General Sticking brake disc caliper

[unostar]

My nearside front brake is sticking on intermittantly on my 1989 45s 999cc. I have removed caliper from the fixing but the piston is covered by a thin rubber seal. This looks in tact so i don't want to break it if its doing its job. Anyone had the same problems? Is it a case of stipping out the piston to see if there is any pitting on the cylinder bore? Your thoughts please fellow Uno lovers!!

regards Unostar

 

[johorridoh]

If you can´t easily move the piston by hand ( pushing or turning ) , it is corroded inside.
I tried everything trying to fix that but it is the best idea to get refurbished ones.
Anyway, by pressing the brake a couple of times, the piston will fall out.
If there are grooves in the alloy bore inside, it has to be replaced.
The rubber seal is sitting in a bezel and can be easily removed.
Don´r try to wash it with cold cleaner, it will macerate.
The piston can be corroded. If that is the only trouble you can try to polish it.
Good luck Jo

 

[Barney vd Merwe]

Undoubtetly the caliper is not at fault here, I experienced the same problem twice on 2 different Uno's. The brake hose is blocked - save yourself the trouble and money, don't dismantle the piston on the caliper as yet. Buy a new hose at your local spare shop - don't even try to unblock the "old" hose after removal - Trust me !

Good luck!

 

[alexGS]

Well I believe that you are both right. Both situations are possible.

If the caliper piston is hard to turn/move even with the bleed nipple slackened off, then the piston is corroded. It can be cleaned up (using a wirebrush mounted on a bench grinder) - don't try to clean the aluminium bore in the caliper - and as Jo said, don't try to remove the rubber seal, just press the brake pedal until the piston comes out. You can get replacement seal kits and I have replaced them in the past, but to be honest, it's rare to see a leaking caliper.

Seized/sticking pistons were a common problem with X1/9 front calipers, which are practically identical to the Uno calipers.

Meanwhile a blocked brake hose causes the caliper to stick 'on' because the fluid, while pumped in past the restriction under pressure, cannot escape because there is no pressure generated by the caliper to push the fluid back.

I imagine in a dry place like South Africa it is less common to see piston corrosion problems, which are due to water absorbed in the hydraulic fluid (from atmospheric humidity, etc.) and possibly salt water from the outside if the seal is damaged and the brakes are really drenched in winter driving.

There is also the third possibility that the wedges on which the caliper slides could be rusted/seized.

-Alex

 

[unostar]

Well I believe that you are both right. Both situations are possible.

If the caliper piston is hard to turn/move even with the bleed nipple slackened off, then the piston is corroded. It can be cleaned up (using a wirebrush mounted on a bench grinder) - don't try to clean the aluminium bore in the caliper - and as Jo said, don't try to remove the rubber seal, just press the brake pedal until the piston comes out. You can get replacement seal kits and I have replaced them in the past, but to be honest, it's rare to see a leaking caliper.

Seized/sticking pistons were a common problem with X1/9 front calipers, which are practically identical to the Uno calipers.

Meanwhile a blocked brake hose causes the caliper to stick 'on' because the fluid, while pumped in past the restriction under pressure, cannot escape because there is no pressure generated by the caliper to push the fluid back.

I imagine in a dry place like South Africa it is less common to see piston corrosion problems, which are due to water absorbed in the hydraulic fluid (from atmospheric humidity, etc.) and possibly salt water from the outside if the seal is damaged and the brakes are really drenched in winter driving.

There is also the third possibility that the wedges on which the caliper slides could be rusted/seized.

-Alex

When the snows stop I will remove caliper and clean up the wedges as they did have rust on them when I removed them last. If the problem persists I will try to move the piston in the caliper body and take it from there. Thanks to everyone for your thoughts.
Kind regards Unostar

 

[jermont]

Undoubtetly the caliper is not at fault here, I experienced the same problem twice on 2 different Uno's. The brake hose is blocked - save yourself the trouble and money, don't dismantle the piston on the caliper as yet. Buy a new hose at your local spare shop - don't even try to unblock the "old" hose after removal - Trust me !

Good luck!

Yes, I supported the idea of barney, I experienced the same in my FIAT UNO 1.3 diesel.

 

[unostar]

Stripped the caliper from car today. The flexible hose was clear but the piston was very tight in the bore. I have decided to buy a recon unit for £24. I had to cut open the old caliper to see what was causing the problem only to find that the piston was very rusted and the bore of the caliper was badly pitted. Here in the UK we have non-ferrous scrap merchants so the old caliper will be going in for cash!!! I was surprised to find that the solid pipe to flexible joint undid without snapping as my car is a 1989 Uno 45s!! Will keep you posted of events.

 

[alexGS]

Thanks for the update. I think I tripped over a couple of appropriate calipers in my garage just the other day. Pity that postage to the UK is likely to be expensive and take at least a week...

-Alex

 

[UnoMia]

I had a very similar problem with my Uno a couple of years ago. The one front brake was binding. I tried everything before changing the flexible rubber hose that supplies the caliper. After that it was working 100% again! I found that the hose had collapsed internally and was not allowing the fluid to flow back towards the master cylinder when the brake pedal was released. This resulted in the one caliper effectively staying 'on' until the fluid gradually flowed back past the blocked hose. From the outside the hose looked in good nick, that's why I only changed it as a last resort.

 

[sludgeguts]

I had a brake binding problem only after driving a few miles. After replacing the complete system (and I do mean everything!) an email from a panda driver in the USA directed me to the switch operated by the brake pedal.
10 minutes under the dash cured the problem.
It seems that the switch had somehow managed to find a way of getting closer to the brake pedal, therefore pressing it ever so slightly. Of course, the tolerances between pads and discs (especially when brand new) are very fine. The pressure of the switch on the pedal was just enough for the pads to 'just' skim the disc - as the pads & disc skimmed past each other, they heated up to the point where they would bind.
Complete brake system inc pads, discs, callipers, drums & shoes - £900
13 hours solid internet & leaving messages on every forum I could find then discovering the fix is a simple 10 minute job costing nothing - priceless:bang::bang::bang:

 

[UnoMia]

Hi,
Yes, I've heard of this problem before. The brake light switch, which acts on the pedal screws itself down onto the pedal after a time and can cause the brakes to effectively stay slightly on. I read about it somewhere a few years ago but it's never happened to me - but it can happen!

 

[tsirhclig]

The the same problem before. The hose is the culprit. After replacing it wooolah it's not sticking anymore

I had a very similar problem with my Uno a couple of years ago. The one front brake was binding. I tried everything before changing the flexible rubber hose that supplies the caliper. After that it was working 100% again! I found that the hose had collapsed internally and was not allowing the fluid to flow back towards the master cylinder when the brake pedal was released. This resulted in the one caliper effectively staying 'on' until the fluid gradually flowed back past the blocked hose. From the outside the hose looked in good nick, that's why I only changed it as a last resort.

 

[unostar]

Replaced the caliper today and rebled the system and the car is like brand new. Thank you all for the advice. Kind regards Unostar