Vette Master Cylinder

Not for anything....none of those NAPA adaptors worked for me...now I am wondering if the Vette master cylinder is even the right application...
I am picking up a new vette master tomorrow morning around 11am...hopefully,it will work or else I may go with WetCJ used...a 4 wheel drum application for a 70 IMpala.
I should have just stuck with the stock master cylinder...like the old saying "if it ain't broke, don't fix it!" This master cylinder swap is a total pain in my you know what between all the wrong brass fittings and now this!

You know...if the corvette master is for 4 wheel discs, why would anyone recommend using it on a truck with 4 wheel drums? Maybe this is the problem...since others are having the same problem as me. I doubt all of us have a bad master cylinder! And considering all of the other information that was listed here as far as adaptors, etc., was incorrect, I am thinking that getting the drum brake master cylinder may be the answer. Seems that peope who are running the vette master are having problems with it or don't have much front braking capability like the one guy whose front drums are cold and his rears are warm after driving the truck....

I'm going to do a little more bleeding when I get time on Monday. Tonight I checked and my brake lights come on when I press the pedal down. Also, I hear the front drums working now that I didn't before. Could be that there's some air still trapped in the lines.

OK, lets discuss a few things:

First off, the part numbers probably came from me. I did my swap in Feb 2005. I bought everything from NAPA and made a tech post about it at the time. I left 1 part number off the list because my NAPA didn't have it. (One of the small adaptors) 4 different members bought the same parts and installed them on their trucks with no troubles. All 4 of them PM'ed me the missing part number. They all sent me the same one. I added them to my tech sticky. That sticky died with the Post nuke Zone.

I have not seen a picture of a "Corvette" master cylinder that looks like mine in months.

That is my "don't blame me" speech.

Why the Corvette mc? A former member,Tom Lawlor aka Spicergear, spent the time to look over all the brake mc catalogs all the auto parts stores he could find had. He was looking for a mc built to be used with the same design at all 4 wheels. Then he wanted the biggest diameter bore that was made for the same design at all 4 corners. The 1976 Corvette non power master cylinder was the winner. The 1976 Corvette was the last year Chevy offered it without power brakes. They had to make it so it would stop just as good as the power braked cars, just more effort. Therefore, it had a bigger diameter piston. Tom mounted one to his truck and it worked great. He told the Zone about it. I was probably about the 30th zoner to do the Corvette mc swap. I talked two of my female students through the swap in about 45 minutes. No problems were encountered except since they had never worked on brakes before, fluid was rubbed on my paint to get it off their hands.

Why disc/disc? This is were it gets complicated. Check valves, residual pressure valves, proportioning valves, etc... Brakes can be complicated. A disc brake requires very little movement of the piston to apply the brakes. A drum brake requires more movement. Depending on how your brakes are adjusted, it could be a lot of movement before the brakes actually do anything useful. We have it easy. We have the same style of brakes at each corner and they are all the same size parts involved. Therefore, we don't need a proportioning valve to determine how much fluid to not send to either the front or back. Residual pressure valves keep just a little bit of pressure in the lines so the shoes/pads don't have to travel as far to make contact. A check valve does the same basic thing just a little bit differently.

A principle of hyrdaulics is that only fluid in motion does any work. So, if you have 3 corners out of adjustment and 1 just right. Here is what happens. You push the pedal and it travels a little, but you don't really slow down. You pump it real fast and the pedal is a little higher and you are stopping more. You do another fast pump and you are stopping better still. The fluid stopped moving when you got pressure at the one good corner, the other three were just doing nothing. Your first pump pushed the other 3 out a little more, but not all the way. Your third pump got all 4 to finally working together and the pedal real high. A residual pressure/check valve would keep those other 3 closer to the drums and eliminate the 2 extra pumps for the most part. But, your one adjusted corner would probably be dragging and wear down to be equal to the other 3.

My mc is a true disc/disc and has no valves in the system. I can feel brake shoe wear with my foot because of pedal travel. I adjusted them just right before the Texas FE. I dragged Pistolnuts M715 500 miles behind mine on a trailer. I had a pedal about 1 inch lower by the time I got home. One pump and it was super high. When I adjusted it, 3 clicks on each brake brought it back up. I towed a M35 40 miles and gained another inch of travel on that trip. 14000 pounds flat towed with no extra brakes will do that. 2 clicks brought it back up. I didn't measure the shoes, but they look the same. So, the wear is miniscule but very evident to the amount of fluid needed to move them that much further. I like it this way because I KNOW the state of my brakes any time I push the pedal. I also like manual transmissions, tail dragger aircraft and exposed hammer guns so I might just be "convenient challenged."

Would a drum/drum mc work? You bet it would. Joe has one and it works great. But, it has a smaller cylinder bore than the Corvette one. If you are not going to add a booster, you will have to push the pedal harder to stop.

