How hard is it to rebuild a master cylinder?

[odog]

Just like the title says, I can get a rebuild kit for a master cylinder from a 67 3/4 truck with front and rear drums for $8. Is it worth doing, or is it a big pain and not really worth the trouble.

I have said master cylinder on my 69 and basically no breaks. The pedal goes to the floor and has little resistance. I have to add fluid about once a month, I have blead the system and cant find any leaks. The only thing I havnt tried is replacing the master cylinder.

[71K20chevy]

Do you have power brakes? Maybe fluid is leaking into the brake booster? Just a thought.

[odog]

No power brakes, just manual, I am at a loss as to where the fuild can be going. I checked the brakes cylinders, the lines, the bleeders, everything and can find no wet spots, or anything indicating a leak.

[MacGyver72]

I had the same thing with a 62 impala. Replaced the MC and no more issues. I was told that the MC wasn't holding pressure and back bleeding itself. Whatever that meant.

[Wrenchbender Ret]

The single master cyls are easy to rebuild. The dual cyl. is more difficult but not all that hard. I used to do the duals myself but the kits were almost the same price as a Reman. so I just exchanged them. I dont know how you can get a kit for $8.00.

[odog]

A friend of mine went through his dads old parts stash and came across one, said I could have it for a 12 pack of beer, basically $8.00.

[Andy4639]

There is got to be a leak some where! If your adding fluid every month are so. Have you took the drums off and looked inside at the wheel cylinders. They may be leaking but the heat of the brakes is causing it to appear as they aren't. Brake fluid will evaperate pretty quick when hot.
Cheap insurance is to replace them if they haven't been replaced before though.
MacGyver72, un like his your's is loosing fluid so it's got to be a leak somewhere in the system.

[MacGyver72]

You are correct sir. Definitely has to have a leak.

[Stocker]

I agree with the above posts -- if you have to add fluid, it's leaking out somewhere, you just haven't found the leak yet. The MC might be bad -- but a bad MC can't make fluid disappear.

[long69]

had a M/C leak at the rear. if i had carpet never would have known maybe. this was in a chevelle, took about a day and a half to go dry. the rust holes let it drain out the floor.

[bk2life]

rebuilding a MC is pretty straight forward and plenty of-how to's on the 'net, but if it were me id go to the parts house and pay 20 bucks and get a new one, with a warranty.

and if you have even the slightest leak the pedal will go to the floor. if it is a dual MC then if you had a leak at the rear the pedal will still go to the floor but youd have some breaking ability to stop your truck.

BLUF: find the leak

[odog]

I guess I need to keep looking for the leak, I am going to take another look at the wheel cylinders.

[MAK191]

In my experience, the wheel brake cylinder is more likely the problem. Those are easier to replace and are cheap
Posted via Mobile Device

[ole dollor]

odog: look and see if your firewall inside the truck is wet where the master cylinder is bolted and the brake rod is, you can rebuild one fairly easy, just take if off and remove the clip that hold the pistons and seals and springs. take note of how all the stuff inside comes out, you may have to use air pressure to get the pistons and springs and seals to come out, clean the cylinder up real good and use a hone to run in the boar , and after honing the boar out check and see if you have any pits, if everything is smooth then you can rebuild it yourself, if its pitted real bad than you need to replace it...you said your friend has a kit, if the kit is real old than make sure the rubber cups are still good, and will seal properly ....its not hard at all, but at the price of a new or rebuilt master cylinder these days. it would be up to you....good luck on the truck

with a bad rubber inside the master cylinder it can bypass fluid , with the pits,wore out rubber seals, and dirt that live in old brake fluid...

[odog]

Thank you guys for the answers. I will tear into the wheels and check the cylinders. The firewall has paint peeling off around the master cylinder, like it has gotten brake fluid on it, and that is what has been leading me to believe that was the problem. I will try to get into it as soon as I get a free minute. I will let you all know how it goes.

[Andy4639]

Originally Posted by odog

Thank you guys for the answers. I will tear into the wheels and check the cylinders. The firewall has paint peeling off around the master cylinder, like it has gotten brake fluid on it, and that is what has been leading me to believe that was the problem. I will try to get into it as soon as I get a free minute. I will let you all know how it goes.

That right there could very well be the problem. If it's leaking then you get the rebuild kit and go at it.

[Wrenchbender Ret]

Ole dollar gave a good rundown on rebuilding it but on a dual master cyl. you have to remove the pin that locksout the rear cyl. Some models screw in from the bottom & some are in the bottom of the reservoir.