Wilwood rear disc brakes not working!

[Chris 68]

I bench bled the new stock power master cylinder on my 68 camaro, hooked up the lines and bled the brakes. My front wilwood 6 piston brakes seem to be working just fine, however my rear wilwood 4 piston brakes are not working. I bled the whole system 3 times, and had fluid going to my rear bakes, but the pistons in the rear calipers are not really moving. I think the problem may be the distribution block (picture attached). The distribution block came with the master cylinder and booster assembly, I believe the block is for a disc/drum set up, however I was told I could remove a spring in the distribution block that would allow me to use it for an all wheel disc set up (spring was not found when I opened it up). The pedal is soft at first but becomes really firm towards the back half of the stroke. I would like to retain the lines I just bought as well as the master and booster assembly (if these are not the root of this problem).

If this distribution block is the problem, is there a distribution block or proportioning set up that will roughly fit in the location of the faulty/incorrect distribution block? I was thinking this might work: http://wilwood.com/MasterCylinders/MasterCylinderProd.aspx?itemno=260-11179


https://static1.pt-content.com/images/noimg.gif

https://static1.pt-content.com/images/pt/2012/01/720169-1.jpg

[badazz81z28]

Your assumption is right on, You have a drum prop valve installed. You need a disc/disc prop valve
look here: http://www.ebay.com/itm/GM-BRASS-PROPORTIONING-VALVE-DISC-DISC-PB-215-/350481099781?hash=item519a4d2c05&item=350481099781&pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr

[Chris 68]

Thank you for the confirmation and the link! Also, will my stock master work well with my set up? I see almost everyone is using Wilwood's master and, besides any cosmetic differences, what is the benefit of running a wilwood master as opposed to stock. This will be a daily driver so brakes are on the top of the list of priorities.

I'd like to stick with the master I already have since it's paid for but if there is a big benefit running the wilwood piece then I don't mind dropping the $$$

[TheJDMan]

According to Inline Tube, the original Drum/Drum distribrution block can also be used for Disk/Disk applications since it does not change the pressure from front to rear. Factory Disk/Drum cars were equipped with the same distribution block with the addition of a hold off valve at the master cylinder and a proportioning valve down on the frame in the front to rear line. My 68 was originally a Drum/Drum car so it does not have the prop valves. When I installed front disks 35 years ago I always had the sense the rear brakes engaged first so to compensate I simply backed off the rear brake adjustment. Now that I have upgraded to C6 Z06 Disk/Disk system I understand the stock distribution block will work just fine. Check this page out for more info.

http://www.inlinetube.com/Prop%20Valves/pro_valves.htm

From Inline Tube(check out the last sentence specifically):
Proportioning valves come in various shapes and sizes depending on the car you have and modifications to the braking system.

The first year for disc brakes on GM and Chrysler products was 1967, Ford was 1966. All American cars built prior to this had four wheel drum brakes. Disc brakes were introduced as an option from 1967-1972. Starting in the 1973 model year, front disc brakes were primarily standard and front drums were rarely available. The dual master cylinder that separates the front and rear braking systems was introduced and standard on all cars in 1967. Therefore, all 1967 and newer cars came with dual master cylinders from the factory. Disc brakes require over three times the line pressure of drums, so the master was divided to provide pressure to the front and rear separately. This also meant that if a front line blew out the car would still have pressure to the rear brakes and vice versa.

All 1967-68 GM factory disc brake cars came with dual piston calipers. If the car is a 1969 or newer car, it came with single piston calipers. All aftermarket conversions come with the single piston calipers, but they are not factory correct for the 1967-68 cars. The single piston conversion will bolt on 1964-72 GM A-Bodies, 1967-69 F-Bodies and 1968-74 X-Bodies and function perfectly.

