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?
Monday, October 7th, 2019 AT 7:37 PM

6 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
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
  • MECHANIC
  • 11,004 POSTS
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
  • 3 POSTS
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
  • MECHANIC
  • 110,176 POSTS
Let us know what happens.

Joe
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Monday, October 7th, 2019 AT 9:15 PM
Tiny
PATRICK A. KNOX
  • MEMBER
  • 3 POSTS
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
  • MECHANIC
  • 110,176 POSTS
Sounds like a plan.

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

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