Whits end with brakes

[Gunnin4ya]

Really at a complete loss on my brakes. I have a 65 with an LS swap, rebuilt the truck from the frame up. New brake lines, El Camino brake booster and GM d52 calipers in the front. I left the rear drums and used a factory gm proportioning valve for the setup. Bled and bled and bled the brakes using a gravity system and a pressure system. I never could get the front brakes enough pressure to stop me. I could push so hard the back would lock up but never the front. Got pissed off and ordered a willwood setup with brake booster, calipers, braided lines, master cylinder, proportioning valve and made new lines front and rear at the correct sizes. Bled the system and got the same results. I tried changing the angle of the rod placement on the pedal and got the same results. I am running over 20 psi of vacuum. Thought maybe the vacuum may be a problem. Tried an electric vacuum pump and got the same results so I took it back off. Hoping someone can just say, hey dumbass do this. I am wondering if I just went hydroboost if it would even make a difference. Just feel like I keep throwing money at it and not coming up with any new results. Any ideas? Thanks in advance.

[lil hoodlum]

Sounds like you've covered all of the usual things. I'm not much help, but the only thing I could think that may have been installed incorrectly are the disc brake calipers. Are the bleeders facing up or down?

Another thing I've had to do with a stubborn brake system that had an air pocket was to get a turkey injector with the needle removed. Fill the injector up with brake fluid, attach it to small hose that fit over it, and forced brake fluid up through the bleeder to the master cylinder. Air bubble was forced up and out the master cylinder.

[Nick_R_23]

Have you tried swapping the lines onto the opposite ports on the master cylinder? Wondering if you have the disc port going to drums and drum port going to discs, or the proportioning valve plumbed wrong.

[rideblue00]

I dont know the details about the actuator rod, but research what length it should be. And look into what Nick said above. Sometimes you may not need the prop valve. Thats my 2c. I still have drum/drum lol

[Gunnin4ya]

I will give all that a shot this weekend hopefully. I appreciate all the replies.

[theastronaut]

Did you bed in the brake pads? Bedding in the pads transfers a layer of pad material onto the rotor and substantially increases the coefficient of friction so it'll stop much better with less pedal pressure.

Did the brake kit come with ceramic pads? Ceramic pads have a lot lower coefficient of friction compared to semi-metallic pads. On my daily driver, when I bought it the front brakes were almost inadequate, to the point I thought something was wrong. Everything was 100% stock and an working condition but it took a ton of force on the pedal to get the car to stop quickly. I swapped to semi-metallic pads and bedded them in and now it stops great with the normal amount of pedal input.

[jayoldschool]

What year El Camino master??

[Gunnin4ya]

It was an 80 something year, then I switched it to Willwood.

[jweb]

Your truck should stop fine with the components that you have. Unfortunately there's an issue somewhere in your system. It took me a long time to find the problem on my 51 and it was the simplest thing. The vacuum check valve ( plastic piece on the booster) that the vacuum hose connects to was bad. Air should only go through one way and no air flowed through mine.

Here are few things I would check other than mentioned above.

Booster pushrod length
https://mpbrakes.com/got-a-soft-peda...-cylinder-gap/

Do you have a residual valve on the rear? I doubt this is your problem but they do recommend it
https://mbmbrakes.com/typical-brake-...onfigurations/

Bench bleed Master
https://www.youtube.com/watch?v=qnsg...woodDiscBrakes

There is also some good info in this guide:
https://mbmbrakes.com/content/mbm_tech_guide_V1.0.pdf

[PapaJbbq]

Originally Posted by lil hoodlum

Sounds like you've covered all of the usual things. I'm not much help, but the only thing I could think that may have been installed incorrectly are the disc brake calipers. Are the bleeders facing up or down?

Another thing I've had to do with a stubborn brake system that had an air pocket was to get a turkey injector with the needle removed. Fill the injector up with brake fluid, attach it to small hose that fit over it, and forced brake fluid up through the bleeder to the master cylinder. Air bubble was forced up and out the master cylinder.

That is a great idea that I'm keeping, and hope I never have to use!

[SCOTI]

Originally Posted by rideblue00

I dont know the details about the actuator rod, but research what length it should be. And look into what Nick said above. Sometimes you may not need the prop valve. Thats my 2c. I still have drum/drum lol

x2.

The pedal ratio is different between the drum & disc apps for 67-72. You might need to adjust the pedal pivot for a better stroke.

I had to do this for my '68 (drums to 71-80 C10 discs) as well as my '89 dually (OE hydraboost to 81-87 3/4-ton Suburban vacuum brakes).

Also.... You need a prop valve for disc + drum apps. You need a prop for most vehicles simply because of the brake bias & inertia of slowing front heavy vehicles. Most OE prop valves also offer a safety feature in the event of a hydraulic failure on one end of the vehicle vs. the other

[theastronaut]

Originally Posted by SCOTI

Most OE prop valves also offer a safety feature in the event of a hydraulic failure on one end of the vehicle vs. the other

That reminds me... you have to have a bleeder tool to lock the shuttle valve in place with an oem combination valve, otherwise it can move and shut off half of the brake system. That may be what happened here?

https://mpbrakes.com/proportioning-valve-bleeding-tool/

[SCOTI]

Originally Posted by theastronaut

That reminds me... you have to have a bleeder tool to lock the shuttle valve in place with an oem combination valve, otherwise it can move and shut off half of the brake system. That may be what happened here?

https://mpbrakes.com/proportioning-valve-bleeding-tool/

Yes. It's happened to me twice. BOTH times it happened I was towing a loaded trailer & had to slam on the pedal.

The brakes 'worked' after, but I noticed stopping seemed different. I dismissed it initially but then decided to verify things & found no rear braking. Had to re-bleed the brakes which led to jacking w/the prop valve.

[rideblue00]

Gunnin4ya, did you ever resolve your issue?

[twoskies]

watching
ive got a 1966 Chevy C10 that im rebuilding
Also got a 1972 Chevy C10 that i Drive

Bought all the Components to go Front Disc and stay rear Drum
Figured i could pretty much copy the 1972 Install Including ordering the Brake Lines and Proportioning Valves From Inline Tube

If there,s Anything i can Check on the 1972

Let Me Know

Thank ,s and Good Luck

[theastronaut]

Adding this here since it got bumped up-

Check the caliper seal grooves. I recently ran across a disc brake kit that had low-drag calipers in it, and couldn't get the front brakes to build pressure no matter what. I eventually figured out that the calipers were the low drag version where the piston seal grooves are cut at an angle that cause the piston to be over-retracted for less pad drag and better mpg. The problem with that is those need a special step bore master cylinder which pushes a ton of fluid initially to get the piston back out to the pads, then internal passages switch to a normal size bore that makes adequate hydraulic pressure (thats what causes the whooshing noise when you hit the brakes on 80s/90s GM trucks).

[SCOTI]

Originally Posted by theastronaut

Adding this here since it got bumped up-

Check the caliper seal grooves. I recently ran across a disc brake kit that had low-drag calipers in it, and couldn't get the front brakes to build pressure no matter what. I eventually figured out that the calipers were the low drag version where the piston seal grooves are cut at an angle that cause the piston to be over-retracted for less pad drag and better mpg. The problem with that is those need a special step bore master cylinder which pushes a ton of fluid initially to get the piston back out to the pads, then internal passages switch to a normal size bore that makes adequate hydraulic pressure (thats what causes the whooshing noise when you hit the brakes on 80s/90s GM trucks).

Yep.... Seems like it was on the LtDuty C10's (81-87) as well as S10's & g-bodys (for sure) in those years.