Thread: brakes - testing master cyclinder and servo

Do you need to rebuild it or replace it?

20 pounds plus postage will get you a rebuild kit from Paddocks in the UK. I noticed you can also get a seal kit for the brake booster.
I bought one (MC kit) and did it myself as mine was leaking from the reservior rubbers.

$125 was the cheapest I found locally for the brake master cylinder kit.

Originally Posted by Utemad

Do you need to rebuild it or replace it?

20 pounds plus postage will get you a rebuild kit from Paddocks in the UK. I noticed you can also get a seal kit for the brake booster.
I bought one (MC kit) and did it myself as mine was leaking from the reservior rubbers.

$125 was the cheapest I found locally for the brake master cylinder kit.

Prefer to replace it, as I have no idea what condition the cyclinder is in and would hate to get the kit and have it fail on me.

$298 for a new Master Cyclinder from Ritter's is the best price I have got so far.

More interest though in the process of testing if it is faulty or not ?

Originally Posted by matbor

Prefer to replace it, as I have no idea what condition the cyclinder is in and would hate to get the kit and have it fail on me.

$298 for a new Master Cyclinder from Ritter's is the best price I have got so far.

More interest though in the process of testing if it is faulty or not ?

From my experience, it would be faulty if it let fluid leak out or it let fluid by-pass the seals. Either way the pedal would slowly depress on heavy pressure.

I have only worked on series vehicles and my old trusty XY Falcon.

Maybe the newer braking systems are different.

pump the breaks 5 or 6 times that should exhaust the vac reserve and give you a firm pedal.

if thats all good then the master cylinder is ok providing that the pedal dosent sink

now start the car the pedal should sink to about the 3/4 of max travel position

if that happens then the vac application is good

shut the engine down

you should be able to apply the brakes at least twice with the vacume reserve which you will here letting go

Originally Posted by Utemad

Do you need to rebuild it or replace it?

20 pounds plus postage will get you a rebuild kit from Paddocks in the UK. I noticed you can also get a seal kit for the brake booster.
I bought one (MC kit) and did it myself as mine was leaking from the reservior rubbers.

$125 was the cheapest I found locally for the brake master cylinder kit.

I bought a full seal, rubbers and O rings set for my Disco 93 from the local brake bloke for $25, less than an hour and was back on the road, working well, Regards Frank.

Originally Posted by Tank

I bought a full seal, rubbers and O rings set for my Disco 93 from the local brake bloke for $25, less than an hour and was back on the road, working well, Regards Frank.

I know the older Disco brake master cylinder is heaps cheaper so it would make sense the kit is cheaper too.

Lets be thankful we aren't talking about P38 master cylinders

Originally Posted by Blknight.aus

pump the breaks 5 or 6 times that should exhaust the vac reserve and give you a firm pedal.

if thats all good then the master cylinder is ok providing that the pedal dosent sink

now start the car the pedal should sink to about the 3/4 of max travel position

if that happens then the vac application is good

shut the engine down

you should be able to apply the brakes at least twice with the vacume reserve which you will here letting go

This seems all ok, when I sit at the lights for example, it slowly, and i mean slowly sinks.

if it sinks slowly while the engine is idling I suspect that you have a slight leak from the booster somewhere.

Providing you can get a rock hard pedal with the engine off but hot and it stays up and firm for a prolonged period then the hydraulic side is all good.

the very slow sink might be a case of a stuffed one way vac valve but as I cant put test gear on it from here Id suggest taking it to a brake specialist to confirm it.

fixing the booster generally means taking it and the master cylinder out so you might as well recondition them both.