Trouble bleeding brakes

[Jemo]

I initially bled my MC off the truck and brakes, got all the air out and while driving it onto a trailer this week realized the brake pedal almost goes to the floor and doesn't stop very well. It's a frame mounted MC/booster. I jacked up the rear end and measured 21" from the bleeding valve to the ground and measured the distance from the top of the MC to the ground, it's around 19".

I'm going to bleed again. Is this enough of a difference? Any other tips?

Jeff

[OrrieG]

If its a two wheel drive truck you might need check valves in the lines between the proportioning valve and calipers and/or wheel cylinders. If they are close to or above the MC they will not maintain pedal pressure. There are two different sizes, one for drums, one for discs.

[mr48chev]

More information would help.

Disk brake conversion, dual master cylinder conversion or stock brakes?

I had a similar problem on my wife's van a while back and finally figured out that I had a bad flair on the line that I was having all the problems on. It didn't show a leak of fluid but was bad enough that it would allow air to be drawn in the line.

Orries suggeston of the need for residual valves usually is correct if you use a disk brake master cylinder as they don't have the residual valves that drum brake master cylinders normally have. Somewhere in the line you do need a residual valve.

If the brake cylinders are old they may not hold well after bleeding the brakes if the rig has sat a long time before you bled the brakes and sits a lot after you bled the brakes. This happened on my 48 when I let it set a lot after driving it for several years with no changes in the brakes except replacing shoes once. I could bleed the brakes and a week later they were a bit mushy again if I didn't drive it every day. It has a 68 Chev pickup (and car) master cylinder that is a popular swap for going to a dual master cylinder.

If the brakes are old I'd go through and rebuild or replace the brake cylinders even if I used the old shoes again. If it's a dual master cylinder just replace it as I for one have never had luck rebuilding them and the kit costs as much as a rebuilt cylinder with a guarantee on it.

Also make sure that the brakes are adjusted up right before you bleed the brakes as that seems to help keep things in order.

[Jemo]

ok, well I have a front disc kit (everything new) and rear drums/rear from a late 80's Camaro. I replaced the wheel cylinders and shoes on the rear. The MC is a dual w/booster and new from CPP. It does have a prop valve and is intended for a disc/drum like I have. I did look very carefully for leaking lines which are also all new but I see no leaks.

I'll plead ignorant. What is a check valve, where does it go, what's involved in installing, and where do you buy?

[_Ogre]

with your mc so low, you need residual pressure valves to keep the fluid on the calipers and wheel cylinders.
2lb for discs and 10lb for drums, inline tube has these

also check to see if your rear brakes are adjust up tight to the drum,
if not it takes a lot of fluid and pedal travel just to get the shoes up to the drums.

[GMtrucknut!!]

The residual check valve should be located in the master cylinder in the set up that CPP sells.I would check my packing slip and be sure that it doesn't show 4 disc on the description . I questioned CPP when mine arrived and it was explained by the tech department.

[Jemo]

Guys,

I confirmed that there is a residual valve already in the MC. I guess I just have to jack up the rear as high as I can get it and try again? I'll check again that the rear drum brakes are adjusted correctly. Anything else?

Jeff

[GMtrucknut!!]

An old trick that I use is putting clear hose on the bleeders and a little brake fluid in a clear jar filling the system leaving the bleeder valves open and let them gravity bleed overnight. Then bleed them the next day after adjusting the brakes