The Stovebolt Site Forums The Parking Lot Big Bolts brake problem on 1957 6400

A buddy picked up a pretty solid 1957 chevy 6400 and month ago or so that needed some brake work done to it. I'm helpimg him get it all straightened out and we found that there was a leaking wheel cylinder on the right rear wheel, the brake hard line connecting the two wheel cylinders was cracked, and the seal on the master cylinder for the push rod was shot. I replaced all of those parts which brings us to where we are now. Little fyi this thing had no brakes at all because of the bad m/c so I don't know how it acted before it lost all of its fluid.

Replaced all of the parts listed above and went to bleed the brakes. Started at the right rear wheel bleeder, left rear, right front, then left front and once we start to get a decent pedal from pumping and bleeding you let off of the pedal and brake fluid burps and shoots out the fill port on the m/c. So for example say it has good pedal and brake feel right around the middle of brake pedal travel, you let off of the pedal and the fluid "burpes" into and out of the m/c and now we have no pedal at all(goes right to floor). Pump it up again and it does the same thing.

I've tried bleeding it at the 2 bleeders on the hydrovac and that didn't change the outcome. I took the drain bolt out of the front of the hydrovac after reading something about a seal going out inside and letting the canister fill up with b/f but it was dry inside.We tried another m/c thinking that the rebuilt one we got may be garbage but no luck with that either.

Any idea's?

You should start your bleeding process at the hydrovac first

The "burping" you describe MAY be normal back flow through one of the ports at the bottom of the master cylinder. All of my trucks do this. If you let up on the pedal very slowly it won't splash out, otherwise replace the fill cap each time you fill it. If "burped" aggressively, you may be introducing air into the system. You need to also be sure the master cylinder doesn't have air in it itself, so some people bench bleed the M/C before installation.

Don is correct about the hydrovac, it should be bled first. Start with the bleeder in the center of the unit, and do the one near the line outlet to the system, second. Then bleed your cylinders. You are correct about the possibility of leaking brake fluid into the vacuum cylinder of the hydrovac, so it looks like that is not the problem. Since you have found the drain port this would be a good time to lubricate the vacuum chanber. People have suggested using Marvel's Mystery Oil for this; use an ounce or two.

Kent

I will give those things a try and see what happens. I'm pretty sure that we tried letting up on the pdeal really slow and it still burped back. Its aggressive enough that it pushes a good amount of fluid out the fill hole

As Don said, you start your bleeding process and the hydrovac, but you also end there. Meaning, bleed hydrovac (2 bleeder screws) > wheel cylinders > hydrovac.

If it flows alot of fluid back, it's coming from the wheel cylinders returning to their fully compressed state. Sounds like you need to adjust the brakes up so the cylinders arent expanding so much. That would explain the pumping to get pedal, you're trying to fill the cylinders that are expanding too far,
Scott

I replaced the entire hydro vac on my 59 gmc 2 ton with a fire wall mounted unit.... dual master booster assembly, I was a little skeptic at first, because the vacuum booster was so much smaller....I was amazed at how much better this worked! I also got rid of a wheel barrow full of rusty stuff in the process. I use this truck like a truck as well...........never have had a lack of brakes. easy install & easy to bleed. Has a reservoir for the front and one for the rear. 378 bucks for a very nice kit!

encoredemon....where did you get a kit like that? came with 1.25" bore m/c and you relocated from frame to firewall?

Your better off using a non-petroleum based lubricant. The seals in these things weren't designed for petroleum products.

Jeff

Jeff,
What specific lubrication product would you recommend for a Hydrovac? Bendix had a lubricant for this purpose but I have never been able to find it or find an equivalent.

Kent

american classic truck parts inc.
part # BR2941 $378.00

I've been doing brake work on my 2 ton Chevy too. According to the book the bleeding order is :hydrovac slave cylinder,hydrovac valve bleeder valve,left rear wheel, right rear wheel,left front wheel, and then right front wheel.
So even after you do the hydrovac it's not the "normal" farthest wheel.
See if that does it.

I just finished this job yesterday on my 48 1.5 ton.
Bought all the parts from Alretta in Massachusetts. http://www.alretta.com/ . Nice helpful folks and GREAT customer service...

The new hydrovac instructions per the vendor for my single piston unit: 1 oz or 30 cc. of "hydraulic JACK oil".

Bleed the Top hydrovac valve first, then second one, farthest wheel then closer till all four. then hydrovac AGAIN. I have a nice pedal...

I drove and stopped the truck for the first time yesterday without having to use the emergency brake! woo hoo...

Motoswiz

also, you have to use common sense trying to consider "farthest".

Via the "brake line length" on my truck the left rear wheel is the FARTHEST because my rear "T" is close to the right rear wheel with more pipe to the rear left...make sense?

Motoswiz

Kent,

I use mineral oil in mine, found at your local grocery store next to the laxatives . Probably the most ideal thing to use would be a natural corn based lubricant.

Jeff

As suggested, I've gotten into the habit of replacing the Master Cylinder fill plug in-between fillings while bleeding. Doing that, as well as the suggested bleed order, has given us good results on several trucks, with far less fluid on the floor under the M/C!

Pretty rewarding to get good brakes on a truck that wasn't stopping before.

-Michael

following

Chuck P.,

Have you tried to follow a thread by clicking on the Thead Options at the upper left of the first post?
Then, select "Follow Thread".

as stated, hydravac 1st, BUT, you also need to loosen the upper brake shoe on each rear wheel all the way before you start, otherwise it will trap air in the wheel cylinder. Here is a link to the online manual for a 55. I am not sure which side your hydravac is on, my 55 has it on the pass side, my 58 it is on the driver side so the "farthest wheel" may be the opposite side than the manual depending on your truck. I also built a pressure bleeder that makes it a lot easier!
http://chevy.oldcarmanualproject.com/shop/1955truck2/55ctsm0507.htm