Dark Ember

Alright guys, when I bought my firebird with the J65 rear disc brake option, it was the poorest braking car I had ever driven. I browsed the forums and found a lot of posts, most of the posts were filled with confused people just asking and guessing about the problem. Mine work awesome now. Before I tell you how to fix them, lets diagnose yours.

If you are like me before I fixed my brakes, you probably feel very nervous driving through traffic because every time you need to stop quickly, you cant. If you depress the pedal even remotly hard, the front tires just lock up and the car just slides and takes forever to come to a stop. The threshhold of slowing down before lockup occured was equally dissapointing. If that sounds familar, read on.

Easy Diagnosis:

There are 2 different ways to find out if your J65 brakes dont work properly.

Method #1(not for ABS cars) Go to a choice parkinglot and get up to about 10mph. Slam on the brakes as hard as you can. Once the car stops, put it in park and get out. Look at your tire marks. If you dont count 4 sets of skid marks, your rear brakes arent locking up like they should. I say go only 10 mph because if you are going much faster than the skid marks will be so long your front skid marks would cover up the rear skid marks. If you are dead set on doing it at a faster speed, then get up to the desired speed, turn, and then slam on the brakes. This way, the front tire marks will not overlap with the rears. If your car is like my car was, then nothing you do can ever get the rear tires to lock up.

Method #2 Jack up the car, start it up, and put it in drive. Your rear tires will quickly get up to speed. Now slam on the brakes. If your car is like mine was, your back tires wont even slow down. This is a true indicator that your rear brake pads are not contacting the rotors with enough force to even stop a tire.

And The Problem IS:

So whats the problem? Well, you know that aluminum block below your master cylinder? Its got 2 brake lines going into it from the master cylinder and 3 going out. Its the combination valve and thats the problem. You dont have to remove the master cylinder or brake booster to replace this component.

Pic: http://img641.imageshack.us/img641/9...ationvalve.jpg

Its a sad fact that almost nobody maintains their cars, and brake fluid flushes are one of the most denied maintenances. Its supposed to be flushed every 2 years, reguardless of what make, model or year your car is. Current technology on the market gives us a fluid which becomes highly corrosive and acidic with time. In our case, our cars are nearly 20 years old and most have never had a brake fluid flush. If you like replacing brake components, dont ever flush your brake fluid.

Explaination of the Valves:

Normally when you depress the brake pedal in an automobile, there are a few different valves which each have their own specific task.

Metering Valve:

The metering valve is there to ensure all wheels get brake line hydralic pressure at the same time. Disc and drum brakes differ in operation and as such drums needs pressure a fraction of a second before the discs in order to actually begin stopping the car at the same time. This is because there is a gap between brake shoes and drum brakes, while brake pads have no gap between them and the rotors. So drum shoes need to move a small amount before they actually begin stopping the car. The metering valve stops the rear brakes from engaging first. Or in a 4 wheel disc car, it makes sure all wheels get pressure at the same time.

Proportioning Valve:

A proportioning valve is a valve which sends different amounts of pressure to the front and rear. The goal is to have the rear tires lock up at the same amount of pedal pressure required to lock up the front. Because of the nature of weight transfer while braking, it takes less pressure on the rear than on the front to lock up the tire. These let you tune your brakes so all 4 tires reach the lock up threshhold at the same amount of pedal pressure. If you have different suspension and wheel/tire combinations, this is probably a good investment.

Combination Valve

This is both of the above valves built into 1 unit, thus the name.

Unfortunatly its not easy to find a replacment. I like using manufacturer parts. I went to a dealership and picked mine up. Beware though, I got the last one in the Houston area warehouse, because GM is not making it anymore. Its called a Valve Assembly and here is the GM part # 10164112. This will only work with the J65 cars. The list price is $127. I am sure someone in the aftermarket makes these but I couldnt find out who it was.

All Better

After replacing this valve, and bleeding out the air, my car leaves 4 tiremarks any time I get excited enough to brake hard. When I jacked it up and hit the brakes, the rear tires stopped immedatly. The car stops so much quicker now. The days of barely slowing down and having the front tires lock up are long gone. Now, if I am braking hard enough to lock up the front tires, the rear tires are locking up as well. This car brakes every bit as good as you would expect a 3400lb car with 4 wheel discs to stop now.

chazman

iTrader: (4)

Are you sure the valve was bad or did the system just need bleeding?

Dark Ember

Yes, I had flushed, not bled but flushed the entire brake system before hand because I had replaced all the rubber lines, both front calipers, front rotors and front brake pads. The brake system operated that way before and after the repairs I performed. Air was definitly not a factor.

