Brake proportioning valve question

[rocketrx7]

I've got a question concerning what should be an easy procedure. I had to replace a rear brake line last week after it corroded to eventual failure. Once I replaced it, I tried to bleed the air but couldn't get anything out at all. So I checked the master cylinder, bled the lines before the proportioning valve just to make sure. The front brakes work fine but nothing is going to the rear lines from the valve. It appears as if the valve is plugged at both rear outputs, but I can't understand why. I've bled them in the proper sequence and I've even tried a different proportioning valve. They were working fine before since I was expelling fluid out the corroded line. Is there a procedure I'm unaware of?

 

[Defiant]

ABS? Pay a shop to flush the system for you.

 

[GTM]

Originally posted by rocketrx7
It appears as if the valve is plugged at both rear outputs, but I can't understand why. I've bled them in the proper sequence and I've even tried a different proportioning valve. They were working fine before since I was expelling fluid out the corroded line. Is there a procedure I'm unaware of?

When you say "proper sequence" what do you mean? It's been a while since i've had this problem and I don't remember all tricks but if I remember correctly the PV piston has exceeded the normal travel and can't recover. In all probability you need to pull the PV and with the plastic covers held firmly smack it down on a block of wood to get the piston back close to being centered. Wear plastic gloves if brake fluid is corrosive to your hands. Hopefully you have a vise which you can use some cardboard as safe jaws. Now you need to completely bleed every bit of air while on the bench... I don't care if it takes you 1/2 hour this is critical. I like using a screwdriver handle to rap on the body as fluid is added, the shock dislodges the bubbles and you just keep adding fluid until you _KNOW_ both sides are filled and have no air. Cap all the openings before you leave the bench to the car.

Bleed the master cylr and as the last thing you will jam a stick / dowel between the seat cushion and the brake pedal so it's about 1/2 way down. This prevents the fluid from draining through both Master cylinder pistons. I would be good if you have some way to hook a hose to the rear brake lines at their PV connection so you can get a gravity flow to the rear brakes for bleeding. Now you can install the PV pulling one cap at a time and snugging the lines down until they are all secure. It may be helpful if it's not mounted to the body until all the line are on. It is important to not let air enter the system while making these connections. Once all is installed and tight check the resivoir and add as needed, then you can release the brake pedal. Again to the rear wheels you will open the bleeder and watch for bubbles for a min or so for each wheel. Close the bleeder off, jam your dowel on the pedal bleed one wheel at a time for a couple of sequences. If you have done everything right you should have full brake pedal. If not, then you will slowly pump 3 times, hold the pedal down and bleed each 2-4 times for the 3 pumps. You don't want to be pumping violently or with great force for if there is a large charge of air trapped it could shove the PV piston all the way down again. It's not as bad as it seems and it took longer to write this than the actual job if you use a clear plastic bleed hose and bottle. You must not allow the resivoir to run dry. Once you have a solid pedal go for a road test if ok then you should check in a week by just cracking each rear bleeder and watch for bubble.

Any questions?

Cheers,
GTM

 

[rocketrx7]

The system is non-ABS by the way. Was ABS available on the Talon in 1990?

You mentioned plastic covers on the valve. I don't have any plastic covers, please clarify.
Anyway, it appears as if you've properly identified the root cause here.
There must be an easier method to remove the air from the valve. I can't imagine that a technician would need to remove the entire valve and tap on it in hopes of removing all of the air. It seems inevitable that you would lose some fluid when you reconnected the lines. I wonder if the piston will reposition if you applied vacuum to the input side to draw fluid from a full canister at the caliper.

 

[GTM]

Originally posted by rocketrx7
The system is non-ABS by the way. Was ABS available on the Talon in 1990?

