Hello All, I apologize of this has been addressed already but I couldn't find anything that fit my issue.

I have a 90 Camaro that was equipped with Drum Rear brakes. I replaced the rear end with a 1997 Iroc 342 Posi rear end which had disc brakes on the rear. I placed a Wilwood proportioning valve and redid the brake lines from the front to the rear with 3/16 inch brake lines. The proportioning valve is adjustable from 100-1000 pounds of pressure. After bleeding the master cylinder and the system the rear disc brakes would barely engage, even with the proportioning valve up to max pressure.

I decided the cork screw style calipers sucked anyway, so I purchased the rear Wilwood 4 piston rear caliper kit. I put those on, bled the system again and still the same result. I then decided to replace the master cylinder. Bled the master cylinder and the lines again. If I press the brakes they do not slow down the wheels unless you pump the brakes one time then they will at least stop the wheels (I am conducting these adjustments with the rear wheels off the ground). I tried bleeding the system again and there was no air in it. I am at a loss. I have attached photos of my current setup. Any suggestions would be great.






Thank you for any suggestions.

 

First things First... I am not an expert in the 3rd-Gen Brake Systems.
However I am very knowledgeable in regard to Brake Systems overall...
I would double check what I have to say regarding 3rd-Gen Brakes.

I am assuming that you obtained a used 1987 IROC-Z rear Differential (as you typed 1997 IROC... and there is No such thing).
In this situation, I would obtain and use a Brake Fluid Pressure-Gauge in order to see how much pressure is applying the Brake Calipers.

The Brake Master Cylinder that was originally in the 1990 Camaro for Drum-Brakes, most likely does not generate enough Brake Fluid pressure for the Brake Calipers to operate properly.
In most GM Brake Systems from this era, Disc Brakes will require approximately double the Brake Fluid pressure over the pressure required for Drum Brakes.

I would recommend changing to a Master Cylinder and a Brake Combination Valve for a Four-Wheel Disc Brake 3rd-Gen.
Note: I did say "Brake Combination Valve", which consists of multiple Valves in-one and not a Proportioning Valve alone.
Here is an image of a Brake Combination Valve below:


Also the original Brake-Line from the engine compartment to the rear differential was a Metric 6mm Line.
The closest American sized Brake-Line to 6mm, is 1/4" Line.
I believe that 3/16" Brake-Line is too small, and I would install a new 6mm Line as they are widely available.
Purchasing a "Pre-Made replacement Brake-Line" from one of the Sponsors/ Vendors of the Forum... would be the easiest route to take.

Lastly, be careful not to mix the Metric Bubble-Flare fittings/ threads with American Double Inverted-Flare.

Good Luck and have fun!

 

Thank you for the response. I stand corrected. The rear end of from a 1997 Z28, not an Iroc.

I have read some posts where people have done the conversion and only had to add the proportioning valve. But I believe the 6mm line was not replaced.

After reading your reply, and seeing your signature, I went to summit racing and purchased a combination valve specifically for 4 wheel disc brakes. I will install that and then if that does not work I will replace the line with 1/4 inch.

I do know that on some models of the 1992 they came factory with 4 wheel disc brakes. I researched the master cylinder and they are the same part number. The combination valve is different but couldn't find that information. Once I do the swap of valves I will post my findings. Thanks again!!

 

I think the worst that could happen with an undersized line is slow response time, but the calipers should clamp regardless. Half of my rear brake line run is 3/16" and I have no ill effects from it that I can perceive. I was questioning it myself too and Steve (engineer and owner) at SJM Manufacturing told me 3/16" is fine. It's definitely a lot easier since aftermarket prop valves are designed for smaller 3/16" tube.

The Wilwood prop valve has a hysteresis point adjustable from 200-900 psi where pressure is 1:1 with front brakes before proportioning happens. The rear line pressure continues to climb above the hysteresis point but at a "proportioned rate" of the front. If the rear brakes aren't clamping to the rotor, then it's either a lack of line pressure at the caliper, or maybe the rotors are too narrow and the piston has run out of travel, or the brake backspacing is wrong for the axle.

