CK5
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Bad m/c?
- Thread starter 79k20350
- Start date
British Slave
1/2 ton status
- Joined
- Jul 25, 2007
- Posts
- 2,086
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- 2
Sounds like the M/C to me.
lectric80
3/4 ton status
This is the first signs of MC failure. Time for a new MC.
troutbum_mt
1/2 ton status
Just out of curiousity, how can you tell when it is the booster? Seems like everybody always says master cylinder first when it comes to brake issues. How do you know when it is the booster? Curious because I have a brake issue as well.
lectric80
3/4 ton status
The booster is going to cause a weaker brake force when it fails. They rarely fail, it is more common that a vacuum leak would be the issue with the booster, with the exception of hydro-boost setups.
In this case, a pedal that slowly bleeds off is generally a master cylinder that is allowing the pressure to bleed off. Usually caused by bad seals in the MC. I tend to make suggestions based on known issues, in this case a brake fade in the pedal.
You SHOULD also trigger your brake warning light...you getting that?
When my MC failed, my brake light would come on. Bit different, but I'd be sitting at a light, then my pedal would drop to the floor and I'd start rolling. Pumping the brakes worked.
Easy MC test (per the GM manual) is to idle the truck for about one minute without applying the brakes. Turn the truck off, wait for awhile (I think the manual says 45 minutes, but that's excessive IMO) then without starting the truck, test pedal apply. You should get 2-3 full pedal assists before pedal effort increases.
Of course, if your brakes are weak all the time, and won't "pump up", this test may not work.
As mentioned above, booster failure will result in MUCH higher pedal effort.
When my MC failed, my brake light would come on. Bit different, but I'd be sitting at a light, then my pedal would drop to the floor and I'd start rolling. Pumping the brakes worked.
Easy MC test (per the GM manual) is to idle the truck for about one minute without applying the brakes. Turn the truck off, wait for awhile (I think the manual says 45 minutes, but that's excessive IMO) then without starting the truck, test pedal apply. You should get 2-3 full pedal assists before pedal effort increases.
Of course, if your brakes are weak all the time, and won't "pump up", this test may not work.
As mentioned above, booster failure will result in MUCH higher pedal effort.
