Dave repairs a reluctant rear caliper. - many pics.

[dave21478]

The left rear caliper of the MGF has been binding slightly for a while now, which manifests as one wheel hotter than the others after a run and a slight feeling of braking when rolling slowly and increased fuel consumption. (By the way, tracking your fill-ups with an app like Fuelio isnt just for nerdy MPG-bragging, its a reasonable indicator of something going wrong with your car...the MGs average dropped from 6.something litres per 100 km to 7 litres without a change in driving style showing more fuel was being used due to a problem.)

Today it got worse, gripping hard enough to overheat and boil the brake fluid, meaning braking needed a few pumps on the pedal to build enough pressure to compress the vapourised fluid at that caliper and actuate the rest of the brakes. I stopped to let it cool down and nursed it home, then had a peek....

 

Jack, axle stand etc blah blah - if you need to be told this sort of thing, dont go fucking with your brakes.

Clamp the flexi hose gently with mole grips and remove the caliper and the carrier from the hub....this is a million times easier on the workbench than dangling under the car.

 

Single piston sliding calipers like this need to be able to slide freely side to side in operation. The two pins in the carrier should move freely.

Still grease here...

The other was a bit manky, but cleaned up fine with emery paper.

 

You need to get the piston out. The MGF has the handbrake mechanism integrated so it can be used to move the piston. Front calipers might need brake fluid forced in using a clean grease gun screwed into the fitting for the flexi hose.

 

Use a spanner on the handbrake lever...

 

and crank it out....

 

You can see the central threaded part here, along with the main sealing ring around the top of the hole the piston slides into. It was all full of slightly gritty dirt, so needed a good clean out...

 

The piston was dirty and had very minor corrosion in places, which cleaned right up with ease using wire wool and brake cleaner.

 

 

Aerosol tins of brake cleaner are a fucking God-send for the home mechanic. I buy them in cases of 24 via ebay where it works out pretty cheap so I dont feel bad hosing half a can to clean up a few bits and pieces.

 

If there is a lot of corrosion or pitting on the piston, its fucked and needs replaced. Depending on the car you might get away with just a new piston and a seal kit, but its then maybe not much more for a whole reconditioned caliper.

 

Unscrew the bleed nipple. Get the right size spanner on it and go gently, working it back n forth a tiny amount to free it off to hopefully avoid snapping it.

 

Im missing a photo here, but basically there was no sign of damage on the seal around the edge of the hole in the caliper, so a good clean out and it can go back together.

 

It can be a twat to get the seal to sit right. In this case, it was easier to take the seal off the piston and fit it to the caliper, then press the piston in place while pulling the lip of the seal over the edge of the piston.

 

You will need this style of caliper wind-back tool....

 

Yeah, you can fuck about wedging pointy pliers into the dimples on the piston and screwing it in that way, but its just so much easier with the right tool, and they are cheap enough on the ebay.

 

Lube the seal with clean brake fluid and wind it in.

 

On the carrier, use a wire brush (I used one mounted in a grinder because lazy) to clean up the faces where the pad retaining slips sit. Corrosion here will make the pads jam and stop the piston sliding easily.

 

Reassemble and bleed the brake.Frankly, just unscrewing the nipple and letting the fluid slowly run out does most of the job. 

make sure the level in the master cylinder doesnt drop far, then for the last little effort the body of an old syringe and a bit of rubber tube on the nipple means you can draw out any remaining air.

 

Wheel on and with the engine running gave the pedal a few pumps to push the piston out and make the pads contact the disc.

 

Job done, have a beer.

 

[clayts450]

Nice write up, Dave, and very timely for me as I'm fitting a replacement caliper on the 45 tomorrow.

 

The BOL for the 45 suggests you can forego clamping the brake hose by putting clingfilm over the master cylinder and sealing it with the cap. Seems a bit of a bodge, and I'd prefer clamping the hose, as recommended by RAVE.

 

Handy tip on the syringe too - never would have thought of that.

[beko1987]

That's more of a full overhaul isn't it?

 

 

Watch the other side seize up in 3 weeks... My cheap ebay caliper rewind kit has been amazing, could not live without it now!

[DodgeRover]

Nice write up, Dave, and very timely for me as I'm fitting a replacement caliper on the 45 tomorrow.

