The Stovebolt Site Forums The Shop Area Engine Shop Dems da Brakes, CPP style

I've been stumbling along for the better part of 3 years on my '50 3100 project and have reached the point where it feels almost complete. I finished insulating and carpeting the interior a week ago, just in time to take my dad on a drive as he passed through town.

After about 4 miles, we pulled over because something was burning. The front brake rotors were at 325 degrees. This is the complete front disk brake kit from CPP with the power brake master cylinder mounted on the frame.

Some research found that the brakes were slightly preloaded because the push rod is too long and is still preloading the brakes with both ends bottomed out. I'm in search of a shorter push rod but have had no luck finding one. I thought of cutting, drilling out and retapping the push rod but that seems like a lot of work for something that has been used many times before. Can't think of another (simple) way of fixing this dilemma.

Even with no load on the master cylinder, the brakes are still really tight. It seems the inner pad is almost too wide. I've looked on CPP website to adjust this with spacers or something but all their troubleshooting points to everything except their components. 'magine that. It couldn't be their fault. Can you buy thinner pads for disk brakes? The only thing I can think of that may keep the piston from settling all the way back in is the 2-lb residual valve. Would that do it?

Anyone else have any similar situation with some simple solutions? This is the only thing keeping me from driving the truck. I'd really like to resolve it.

redgreen: I was looking through the catalog for Piratejack.net out of Asheville N.C. and they list SEVERAL lengths of rods like your talking about. Give them a call at 866-601-4455 Ext.298. If Tammie Earwood answers tell her the STovebolt fellow in S.C. told you to call her. She seems very knowledgeable and their prices are as good as anyone and better than most!! You can access there catalog on line but a phone call will get "first hand" information.

Alvin

Thanks, Alvin. I appreciate it. That will definitely solve one of the issues.

After heating the rotors to 325+, I may have to turn them because the left one seems to rub in one spot more than the other, so it could be slightly warped.

Thanks for the info guys.

I know for sure that Harley's ( I'm an H-D wrench) use a residual pressure valve for drums, but not for discs. I think it's because drums use the return springs to pull back the pistons, where discs get pushed in via the spinning rotors ( high spots) You MIGHT need to ditch the residual valve with discs. Emphasis on MIGHT!

I am probably going to put my foot in it, but here goes.

Anyone, and I mean competant mechanics but especially those with little mechanical knowledge, who purchases an after market brake kit and expects it to be a bolt-in are in for disapointment.

#1. The MC pedal and linkage system must have "free play". The pedal must be held away from contacting the MC piston by a spring. This is how GM and all auto engineers design the systems, therefore it is common sense that the builder of a custom system must follow sound engineering practaces.

#2. The caliper is susposed to be free floating and the caliper piston location is governed by the fluid accumilation in the cylinder and brake lines. In regard to the residual valve holding the caliper piston from returning, the GM system is a zero clearence system. There are no springs to retract the caliper piston. The 2# of residual pressure will not hold the pad against the rotor. Because of this the parts must me assembled so that there are no binding in the parts. Caliper bracket offset and straightness was a problem with my CPP parts and at least one other 'Bolter that I have talked with. So I imagin there is a problem with CPP's quality control program. To fix this the brackets need to be tweeked to get all of the components in the correct place.

#3. Depending on the MC that you are using, you will need to install 2# front and 10# residual valves with a disk/drum system. If the MC has built in residual valves this is not required. But, you do need residual valves with the MC under to floor. You may also need an adjustable Proprotioning valve.

So, this is my recomendation. Start over. Make sure the MC linkage system has free play. Reference the repair manual for a recomendation, but about 3/4 inch should be OK. This is at the pedal. The pedal return spring should hold the pedal tight aganist the floor. You will most likely need to make a new connecting rod from the pedal lever to the MC piston. BTW, make sure the MC has a deep recess in the piston where the connecting rod goes so that the rod cannot fall out.

Now go to the caliper mounts and calipers. Take them apart and carefully measure the caliper bracket to make sure it is true to the rotor. It must be paralell to the rotor contact surface in both axis. The offset must be such that a caliper loaded with new pads can be installed with the bolts tightened and have the rotor spin freely.

This is a condensed version of many post on this subject. Do a search for this and you will get an education about the frustration of using so called bolt-in conversion parts.

With brake systems, if it does not feel right or look right, get someone with good sound mechanical knowledge to look at it for you. Do not think good enough is OK.

Look at my build picture under brake problems for some pictures of a CPP install.

Sorry for the SP errors, it is late.

