Brake Problem (lost braking efficiency)
 

I’ve noticed a very occasional burning smell in my car (2004 Rover 75 CDTi) over the course of the last couple of months which I suspected was the clutch on its way out (desperately hoping that this was not the case). However, the clutch does not slip and although it is fairly heavy, appears to do its job, so I’ve just left it alone to see if it does start to slip.

This morning, after starting off my journey to work, I applied the brakes at a junction near my house and had to use an awful lot of pressure to get the car to stop (no skidding in the snow/abs not kicking in). The problem appeared to get better during the journey although it could be that I was getting used to them. I suspected a problem with the servo unit, valve or pipework but these appear to be ok – no audible air leaks, wear or splits and the brake pedal depresses further when the car is started. Checked the brake fluid and it is low and I’m now starting to suspect that a caliper may be sticking intermittently (causing the smell) and may have boiled the brake fluid causing the brakes to lose efficiency.

Pads and discs are OK, no sign of any leaks from the caliper seals (although its very difficult to see in this weather). I intend to bleed the system tonight with fresh fluid and check out the calipers at the weekend, with a view to either re-build with new seals or fit recon units (depending on cost). Does this sound sensibly? Any other ideas/suggestions?

Sorry about the lengthy post!

Many Thanks

Toby

Toby, have a good look at the callipers. I had exactly the same problem with a burning smell and it turned out my OSR calliper was jammed. It wasn't obvious either - no dragging or squealing but a hot wheel at the end of a journey accompanied by the burning smell. I took the calliper apart and cleaned it thoroughly and used very fine wet & dry on the piston to clean it. Again there was nothing obvious on inspection but it's worked fine since.

HTH.

Thanks Colin. That's reassuring. I'll change the fluid tonight and bleed then have a look at the calipers at the weekend.

Toby

no smoke coming from the exhaust is there?
if there is this could be where your brake fluid is going.
blown vacuum. so far as i know, you will need a new one.

Checked out the calipers last night. Could see any tears in the dust seal or any leaks. Could be a leak in the brake pipes due to corrosion, or perhaps fluid loss is just due to pad wear and the loss of braking is down to aged fluid?

Couldn't see any smoke, but the burning smell has been intermittent, only occuring occasionally, normally on a long commute, when its not possible to stop and investigate.

I'm probably going to strip down the calipers, clean, reassemble and bleed (letting plenty of fluid run through). I'll also check all the visible brake pipes.

I once had a sticking caliper piston on an XJ6 Jaguar. I kept intermittently losing all the brakes, (which a pedal pumping restored some braking), and it culminated in me losing them downhill going on holiday, on the Telford-Bridgenorth road, and me getting that funny feeling on the back of my hands. Pulling into a conveniently situated garage , found white smokle pouring out from the rear wheel arches etc. The pistons on both had finally stuck fast, the friction had heated up the caliper and toasted the seals.

It was new discs and calipers time !!

Another thing to be aware of. Pads can stick in the carriers. Caused by a build up of corrosion which is thicker than the steel it replaces. So everything looks OK, and the pistons aren't stuck, but things improve by removing and refitting the pads. Real cure is to clean up the mating surfaces on the carriers.