Grr. Stuck disc brake!

[Bumpa]

I recently had new front tyres on my Z3 and afterwards I found I had wheel vibration at 60+ mph. So back I went to the tyre dealer, who is a local man I have dealt with for years. He couldn't understand it, but rebalanced the wheels carefully. Today I went out in the car and the wheel vibration was back with a vengeance. What's going on, I thought.

When I got home and got out of the car there was a strong "hot" smell from the right front. The right front wheel was almost too hot to touch. The left front wheel was cold. These are single piston calipers aren't they? (it's a 2002 2.2 Sport). I suppose the sliding caliper has got stuck. Do you think that's right?

Ah well, it will have to wait until after the hols. My garage is full of dismantled V8 MGB at the moment and I have no time to tackle anything else. Bah.

 

[Synclare]

Quite common issue, more likely a binding piston in the caliper. Fronts fortunately are not expensive, think @seand found a cheap source.

 

[Grumps]

I've had a front one seize on me. Very common and not dear to repair.

 

[Brian4]

Hi @Bumpa as above a common issue with sticking piston especially if it has had new pads and/or discs recently. I guess you are handy with spanners as is is fairly easy to change just the pistons and seals. The chrome coating on the piston corrodes so no worth trying to clean the existing piston.

Old and new pistons. These are from Brake parts

 

[Bumpa]

It had new pads and discs just before I bought it and it has only done a couple of thousand miles since, but with fairly long periods of inactivity. I really don't want to have to get into the hydraulics. These things with ABS and lord knows what else, frighten the life out of me. Give me my simple MGB any day. Is there any special procedure for bleeding the brakes?

 

[t-tony]

I would let it gravity bleed personally. Just going out can explain more later.

Tony.

 

[Brian4]

If you take the calipers off you need some of these blanks to put on the end of the steel pipes and then you will get minimal fluid loss. When reconnected you can use a normal pressure bleeder. As long as air doesn't get back up to the ABS pump you will have no probs.

is it a bleed nipple screwed into a brake joint collar. Mine were left for a few days whilst I refurbed the calipers.

 

[Pingu]

There's probably no need to replace anything. Just work the piston back and forwards a few times.

Push it out using the brake pedal - use a block of wood to stop it going too far.

Pushing it back is not so easy. I've used a small woodworking vice like this...

but I recently made a tool which make life much easier (https://zroadster.org/threads/brake-piston-tool.26236/#post-437740).

Don't put any stress on the brake hose. I hold the caliper with a bungy tied to the spring. If you forget to undo the bungy afterwards there is a nasty rattling noise that is embarrassing to identify.

 

[Mint]

Pushing it back is not so easy.

I use a big woodworking 'G clamp'

 

[mwpe]

I had this problem several times over the years with my old Triumphs. I always exercised the pistons a @Pingu suggested, a G clamp is good for pushing them back. I also used to squirt a little drop of brake fluid behind the seals.

 

[Mint]

Had to 'exercise the pistons' as Mike says on my 2.2 a few times over the years. May go for some new ones next time.

 

[the Nefyn cat]

There you go, used their stuff before with no problems.

https://www.ebay.co.uk/itm/BMW-Z3-E...nvertible|Engine:2171ccm+170HP+125KW+(Petrol)

And a bit of cling-film over the filler hole on the master cylinder and putting the cap back on will stop the fluid draining out.

 

[colb]

Price wise you might as well get calipers off ebay and just put them on with no faffing about cleaning the old ones up.
example https://www.ebay.co.uk/itm/BMW-Z3-R...itm=352093443837&_trksid=p2047675.c100623.m-1

Do shop around with the usual on line suppliers to find the best price also look for their discount codes and offers pays to sign up to the sites that offer deals then you get their emails with discount offers.
Carparts4less
Brakes International
GSF

 

[Bumpa]

If you take the calipers off you need some of these blanks to put on the end of the steel pipes and then you will get minimal fluid loss. When reconnected you can use a normal pressure bleeder. As long as air doesn't get back up to the ABS pump you will have no probs.

is it a bleed nipple screwed into a brake joint collar. Mine were left for a few days whilst I refurbed the calipers.

View attachment 94049

Brian, how would I specify the correct bits to make a couple of those plugs? Looks like a good idea.
Mike

 

[Bumpa]

I would let it gravity bleed personally. Just going out can explain more later.

Tony.

Yes please Tony. Further explanation would be welcome. I've done bottom up bleeding on empty MGB systems, but have never tried the gravity technique. How long does it take?
Mike

 

[Brian4]

Brian, how would I specify the correct bits to make a couple of those plugs? Looks like a good idea.
Mike

Hi Mike they are M10 bleed nipple and M10 female connectors. Just found these as well. M10 female blanks.
https://www.automec.co.uk/products/brass-brake-pipe-fitting-female-m10-x-1mm-blanking-plug.

They do sell the connectors.
https://www.automec.co.uk/collectio...ducts/brass-inline-connector-female-m10-x-1mm

 

[Bumpa]

Thanks Brian. I'll get some.
Mike

 

[Nodzed]

If the piston(s) is corroded just change it, its a cheap simple job did my rears in February, not worth future hassle in my opinion.

 

[Pingu]

Gravity bleeding is OK as long as the pipes and hoses don't loop from up to down at any point in the system.

If they do, the fluid will only flow enough to go over the top of the bend, thus leaving a potential air gap at the top of the loop above the fluid.

When pressure is applied to the system, the air bubble will be moved over the loop and the "solid" fluid will be compressible.

 

[t-tony]

Gravity bleeding is OK as long as the pipes and hoses don't loop from up to down at any point in the system.

If they do, the fluid will only flow enough to go over the top of the bend, thus leaving a potential air gap at the top of the loop above the fluid.

When pressure is applied to the system, the air bubble will be moved over the loop and the "solid" fluid will be compressible.

Wrong info. If the master cylinder is the highest point of the system it will push all air out.

Tony.