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Damage master cylinder by "over extending"?


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fat-katie
User

Jun 17, 2021, 2:07 PM

Post #1 of 3 (252 views)
Damage master cylinder by "over extending"? Sign In

I've just replaced all the brake lines on a 1995 Skylark. The master cylinder is new and has been used quite-a-bit in engine off bleeding. It was not leaking.

When it came time to bleed the new lines and I had my wife work the brake pedal. Sometime in she said she heard something. She was fully extending the brake pedal, all the way to the floor. The master is now leaking out the back and onto the power assist.

Did fully depressing the brake do this? Are these easily damaged? Is it leaking because there is no pressure to seat seals? Or what?

Thank you.


(This post was edited by fat-katie on Jun 17, 2021, 2:08 PM)


Hammer Time
Ultimate Carjunky / Moderator
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Jun 17, 2021, 2:18 PM

Post #2 of 3 (246 views)
Re: Damage master cylinder by "over extending"? Sign In


Quote
Did fully depressing the brake do this? Are these easily damaged? Is it leaking because there is no pressure to seat seals? Or what?


If this is a used master cylinder, then yes definitely. Normal travel for a master cylinder is only about 1/3 of the total travel. During this time the cylinder builds corrosion and rust in the area it's not traveling. When you suddenly push the rubber seals through that corrosion it just tears them up.
If this was a brand new master, then it shouldn't have done that and I would just return it as a defect.

Remember this for the future, when bleeding with a used master, do not allow it to bottom out.



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(This post was edited by Hammer Time on Jun 17, 2021, 2:19 PM)


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jun 17, 2021, 3:47 PM

Post #3 of 3 (230 views)
Re: Damage master cylinder by "over extending"? Sign In

Hammer just said EXACTLY what the risk is putting a used Master to the floor where it's never been. YOU said it was new?
If new was properly wet, bench first and really new matched up with old one if with a pushrod or not real new should have taken it IMO.


IF that unit was "rebuilt" (it's illegal to sell rebuilt masters to anything in MA) they line bore them (used to sell them or do yourself) with a "hone" it's called or pro job maybe up the size within next to nothing and match with seals for what you did.
So what was it? A rebuilt you took a risk they did sell them once 1/2 didn't work out so made them illegal to sell. Same as wheel cylinders this age still had plenty out there redo your own.
That or just plain bad luck if purchased as new that should have a looooong warranty.
Other? Did it fall off inside car somehow or pull it away from booster see if it moves at all??


Not common to me and not the fault of a helper to ruin one IMO again.
Will it still push out fluid in a criss cross or front vs rear only?
Another law is if one of two sections fail the other is supposed to give you something (not much) so tearing seals really shouldn't be both?
You done a ton of work no doubt for this mess of a nightmare of a bad part or some dang thing overlooked.


Sorry for long posts - loosen it and see if it just pours fluid down booster make sure it's brake fluid if so will rinse of you finger with plain water some other would not. That's for DOT 3 or DOT 4 if you somehow mixed in oil of any kind it might blow/swell seals this fast is one hell of another expense so HOPE NOT! Tom






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