2nd Gen Non-Engine/Transmission Brake pedal goes to floor after bleeding

[phantomusa]

If that be the case then three master cylinders have all had the same problem and one of them was brand new. And there have been no leaks detected and no fluid loss.

I can't answer that about all those masters but everything is pointing to the master bypassing fluid if you don't have a leak have you checked all your brake lines for weeping pin holes ??
And are you sure your system has no air in it I've seen that happen too many times people think they have a good pedal pressure but there's still air in system and they think something else is wrong instead of addressing the real problem air in system
I did a atv for a buddy and ended up bleeding his system 10 times over 2 days we when thru 1 qt of brake fuild before I could get all the air out
Pappy

 

[tugboat1st]

I think like you. I find it hard to believe that three master cylinders would all be leaking by which is why I changed them all. I might be having a problem with the proportioning valve. I just ordered a new one of those. I think that might have been creating a problem with bleeding the front part of the system. We'll see if that licks the problem.


Thanks for the reply.

 

[fest3er]

I think like you. I find it hard to believe that three master cylinders would all be leaking by which is why I changed them all. I might be having a problem with the proportioning valve. I just ordered a new one of those. I think that might have been creating a problem with bleeding the front part of the system. We'll see if that licks the problem.


Thanks for the reply.

Now that I think about it, you may have a truck with a nearly dangerous rear wheel ABS controller; when it is activated, the pedal goes almost to the floor and most braking power is eliminated. Mine has done that since the day I got it (10/1997); the only thing that helped was tossing the OEM shocks at about 10k miles and installing KYB GasAjust shocks.

As to why it activates unexpectedly,

• the rear axle could be locking up when the brakes are applied
• the speedo could be dropping to zero when the truck is moving faster than about 5MPH

 

[RALLER]

I am 81 retired repair shop owner. Way to go if you can live long enough, 81 years young & having lots of fun!!! Anyway, I took a 1 gallon can of brake fluid, Reversed the spring on the pump, rubber hose from pump to bleeder screw at wheel cylinder, pull up on pump plunger,open bleeder screw. Now you are reverse bleeding to master cylinder. Some times this will save you a lot of time. If one method will not work, try another. BAD BOB

 

[tugboat1st]

I looked into buying a reverse bleeder. It makes excellent sense but they are a bit too expensive. I did get a pressure bleeder but I didn't go through the proportional valve procedure. I think this may be my problem. Plus I converted the front brakes to disc so I found a used proportioning valve and I question its condition. I ordered a new one and hope this has an effect on my brake situation. This is all complicated by the fact that the brake system is a '93 in a '74 W100. The "abs" has been eliminated. I stuck with the '74 brake system other that the booster and master cylinder. That made it very difficult to find the right proportioning valve ('74 was the first year for disc brakes in the front).

 

[Bromiley99]

If you have a leak, 9 times out of 10 I find that a wheel cylinder is the culprit. One simple thing that could of happened, is during the shoe install a wheel cylinder plunger could of popped out of place, always a little tricky lining all that stuff up!!