I don't think swapping out prop valves will do you any good yet. OE prop valves are calibrated to deliver a brake bias suited for the vehicle and it's not highly interchangeable between cars in terms of performance outcome. Those generic combinations valves sold by Summit Racing aren't specifically for your car and the front/rear bias is going to be a mystery until you see what happens. I would leave the Wilwood valve on the car for now until proven to be an issue. You'll be glad you have it when it comes time to dial in the brakes.

 

A few years ago I put factory 89-97 rear disc on my friends 91 formula 350 (came with drums due to the shortage) Used the stock 91 master and drum prop valve and it works just fine.

 

With that being said, that would mean something is stopping the pressure from reaching the back, or the proportioning valve is bad. The Wilwood was a brand new product. With that being said the brakes have done the same thing with the corkscrew setup, which was original for that rear end, and the Wilwood four piston setup. There has been no difference in activity and response.

I have the Wilwood adjusted to maximum pressure, apply the brake to the floor and they will slow the wheels down. If I release and pump the brakes again the wheels will stop. Correct me if I am wrong, but that would indicate air in the system even though I have bled them multiple times. I can make a pressure bleeder for around $25.00. I was thinking about trying that as well.

I am perplexed. I am trying to avoid just throwing stuff at it and spending money, like I obviously did with the Wilwood setup since the result is the same. I am not disappointed in the Wilwood purchase because overall they are superior to the cork screw calipers. But I would like to find out the problem.

How much of your line is 1/4 and how much is 3/16 QwkTrip?

 

Interesting. Maybe I will throw on the original to see.

 

This would be my main concern...

and again I would want to put a gauge on the lines to the rear Calipers.

 

About half and half. I put the union under the car where it was easy to access.

I notice you've got 3/16" tube for rear brake line from master cylinder to prop valve. Where did you find a M12 metric bubble flare fitting that can accept a 3/16" line? I've never seen such a thing (because flare is too small). Need a 1/4" tube to make a good seal.

 

For what it's worth, I use Edelmann 265000 at that location. This adapts from M12 bubble to 3/8-24 inverted flare for 3/16" tube.

 

In this Kit from Summit.

https://www.summitracing.com/parts/urr-br-ez316

 

I think they made a mistake. I can see in your photo there is a significant gap between the tube and the nut. I'll bet that nut slides right over a 1/4" tube like it was meant to be.

All the nut does is clamp everything together. The seal is actually made by the flare on the end of the tube. All the M12 bubble fittings I've seen have a center hole and cone designed for a larger 1/4" tube. And the stock setup used a 1/4" tube too (well, 6mm actually). The flare of a 3/16" tube will cover the hole but isn't large enough diameter to make a reliable seal to the cone. So even if that really is a fitting for 3/16" tube, it's still not proper for that use. I'd redo that connection. It could be a life and death decision you know.

I didn't make this up. I also wanted to avoid an adapter fitting at that location so I talked to Steve (engineer and owner) of SJM Manufacturing and I'm relaying what he told me.

 

Sounds good, I will get a new connector and replace that one connection with the 1/4 inch tubing. I will have to get an adapter due to the fitting on the Wilwood valve not being able to house a 1/4 tube due to the diameter. It was meant for a 3/16 inch tube. I will keep you all updated and thanks for all the information.

 

The part number I shared will reduce to 3/16" tube at the master cylinder. It was an easier solution for me. Fitting screws directly into the master cylinder and makes the seal. Then another tube nut screws into that and connects up the tube.

 

Also check your connection to the hose that drops to axle. That's another M12 fitting and needs a 1/4 inch line into it. That's why I had to transition to 1/4 inch before I got to the axle. Or reuse part of your stock line.

