Brake proportioning valve??

[Boomyal]

How often and likely are these to fail? When you hit the brakes on my son's '87 Pontiac Sunbird they almost lock up and rear end really squats down. I thought maybe the rear wheel cylinders were leaking but an inspection showed not.<br /><br />I'm thinking the the proportioner valve has quit.<br /><br />What say ya'll?

 

[Pascal]

Re: Brake proportioning valve??

That model should have a diaginally split and the proportioning valves mounted at each outlet of the master cylinder. <br /><br />What kind of shape are the back shoes in??<br /><br />If the back wheels are braking evenly, (not with one side not locking up and the other locked up, I would look at the effectiveness of the front brakes. Unlikely that both proportioning valves would go bad at the same time. Still a small chance tho I guess but it sounds like the backs are doing most of the braking for you.<br /><br />JD

 

[Boomyal]

Re: Brake proportioning valve??

Pascal, I just consulted the manual re the Proportioning valve. It is as you say on that model. Very slightly early models were not diagonal and had a frt and rear Proportioning valve that screwed into the side of the master cylinder. On this one they are built in to the M/C.<br /><br />First off the rear shoes are near new. We changed out the originals (maybe half worn w/ 105K mi) about 10K mi ago. The current problem appeared maybe 1-2k mi ago and it seems that the problem is predominantly on the right rear. <br /><br />It seems that unlike the earlier non diagonal M/C whatever proportioning occurs with the front pads must be controlled internally in the M/C as there is no external valve for the fronts. There is no indication that the front brakes are not functioning.<br /><br />Just this afternoon I picked up a rebuilt M/C as a rebuild kit cost fully half of the complete deal. Hopefully that will solve the problem. <br /><br />These things just should not fail at 115k. I guess that is why 10-15 y/o Toyotas still cost so much.

 

[Dunaruna]

Re: Brake proportioning valve??

In my experience (and I'm a brake mechanic of 25 years), the proportioning valves rarely fail - but they are not failproof. Also, these type of problems don't usually just appear suddenly, usually there are warning signs (smoking brakes, pedal 'feel' changes, etc etc).<br /><br />Has ANY brake work been carried out recently?<br /><br />EDIT: Didn't see your second post.<br /><br />Try bleeding first before replacing (could just be crud in the fluid)- or is it too late for that?

 

[Boomyal]

Re: Brake proportioning valve??

Originally posted by Dunaruna:<br /> Has ANY brake work been carried out recently?<br /><br />Try bleeding first before replacing (could just be crud in the fluid)- or is it too late for that?

Oh Aldo, it's so good to hear from you. This is all your fault, I think. You were the first one to inform of this POS's status as a 'World Car', at least the engine anyway. I pity the rest of the world. <br /><br />But no, it's not to late, I can still bleed them. The last work that was done was last summer when we installed new rear shoes as part of the educational (as in the blind leading the blind) restoration project.<br /><br />Per the manual, the proportioning parts of the master cylinder look super simple. There is a spring and a seal for each rear shoe. There also must me some metering built into the cylinder body. Hard to see how they would fail unless those little seal cups were breached. <br /><br />On the other hand it probably wouldn't hurt to see if the front pads move when you apply the break pedal. I didn't, however, want to take on a new career over this issue but mama is convinced that young son will die if I don't get it fixed.

 

[Dunaruna]

Re: Brake proportioning valve??

Indulge me will ya, is your son's car a wagon or a sedan?<br /><br />Does it look like any of these?<br /><br /> http://www.carsales.com.au/pls/carsales/!cs_content.private_results?make_id=10&model_id=118

 

[dolluper]

Re: Brake proportioning valve??

Bench bleed the master before you throw it on<br />Make sure parking brake is not sticking on right side<br />Right drum not out of round<br />Check for grooves in backing plate shoes getting caught then applying abruptly ,if so grind down smooth if enough material left and lube throw shoes back on,or braze fill grooves then grind smooth

 

[Pascal]

Re: Brake proportioning valve??

That master cylinder is what is known as a "quick take up" type. The front calipers are designed to run extra clearance between the pads and rotors for fuel efficiency reasons.<br /><br />There is a special quick takeup valve in the mastercylinder and it must be bled according to instructions. Definitly bench bleed like dolluper says. Follow them exactly! or you will have no end of problems getting the air out.<br /><br />You do not pump these brakes to bleed them. Only push the pedal down once, release the air/fluid tighten the bleed screw and release the pedal. Wait 15 seconds and repeat. Because of the quick takeup valve, any other method will have you pulling your hair out -or more-..... The correct proceedure is a PITA but the alternative is like a hemorrhoid operation in comparison.<br /><br />GOOD LUCK<br /><br />JD

 

[Boomyal]

Re: Brake proportioning valve??

Originally posted by Dunaruna:<br /> Indulge me will ya, is your son's car a wagon or a sedan?<br /><br />Does it look like any of these?<br /><br /> http://www.carsales.com.au/pls/carsales/!cs_content.private_results?make_id=10&model_id=118

Very close to this one Aldo. Just minor differences in the nose and frt and rear bumper treatments. Also the engine is a 2.2 litre OHC<br /><br />http://www.carsales.com.au/pls/carsales/!cs_content.private_vehicle?vehicle_id=2513208&current_rec=7&used_rec=2&total_rec=13&sort_type=&total_rec=13&sort_type=&make_id=10&model_id= 118<br /><br />Thanks Pascal and Dolluper. All good suggestions that I will pursue in order. What happened to simple hydraulic brakes??

 

[Dunaruna]

Re: Brake proportioning valve??

OMG!!<br /><br />From the entire Aussie population, I offer our sincere appologies.<br /><br />It would seem that it's not only the motor we exported . They are known downunder as the 'Camira'. Started life in germany as the 'Opel'. We got 'em and started building them in the early '80's. First a carby 1.6, then 1.8 carby and EFI, then the 2.0 & 2.2 efi. Nissan also used the 2.2 in their 'Pulsar'. Daewoo & Kia have used them also.<br /><br />The seperate valve train/cam box made them distintive (notice I didn't say 'good'). Renowned for - oil leaks, headgasket problems, floor pans twisting (no chassis), oil burning, the loom breaking away from the distrubutor etc, etc....<br /><br />Sorry, sorry, sorry, sorrry...................

 

[Boomyal]

Re: Brake proportioning valve??

Originally posted by Dunaruna:<br />The seperate valve train/cam box made them distintive (notice I didn't say 'good'). Renowned for - oil leaks, headgasket problems, floor pans twisting (no chassis), oil burning, the loom breaking away from the distrubutor etc, etc....

The cam cover bolts won't even stay tight, oil everywhere. I had to do the head gasket during the resto as well.<br /><br />Yep! I can just see you lowering your collective heads in shame. <br /><br />You may remember this project for my son's first car.<br /><br />

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[Dunaruna]

Re: Brake proportioning valve??

I'm cringing as I look at the pics, what the h#ll was GM thinking?????<br /><br /> These days, they are one of a few cars that I refuse to let into my workshop. <br /><br />The cam box needs to be sealed with oxy safe silicone, that's the only way that I have found to slow down the oil exodus.<br /><br />I need to say sorry again.