Binding brakes

[Mike Bey]

I have a problem. It's with my rear brakes, you see. Shall I tell you what happens?

 

This is the way it goes:

Step 1: Go to nice race track for track day.

Step 2: Drive round in circles.

Step 3: Suffer brake fade.

Step 4: Come in to pits to give poor little things a rest.

Step 5: Go out again with brakes refreshed.

Step 6: Come in & park in pit garage.

Step 7: Attempt to go to petrol station (yet again) only to find rear brakes binding on. Call it a day.

Step 8: Drive home, trying to ignore scratchy grinding noise from rear brakes, and requiring only to lift off for T-Junctions as car virtually stops itself.

Step 9: Replace rear pads & discs.

Step 10: Go to nice track for track day.

Step 11: Same thing happens again etc etc.

Step 11: .......and at the next....etc.

 

Now, is this all a function of my having standard front brakes on my de Dion and them not being up to it, overheating, putting too much stress on the rears, which overheat & then bind on? This has happened 3 times in 3 months. This time I am replacing the rear calipers as well as the discs & pads, as I am beginning to suspect that the rear calipers are buggered. Am I just adressing the symptom and not the root cause?

 

Should this be happening, or do I need to upgrade the fronts to 4-pot, or is it likely that it is just shagged rear calipers?

 

Help?

[Nick]

I have a de Dion with standard brakes and have never had the problem you describe, so it can't be a case of TADTS (They All Do That Sir).

Apart from that, I can't help I'm afraid.

Nick

[Graham Perry]

Have you tried bleeding them ? It sounds like your front brakes are not working as they should. About 85-90 % of the braking effort is done by the front brakes, so if problems were occuring there would be the first place to look. Perhaps the fluid in your front brakes is boiling, through either being of poor quality or having absorbed moisture.Brakes often go 'off' over a period of time without you noticing. I just changed the fluid in my road car for the first time in 3 years and 'hey presto' instant bite, a solid pedal and no fade at motorway speeds. Replace the fluid with with some nice high temperature Dot 5 fluid then see if there is a difference. For a fiver and half an hours work it might save you a brake upgrade.

[Mike Bey]

The brakes were bled the last time I had new front pads (6 weeks ago?). The binding at the back is so bad that the new pads that were fitted with new discs before the last track day are down to the metal. The heat was so great that the pad metal is purple & has melted and smeared over the edge of the pad - maybe I should try taking Paddock flat in top??!!**

[Lawrence_Z]

Did you rewind the rear callipers?

 

Lawrence Hoy

Scottish AO smile.gif

[Mike Bey]

Sure did - and they're fine for road use, but during track days they clearly unwind more than they should, so they end up constantly pushing the pads against the discs. This happens to such an extent that the pads last one track day until they're down to the metal!! There is always a lot more brake dust on the rear wheels than the fronts even before the binding occurs, but I think this is a common problem with standard brakes due to the rearward bias.

 

Mike

[Graham Perry]

Having read the subsequent comments. I am more inclined to think that the pistons in the calipers are 'sticky'. This does occasionally happen with Calipers. You don't mention how old they are but I think I might be now tempted to disassemble the rear calipers and see why the pistons are maybe not releasing The rubbers do perish but then they tend to leak as well. You always get a small amount of pad to disc contact but it sounds like your rear brakes are nearly always half on ! Other suggestions - Damage internally to the flexable brake hose between the Chassis and the Di-Dion tube (I have seen this on airbrake systems on trucks, ie a constriction allowing the air or this case liquid to flow in one direction only) , or a fault with the rear brake circuit at the master cylinder ? These are both pretty unlikely though. It sounds a challenging one.

[Allan Haighton]

I don't know whether this helps , but....

 

Once upon a time I had a Reliant Robin (yes, honestly). It suffered the same sort of problem once - the brakes (not disks, of course) locked up solid after a few miles of road driving, and then it shuddered to a halt. (It was actually blocking a minor country road and passing rugby team helpfully lifted it out of the way.....but half a mile earlier I crossed the A1 - just.)

 

Half an hour later it had freed up and could be driven again.

 

The problem turned out to be a master cylinder fault - every stoke of the brake pedal retained a bit of pressure in the system, until eventually the brakes were on full time.

 

Worth checking it? Good luck.

 

Allan