The Stovebolt Site Forums The Shop Area General Truck Talk please help! brakes!

getting frustrated with my brakes. did the front disc swap with a kit from vendor. 73-8? parts and new lines. went with the new power booster as well and used an old(used) GM dual master cylinder and prop valve mounted at the firewall. now the brakes work but it takes about 3/4 of the travel in the pedal to get them to engage and it goes all the way to the floor. feels a little slow to engage as well. bleeding dosent seem to help anything. i bought one of those hand pump bleeders and its bleeding fine. the lines are new and i have checked for leaks and kinks or pinches. im not losing any fluid. at a couple of points since the swap I have had full pressure on the pedal but it seems to loosen up over a few days. im at my wits end here! any suggestions guys?

thinking about it it almost seems like the front discs arent engaging at all... the booster is working but its stopping slowly like drums. i will check to make sure the discs up front are engaging tomorrow perhaps i have the prop valve lines switched??? but would that cause so much travel and losing pressure in the pedal?

If you are loosing pressure, and the brakes feel spongy, that would be a sign of air in the lines. Did you rebuild the master cylinder? If the master cylinder is not sealing good on the inside, that could lead to failure of the front or rear brakes and give extra brake pedal travel.

Are you still running drums on the rear? If you are, you may meed to adjust the rear up to get the pedal back. The master cylinder may be bypassing internally-I'd suggest looking into an overhaul or replacement.

Bill said what I was going to say.

napas got rebuilt masters for $15. i'll just go buy one and replace it to see if that fixes the problem.

Questions:
considering this is a firewall mount dual m/c with prop valve and power booster how would i go about bleeding the M/c before hooking up the lines?

i do have a hand pump "speed bleeder"

would i want to bleed the m/c before or after the prop valve?

also when bleeding at the wheels do i go furthest from m/c to closest or closest to m/c to furthest?

sorry to ask so much... searches yeild differing information and I want to make sure this is done right this time.

Bleed the M/C, BEFORE installing on the truck. Instructions should be in the package, if not grab a Chilton manual at the store. You will save yourself a LOT of work if you don't introduce anymore air into your lines.

Always start bleeding the wheels at the farthest from the M/C and end at the closest.

You shouldn't need to bleed at the M/C if you bench bleed and then bleed at the wheels.

A little trick I do in the shop is to bench bleed the m/c as stated in the instuctions that comes with the m/c. After I installit on the vehicle, I get a helper to SLOWLEY push the pedal down after loosing the lines at the m/c. The fluid will push the air to the path of least resistance, and squirt out at the fittings. Have some rags handy to wrap around the lines to catch the fluid. Have your helper hold the pedal down as you tighten up the lines. This shuold take care of most of the air in the lines, you may still have to do a convential bleeding of the system if the padal is still a little mushy.

Just make sure you dont leave the rags under the hood when you are done... they tend to catch on fire.... I almost lost a 68 Cutlass convertible that way.

good info here guys. thanks

Troy,
Here is your master cylinder bleeding procedure.
I think you may need to "recenter" your proportioning valve. I'm trying to find that info for you. It's been a while since I've done one of these. The procedure is foggy. I'll get back to you on that.

Jim Sgrig

THIS PROCEDURE CAN BE PERFORMED WITH MASTER CYLINDER ON OR OFF VEHICLE .


Disconnect brake lines at master cylinder, if necessary.
Connect suitable lengths of brake lines to master cylinder and immerse other ends of lines in master cylinder reservoirs.
Apply master cylinder pushrod or brake pedal with full strokes until air bubbles have disappeared in reservoirs. It may require 20-30 applications to fully eliminate air bubbles.
Remove bleeding lines from master cylinder, then install master cylinder on vehicle, if necessary, and connect brake lines.
Fill the reservoir. Normal bleeding procedures should be followed after the master cylinder is installed.

Piewagn, I learned somthing . Not even doing this job but will carry your instructions till I use them. thanks.

What about residual vavles?

nm51
no residual valves. its firewall mount on a 63. to my understanding residual valves are only needed when you are running frame mount m/c to keep gravity from drawing fluid back to the reservoir.

I've done it many times by myself just letting gravity do the work of the helper.

Residual pressure valves will prevent the pucks from vibrating back in and pushing the fluid back to the reservois, could be what's happening.

update.... problem resolved. i went out and pulled the m/c to take in to napa to make sure i got the right one. turns out the m/c was from a 72 3/4 ton... hmmm. dont know if that had anything to do with it. well anyways, the replacement was a little pricey so i just got a m/c for a 72 1/2 ton remand for $14.00 from oreillys. made sure lines were the same and bore was too. slapped it on the booster and hooked up the prop valve then "bench" bled it on the truck by running lines back into the top of the resoirvor. about 30 pumps and all air was out. hooked up the lines and started the bleeding at the wheels. a couple of weeks ago i bought one of the pump speed bleeders and it was acting up... that frustrated me. then a bleeder valve in the rear cylinder stripped out. so off to autozone to get another cylinder. slap new cylinder on then manually bleed with some help from my gal and voila! i have brake pedal pressure! darn well better considering the only thing not new on the brake system is the prop valve and a couple peices of brake line...

anyways thanks for all the help!

Troy, Baldy is right.

Willwood makes residual pressure valves for such installations. There are two types, disc/drum so make sure you select the right one. I did the same as you, plus the RP valves and my rig stops on a dime!
Good Luck!