poncho9789

I haven't posted this before now but after all the complaints I have seen about the rear brakes I thought I would post this and let you guys decide what you want to do when it comes to your brakes. We tried it on a 88gta and the guy was extremely happy about about the brake performance when finished and has had no ill effects after 8 months or so. I did it to my car but I haven't had it running verry much since doing the swap and had great brakeing from doing the mod.

This mod was developed by a gm tech and I have heard of many people doing it and totally turning their attitude about their rear brakes completely arround.

http://discussions.gmforums.com/show...?threadid=7614

Happy reading, good luck, and havefun.

PF Flyer

... there was a TSB put out by GM regarding this and it only applied to the non-PBR brakes in the rear.

If you need the TSB info, you can do a search, as I posted it and the repair kit info some time ago.

poncho9789

I have the 89 pbr calipers and had no ill effects

Boxeat2469

Please pardon my ignorance, but what are the PBR brakes?

poncho9789

The pbr calipers are the ones used on 89 and later rear brakes they are different from the 88 earlyer rear brakes.

Boxeat2469

Well I'm gonna' have to try this fix out. I had my tranny rebuilt and a 2400 stall put in. I can't even get the car to 2000 rpm without spinning the tires. I told the trans shop this and they said it was because my rear brakes weren't holding. Sure enough, with the car in the air running in gear the tires still slowly turn with the brakes to the floor. I replaced the master cylinder, proportioning valve, rotors, pads, and calipers. No improvement! I have an 89 Formula, so those should be the PBR brakes. I'll try this fix and post back.

Boxeat2469

Well, I tried this fix out today. It definitely improved my brakes by removing the spring and plunger. The pedal still doesn't feel as firm as I would like though. I'll have to try and bleed the crap out of them again. But at least now with the car in the air I can hold the tires still.

'87FAKE-IROC-Z

Hey guys.
I am switching to a '87 disc brake 9 bolt rear. I am guessing it does not come with the above mentioned calipers.
Should I expect any problems like these with the older style brakes?

cg91ta

Is this fix for rear calipered brakes only, or will it help us drummers?

PF Flyer

It's for rear disc brakes only.

87Fake-IROC-Z - that 9 bolt may come with the PBR calipers and the 12" rotors, so you wouldn't have to deal with this mess.

ANDYZ28

Pre '89 disc brakes are all of the non-"PBR" type.

BMmonteSS

I'm swapping from disk to drums. Has anyone tried removing the valve from a drum pv? I'm ASSuming that it will have the same effect. Check out my cheap disk for 9" ford thread.

p.s. no rear brakes with the stock pv valve in place.

poncho9789

I am no brake expert by any means but I think the rear drum brakes have the same proportioning valve that the disk brakes do but I dont' think that the drum brakes take as much preasure to opperate as the disk brakes. You need to talk to some more experanced guys to know if you might want to do this in a situation other then the rear disk brakes.

BMmonteSS

well i have the rear disk now.... but i still have the drum proportioning valve. Just woundered if removing the spirng and valve would get the pressure up enough to work

ANDYZ28

The rear drum brake propotioning valve is different from the rear disc proportioning valve.

Thanx,ANDYZ28

sIcK pUpPy

I did this last night and all I can say is WOWIE! My stopping power has doubled. I bled them just like the link said, but I am giong to bleed the entire system tonight. I've done alot of research on this and i'm here to tell you that this works. Don't expect Baer or 1LE stopping power, but you will notice a huge difference, I promise :rockon:

Lates,
JD

ebby53

OK... so I understand this right......Mine is a flat nut..pointing straight to the front...its not brick red...oh well....after removing the spring and tube, do not replace either one right? Why must the hole in the nut be sealed?.... or.. When it says it can be replaced with a plug...it means instead of the original nut.....right?

If this works it is definately one of the better (as in for safety) MODS.

Thanks...........

sIcK pUpPy

You are right on the money. And if you don't plug that little hole, your engine bay will have a nice fresh coat of brake fluid all over it. Don't mess with the rear plug, just do the one facing the front of the car. Hope this helps. You will probable notice an unusual odor at first, it's your rear brakes actually working .

Lates,
JD

ebby53

Yeah Man, cool Man, Far out.............Thanks for the help......

MY-92-RS

iTrader: (3)

this looks good I am going to try this . I flat spotted my front tires because the rears are not doing anything :hail:

sIcK pUpPy

Yea, I did that slick move one time when I second guessed myself on a yellow light. I slid right through that bitch Needless to say, my tires gave off a little vibration after that.

Keep the rubber side down,
JD

ebby53

Hey Guys......Is the hole that must be plugged on the outside of the Nut?????? The place that has what looks like a it has a small rubber plug in it now??

sIcK pUpPy

That is just a dust cover. You need to pull that off and plug the hole. Keep in mind that what ever you use mustwithstand pressure and not corrode from brake fluid. I useda 1/2 self tapping machine screw and a self-sealing washer (it's a washer with a rubber grommet on one side. I picked these up from ACE hardware for a total cost of 28 cents . Happy stopping!