Lonnie

Good poimts, but I did'nt mean to say that there are springs in the disc system, rather that there are springs in the drum system. If you had no residual pressure with drums the springs would retract the pads until they hit something ( probably bottoming in the wheel cyl.'s), causing you to have to pump the pedal multiple times before the pads contact the drums. I'm not well versed in the auto systems, so I find it odd that disc systems would require any residual pressure. However I happily defer to your experience as I have yet to mess with these disc conversions. I guess maybe if the master resides below the wheel cyl.s, it could drain back with gravity or something. Some calipers I work with have square sealing rings that cock themselves in the grooves, and provide some springing action to return the pistons, but most just rely on the slight highs and lows to knock the pad back in a little. This is why drums used to be preferred for drag racing, because they positively retract via the springs, thereby ensuring no drag.
I re-read the original question, and see that there is a free-play issue. Obviously there must be freeplay at the pushrod, or pressure will continue to rise as the pedal is pumped. Also I could see where a misaligned caliper bracket could cause drag.

Thanks for all the info. I have fixed the free-play issue on the master cylinder and have now focused on the disk brakes. I have residual valves and adjustable proportioning valves where they need to be.

Lonnie, you've done a great job of explaining where the problems may be and documenting it with pictures. The million dollar question is how do I fix it? The parts are 2 years old, so CPP is not going to be willing to exchange them for me. The old huck brakes are in the salvage yard, so there's no going backwards. What is the fix for a weekend shade-tree mechanic? I don't have the resources to fabricate a new bracket and the truck can't go to the nearest tire shop until this is resolved.

this is the email reply I sent to another bolter. I hope it helps. There was more to our emails, but I cannot seem to find the later emails.


I am sorry to hear you are having the same problems I encountered with the CPP 6 lug kit.

I am assuming from your comments that you have read all of the posts over the last couple of months concerning brake kits. You did not indicate that you had looked at=2 0the pictures on my build site. Here is the link. http://s101.photobucket.com/albums/m48/lonniegallaher/54chevy/Front%20brake%20problems/

I had some what of an advantage in that I am working on a total rebuild. Therefore everything is a lot easier to see and check. After you look at my pictures you will see that the quality of some of the parts is not so good. I think the engineering is sound, having been based on good GM factory parts. But the bending of the caliper bracket is not so good.

After an hour of so of measuring I found that the offset in the caliper bracket should be about 1/4 inch. This may vary with your hub/bearing configuration. This offset is the difference in the plate surfaces as it is laid on a table. My method of fixing these bend problems was to remove the bracket from the axle and clamp it to a heavy steel plate and with shims and clamps I adjusted the offset.

This took me quite a bit of time, only because I am some what of a perfectionist, when it comes to these things. Later when I was trying the caliper to rotor fit there was still some misalignment and I found the caliper bracket bends easily with a large adjustable wrench. In hind sight I would have started with the bracket bolted to the axle and tweaked it in this position.

Basically the area of the bracket where the caliper slide bolts attach need to be in line with each other and in line with the rotor surface. If you achieve this the caliper should work fine. Shimming or grinding is not the answer. Tweak the bracket until everything is lined up properly.

The caliper is self centering so once the bracket is in good shape it will work. A good way to check the caliper bracket alignment is to use a straight edge across the surfaces and across the rotor and measure the offset. After you get it as close as you think you can, mount the caliper and slide it up against the rotor. It should contact the rotor surface without any gaps. With the caliper installed you can also check to make sure that the offset is correct. These last steps are done without the pads installed. With the caliper installed you will be able to tell if the pads are going to fit without binding on one side.

John, I hope this helps. If you have any other questions, just send me an email.

BTW - Great looking truck.

Lonnie Gallaher
909.213.7686

I found the other part of the communication.

I did some more measuring to make sure what I have for clearance and offsets.

With the caliper installed it is hard to get an accurate measurement, but these are close. With the caliper tight against the bracket I got the following dims. This is what would be needed for the pads to fit. So they are the clear dims between the caliper and the rotor. Piston side of the rotor is about 11/16" plus a little. The outside dim is 9/16" plus a little. I know they are not accurate but, they are workable dims.

The offset in the bracket is 1/4", this gives 3/4" from the inside of the rotor to the inside of the bracket where the caliper mounts.

The caliper with the pads installed has clear between the pads of 1.37". The rotor is 1.29" thick. This gives .08 clearance.

With the pads installed and the caliper installed I can put a .62" straight edge between the outside pad and the rotor and still be able to rotate the rotor. It is tight, but I can rotate it by hand.

My pad dims. outside pad is .540" thick and the inside pad is .60 thick.

Inside the caliper mounting tabs where the bolts go is 3.033" clear.

Caliper bracket is .345" thick.

With the caliper and pads installed the rotor moves freely.

The bracket can be bent cold, no need to heat it.

Just to let you know, as hard as I tried, the offsets and parallel and straightness of the bracket is not perfect. On the one side I was doing most to the checking on, when I slide the caliper up against the bracket the top touches before the bottom does. It is close enough though, that I can push it and make contact at the bottom too.

After measuring everything again, and I were starting over, this is what I would shoot for with the caliper installed. These dims are without the pads installed. Outside 9/16". This can be a few thousands less, but it cannot be the thickness of the pad or less. If this is obtained the inside should take care of itself.


I hope this is some help.

Lonnie