You mentioned plastic covers on the valve. I don't have any plastic covers, please clarify.
Anyway, it appears as if you've properly identified the root cause here.
There must be an easier method to remove the air from the valve. I can't imagine that a technician would need to remove the entire valve and tap on it in hopes of removing all of the air. It seems inevitable that you would lose some fluid when you reconnected the lines. I wonder if the piston will reposition if you applied vacuum to the input side to draw fluid from a full canister at the caliper.

I've been told ABS was not available for this year model.

When you buy new/rebuilt hydraulic parts they come with plastic caps/plugs to keep the dust and dirt out. I've never found a good substitute for these throw-away parts so I kept a drawer full of various sizes. You might try 1/2" sections of the foam window and door sealers used at your home. This has a peel off paper exposing the adhesive but the brake fluid might attack the foam or adhesive.

I'm not going to tell you to take a metal hammer to the cylr for it makes me cringe when I see this. With the output lines especially to the rear loosened and a hard plastic hammer you might be able to coax the piston back to the center position where it will expose the proper ports. If you hadn't guessed I'm a retired professional and I've seen my peers fight these things just as you have, I've had a couple stick on me and pulled them apart to understand why this should happen and it's my guess it's a design to protect the driver should their be catastrophic failure that it blocks off the failed system. You won't find this in any book because I've not written it yet. I don't know where the PV is located much less what it looks like, if it's tucked up where you can't get to all the fittings you may just be making problems for yourself trying to see that the PV is clear of all air. Sure it's a bit slower but by doing it on the bench you know that it's been bled. You should have put the dowel on the brake pedal _before_ you opened the system and what you experienced _might_ not have happened. What I've told you will work though if that piston is jammed tight you may end up pulling the large bolt out and using a dowel shoving the piston back to the center. If you find a lot of "mud" in there you probably should take it (piston) out and wash everything in brake fluid. A cutaway looks worse than it really is but spread the parts out on a clean lint free towel.

Now you have a basic understanding of what is happening and why to not pump hard and fast this first go round. Sure you can take short cuts but you run the risk of spending more time bleeding and wasting brake fluid (you will need to have at least a quart so you don't run out. Your choice but don't blame me if you end up having to pull the unit when you get too much air in the system again.

Any questions?

Cheers,
GTM

 

[rocketrx7]

Yes, I arrived at the same conclusion after I dismantled one yesterday. It appears as if the piston is designed to block the rear port if you lost a large volume of fluid. I may have avoided this whole mess if I'd only bled the brakes slowly.
The design of the PV doesn't seem to be an item that's readily serviceable. It's on the firewall, but it's the design that doesn't lend itself to easy repair. The two spring loaded pistons are pressed in from the bottom and held in place by a spring clip. Unfortunately it's coutersunk and lacks any type of fitting to remove them.
Thanks for the input.

 

[GTM]

Originally posted by rocketrx7
Yes, I arrived at the same conclusion after I dismantled one yesterday. It appears as if the piston is designed to block the rear port if you lost a large volume of fluid. I may have avoided this whole mess if I'd only bled the brakes slowly.
...........
The design of the PV doesn't seem to be an item that's readily serviceable. It's on the firewall, but it's the design that doesn't lend itself to easy repair. The two spring loaded pistons are pressed in from the bottom and held in place by a spring clip. Unfortunately it's coutersunk and lacks any type of fitting to remove them.
Thanks for the input.

People never think to push the brake pedal down 1/2 and jam it there when they know they have major surgery. Another trick which must be used with common sense is a pair of Vise-Grip on the flex hoses. This just keeps the fluid from getting knocked out and taking in a charge of air. So had you bled the pipe before connecting, hooked up the flex line you probably would not have driven the piston all the way to the end where it got stuck.

You mentioned a vacuum pump to help bleed, that may not work where the exit fittings come out the bottom thuse you would only suck fluid in and through the PV without removing the air. If they all come out the top then this could work but the screwdriver handle taps can't hurt.

If this is your first PV or anti dive excursion consider you have learned something akin to an ounce of prevention/preperation is worth a pound of cure.

Let us know the final process which worked for you.

