How hard is it to rebuild a master cylinder? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

odog · 10-25-2012, 09:29 PM

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 · 10-25-2012, 10:14 PM

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

odog · 10-25-2012, 10:26 PM

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 · 10-25-2012, 10:38 PM

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 · 10-25-2012, 10:47 PM

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 · 10-25-2012, 10:52 PM

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 · 10-25-2012, 10:53 PM

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 · 10-25-2012, 11:10 PM

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

**Stocker** · 10-26-2012, 01:22 AM

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 · 10-26-2012, 04:19 AM

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* · 10-26-2012, 05:17 AM

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 · 10-26-2012, 09:01 AM

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

MAK191 · 10-26-2012, 10:01 AM

In my experience, the wheel brake cylinder is more likely the problem. Those are easier to replace and are cheap
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ole dollor · 10-26-2012, 10:31 AM

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 · 10-26-2012, 10:02 PM

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 · 10-26-2012, 10:14 PM

Quote:

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 · 10-27-2012, 04:03 PM

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.

10-25-2012, 09:29 PM	#1
odog Registered User Join Date: Oct 2007 Location: Wendell, Idaho Posts: 608	How hard is it to rebuild a master cylinder? 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. __________________ 1969 4x4 Nothing beats a good rock drill and some dynamite

10-25-2012, 10:14 PM	#2
71K20chevy Registered User Join Date: Jul 2012 Location: Ft Wayne Indiana Posts: 1,204	Re: How hard is it to rebuild a master cylinder? Do you have power brakes? Maybe fluid is leaking into the brake booster? Just a thought. __________________ 71 K20 64 GMC mud truck

10-25-2012, 10:26 PM	#3
odog Registered User Join Date: Oct 2007 Location: Wendell, Idaho Posts: 608	Re: How hard is it to rebuild a master cylinder? 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. __________________ 1969 4x4 Nothing beats a good rock drill and some dynamite

10-25-2012, 10:38 PM	#4
MacGyver72 Registered User Join Date: Sep 2011 Location: Greencastle, IN Posts: 132	Re: How hard is it to rebuild a master cylinder? 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.

10-25-2012, 10:47 PM	#5
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	Re: How hard is it to rebuild a master cylinder? 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.

10-25-2012, 10:52 PM	#6
odog Registered User Join Date: Oct 2007 Location: Wendell, Idaho Posts: 608	Re: How hard is it to rebuild a master cylinder? 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. __________________ 1969 4x4 Nothing beats a good rock drill and some dynamite

10-25-2012, 10:53 PM	#7
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Re: How hard is it to rebuild a master cylinder? 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. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

10-25-2012, 11:10 PM	#8
MacGyver72 Registered User Join Date: Sep 2011 Location: Greencastle, IN Posts: 132	Re: How hard is it to rebuild a master cylinder? You are correct sir. Definitely has to have a leak.

10-26-2012, 01:22 AM	#9
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,722	Re: How hard is it to rebuild a master cylinder? 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. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

10-26-2012, 04:19 AM	#10
long69 Registered User Join Date: Oct 2006 Location: lost angeles Posts: 159	Re: How hard is it to rebuild a master cylinder? 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.

10-26-2012, 05:17 AM	#11
bk2life Account Suspended Join Date: Oct 2012 Location: phx, az Posts: 868	Re: How hard is it to rebuild a master cylinder? 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

10-26-2012, 09:01 AM	#12
odog Registered User Join Date: Oct 2007 Location: Wendell, Idaho Posts: 608	Re: How hard is it to rebuild a master cylinder? I guess I need to keep looking for the leak, I am going to take another look at the wheel cylinders. __________________ 1969 4x4 Nothing beats a good rock drill and some dynamite

10-26-2012, 10:01 AM	#13
MAK191 Registered User Join Date: Nov 2009 Location: FL Posts: 335	Re: How hard is it to rebuild a master cylinder? In my experience, the wheel brake cylinder is more likely the problem. Those are easier to replace and are cheap Posted via Mobile Device

10-26-2012, 10:31 AM	#14
ole dollor Registered User Join Date: May 2012 Location: Anton, Texas Posts: 2,364	Re: How hard is it to rebuild a master cylinder? 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...

10-26-2012, 10:02 PM	#15
odog Registered User Join Date: Oct 2007 Location: Wendell, Idaho Posts: 608	Re: How hard is it to rebuild a master cylinder? 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. __________________ 1969 4x4 Nothing beats a good rock drill and some dynamite



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10-27-2012, 04:03 PM	#17
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	Re: How hard is it to rebuild a master cylinder? 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.

Register or Log In To remove these advertisements.