Master brake cylinder overhaul

[kenhug]

Having been persuaded by several knowledgable folks on here that I need to overhaul my brake master cylinder I have purchased a seal kit (at extraordinary cost, but that's what you get for trying to keep a bit of history on the road I guess) and I removed the master cylinder this morningwhile the sun shone ... but no way can I see how to get the piston out to replace the seals ! Can anyone help with a simple solution ? The manual says "Pull the piston and valve assembly from the cylinder." The problem is there ain't no way to get hold of the piston. I've tried shoving it in with the push rod and releasing it quickly, but it seems to be held in place somehow and comes to a stop in the same position every time. I've also tried pouring boiling water over the outside, in the hope of causing sufficient expansion to release the piston, but it stayed obstinately in place with a smirk on its face.

[types26/36]

You have of course taken out the circlip in the end of the bore
If it is just a single circuit master cylinder then banging it down onto a piece of wood usually pops the piston out far enough for it to be gripped with pointed nose pliers, if it is a tandem master cylinder that I believe there is a locating grub screw that has to be removed (others will know better)

[bill308]

I've never had very good luck rebuilding hydraulic cylinders, except calipers. My recommendation is to purchase a new master cylinder if you can find one and take good care of it.

Bill

[mdf]

After removing the circlip cover the reservoir hole with your hand and blast Compressed air into the outlet pipe hole - this should shoot the piston out unless it is totally stuck.

Good luck.

-MF

[Frank Howard]

Whatever your name is,

If you have a tandem master cylinder there is a thing called a tipping valve that mechanically holds the piston in. It must come out before the piston is removed. Here is a direct quote from the Girling rebuild kit instructions:

"Access to the tipping valve securing nut is gained by pivoting the tank at the center valve end...Unscrew the tipping valve securing nut and remove the face seal. Depress the primary plunger and remove the tipping valve. The internal part may now be removed either by shaking the cylinder body or by applying compressed air pressure to the centre valve inlet connection."

Hope this helps.

[kenhug]

Yep, I've removed the circlip that holds the push rod in place ... wish it was that simple It's a UK spec cylinder, so not a tandem system. A friend suggested the compressed air trick last night, so that seems to be favourite. Thanks all for your input !

Ken
Poole UK

[512BB]

Hi Ken,

The compressed air route is the way to go. I keep a piece of old brake hose with a male fitting to hand when doing this job.

However, a difficult to remove piston is quite often indicative of the piston starting to rust in the bore, and that will mean a new unit. They rust readily if the brake fluid has not been changed frequently enough, allowing the ingress of water into it, and hence the rust. The same with caliper pistons if they are not stainless.

Good luck,

Leslie

[paddy]

Another possibility is that there is a slight burr in the bore where the (outer) circliip land is. If you force the piston out past the burr you may score the piston, so worth checking.

Paddy

[alexblack13]

Hi, Take care with the compressed air method. The piston may exit at high velocity. Do not have it pointed at anyone when you do this. It should shift it. Slight burs are a problem where someone has had a 'fiddle' with the circlip. So have a look 1st and carefully remove if you can. Shouldn't mark your piston though, its steel and the cyl is ally.

I normaly use a grease gun applied to a screwed in grease nipple. Not quite as explosive. Make sure its spotless when rebuilding. I also use a small Delapina type hone (three legger. Very fine stones) to clean up the bore. Follow the kit instructions to the letter re lub etc, and it will be fine.

Take care here...

Alex B....

[kenhug]

Took the master cylinder down to the local classic car garage (the ones who failed so dismally to sort the brakes out in the first place) and suggested they might make partial amends by helping me to get the piston out. I mentioned the compressed air trick, but they first tried tapping the cylinder hard on a block of steel and that did the trick nicely ... not something I wanted to do on the kitchen worktop, especially as I rent the flat rather than own it. To everyone who suggested that the cause of the fading brake pressure might be the master cyclinder seals, award yourselves 10/10. The small seal at the far end of the piston had turned to a very nasty black sticky mush that stuck to everything and took much cleaning with white spirit to get rid of. The whole thing has been cleaned with meths and re-assembled with new seals ... the next challenge is to re-fit it (needing to be in two places at once, the driver's foot well and the engine bay) and then bleed the brakes in a confined space. I've enlisted a mate to hep with that, so thanks to Leslie for the offer of help on one of his trips to Bournemouth but I think I've got it sorted mate

Ken
'67 Elan S3 dhc