look.

 

I've just checked for play in the wheel and there is obvious movement when I try to rock the right hand wheeltop to bottom. This movement is not apparent on the left hand side. It's got to be the bearing. So it's wheel off tomorrow. Can't do it tonight - I've got to watch the Champions' League Final.

 

Any top tips on wheel bearing replacement. Do I need any special tools (slide hammer?) beyond a puller?

Edited May 21, 2008 by gwr

[Tr4Tony]

Hi

 

Could be a bearing failure - dont drive the car any more until you've sorted this as the whole hub could detach if the stub axle or end nut detach. See this happen and its not pretty.

 

Ive had this before and id expect to see the inner bearing quite heavily mullered so be prepared to swap the stub axle too if its badly scored or worn. Go carefully and the hubs should be ok. Best plan is to detach the caliper etc, remove the hub and disc assembly, mount in a vice and tap (heavily!) the stub axle out ... not special tools needed ....all should be clear from there on in.

 

You may want to fit an anti knock kit (TR Enterprises sold me mine) .... while your there, stops the stub axle bending quite so much and the resultant pad knock is reduced. Easier on the bearings for their life.

 

Hope this helps.

 

Regards

 

Tony

[gwr]

Yeah, definitely the wheel bearing! I'm lucky that it (and I) made it back from Prescott.

 

The pics are of the stub axle and the outer wheel bearing.

[RogerH]

Hi Gordon,

you want to mount the bearings on wooden plinths and make your own rogues museum to cheer you up on rainy days. Do this with all you knackered parts. You might make a profit on admission charges.

 

Roger

[Rhodri]

I am glad you got it sorted, quickly, and safely!