1991.5 mopar

Im replacing my master cylinder for the 3rd time this month because they all want to leak out of the top of the reservoir and they are new units. The booster is a reman and i have bled the brakes 4 times and i cant get the pedal not to go to the floor. solid stream of fluid out of all 4 wheels. havent noticed any more air coming out of the lines. bled them by going from rwal,rr,lr,rf,lf. thinking about deleting the rwal valve. will this help? if not im thinking about cutting a hole in the floor board and stop the old turd like fred flintstone

maybe368

Do yourself a big favor and get yourself a new Bendix MC. You won't regret it. and yes it is possible to get 4 or 5 bad rebuilt units n a row...Mark

RamGuy84

Also try Gravity bleeding them see what happen's .

1991.5 mopar

If this oriley brand mc leaks again I'll definately look into a different brand. Is bendix guaranteed not to leak?

dan123dbl

I was lucky and only had to go through one reman unit to find one that didn't leak the day after I installed it..

And about the rwal, I would delete it. It's very simple and theres a write up about it in the sticky. Before when my rwal would activate my pedal would drop to the floor and the truck would shake violently. Now I can stop MUCH better.

You just have to keep in mind to let off the brakes a bit if the tires do lock up on you.

maybe368

Bendix is a brand new unit, not rebuilt. It solved my soft and collapsing pedal problem...Mark

NJTman

Mark is correct. Bendix is the only master i could find that wont leak... At least not for a couple of years anyway....

When u put the new one in, and are done bleeding, and your finshed wrenching, make sure the fluid sits down below the reservoir top about 1/4" or so. Need to have a bit of room for any expansion in there of the fluid.

sooty

the or brand is new too, im guessing your bench bleeding in a vise, then transferring to install, do you know the rear brake shoes are adjusted without play? if they fell out of adjustment, while bleeding they will return fluid to the reservoir, so, what was the reason for the replacement?

1991.5 mopar

A new bendix mc will be on order today but I still have the problem of not having any pedal, I have a nice stream of fluid at all 4 wheels, no air in the lines. The pedal is much harder with truck off while bleeding but when the truck is idling the pedal will go to the floor like nothing

j_martin

When the truck is running, the booster is effective, and it takes much less pedal effort to develop the same pressure. When running it can develop a couple thousand psi pressure.

If there were clearance problems, the pedal would go down either way. If it varies with pressure, ie goes down when boosted, but not under low pressure, it could be
1. Air in the lines.
2. Caliper installed on wrong side, trapping air. It's hard to do, but has been done.
3. Something bending or expanding under pressure, either a failing hose or hard parts wrong in some way.
4. Master cylinder failing by allowing fluid to bypass the cups on the piston. These MC,s aren't supposed to be honed, and I think the rebuilders do it anyway, so no surprise most of them fail.

The vacuum booster on these things is a dual diaphragm unit. It puts a lot of pressure on the MC when it's working properly.

maybe368

I would wait for the Bendix to come in before you do much else. Make sure that the rear drums are adjusted properly, this is very important, as has been said. When I put the Bendix on, I was able to reconnect the RWAL module and the warning lights went out for the first time in years...Mark

maybe368

Also I think that you still have air in the system , I went around with this exact problem. I was happy after I converted to disk brakes, bled perfectly normally. then one day they went to the floor again. Went to the Bendix MC, perfect brakes since...Mark

1991.5 mopar

Thanks mark. Bendix unit will arrive on Friday, I will go from there. Do you recommend bench bleeding before install?

maybe368

No Doubt! The MC comes with instructions on how to bench bleed it. Be patient and try to get every drop of air out of it before you install it. If you don't have a good place to clamp it up, you can install it and, with 1 person watching the MC, the other can ever so carefully push the brake peddle to bleed the MC. You have to be careful doing that, better in a good vise...Mark

Of course, don't connect the brake lines while you are bench bleeding it, it should come with plastic plugs for the brake line ports...

1991.5 mopar

Okay thanks I will keep you informed on what happens after I install the new mc