 

The BOL for the 45 suggests you can forego clamping the brake hose by putting clingfilm over the master cylinder and sealing it with the cap. Seems a bit of a bodge, and I'd prefer clamping the hose, as recommended by RAVE.

 

Handy tip on the syringe too - never would have thought of that.

Vacuum using clingfilm will work but a fair bit of fluid will be lost, until enough vacuum is established to stop the flow, gentle clamping will avoid this.

 

Nice write up too Dave.

[twosmoke300]

Very good apart from mole grips on the brake hose . Makes me wince !

As well as clamps I also have an old pair of mole grips that I welded a bit of 8mm bar at 90deg to each jaw.

Or just hold the brake pedal down an inch with a bit of wood. No fluid will drip out then

[Pillock]

Really good writeup that, thanks Dave.

 

Weird innit.... I'll get involved with changing an engine or a gearbox by myself on the driveway but brakes scare the living daylights out of me. I'll change disks and pads but anything involving hoses being disconnected and fluid.... Straight to a garage

[steveo3002]

i find clamping used hoses often results in a buldge soon after ...prefer to let it drip or make up a blank , nipple covers will seal a flared pipe well

[dave21478]

The danger in letting it drip is your repair takes longer than planned and you run the master cylinder low, needing a full system bleed afterwards.

The key word when clamping is "gently". If it takes any real effort to lock the mole grips, they are too tight....you are supposed to be just closing the pipe, not crushing the life out of it.

[clayts450]

I've got one of these for piston winding back, supposed to do the do on Rovers anyway (not much use for the Streetwise as that has drums for rears). The PT Cruiser is straightforward,  a G clamp works on the rears.

 

 

https://www.amazon.co.uk/Draper-52334-8-Inch-Square-Caliper/dp/B0001K9V0E

[Simonsays]

Excellent post, would read again!

[Guest Hooli]

I've always used red rubber grease to lube things up before reassembly. Seems to stop the white crustyness that often appears where the fluid & water mix.

 

Syringe is a good tip & if you've got a dry system where the master cylinder won't prime then you can suck it all the way through like that too. Or just fill it backwards - both can be damn handy on bike front brakes.

[sierraman]

Buy the hose clamps. They are only cheap, a set is less than a tenner.

[Tamworthbay]

I've always used red rubber grease to lube things up before reassembly. Seems to stop the white crustyness that often appears where the fluid & water mix.

 

Syringe is a good tip & if you've got a dry system where the master cylinder won't prime then you can suck it all the way through like that too. Or just fill it backwards - both can be damn handy on bike front brakes.

Another vote for red rubber grease here, but it seems not many use/ know about it. Took a while to find some when I needed it.

[Guest Hooli]

Another vote for red rubber grease here, but it seems not many use/ know about it. Took a while to find some when I needed it.

 

I found mine on ebay & think this pot will probably last a lifetime as you never need much do you?

[overrun]

Nice one Dave.

I stuck a new piston and seal kit in a front caliper on my Ssangyong, the other week.

Mole grips on the brake hose, and 30 quid on a Bigg Red kit (both sides).

Bleed that one corner afterwards. Piece of piss and happy days.

[Rave]

Yes as others have mentioned a new piston and seal is pretty cheap from Bigg Red, 15 quid a side for my 106 ones, so it is a lot cheaper than a reconditioned caliper, and if you're going to go to the bother of stripping it all down it seems to me you might as well have a nicely chromed new piston in there that will hopefully last a bit longer than one that's been rubbed down with emery paper. Not being in the UK may complicate the calculations of course!

 

As for red rubber grease, it's easy to get hold of:

 

https://www.eurocarparts.com/ecp/p/-/-/-/-/?526770270&&ws5_0023

 

For some reason they seem to have banged the price up and the current discount code doesn't do anything, I'm sure I paid about a tenner for my pot.

 

Oh hang on, here we go:

 

https://www.carparts4less.co.uk/cp4l/p/-/-/-/-/?526770270&0&ws5_0023&gclid=CjwKCAjw9-HZBRAwEiwAGw0QcSNONPHVTJfnD9xmvLuUG5m8A3BQvTGaW-5nvxAcBwSYBY0ZiUnG4xoCHzcQAvD_BwE

 

£9.69 with the current code.