GM #3878944 Kelsey Hayes Brake Proportioning valve. Just so you know what to look for if you see one. I ran one on my 70 Z28 race car and it helped tremendously to keep the rear drums from locking. The C3s have perfect brake balance up to 1.1-1.2 Gs braking and do not really need it. Perhaps why they may have dropped it even off the L88s. It was also available over the counter as a race part. Last one I saw for sale was very expensive. Once you get beyond 1.2Gs braking, the rear may start to lock first and you may find some slight advantage. I would call this an optional part.


Aluminum version of useful J56 front caliper stiffening bracket. The stock brackets without this have been known to bend. I would use it.



MB Left & PB right pedal brackets. The MC pushrod clevis connects in two different positions. Both holes are on the pedal bracket in all cars. Get it wrong and the pedal ratio will be so bad you will not be able to lock up the brakes. I would guess that is what happened on your conversion. Me personally, on a race car I would use PB. For safety. IIRC ALL the J56 came as PB. You may want/need to run some very hard/high temperature/ heavy brake pedal pressure, brake pads, and the PB system will keep the pedal pressure more comfortable for the driver.

The one thing I did not see mentioned is your engine. Looks like a 454.
If you are racing with iron heads you would be well advised to find some of the factory aluminum cylinder heads and run them. They will drop 150lbs of weight off of the front wheels. They were used on the 1971 454 LS6, so may be allowed in your class. Well worth the weight savings.

My 10.5 CR LS6 clone weighed 545# as it sits, and made 485HP at 5700 rpm and 550 ft lb at 3500.
OEM 71 aluminum LS6 heads are # 3946074.
The heads are about 150# lighter than the oem cast iron ones.

 

I run vintage here in the US. I use the stock master cylinder and it seems to work OK. The aluminum caliper stiffener was made here in Denver by a place called 3R Racing. Whether or not that they still offer them I do not know. They also made titanium packing plates for the brake pads as a heat shield. They just slip behind the pads. You have to be a bit careful with new pads with the plates as they fit too snug. I have a 68 and the caliper stiffeners are made for 69 and newer. I changed to the later year spindle. If you want, I can check if these parts are still available.

 

Yes it is 454, 430hp @ 4,500/513ft/lb @ 3,000. Unfortunately, despite the aluminium heads being available on earlier models, because they were not offered from the factory for the 1974 model year (unless someone knows something I don't?), I am not able to run them. Funily enough, intake manifold is free, however heads and carburetor must be standard (but are permitted to be modified, so long as retaining outward stock appearance), so it doesn't really help me. I run a road-race modified Quadrajet.
I see from the photo that it appears the PB use the upper hole for the pushrod, and the lower for the brake light switch, wheras the MB models use the lower hole for the pedal, and the upper for the switch? My brake pedal rod appears to be in the correct lower hole position, but I will confirm that. I am still in two mindsabout which option totake, PB or MB. I have really been looking for photos of period race cars and what they ran, but trying to get Google to find such a specific thing is hard.
My only reservation with the aftermarket stiffeners is the entirely non-factory appearance.
With regards to the Kelsey Hayes proportioning valve, that appears to be the one we have been talking about, discontinued in 1968? Probably optional at this point, as you say, maybe have a look further down the track once I get some brakes that can at least lock something .

Thanks for the lead. I cannot see anything on 3R Racing's website, maybe you could see if the bits are still available, that would save me having to get pads with the inconel/titanium backing plate?

 

You have these backwards, check 69ttop502's photo above, he states the MB pedal box is on the left. I had to reread his post, I initially thought the old one was the PB assembly.

I just installed a pedal assembly in my car and had to verify I had things arranged correctly for my PB.

 

Does anyone have a good picture of the J56 brake pad backing plates? It seems like that would be an easy item to fab yourself, as long as there is still a source for the pads themselves, and a rebuilding service.

 

Fabricating the backing plates might not be as easy as one would think, especially if the original material (inconel) is used. Not sure how easy it is to work with.

Backing plates




Pad set



The last price I saw on the pads from GM (when they were still available, over twenty years ago) was over $1,000.

Regards,

Stan Falenski

 

Also, for the OP, the original caliper pistons with the phenolic insulators were functional back in the 1960s when they were introduced. They’ll still work today for moderately competitive racing, but there may be better options available. I know that at some point, one vendor was offering titanium pistons for use with the Delco caliper castings, but I can’t recall who that was. Almost certainly worth looking into if the rules for your class allow them.

Regards,

Stan Falenski

 

I contacted 3R and they think that they still may have some of these caliper stiffeners laying around. They will get back in contact with me maybe today. I will let you know if they do and the cost. Yes, they are aluminum and are exactly as the one pictured above.

 

You do not have a picture of the existing brake caliper on the car. For my car, I used the existing brake shield and welded on a piece of exhaust pipe and fitted the cooling tube to it. Direct the air as well as you can to the center of the rotor. As far as drilled and slotted rotors, I would only use the slotted rotors. Modern pads do not out gas and that is what the holes were for. I use Performance Friction pads.

 

Yes my pic did not post. But the MB definitely uses the upper hole. More leverage ratio at the pedal. Most frequent mistake when converting MB to pb or reverse. Get it wrong and you double the pedal effort.

 

Yes, 3R does have some aluminum caliper stiffeners left. They would be about $450. I also found a pair of titanium C3 inserts on eBay. If I can be of any further help.

 

At one point CSSB company made Stainless steel pistons.

 

I just ordered my J56 brake brackets from 3R racing. One other set is spoken for. And they have one set left now.
Those brackets, and the 90* lip J56 pad backing plates, helped eliminate some really weird pad wear issues, due to parts bending under pressure. This motion may also be related to vibrations and air pumping.

Heat Transfer:
Thermal Conductivity of metals in brake system:
Copper & Silver = 400 W/m K
Aluminum 237
Cast Iron 52
Carbon Steel 43
Titanium 24
Inconel 15
Cr Ni Steel 15
304 Stainless Steel 14

The pistons conduct the heat from the brake pad directly into the brake fluid. And then it will boil.
The pads themselves can easily hit 1300*F...and they touch the pistons directly.
Aluminum pistons just conduct too much heat, too easily.
The "phenolic" insulators GM used on the pistons in the 60/70s are fragile and prone to failure.
Stainless pistons are a much better idea - 3R Racing made their own from scratch - and modern brakes almost all use stainless pistons
The iconel backing plates are also a good idea
But a stainless pad shim work work almost as well. The thicker the better.

All the better to insulate the fluid from the heat of racing.

3R also made some custom pistons. Their testing showed the pistons were a real hot spot. They tried both both titanium and aluminum and made some cooling modifications. I forgot to ask if they have any left.

I am running the Wilwood DB4s that have stainless pistons. With low heat transfer.

 

I've been running stainless steel insulating shims for quite some time, starting out when I was running the stock calipers, and now with the Wilwood calipers on my 69. The shims are simple to cut out, and I have multiple thicknesses to swap in as the pad thickness decreases with wear.