Since disc brakes were new in 1967, the valve was still being worked out for the next few years. The 1967-70 valves could consist of as many as three elements and the valves would not work properly without all the pieces. Both 1967-70 factory drum and factory disc cars have (or had) a distribution block which is identical whether the car was drum or disc. Although very similar in appearance to a proportioning valve, the distribution block does not alter brake line pressure. The distribution block keeps front and rear systems separate, splits the left and right front lines and houses the sending unit for the brake failure warning light. The 1967-1970 factory disc vehicles employed an additional valve, referred to as a hold-off valve, mounted at the master cylinder. The final component in the 1967-70 factory disc brake systems was a correction valve typically located in the front to rear brake line for the rear brakes. This valve was not used in every factory disc brake car, but would make the front to rear line two pieces with the valve usually found mounted near the floor pan of the car. An original 1967-70 disc car can be factory correct without the correction valve, but not without the hold-off valve at the master cylinder.

1967-69 GM F-Body Camaro/Firebird distribution block. This block was used on all cars, either disc or drum. The block is bolted below the master cylinder and is not a proportioning valve as it does not modulate line pressure. If there is a loss of pressure in either the front or rear braking systems, it will activate the brake warning light in the dash. From 1967-74 this block was used on all drum cars and with the round hold-off valve at the master on 1967-70 disc brake cars. In 1971, disc brake cars used a different one piece valve and the drum brake applications continue to use the distribution block. Since this block provides equal pressure to the front and rear brakes it is also great for 4 wheel disc applications.

[Skip Fix]

Still sounds like you have soem air or a bad MC if it gets firm at end of stroke. If it were a Disc.Drum with a residual P valve it would not be releasing the rear discs and pedal would almost be asier as pistons not retracting.

I've recently had a bad "new" MC as well as my Strange MC took a LONG time to bench bleed all the air out.

[Chris 68]

Still sounds like you have soem air or a bad MC if it gets firm at end of stroke. If it were a Disc.Drum with a residual P valve it would not be releasing the rear discs and pedal would almost be asier as pistons not retracting.

I've recently had a bad "new" MC as well as my Strange MC took a LONG time to bench bleed all the air out.

I don't think there is any air left in any part of the system (I bled the system for 2 days banging mallets, and put 2 big bottles of brake fluid in and out of the brake system). What were your symptoms of the new bad MC.

I'd like to try and pinpoint the culprit before I buy things I don't need to.

[ehummelman]

The Wilwood MC is not any better/worse than the one you have as far as function goes. It's pretty, that's the extra $. As long as you get the bore size correct, you're good with any OEM master.

[Chris 68]

The Wilwood MC is not any better/worse than the one you have as far as function goes. It's pretty, that's the extra $. As long as you get the bore size correct, you're good with any OEM master.

Thanks everyone for the quick replies, I'm going to go ahead and buy that new distribution block and hopefully everything will work properly.

[dontlifttoshift]

It sounds like the combination valve isn't centered. hook a test light to the positive side side of the battery and probe to the pin where the brake light wire would hook. if the test light lights up the valve off center. I don't remember the exact procedure to fix it but it should turn up quick with a search.

That said, throw the combination valve away. It was engineered for factory or near factory systems and likely will not work with your setup. Get rid of that and add an adjustable proportioning valve of your choice and enjoy.

The master cylinder you have should be fine but the screw on cover that wilwood doesn't leak fluid during spirited driving like the some of the oem type MC with a bale retention system....just an FYI.

Donny

[badazz81z28]

I don't think there is any air left in any part of the system (I bled the system for 2 days banging mallets, and put 2 big bottles of brake fluid in and out of the brake system). What were your symptoms of the new bad MC.

I'd like to try and pinpoint the culprit before I buy things I don't need to.


When I had a bad MC, it leaked out the back. When I had a bad booster, I had no pedal firmness at all, even with the "pumping" technique.

[Skip Fix]

My MC just didn't have decent pedal. OK pedal but not real firm, regardless of how much it was bled. Didn't get real good pressures on gauges. No visible leaking I think it was all internal.