Front brake conversion

Tiny
PATRICK A. KNOX
  • MEMBER
  • 1968 PONTIAC GTO
  • 6.5L
  • V8
  • 2WD
  • AUTOMATIC
  • 11,879 MILES
I converted from drum to dis brakes. For the past month I have repeatedly bled the system. The power booster air supply when connected the pedal goes straight to the floor, but if I plug the p/b with my finger I have pressure on the pedal. Can you help?
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Monday, October 7th, 2019 AT 7:37 PM

6 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome to 2CarPros.

Was the master cylinder replaced? If the pedal is going to the floor (boost or no boost) the is most likely the cause. Take a look through this link.

Also, I did this same conversion on a 70 lemans a few years ago. I had to replace the booster, master cylinder, and so on.

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

I noted you are a mechanic, so I assume you checked for leaks and confirmed the rear brakes (if still drum) are properly adjusted.

Let me know.
Joe
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Monday, October 7th, 2019 AT 8:46 PM
Tiny
CJ MEDEVAC
  • EXPERT
Have you tried adjusting the push rod between the master cylinder and the brake booster?

The rule of thumb. (Basically, winging it)

The longer you make the rod (to a certain point) the better your pedal gets.

If you get it too long, your brakes will start applying and they will drag. I always put the Jeeps on four jack stands so that I can crank them up and see if I can still spin the wheels with my hand.

If you get the rod too short, your pedal will get spongy or drop off to nothing.

For me, it's a trial and error thing, it may take me five or six master cylinder removals and installs to get it right. Patience is a good attribute to have.

Let us know how it goes.

The Medic
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Monday, October 7th, 2019 AT 9:01 PM
Tiny
PATRICK A. KNOX
  • MEMBER
Thanks, I thought about that, the rod that came with the conversion kit was too long and I cut it to fit. Again thank you and I will let you know the results.
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Monday, October 7th, 2019 AT 9:13 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Let us know what happens.

Joe
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Monday, October 7th, 2019 AT 9:15 PM
Tiny
PATRICK A. KNOX
  • MEMBER
I will let you know. I'll be out of town for a couple days, hopefully I'll let you know by Friday.
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Monday, October 7th, 2019 AT 9:21 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Sounds like a plan.

Joe
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+1
Tuesday, October 8th, 2019 AT 5:14 PM

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