Everyone should go out and check their brake fluid level - The 1947 - Present Chevrolet & GMC Truck Message Board Network

pritch · 08-28-2013, 10:20 PM

My brakes are really good. Power drum/drum, but I can stop on a dime and leave 7 cents change. I rebuilt them with all brand new stuff, and have never had an issue. I can lay on them at 60 mph with my hands off the wheel and it stays straight as a string.

But the other day, I came up to a raised railroad crossing just around a little bend in the road and I was going a little bit faster than I should have been so I stomped on the brakes. I slowed down OK, but my brake light came on. "That's odd" I thought, and figured it was just a combination of the hill and turn and hitting the brakes harder than normal, but I stopped at the next gas station I came to and popped the top off my master cylinder and sure enough, the rear reservoir was empty! I looked all over and couldn't see a leak anywhere. I guess it's a mystery where the fluid went, but I filled it back up and gave it a bleeding when I got home. I still can't find a leak anywhere. I guess I'll have to pull my wheels off and look closer, but it's a strange deal. So go out and check your brake fluid level. I'll make that a check I do when I check my oil from now on.

**LockDoc** · 08-28-2013, 10:36 PM

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This is really a coincidence. I was starting the vehicles today that hadn't been started in a while and I backed the Green '67 up so I could get the wife's Jeep up to the shop to change the oil. When I put on the brakes they didn't feel right so I checked the fluid and sure enough the rear reservoir was almost dry. I can't see any obvious leaks either. None of the brake drums look wet on the bottom side. I put fluid in it and they pumped up good. I will check it in the morning to see if I can see anything. I checked all of the master cylinders after that. The Blue '67 rear reservoir was low also.

LockDoc

slow-1 · 08-28-2013, 10:48 PM

Brake fluid doesn't evaporate...y'all have a leak somewhere...mine were in two different lines leading to the rear along the frame...neither were obvious on first inspection.

40 year old brake lines rust and get pin holes in them ...now go spend some time under your trucks and find those leaks.

hotrod100 · 08-28-2013, 11:06 PM

You might want to unbolt the master cylinder and pull it forward a bit to check for a leak from the piston. If the master cylinder is leaking from here it will deplete the fluid in the rear reservoir and is also hard to see without taking the two mounting nuts off.

**LockDoc** · 08-28-2013, 11:16 PM

Quote:

Originally Posted by slow-1

Brake fluid doesn't evaporate...y'all have a leak somewhere...mine were in two different lines leading to the rear along the frame...neither were obvious on first inspection.

40 year old brake lines rust and get pin holes in them ...now go spend some time under your trucks and find those leaks.

I replaced all of the brake lines on the Green '67 two years ago.... I'm suspecting a wheel cylinder.

LockDoc

J kippin · 08-28-2013, 11:37 PM

Had a similar problem with my 71 super. I knew I had a leaking rear wheel cylinder. I replaced all the rear brake hardware and sure enough A while later I "lost all the brake fluid again.
As I was getting ready to add more fluid I randomly pulled the vacuum line off the booster to my surprise it was wet with fluid.
I replaced the master cylinder with a new unit but found the booster was half full of fluid.
pull the master cylinder and check the rear seal if you are loosing fluid,you may be surprised.

**LockDoc** · 08-29-2013, 12:02 AM

Quote:

Originally Posted by J kippin

Had a similar problem with my 71 super. I knew I had a leaking rear wheel cylinder. I replaced all the rear brake hardware and sure enough A while later I "lost all the brake fluid again.
As I was getting ready to add more fluid I randomly pulled the vacuum line off the booster to my surprise it was wet with fluid.
I replaced the master cylinder with a new unit but found the booster was half full of fluid.
pull the master cylinder and check the rear seal if you are loosing fluid,you may be surprised.

I don't have a booster but I will check on the inside of the firewall and under the floor mat in the morning...

