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Brake master residual valve

Posted: 26 Feb 2018, 18:01
by Aussiexr7
Hello. I’ve unfortunately joined the legion of owners with frustrating brake issues. This was preceded by replacing my master cylinder and booster due to bad master leaking back into booster and eventual complete failure (unbeknownst to me PO had removed brake warning light at distribution block so no warning).
‘While I was there’ I replaced rear cylinders, hard lines, soft lines, rebuilt front Caliper and new rotors. After MUCH bleeding I have a pedal but first 2 inches is soft.
I’m starting to think the new master does not have a residual pressure valve on the rear circuit as when I took drum off and got a helper to slowly press pedal down and release the pistons move straight back to fully retracted position.
Is there any way to definitively tell if the RPV is there (other than removing flare seat from master? Or have I just proved this (should pistons stay extended in slaves If there is an RPV present)?
Thanks all in advance!
Steve

Re: Brake master residual valve

Posted: 12 Mar 2018, 16:30
by Aussiexr7
Interim update and some progress to report. Inspected rear brakes again and found an issue with LHS where the ‘spreader bar’ (don’t know what the proper name is) was not in place correctly. Must have come unseated when I assembled previously. Also a leaky slave cylinder on RHS which hopefully a light Home and new cups have addressed.
While centring the distribution block piston before bleeding I think I’ve found another issue though - when I removed my dodgy pin to hold the piston it had some fluid on the end. Unless I’m mistaken that should be dry in the center?https://classiccougarcommunity.com/cccg ... _thumb.jpg

Re: Brake master residual valve

Posted: 18 Mar 2018, 23:35
by Aussiexr7
So it continues. Adjusted rear brakes and e brake on the weekend and went for a test drive. Which was very exciting in itself as it’s been about 5 years since the car escaped the driveway. Brakes were still terrible and although pedal not sinking it feels like there is no boost assist (takes a lot of pedal effort to brake) and could not lock up front or rears. So will be testing booster tonight (which was new 5 years ago when I installed it). Also think I need to pull master and verify diameter plus check booster rod adjustment as may be too much play.
On the upside was great to test the secondaries - got a good chirp into second. Unfortunate also a significant cloud of fine rust from the exhaust which I’m sure the neighbors appreciated. My 12yo son didn’t know whether to be impressed or concerned that his conservative dad was acting like a 17yo hoon on the street in front of the house!
Steve

Re: Brake master residual valve

Posted: 19 Mar 2018, 16:34
by Aussiexr7
Tested booster last night with mity vac, passed all the tests which is good. Held vacuum, used about 8” per pedal application and held vac for 30 secs with pedal held in.
Kinda mixed feelings as a dud booster would have been an easy (but expensive) fix. Next step (which I’ve kind of been avoiding) is to wrestle the master out to check pushrod length and verify bore diameter.

Re: Brake master residual valve

Posted: 19 Mar 2018, 17:18
by Cougar Bill
you state it has been "years" since it was on the road. Lots of things happen sitting for that long. Maybe check the check valve before removal of other brake items. Any thought that the master cyl might be bad? If the prv is bad, a repop is avail for$ 70ish. A great piece!

What about the hoses. 5 years sitting is not good. replace all 3

Hope you find the issue as good weather is almost here, topside.... ;-)

Re: Brake master residual valve

Posted: 20 Mar 2018, 01:05
by Aussiexr7
Hi Bill. Check valve tests good so okay on that front. Showing 16” of vac currently at manifold and yes great idea about checking pcv. Plan to cap off all vac inlets on manifold to verify starting point for any leaks.
I’m suspicious of tilt away vac as that is inop (most components removed), do you know where the vac traces back to on the manifold for that?
Back to problem at hand, will verify brake master rod length next. Front soft lines ‘appear’ good and wheels stop when jacked up but of course don’t have a way to verify pressure at the calipers so could be internal hose issue but doubt it would affect both fronts equally.
Steve

Re: Brake master residual valve

Posted: 21 Mar 2018, 17:44
by Aussiexr7
Just re-read Bills post, a repop prv for $70 is hard to beat. And sure beats rebuilding and putting seals in the wrong place.

Re: Brake master residual valve

Posted: 25 Mar 2018, 17:06
by Aussiexr7
Bit the bullet and pulled master yesterday. Found some leakage and brown rusty looking fluid at rear of master so assume it has failed. Will be ordering new master today hopefully. Interestingly looking at rear brake port I can see the residual pressure valve so that wasn’t part of my problem. Fingers crossed new master will do the trick.
One question for the experts- the Factory manual states pushrod length must be set with engine running to apply vac to booster. I did this but it made no discernible difference whether there was vac in the boost or not (ie pushrod didn’t move). Does this sound right as I had expected it to move otherwise why would the manual call it out??

Re: Brake master residual valve

Posted: 25 Mar 2018, 20:14
by Aussiexr7
800|1067|2018|3408.jpg

Re: Brake master residual valve

Posted: 26 Mar 2018, 12:31
by 1969XR7Vert
Aussiexr7 wrote:
25 Mar 2018, 17:06
Bit the bullet and pulled master yesterday. Found some leakage and brown rusty looking fluid at rear of master so assume it has failed. Will be ordering new master today hopefully. Interestingly looking at rear brake port I can see the residual pressure valve so that wasn’t part of my problem. Fingers crossed new master will do the trick.
One question for the experts- the Factory manual states pushrod length must be set with engine running to apply vac to booster. I did this but it made no discernible difference whether there was vac in the boost or not (ie pushrod didn’t move). Does this sound right as I had expected it to move otherwise why would the manual call it out??
Just a heads up that many (all?) new masters do not have the RPV on the rear circuit. In my (first hand) experience is that it can lead to all sorts of "fun", similar to that which you have been going through.