Lates,
JD

scauffiel

Perhaps some pix might help:



There's the spring he's talking about modifying, and inside you can see the piston you need to remove.



Piston being removed.



I tapped this plug for threads and got some of that "gasket material" from Autozone to make a small washer/gasket...



...and installed that from the inside so that pressure wouldn't force it's way past.

Of course, don't ask me if it's worked yet because I haven't been out to try the brakes yet.

Steve

ebby53

OK..a picture is worth a thousand words...just wanted to be sure before I tried this. It a daily driver, and I couldn't afford to be down. Thanks GUYS......

racereno

Many thanks to scauffiel for the pics. Now even I understand it!

scauffiel

I took her for a test drive and while it IS a bunch better I was actually hoping for more. I'll reserve final judgement for later after some higher speed braking to make sure all is well. Regardless it is a damn sight better than the stock bias.

Steve

86iroctpi

I rebuilt my callipers with the GM recall kit and my rear brakes actually work, but they don't work as well as I like. Would this mod be overkill for my rear brakes and cause them to have too much stopping power?

jerflash

iTrader: (1)

i just did this mod an hour ago and let me tell you that this is the best mod i have done to my car the car actualy stops now
and just to let you guys know if you guys were thinking about it
you can still do a power brake if your car is powerful enof HEHEHE
my car originaly came with rear drum and i put an 86 9bolt rear in with disc brakes and i keeped the drum pv and it did not stop for SH*T but it did stop better then the drums
so you can do it to a drum brake pv and i bet it you did it to the drum rearyou would have the same good effects
only thing i dont like is the bolt i used to plug the hole
i taped the hole and screwed the rught size machine screw in the hole but before that i put teflon tape on the threads and made a rubber washer but i dont like it so i have a spare pv and i took the plug off of that one cleaned it up and im having the holein the end weled shut which should be a whole lot safer then puting my life in the hands of a small little screw
i would advice you all to do the same of at least get it brazed because if for some reason the washer or what ever you got sealling it were to give out
lets just say the guy infront of you will not be happy
you will lose al break presure
just my 2 cents

jerflash

iTrader: (1)

oh and poncho:hail: :hail: :hail: :hail: :hail:

99Hawk120

What I'd like to know is, are the springs for the proportioning valves available separately so that you might be able to "tune" the PV action a little?

Also, those of you that have had the PV open, does it ONLY control the brake force on the rear brakes or does it appear possible for it to affect the front brakes as well?

PonchoTA

Hey guys, I read all the posts and see that the spring/piston is supposed to be altered somewhat, but nothing on "how" it is supposed to be altered. Spring length, etc. The original post says to remove the spring and piston and put it on the workbench and spit at it and curse it, but no info on whether or not they are even supposed to be reinstalled.

Anyone shed any light on this?

Thanks,
P.

scauffiel

99Hawk120: Call up a dealer and ask, though I seriously doubt it. The Factory Helms manual says the combo valve is not 'rebuildable' or something like that. I think the whole combo valve is a one piece affair BUT the piston you are removing is what limits the amount of pressure to the rear brakes. I believe there is an identical one in the rear of the valve that controls the amount of pressure going to those brakes. Of course, I could be wrong, hopefully someone will chime in if they know better.


PonchoTA: Leave the spring and piston out.

S.

PonchoTA

Thanks! I'll be trying this out in the next couple of weeks (after I get the whole new rear in!)

P.

racereno

Would an aftermarket adjustable proportioning valve be better?

scauffiel

Better? Probably - actually definitely. However... Easier? No. I'd try this first and if it's not good enough for ya, then move on to an APV. That's where I'm headed eventually, but for now this is better than it was.

S.

ANDYZ28

I am running the stock GM 1LE propotioning valve. After 13,000 miles, it still works great.

poncho9789

The guy that developed this mod tried using different springs and cutting the springs to different leigenths but had no positive effect in braking force.

I have been debating on posting this for a while but I wanted to see the long term effects before I unleashed it on a audience as large as this great community.

It really pleases me that you guys are having such good luck with this mod I was just tired of people complaining about their brake systems and knowing that they could do this mod and get a little better braking from their car not to mention safety.

I need new brake pads and to have my rotors turned to get better braking the car set up for 2 years and this mod helped with very cheep pads and rusted rotors.

thanks for the :hail: :hail: :hail: :hail: anything to help out fellow thirdgeners.

sIcK pUpPy

PonchoTA,
This is what you do with the piston/ spring assembly. After you have finished spitting on it, put the assy. in your domanant hand, step outside, and throw it as far as you possibly can I can't think of any other possible use for it. Any creative thoughts out there?


Lates,
Jd

99Hawk120

See the reason I ask is that I have the rear PBR brakes, and they seem to work fine. It's my front 1LEs that don't seem to stop very well. I was hoping that there was something that controlled the front brake pressure, so I could temporarily remove it and see if it's my proportioning valve causing the problem.

sIcK pUpPy

The distrobution block has a valve and spring for the front brakes as well in the rear. You're treading new ground here, I haven't heard of front brake problems, especially 1LE.