Cheers,
GTM

 

[BISHILVR]

go to the local autozone and purchase a vacuum brake bleeder kit....looks just like a penis pump...(no joke)..this should end all of your problems.....gotta love ohio salt destroying stuff huh? btw i'm only bout 30-45 min from akron....(salem) we should hook up some time!!!

 

[GTM]

Originally posted by BISHILVR
go to the local autozone and purchase a vacuum brake bleeder kit...

That will not pull the PV piston back into position nor can it pull fluid PAST a closed port. I'm not talking about a check valve I'm talking about a piston blocking off the feed port. It will not recenter anything if it's in a stuck or out of position piston. My point is when everything is working properly it _can_ be a useful tool. But we know everything was not working properly and this tool is absolutely useless under these conditions until he fixes the problem.

Cheers,
GTM

 

[BISHILVR]

with all due respect though i've done countless brake job's as well as any other brake work you can imagine and i've NEVER had to remove a proportioning valve assembly and beat on it to get it to work right!!! again no where in the manual does it state that this is the proper solution to a brake job that wont bleed properly....

 

[rocketrx7]

It does sound silly but GTM is correct on this issue. I've never had a problem like this either and I've performed substantial work on many cars. The PV was designed with a stop-gap system and it's not easily reversed once it's engaged. I disassembled one to see what was going on for myself and it's clear that no amount of pressure or vacuum is going to force anything through the rear ports.
My guess is that this has probably happened to many sad souls in the past but the part just gets replaced with a new one. Unfortunately, it could reoccur just as easily if you're not keen enough to figure out how it happened in the first place.

 

[GTM]

Originally posted by rocketrx7

...
My guess is that this has probably happened to many sad souls in the past but the part just gets replaced with a new one. Unfortunately, it could reoccur just as easily if you're not keen enough to figure out how it happened in the first place.

You have opened can of worms which can't be solved here and the reason I left the industry. The makers want parts changers not mechanics, they do not want to pay for knowledge or the diagnostic time which sometimes can kill a job.

The first time encountered this problem was on a MG back in the 70's and I installed a new part. The next was also in the 70's on my own car which I fixed by buying a repair kit thinking there was an unidentified problem within the unit but I understood what had happened. Subsequent others on customers cars have always been just a matter of dislodging the piston and bleeding the unit. I have watch my co-workers fight this problem, install a new unit which they did the exact same thing by not refiling the lines and the unit with fluid prior to install. They then return the part to the parts dept claiming it too is defective and in a couple of cases claimed the second new unit was bad. It doesn't take a catastropic failure to introduce enough air in the circuit for just allowing the master cylinder to run dry while foot pedal pump bleeding the system. It is a situation which has been repeated time and again and caused the customer to pay for a unit which in all probability they didn't need because the mechanic comdemmed the unit as part of the failure. Because someone who has not had the experience or understand what went wrong does not negate the fact IT does happen and IT causes a lot of grief the first time they encounter having the piston lock in the safe mode.

And just because it's not written in a repair manual of which it's safe to assume I've read my share doesn't mean it can't and doesn't happen. The bummer is having to put up with the attitude and attempt at ridicule some people exibit while telling us we are full of crap. Not knowing is one thing, but defending blind ignorance with insults sometimes makes me want to leave a thread rather than participating in a logical conclusion / solution. I've met a lot of people who identified themselves as "mechanics" that cause me to sometimes be ashamed to identify myself because of incompetency. They twist wrenches for a few years and think they have seen it all. After some 10 years I figured I'd served my apprenticeship and identify myself as PROFESSIONAL mechanic. I've never felt a need to be a bs artist to make money repairing people's problems. I kept records of my comebacks and know that at .05%-.1% it is vastly superior to any Doctor's diagnosis and repair of their patients. As far as I'm concerned the "oath" is just the same ... you do no harm.
......... Soapbox mode off..........

BTW got any more experiences that don't fit the norm?

Cheers,
GTM