Front brake conversion

1968 PONTIAC GTO
11,879 MILES • 6.5L • V8 • 2WD • AUTOMATIC
Avatar
PATRICK A. KNOX
  • MEMBER
  • 3 POSTS
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?
Oct 7, 2019 at 7:37 PM
Advertisement
Avatar
JACOBANDNICKOLAS
  • ASE Certified Mechanic
  • 110,194 POSTS
  • ASE Certified Mechanic
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
Oct 7, 2019 at 8:46 PM
Avatar
CJ MEDEVAC
  • ASE Certified Mechanic
  • 11,004 POSTS
  • ASE Certified Mechanic
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



Oct 7, 2019 at 9:01 PM
Avatar
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.
Oct 7, 2019 at 9:13 PM
Avatar
JACOBANDNICKOLAS
  • ASE Certified Mechanic
  • 110,194 POSTS
  • ASE Certified Mechanic
Let us know what happens.

Joe
Oct 7, 2019 at 9:15 PM
Avatar
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.
Oct 7, 2019 at 9:21 PM
Avatar
JACOBANDNICKOLAS
  • ASE Certified Mechanic
  • 110,194 POSTS
  • ASE Certified Mechanic
Sounds like a plan.

Joe
Oct 8, 2019 at 5:14 PM
Join 2CarPros for free, one of the most advanced car repair communities on the internet. From first-time drivers to seasoned mechanics, everyone is welcome to reply, share details, and get better answers. You can add a temporary image or video first; uploads are limited to 20 MB.
Ask a Free Question
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.