residual pressure valve question

57larry · October 22, 2012, 11:19:00 AM

having brake problem on our 56 chevy pickup (we're building a clone to this one) this truck has a 72 camaro front clip with disc brakes and a 78 vette rear end with disc brakes. the master cyl has a power booster and is under the floorboard. we have the blue 2 lb. residual valve on each line coming out of the master cyl. we have had this set up for 10 yrs on this truck with no trouble.

we recently replaced the front rotors, calipers, pads and rubber brake hoses on the front. now when we test drove it, the front brakes are holding when we apply the brakes. rebled the brakes again and again on the test drive when we applied the brakes, the front are not releasing.

would the residual valve going to the front be bad? thanks, Larry

enjenjo · October 22, 2012, 12:08:39 PM

See if it's both front brakes, or just one. Normally residual valve fail by not holding pressure. I suspect a defective brake hose, even though they are new.

57larry · October 22, 2012, 01:51:12 PM

it's both front brakes. hope it's not the $60.00 CarQuest hoses. what now Frank? thanks, Larry

rooster · October 22, 2012, 03:27:39 PM

What master cyc? Ford, GM!!!!!!?

papastoyss · October 22, 2012, 05:27:30 PM

I had a similar issue w/ the "GMmetric " front calipers on my 40 coupe. They were new ,not reman calipers from a reputable street rod vendor. They were also so low priced they had to have been offshore parts. The calipers were dragging so much I could hardly rotate the wheel by hand while jacked up. Cracking open the bleeder valve made no difference so I realized it was mechanical not hydraulic pressure. The pistons were very hard to move even w/ the largest channel locks available. Evidently the piston orings were just too snug on the pistons. I installed reman calipers from OReillys by a reputable supplier I had used before & the problem went away.

unklian · October 22, 2012, 05:44:41 PM

Quote from: "papastoyss"I had a similar issue w/ the "GMmetric " front calipers on my 40 coupe. They were new ,not reman calipers from a reputable street rod vendor. They were also so low priced they had to have been offshore parts.

Incorrect machining, or wrong size O-rings.

Imagine how they were assembled.

kb426 · October 22, 2012, 06:04:50 PM

Is the master cylinder too full?

57larry · October 22, 2012, 06:20:30 PM

it's a GM master cyl that is not too full. after sitting awhile the front wheels can turn, the brakes are released.

kb426 · October 22, 2012, 07:19:49 PM

So you have slow bleed off. How many possibles do we have? If you open a bleeder before the pressure releases, does fluid run out?

57larry · October 22, 2012, 07:31:56 PM

Quote from: "kb426"So you have slow bleed off. How many possibles do we have? If you open a bleeder before the pressure releases, does fluid run out?

don't know yet, will check. thanks

wayne petty · October 22, 2012, 09:33:32 PM

do you have any of the U shaped wheel alignment shims...

loosen the NUTS that hold the master to the face of the power brake booster... slide it forward on the studs..

slip in ONE... 1/8" shim on each side.. snug the bolts down..

see if the front brakes are now free to retract...

there are TINY differences in push rod length between part numbers... not a lot.. just a little...

this is only a test... to see if the push rod is depressing the piston just slightly when its bolted into place...

if so it will block the fill ports from the reservoir.. but also block the return fluid when you let your foot off the brakes..

~~~~~~~~~~~~~~

if you loosen the bleeder screws... and it lets the calipers loose.. you have a hydraulic issue.. close the bleeders.. pump the pedal again... lock them up...

now.. loosen the fitting where the brake hose attaches to the line on the frame... does it free it up?

tighten and re lock them by pumping them up..

check at the residual pressure valve...

check at the other side of the residual pressure valve..

check at the master..

where is the system HOLDING pressure???

its supposed to be almost free flowing when the pedal is released..

there could be a bunch of other issues.. this is only a test... i know return you to the rodding round table members..

kb426 · October 22, 2012, 09:42:29 PM

This is a test. This is only a test. I don't remember what movie or song that came from but Wayne, you put a smile on my face. Thank you for that.

wayne petty · October 22, 2012, 09:45:58 PM

Quote from: "kb426"This is a test. This is only a test. I don't remember what movie or song that came from but Wayne, you put a smile on my face. Thank you for that.

that was probably the OUTER LIMITS...

Warpspeed · October 22, 2012, 11:46:30 PM

Another problem can be that the master cylinder is not coming all the way back which closes off the port to the front fluid reservoir.
As everything heats up, the fluid can expand and lock the brakes.

As others have already said, unscrew a caliper bleed nipple.
That will tell you if it is a mechanical caliper jamming problem, or hydraulic pressure lock.

Arnold · October 23, 2012, 10:47:30 AM

My favourite valves were the early factory ones in the later 1960's..early 1970's where they controlled the brake warning light..AND KEPT moving just enough as you were bleeding them..AFTER you had stopped..and set the light off again haha. Till one learned how to deal with them..(there was a little clip that was used)