Have you checked other possible solutions. IE. bleeding the brakes and/ or flush your system (not insulting your intellegence, just covering all bases), Condition of your pads (are they glazed over?) Just throwing ideas out there.


JD

99Hawk120

Well, I've been messing with this for a while, so believe me, I've tried about everything I can think of.

* All of the hard lines are new
* All of the rubber lines have been replaced with braided stainless steel
* Master cylinder is new (third one)
* Power booster is new
* PV is new
* Calipers were new when installed on all four corners (front calipers are older than the rear by about 1.5 years and 3000 miles)
* No pad glazing evident
* Rotors are new
* Pads are brand new Durastops (front and rear)
* ATE Super Blue fluid (bled more times than I can count, comes out of the calipers the same color it left the can with no air)

The pedal is ROCK hard past a certain point. I've actually managed to lock the rears. There is no brake dive at all. I've tried bedding the front brakes as ANDYZ28 suggested, but I can't seem to get them hot enough to do any good.

Fluid pressure coming out of the rear calipers bleeder is unbelievable. Coming out of the front is low and doesn't even displace much fluid per pedal stroke (far less than the original single piston iron brakes). Fluid pressure / volume coming out of the MC seems fairly equal (checked when bleeding the MC).

I think you can see why I'm suspecting a bad PV now.

sIcK pUpPy

Well the only thing i can suggest, is removing the front brake plunger/ spring assembly as we have on the rear brakes. I'm just theorizing at this point. but after all the work you have put into the system I bet you're up for anything short of Voodoo .

PS. You did check the entire front line system for any kinks, right?

JD

99Hawk120

Man, if I thought a voodoo hex would work, I'd try it.

I bought an adjustable PV and was going to do that and see if it helps, but removing the spring should make it easy enough to verify if it's a PV problem withOUT having to hack up my brake lines.

Glad to hear there's a valve for the front as well. Time to work some voodoo on it.

BMmonteSS

This is a little off topic but not really. I seem to be having the same problem as hawk only with my rear brakes. I swapped from drums to disk in the back and tried the pv mod and had nothin at the rear brakes. I got ticked and just ran strait hard lines to the front brakes and to the rear, no pv. I got the best front brakes i have ever felt in a street car. I have about 3 inches of pedal travel then its like stepping on the pads themself, real direct and strong braking. But I still have no rear brakes. It just dribbles brake fluid when i bleed them. I am using the original drum master cylinder and disk off a 83 firerurd. I have come to the conclusion that either the mast cylinder is shot or doesn't have enough volume to work the rear brakes. Whay do you guys think?

99Hawk120

Your post is no more off topic than mine (albeit in a different direction).

I know for a fact the drum master cyl and drum PV will adequately operate the 82-88 rear brakes. I also know ( from bleeding them a few times) that the pressure of the fluid coming out of the bleeder in that application is what I would call "adequate". Certainly not dribbling. Disconnect the hard line at the junction block and observe the pressure there when the brakes are depressed. It sounds like you have a restriction in the back lines somewhere. Possibly it's the junction block itself.

BMmonteSS

Thanks Hawk I never really thought of the pinched brake lines. I replaced all the hard lines on the rear end itself when i swaped in the 9". I'm assuming when you say junction block your talking about where the main brake line from the mc goes into the flexible line at the rear end. I have no pv valve at all in line with my rear brakes. Hope this isn't too much pressure, does the rear brake side of the mc have less volume than the front side?

99Hawk120

Yes, by junction block I'm referring to the center rubber brake hose.

On my master cyl the amount of fluid displaced by the master cyl seems fairly equal front and rear. There may be a disparity, but it's not detectable with the ol' Mk I eyeballs. With no PV, you should be LOCKING those rear brakes, not suffering from "fluid dribble".

FYI, there's only two MCs for 82-92 F-bodies. One used with 82-88 4WD, and one used for every other brake setup. In my opinion, the "special" master cyl for the 82-88 brakes doesn't really seem to have any measureable effect, and assuming the MC is good, you're unlikely to have serious pressure problems using the drum master.

If you disconnect the center hard line at the rear junction block and get good pressure and volume there, you can eliminate half the braking system, since that verifies the MC is working acceptably and that the center hard line is not plugged. Since it's affecting both rear brakes equally, at that point it's likely that the junction block itself is at fault.

99Hawk120

You know, though, I've been thinking again about your original post. You said you have about 3 inches of travel, which almost indicates total absence of pressure in one braking system (i think we can assume the rears ). If you were to have a restriction somewhere, the pedal should still be fairly hard. It sounds to me more like a massive leak than a restriction. I wonder if the MC is leaking internally (perhaps into the booster)?

I'm assuming you also do not have a "Brake" warning light lit up on your dash.

BMmonteSS

Thats what i was thinking too. You think it could be leaking between the front and rear pistons in the mc? i'm not getting brake fluid all over the booster, buddy had that problem. Ohh yeah no more brake light for me the pv valve is on the shop floor. But when i tried the pv mod the brake light was on. The thing is it worked with the drum brakes. Well i think it worked the brake light wasn't on.