79 brake trouble shooting
Thread Starter
Intermediate
Joined: Jul 2016
Posts: 35
Likes: 2
From: Charlotte NC
79 brake trouble shooting
My master cyl was replaced in 2016 and brakes were 4.0. Left the car undriven for 6mo to return with some what limited if no power assist. The mc is full, good fluid and no leaks. Accumulator problem, air in the lines, pedal will at times bottom out but will return and very hard to depress.
Thanks,
Ron
Thanks,
Ron
Race Director
Joined: May 2006
Posts: 18,755
Likes: 2,589
you have to remove all 4 wheels and start carefully looking at all 4 pistons on each caliper for seepage. It may not be enough to lower the master level but will allow air into the calipers.
If nothing found the other possibility is the master has a leak, check the back of the master by unbolting it from the booster.
A bad booster will give you a rock hard peddle with no movement in the peddle.
If nothing found the other possibility is the master has a leak, check the back of the master by unbolting it from the booster.
A bad booster will give you a rock hard peddle with no movement in the peddle.
Last edited by MelWff; Dec 2, 2017 at 11:47 AM.
Thread Starter
Intermediate
Joined: Jul 2016
Posts: 35
Likes: 2
From: Charlotte NC
Le Mans Master
Joined: Feb 2001
Posts: 6,317
Likes: 292
From: Ocala FL
Leaving it sit for 6 months means the calipers leaked out. Open the bleeder on the far end and fill the master cylinder, babysitting it to be sure it doesn't run dry.
After you have flushed out old fluid and all of the air, bleed each caliper (1 each front, 2 each rear), and then drive it daily if possible for a week. If not, drive it at least every weekend, checking the bleeders for air.
Probably the hard to depress after bottoming is the check valve moving to block off the bad side of the dual circuit. You may have to reset the valve if it doesn't return.
After you have flushed out old fluid and all of the air, bleed each caliper (1 each front, 2 each rear), and then drive it daily if possible for a week. If not, drive it at least every weekend, checking the bleeders for air.
Probably the hard to depress after bottoming is the check valve moving to block off the bad side of the dual circuit. You may have to reset the valve if it doesn't return.
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
My master cyl was replaced in 2016 and brakes were 4.0. Left the car undriven for 6mo to return with some what limited if no power assist. The mc is full, good fluid and no leaks. Accumulator problem, air in the lines, pedal will at times bottom out but will return and very hard to depress.
Thanks,
Ron
Thanks,
Ron
Now no power assist?
And pedal not right!
Fix assist first.
Check wheels for leak.
Bleed properly.
Thread Starter
Intermediate
Joined: Jul 2016
Posts: 35
Likes: 2
From: Charlotte NC
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