On a side note though when I was flushing out the rear calipers before I changed the valve, the brake fluid was barely spraying out of the rear bleeder screws. I had my wife operating the brake pedal and was telling her to push as hard as she could because it was barely coming out. After the valve was replaced I again had her bleeding and again told her to push as hard as she could. This time it was spraying out all the way to the center differential, so there was definitly more pressure getting to the rear calipers.

RBob

iTrader: (1)

I get the feeling that GM re-designed the combo valve. Which is a good thing if folks can get it. As you mentioned NEARLY EVERYONE complains about their '89 - '92 rear disc brakes (leaving the earlier Delco rears out of this).

This previous lack of braking is why I'm still running drums on the back.

The other thing is that until dyno emissions testing became wide spread, the lack of rear braking with disc's was little known. If the inspector can't stop the rollers before shifting into park, then it is obvious that there is something wrong with the brakes...

RBob.

chazman

iTrader: (4)

Interesting, thanks for posting.

chazman

iTrader: (4)

Just did some quick research and it seems like GM part # 10164112 which Dark Ember used sucessfully on his earlier Delco J65's, is actually the 1LE/PBR prop valve.

Can anyone shed some light?

Dark Ember

Wow that is interesting. When the GM sales person was looking up the part for me, he specifically asked me to go check my console and make sure I had the J65 RPO code because this part supposibly called for that. Don't quote me on this, but I do seem to recall him also asking me if I had the 1Le... Anyway though, since 1LE is a rear disc car, its possible that the same p/n combination valve would be used. I mean, fundamentally, all they really need is to be matched to either drum or disc anyway.

chazman

iTrader: (4)

The prop valve which you have "looks" like the one on my '89 which has the PBR rear brakes.

The one on my '83 with J65 looks like this:



I'm wondering if the newer one would work on my '83? My '83's brakes BTW, feel just like your description of yours before the new combo valve.



EDIT: Duh! I just noticed that you have a '90 Firebird so you have the PBR rears.

Dark Ember

Your comb. valve looks a lot different, and yes I do have the original PBR aluminum rear calipers. The combo valve I photographed was my old one after removal, but the new one looked identical. You have to be careful with the years because during my search for a new one, I contacted the following company:

http://www.getdiscbrakes.com/RightStuff/Default.aspx

I called and spoke to their tech department hoping to get a valve from them. The guy I spoke to told me that they did not have anything for my year because sometime in the mid-late 80's GM switched from a standard to a metric thread on their brake line connections, and they only carried the earlier style. I could have made it work but I would have to get into flaring and brake line modifications, and a direct bolt in valve sounded much better to me. You may be in that lucky year where their standard thread combination valves bolt right into your car. Considering how different your valve assembly looks from mine, I would say that further gives you hope of having their threads. But its important to note that GM did change the threads sometime during the 3rd gen production, so note that if you start hunting down a new comb. valve.

Also, I got mine from Munday Chevrolet, and although their supplier only had 1 left on the shelf, that doesnt mean that other dealerships wont have access to the few remaining. But the aftermarket valve's are a little cheaper than GM's.

JamesC

iTrader: (5)

All 82-92 rear disc cars are RPO J65, although the 89-92 models are equipped with the so-called 1LE system.

Info on the 1LE Combo Valve:

14089496 1989 1st design: M1.0 tube nut threads (For 1982-early 1989 applications). The tube nut threads fit earlier models, such as my 85 IROC; the 1.5 below will not).
10136840 1989 2nd design: M1.5 tube nut threads (Late 1989-92).

Here's what Ed Miller has to offer (I'm guessing the p/n changed for the second valve):

http://www.flynbye.com/catalog/c17_p1.html

Chazman, the valve you're showing is the old cast iron model, which looks nothing like the later modes; moreover, it has SAE threads, which means that swapping a new metric valve in may be problematic.

Combination valves apparently have increased bias from drum to standard disc to 1LE.

JamesC

chazman

iTrader: (4)

So, I'd imagine if I ever felt the need to replace my combo valve, I'd want to stay with the original cast iron one, right?

And is there a definitive way to tell if it's bad or not?

Dark Ember

The ways I mentioned in the original post dont rule out other blockages in the lines, hoses and calipers. I should mention that there is another way to remove all those variables. You will need to bleed your brakes after you do this, but...

Unbolt the brake lines coming out of the master cylinder. Just to make sure those lines arent blocked, remove them where they bolt into the top of the valve assembly. Then observe the master cylinder(leave the cap on) while someone else depresses the brake pedal. Note the amount of fluid and the pressure at which it sprays out of both ports. A properly working master cylinder is going to have comparable jets of brake fluid. Because brake fluid is corrosive, I would have some plastuc tub to catch the fluid, or else its going to get all over your engine bay.