LockDoc

**GMCPaul** · 08-29-2013, 05:42 AM

Most common culprit is a small leak on the rear wheel cylinder, it leaks so little initially that quite often the fluid gets burnt off from brake drum heat before reaching the outside of the rear drum. When the seal goes to leaking on the rear of the master cylinder its generally quite noticeable on the reduction of braking quality due to the leak and without a booster you should notice a brake fluid smell in cab when a master cylinder starts leaking on a manual brake truck, where as a small rear cylinder leak you generally do not notice any difference in braking quality until the seal blows completely dumping the fluid out.
Paul @ GMCPauls

08-28-2013, 10:20 PM	#1
pritch Registered User Join Date: Mar 2004 Location: Hoytsville, Utah Posts: 3,365	Everyone should go out and check their brake fluid level My brakes are really good. Power drum/drum, but I can stop on a dime and leave 7 cents change. I rebuilt them with all brand new stuff, and have never had an issue. I can lay on them at 60 mph with my hands off the wheel and it stays straight as a string. But the other day, I came up to a raised railroad crossing just around a little bend in the road and I was going a little bit faster than I should have been so I stomped on the brakes. I slowed down OK, but my brake light came on. "That's odd" I thought, and figured it was just a combination of the hill and turn and hitting the brakes harder than normal, but I stopped at the next gas station I came to and popped the top off my master cylinder and sure enough, the rear reservoir was empty! I looked all over and couldn't see a leak anywhere. I guess it's a mystery where the fluid went, but I filled it back up and gave it a bleeding when I got home. I still can't find a leak anywhere. I guess I'll have to pull my wheels off and look closer, but it's a strange deal. So go out and check your brake fluid level. I'll make that a check I do when I check my oil from now on. __________________ '68 Panel Project Boogie Chillin' '68 C-10 Ol' Green

08-28-2013, 10:36 PM	#2
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,394	Re: Everyone should go out and check their brake fluid level - This is really a coincidence. I was starting the vehicles today that hadn't been started in a while and I backed the Green '67 up so I could get the wife's Jeep up to the shop to change the oil. When I put on the brakes they didn't feel right so I checked the fluid and sure enough the rear reservoir was almost dry. I can't see any obvious leaks either. None of the brake drums look wet on the bottom side. I put fluid in it and they pumped up good. I will check it in the morning to see if I can see anything. I checked all of the master cylinders after that. The Blue '67 rear reservoir was low also. LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

08-28-2013, 10:48 PM	#3
slow-1 Registered User Join Date: May 2013 Location: Central NC Posts: 830	Re: Everyone should go out and check their brake fluid level Brake fluid doesn't evaporate...y'all have a leak somewhere...mine were in two different lines leading to the rear along the frame...neither were obvious on first inspection. 40 year old brake lines rust and get pin holes in them ...now go spend some time under your trucks and find those leaks. __________________ 1972 Cheyene C-10 "Ole Green" My Grandfathers truck (early 70's to 1983) My first vehicle (1983) Original 350 (3 rebuilds) 700R4 from Bowtie Overdrives

08-28-2013, 11:06 PM	#4
hotrod100 Registered User Join Date: Aug 2009 Location: Bullhead City, AZ. Posts: 88	Re: Everyone should go out and check their brake fluid level You might want to unbolt the master cylinder and pull it forward a bit to check for a leak from the piston. If the master cylinder is leaking from here it will deplete the fluid in the rear reservoir and is also hard to see without taking the two mounting nuts off. __________________ My build thread.

08-28-2013, 11:37 PM	#6
J kippin Registered User Join Date: Apr 2012 Location: Cape Neddick Posts: 215	Re: Everyone should go out and check their brake fluid level Had a similar problem with my 71 super. I knew I had a leaking rear wheel cylinder. I replaced all the rear brake hardware and sure enough A while later I "lost all the brake fluid again. As I was getting ready to add more fluid I randomly pulled the vacuum line off the booster to my surprise it was wet with fluid. I replaced the master cylinder with a new unit but found the booster was half full of fluid. pull the master cylinder and check the rear seal if you are loosing fluid,you may be surprised.

08-29-2013, 05:42 AM	#8
GMCPaul Senior Member Join Date: Mar 2000 Location: Rockville,In. USA Posts: 3,718	Re: Everyone should go out and check their brake fluid level Most common culprit is a small leak on the rear wheel cylinder, it leaks so little initially that quite often the fluid gets burnt off from brake drum heat before reaching the outside of the rear drum. When the seal goes to leaking on the rear of the master cylinder its generally quite noticeable on the reduction of braking quality due to the leak and without a booster you should notice a brake fluid smell in cab when a master cylinder starts leaking on a manual brake truck, where as a small rear cylinder leak you generally do not notice any difference in braking quality until the seal blows completely dumping the fluid out. Paul @ GMCPauls __________________ Secure Online Catalog for-GMCPauls Truck Parts Email- GMCPAULS@GMAIL.COM



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