Those two fittings could be your entire problem with a small leak.

 

The following image contains NAPA part numbers for the Brake Line Fittings/ Adapters:

 

The MC for 1989-1991 cars with rear drums or PBR rear discs was the same, so I would think you are good to use your original MC with the new Wilwood rears. MC was different for cars with the Delco Moraine rear discs.

 

It looks like you have your calipers on the wrong sides.

If I'm seeing the picture correctly, your bleeder valve is on the bottom of the caliper and it should be at the top so it allows the air to escape.

Swap them between sides that way the bleeder valve will be at the top and that will help fix bleeding issues and pressure to the rear brakes.

 

The thing I circled in yellow looks like your bleeder.

It should be on the top. Otherwise, you never get all the air out of the caliper.

Very common mistake.

 

There is one on top if you look in the picture. There are actually 4 bleeding screws on the Wilwood calipers. I bled both sides from the top bleeder.

Over the week I pressure bled the brakes as well. They seemed to work a little better but still not like they should on a consistent basis. I checked, and double checked, all of my fittings and there were no leaks. I decided I would replace the proportioning valve, or combination valve, with the one I purchased from Summit for 4 wheel disc brakes, which looks exactly like the factory valve, and see if that solves my problem. I will keep this thread updated in case anyone else has this same problem.

Thanks for all the input and help in trying to locate, and solve, my problem.

 

Well $#!t, I thought I was able to help someone for a change... 🙂

 

Did you bleed the master too? Off the car and level? If its mounted on the car the from is higher and air will be trapped there, no matter how ,many time you bleed the system.
You can jack up the rear of the car to try to level the master, that should work or bench bleed.

 

Yes I bench bled the MC. Made sure there was no air in it, only pumping fluid through it. I hope to have all the new lines ran from the combination valve this weekend and test it. I think the Wilwood valve might be my issue. When adjusting the Wilwood valve, I would tighten it all the way down before the rear brakes would even engage enough to stop the wheels while in motion. If you even gave it the slightest amount of gas it would spin the wheels, not a lot of gas just enough to raise the rpm slightly to engage the TC etc.

 

You ever figure this issue out? Or test line pressure at the caliper?

 

Yes I believe so. I believe it was the proportioning valve. I bought the combination valve from summit intended for four wheel disc brakes. Due to the line positioning on the combination valve being different I had to remake the line to the rear. I kept the line at 3/16 from the combination valve to the rear brakes. I bled the system and it seems to be working as intended now.

When I press the brakes the rear wheels will not move while placing it in gear. When I let off the brake and accelerate (with the rear wheels off the ground on Jack stands) and the press the brakes the wheels stop immediately. While depressing the brake and giving it gas the wheels will brake away fairly easy but that is normal due to the size of the motor and the torque. I still intend to put a pressure gauge at the rear calipers to see what the actual pressure is but I just have not had the time to do that yet.

Thanks again for all the suggestions and help with this issue.

 

see i have this issue and would have expected more bite than just abit of throttle easily breaking loose. I have 800 psi of pressure at the rear ls1 calipers and it cant hold anything it seems. Makes me wonder if something was wrong or i need more pressure bias to the rear.

 

When I have a free moment I am going to jack the rear end of one of my other Camaros up which have factory brakes and see. I will post when I have the chance to do it

 

I just did the grainger spring mod, the stiffest one they make and it made a world of difference. Brake will hold tire on jackstands with abit of throttle now, so it def has clamp force. Can feel it on the road too but my brakes lock up abit quicker than i’d like

 

Hello boy's, I've done a few of these swaps on ford and GM all you have to do is remove the end caps from the combination valve and remove the spring that delays pressure to the front disks so the drum brakes can move the shoes up and engage the drum. Just remove the spring and bleed the valve and it will start working right. If you have rwal like my 92 typhoon the ABS still works fine. even the park brake cables from my truck worked with brake parts i got from the IROC.