Then, reinstall those lines. Now remove all three of the other lines coming out of the valve assembly. Repeat the process. Two of those lines will go to the front brakes, while the third goes to the rears. Again, you should see comparable streams of fluid spraying out of each port, but they will not be the exact same amount. But an improperly working combination valve is going to just barely be bleeding out fluid to the rear port. Its going to be very difficult to compare this because the 2 front ports are facing the ground and therefore gravity is going to send the streams down until they hit the frame/driveway. The rear port is facing up. I would guess that if the rear port doesnt shoot a stream at least 2" tall when depressing the pedal at a normal braking speed, then you have a problem. If you are still unsure, then have the pedal depressor push the pedal down as though it was an emergency stop. The fluid should spray up with enough force to hit the hood.

This test is a little flawed because it relies on your eyes "seeing" a fluid difference. This is why I didin't bother mentioning this in my original post. Brake lines usually dont "stop up". Rubber hoses are the exception, especially in 20 year old cars which didint get fresh brake fluid running through them every once in a while. If you trust your rubber lines, then the 4 wheel skidmark test or the jacked up rear tires brake check should be all you need to know whether or not your combination valve works.

If there is some device out there which pressure tests combiation valves to verify proper operation, I am not aware of it.

ownor

iTrader: (5)

Good info in this thread. Although i'd never do the test as suggested in Dark Ember's last post, you don't want that highly corrosive brake fluid anywhere in your car except the brake system! Can't stress that enough, anywhere it goes it will ruin your paint or other coatings and encourage rust formation.

Although as said there's valuable info in here, I don't think that the combination valve is a generic key to cure any and all J65 problems.

Not to hijack this thread, but does anyone know of an adjustable combination valve that fits our stock lines, especially the metric M1.5 from 89-up?

G92Bill

I have the same problem except all my brakes dont lock up. I cant get them to. I have replaced all the calipers, brake pads, lines, and master cylinder.And I bled the crap out of them. But still the brakes dont work. The car is in the shop as of today. This one has finally beat me.

jermdm

Its crazy that the second design valve 10164122 is so much harder to find. As said before, the part # might of been changed for it and be readily available. If you have the first design valve, its readily available from just about anywhere. Acdelco's website has a listing for it. Part # to look for is 172-2005. The original valve on the car should have a little tag on it and have the code NB on it. Looked on my iroc and thats what it has. Even though mine is an 89, it has the first design valve since it was built in 88.

canb4

I've got an 85 with 4 wheel disc. The brakes will not lock up. Have replaced everything except for the discontinued proportioning valve. Was wondering how you made out at the shop. I'm ready to chuck in the towel.

Camaro86IrocZ

iTrader: (1)

I did the prop spring mod on my '86, stock rear delco calipers work much better... I had been fighting with them for years until I came across this thread pasted below on here... I used the lighter spring rate that they mention... Very easy and cheap to do... Rears actually grab now...

https://www.thirdgen.org/forums/brak...e-upgrade.html

92-Formula

iTrader: (4)

Has anyone done any higher speed testing? As in 60mph, emergency stop? I can get all four to lock up, but at higher speed this produces very bad axle/wheel hop in the rear. I replaced the spring inside the prop valve with a 22lb spring.

Jetmeck

iTrader: (3)

yes................I agree

Valve bad design maybe, clogged no way.

Air in system very likely.

Camaro86IrocZ

iTrader: (1)

Try the Lighter 1NCR5 Spring Rate of 30.82 Lbs/In... I haven't had this problem with it to date... The 1NCF2 has a Spring Rate of 37 Lbs/In.. I based my choice off of this post below specifically... the INCR5 is right in the middle of his testing...

https://www.thirdgen.org/forums/post...3-post139.html

Free91z28

Just reading over this thread and I have a 91 z28 all disc and the rear won't even hold the tires with it in gear on jack stands. Can we gut this block and run a aftermarket adjustable proportioning valve to the rear side and call it a day??

87350IROC

iTrader: (2)

Yes. Exactly. That solution works great.

slowsi

iTrader: (2)

does anybody know what lb spring is in the stock valve

Cosmik Debris

I think it is 13 lbs, some people replace it with a 19 lb spring which supposedly works better.

Another thing worth mentioning is that the parking brake has to be working correctly to ratchet the pads in as they wear, this can cause bad brake performance too.

TTOP350

iTrader: (8)

For those playing the home game, that's only for the old delco iron calipers.