Jetmeck

iTrader: (3)

Have a rear disc converted (all new parts) '87 TA with the low pedal which comes up with the quick second pump of the brakes, have swapped to a 4 wheel disc master cylinder and combo/proportioning valve and bled the entire system to no avail.

Which mod is best ? Adding the washers or removing the spring on the proportioning valve ?

Also have a '89 Gta with the rear PBR calipers which aren't supposed to have this problem, MINE DOES and have read several posts of '89 up owners complaining of low pedal/ weak rear brakes like my '89....so I will be doing this mod to both.

My '89 was built late in '88....all you '89 owners with rear brake problems, were your cars built late in '88 also, maybe we got the old proportioning valve, was it different for the 88 and down cars ? Is the difference the PBR calipers or the proportioning valve ? Most '89 up cars are not having this problem so I am curious what makes the difference ?

Bill E.

Brett H. - 89GTA

Don't bother fiddling around with shimming the prop valve spring or removing it. I'm replacing mine with an adjustable Wilwood unit so I can easily set the brake bias where I want it.

icecold

i removed mine and now i have a little too much rear bias and will be putting an ajustible valve in to knock odd a little pressure
pete
ps i think that if i did it again id just tap the hole and install a shim behind the spring and then use the screw to adjust the spring pressure.i'm going to try this before anything else but have to wait till spring when the snow melts 15 degrees here right now

25THRSS

This mod sounds like an excelent way to have an adhustable unit while keeping the stock prop valve as well. Got any more info on how to do this?

MrDude_1

hmm.


any mod will cost you atleast $5... even if its mostly gas money to the hardware store for $1 in parts.....



so is the $35 you save modding your valve instead of buying a proven aftermarket adjustible one worth risking your life and car?

Jetmeck

iTrader: (3)

Thx for the replies everyone, let me be clear on this I do not want an adjustable proportioning valve on either car. I want the stock look, thx anyway.

Which mod has anyone had success with ? Thx

P.S. I heard of using a front ? plug off another pv to plug rear hole after removal of spring and plunger ????????


Bill E.

25THRSS

It's not to save $ at all. I could care less about cost when it comes down to it. I want to keep my brake warning light and somewhat of a stock look as well. If you just get rid of the stock prop valve all together you lose the warning feature, which I am not willing to let go of. I found some excelent info in another thread in which I think I am just going to gut the stock unit and install an adjustable unit in line to get my desired results.

25THRSS

https://www.thirdgen.org/techbb2/sho...hreadid=127100

Here is some good info. I will be installing an adjustable unit as well to better dial in the rear braking force. This way I can keep the brake warning light, have all the control of braking I want, and look virtually stock as well.

icecold

i agree with your idea 100% i'm also not willing to remove my stock unit. i have already gutted it and like i posted up top will be installing a adjustible valve in the rear line if my other idea dosent pan out. good luck with your project.ill post my results if i can get it to work
pete

Jetmeck

iTrader: (3)

Pete,

By saying you gutted you pv, you mean the rear only right ? Or did you do the front too ?


Bill E.

Brett H. - 89GTA

Gutting the PV is not a good idea. The front and rear brake systems are designed to be independent...that's why you have a dual master cylinder. Gutting the PV combines the two systems. Chickenman35 commented on this awhile back.

I can understand wanting to keep a stock look, but doing the wrong thing with brakes can turn your car into someone's new trailer hitch. Little room for error here.

25THRSS

Gutting it doesn't combine the 2 systems. Did you check out the link? It's been done before and is a proven mod. The front and rear are completely seperate and will not do anything wrong by gutting the rear portion of the prop valve. The only thing it might do is give too much rear braking force which is easily fixed with an adjustable unit in line. There is a lot of good info on this by doing a search. It's a proven mod.

icecold

by gutting it i did the mod posted. taking off the front cap pulling the spring and plunger,tapping the hole and installing a screw into the hole with some sealent then bleading the system . testing with promising results just a little too much bite out back now for my taste.then i did some more searching and saw the spring shim method and thought why not reinstall the spring and plunger then turn the screw around so i can adjust it from the outside and either use it as a limit stop for the plunger or install a shim and use it to adjust spring pressure.dont know if it will work and assume it wont. just because if it would someone would have done it. but who knows it's worth a try as i already have whats needed and adjustible valve for the rear will run at least 30 plus parts
pete
ps gutting the front side of the valve dosent hurt anything and you still have 2 seprate systems like 25rss said

Brett H. - 89GTA

If you're talking about gutting only the back...maybe. Gutting the whole thing...check out this thread:

https://www.thirdgen.org/techbb2/sho...hreadid=214136

I'm putting in an adjustable one. I don't compromise on brakes.

25THRSS

Iv'e read that thread before and it didn't convince me of anything. Several people have performed this mod and it is safe. You are not gutting the front, only the rears. Gutting the front would do nothing anyways. As long as you have control over the rear brakes you can dial in both the front and rear to lock around the same time giving the best possible performance. Losing the warning light is a compromise I am not willing to do.

83 Crossfire TA

iTrader: (2)

I don't know of any car that came from the factory with a proportioning valve…

I'm assuming that you guys are talking about the combination valve that our cars have. Gutting it doesn't accomplish anything but combine the 2 brake systems (don't believe it, do it and disconnect one of your lines and you'll find that all 4 brakes don't work). And disable your brake warning light.

The factory 'proportioned' the brakes by adjusting the brake and piston sizes. If you want to change your brake bias without using a valve you need to change parts, either brake size, piston size or MC piston size.

Brett H. - 89GTA

I had always thought that combination valves are used on disc/drum cars, and proportioning valves are used on disc/disc cars. The combo valve also includes a residual pressure valve for the drum brakes, correct?

83 Crossfire TA

iTrader: (2)

Residual pressure valves are only required with disk brakes where the caliper is mounted above the MC. Off hand I can't think of an OEM application where that's the case

icecold

not quite true. if you totally remove all the internal parts your right that both sustems will be combined.but if you just do the mod and remove the plunger and spring ,then seal up the plug you still have two seprate systems.and from my car results i got much higher rear system pressure.as i already said maybe a little too much.
wont know till spring when i put the racing pads on front and see how she stops with the same compound pad on all four corners(right now only have the racing compound on the rears)