This is one of those situations where you can go 4 different paths to get the same result. If you bought a true disc/disc or drum/drum mc. It should be sending equal pressure to all 4 corners. Why aren't you. The mc is made for a disc/drum set up, you didn't bench bleed the mc and still have air in one of the circuits, you have a leak or loose fitting somewhere(air molecules are smaller than liquid molecules. Air could be sucked in without fluid leaking out.), the piston isn't getting a full stroke for some reason.

I didn't mean this to turn into a lecture on brakes or a justification for the Corvette mc. Lots of guys Luckypabst and Dave are two I can name who installed FSJ mc's and love them.

I would suggest for the problems mentioned in this thread that you guys start over. Bleed the mc at the mc and just go fitting by fitting to each wheel cylinder. If you don't get good pressure from both resevoirs at the mc, look at your pedal linkage and if it is good. Take the mc back to the parts store and demand a real disc/disc-drum/drum mc.

"But, it has a smaller cylinder bore than the Corvette one. If you are not going to add a booster, you will have to push the pedal harder to stop"

Hey Tim, wouldn't that be just the opposite? Won't the smaller bore master cylinder create a higher pressure than the larger bore with the same leg pressure applied? A little more travel will be required of course but isn't that why on a vehicle with both styles of brakes offered (manual and power) the manual system will have the smaller bore? Pressure=Force/Area
(double checked this in my Wagner manual, didn't think I knew that formula did ya? LOL Todd)

Quote:

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Originally Posted by Barrman

OK, lets discuss a few things:

First off, the part numbers probably came from me. I did my swap in Feb 2005. I bought everything from NAPA and made a tech post about it at the time. I left 1 part number off the list because my NAPA didn't have it. (One of the small adaptors) 4 different members bought the same parts and installed them on their trucks with no troubles. All 4 of them PM'ed me the missing part number. They all sent me the same one. I added them to my tech sticky. That sticky died with the Post nuke Zone.

I have not seen a picture of a "Corvette" master cylinder that looks like mine in months.

That is my "don't blame me" speech.

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AHA! So this is all YOUR fault. :p

I think I'll get it worked out. Rest of the swap went so smoothly I knew something had to go wrong. Appreciate your explanation of the selection of the Vette master- great to know information. Thanks!

All I can say is that I bench bled the m/c correctly and there are no leaks at all. I really think that what I may have is a m/c that was set up for disc/drum. I don't think it is defective, but rather a wrong one.
If all else fails this afternoon with the new one, I will return that and go with another m/c. I hope all goes well with it but my luck sometimes runs bad.
Think about it...it seems to me that the disc/disc corvette m/c would be a pretty limited piece to be able to get, especially considering it is 30 years old and is only found on the corvette. I can go to any three auto parts stores locally and get one off the shelf. Seems a bit odd to me that these are so plentiful. I really wonder if there could be that many disc/disc manual m/c's floating around or they just rebuild any GM ones and throw 'em in boxes?

By the way Barrman, I am not blaming anyone here....I am not mad in the least...and I don't think I even got the numbers from you. I am just questioning everything at this point because nothing yet has worked for me, beginning with the fittings and ending with the m/c....and my truck is still on the lift after almost two weeks (inclulding down time for new shoes from Memphis...:(

Joe, you are right about the pedal effort. My bigger bore pushes more fluid for the same travel as you, but I have to push harder. I was thinking about how to write the proportioning valve stuff and just typing the top part on automatic and screwed up. Thanks for catching it.

I think you are right about the availability of the Corvette mc. I had to wait 3 days to get mine. I ordered it from a small NAPA that you always had to wait 3 days to get anything though.

Barrman,

Quote:

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That sticky died with the Post nuke Zone.

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Not dead --- just lying low for a while in my cache. Jon has this and the other stickys.

I think this is the sticky you are talking about.

http://landru.myhome.net/sivart/MasterCylinder.htm

Update.....new master (101371- not a Cardone) on and still the same...trickling out the front bleeders and the front brakes dont even work. I then remove the two lines coming off the brass brake block and have my dad hit the pedal. Just about trickles out. I remove the pressure switch and line coming off the m/c to the top. Have my dad hit the brake, nothing comes out. The block is clean with no restrictions.
I then remove the brake line from the master and blow through that - perfect. Now I am down to the adaptor that screws into the m/c. That is fine. I unscrew that and then put the plastic bleeder adaptor that comes with the master with hose back into the m/c. I hold the plastic hose above the resivoir with the m/c lid off. I have my dad press the brake and some fluid comes out, but doesn't seem as much as it should be coming out. I then put the hose into the fluid and have my dad release the pedal. The pedal rod (stock) had a little play so the piston is coming against the snap ring.

Now what???? Can it be I have another disc/drum setup? I doubt it. Something is wrong here....