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After replacing front brakes and bleeding system pedal goes to the floor

Tiny
DOAUSI
  • MEMBER
  • 1988 GMC S15
  • 2.5L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 179,000 MILES
Had to replace part of front brake line. New pads and calipers on front. Bled brakes until solid fluid came out. Pedal was firm.
Started engine and pedal went to floor. What is the problem here?
What do I need to do or redo?

Thanks.
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Wednesday, December 5th, 2018 AT 10:51 AM

11 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon,

Did you bleed the rears as well?

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

Do you have ABS?

You may need to get a pressure bleeder to force the air out of the system. If all the air is removed then you lost the master cylinder.

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Roy
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Wednesday, December 5th, 2018 AT 11:48 AM
Tiny
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Thanks Roy, No ABS in this old truck. Have not bled the rear brakes, I will jump on that right away as well as redoing the front.
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Wednesday, December 5th, 2018 AT 12:09 PM
Tiny
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Okay, sounds like a plan.

Keep us updated.

Roy
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Wednesday, December 5th, 2018 AT 12:17 PM
Tiny
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Roy! Sent a message about the inspection and findings.
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Wednesday, December 5th, 2018 AT 1:53 PM
Tiny
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Sorry, did not show up here on the post.

Roy
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Wednesday, December 5th, 2018 AT 2:24 PM
Tiny
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Okay! There is no visible leak around the master cylinder, booster, or proportion valve. While my friend was pushing the pedal I could hear the piston moving in the master cylinder. I also noted that the fluid would jump when the pedal was pushed. Is this normal?
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Wednesday, December 5th, 2018 AT 2:36 PM
Tiny
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Yes, the piston seals may be bad internally.
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Wednesday, December 5th, 2018 AT 3:02 PM
Tiny
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Not quite sure of your reply. Are you thinking the seals inside the master cylinder may be worn? I have seen the repair kit on line is this worth the price? I only looking at this from the point that I bought the truck in 1994 and nothing has been changed in the way of booster, master cylinder, or proportion valve. I will still go ahead and re-bleed the brakes just to be sure.
Thanks.
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Wednesday, December 5th, 2018 AT 4:32 PM
Tiny
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Yes, the ones inside.

I would be leery about rebuilding. If the bore is pitted, it is no good. In the old days with cast iron masters, we could hone them and then use new seals. With today's aluminum cylinders, you cannot even clean them up.

I would replace the cylinder only.

Roy
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Thursday, December 6th, 2018 AT 3:32 AM
Tiny
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Thank you Roy, I feel sure that the master would need replacing as it has been decades since the truck was bought. And nothing lasts forever.
Thanks.
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Thursday, December 6th, 2018 AT 7:51 AM
Tiny
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You are welcome.

Always glad to help.

Roy
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Thursday, December 6th, 2018 AT 8:00 AM

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