Pedal 2 floor ?

[1981lemans455]

81 Lemans, factory master cylinder, factory front disc, GM 80's rear disc calipers, factory brake valve replaced with Wildwood adjustable . All new lines, hoses, reman calipers. So the pedal goes to the floor , release and reapply pressure and it holds good ? I thought maybe to much slack in rear pads, so I hooked up the park brake cables and applied the park brake, pedal still goes to floor on first apply ?

 

[1981lemans455]

Forgot to mention, I have a 2 LB pressure valve plumbed into rear line, but nothing on front.

 

[malibudave]

Your master cylinder should have a 24mm bore, I would double check that just to make sure it is not a smaller 7/8" bore. If you are still running the rubber lines, you can clamp off the rear lines to see if your pedal returns, then unclamp the rear line and clamp off your front lines to see if you your pedal returns. This will isolate which brakes are giving you the issue. I suspect it is your rear brakes.

It could be three things.

1. Your master cylinder bore is too small and cannot produce the volume needed to supply the rear calipers the fluid needed to stop the car.
2. Your master cylinder reservoir is too small and cannot supply the extra volume needed to supply the rear calipers the fluid needed to stop the car.
3. Your master cylinder is bad

If you are running power brakes, you might want to use a 1979 Buick Riviera master cylinder that came with four wheel disc brakes. This master cylinder has a 1.0" bore and a large reservoir for four wheel disc brakes. This master cylinder uses the same brake line outlets as a g-body.

 

[pontiacgp]

you need a valve for the front brakes.We used 3 lbs residual valves front and back

 

[1981lemans455]

Great points ! , I have an extra pressure valve, I will try that first in the front curcuit. If that doesn't help then I'll start pinching brake hoses. And see how that goes. Thanks for the advice guys.

 

[pontiacgp]

I'm thinking the pads are backing off without the residual valve so on first pump the pedal is travelling too far and second pump you have a firm pedal cause the pads didn't have a chance to back off.

 

[Schardbody]

I'd start by clamping hoses and see if the problem is front or rear.

I doubt it's a volume problem as soon as the pistons are pumped out it takes very little volume to apply pressure.

Make 100% certain no slides are stuck and there is no air in the system.

 

[1981lemans455]

Update, I installed a 2Lb pressure valve on the front circuit. It feels better, but when left for a couple of minutes the pedal still has a lot of travel? Reminder , that the parking brake is on the whole time, so when I release the parking brake, it is way worse, pedal bottoms out easily? I am still stumped, I may try bleeding again! And if that doesn't fix it , either higher Pressure valves, but leaning toward 30 year old drum brake master cylinder that sat off the car for 10 years ...

 

[1981lemans455]

When I released the parking brake, the rear pads had a lot of "wiggle room" . Maybe a higher pressure valve might fix it ?

 

[565bbchevy]

factory brake valve replaced with Wildwood adjustable

So is this the Wilwood proportioning valve with the adjustable knob for the rear brake bias? And if so have you gone through the adjustments with this prior to doing anything else.