What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Brakes, HELP!!!

I'm not saying that you should go back to drums, but you may need to go with smaller calipers. Before you do that, you should try a larger bore disc/disc MC.

I am running 4 1/2-ton front calipers and my MC nearly bottoms out on hard stops. I'm not sure of the piston size on 3/4-ton calipers, but I believe they are bigger.

I was thinking about the safety risks of a low pedal and I concluded that it's not a big deal. If you can get adequate pressure to the calipers under normal conditions, you can still bottom out both pistons and get the same pressure to one circuit in the event of a blown brake hose.
 
Chaddy said:
For some reason I didn't have to do anything to the M.C. and I have a 60/14 with disc brakes that work perfect:dunno:
Click to expand...

I have heard a a couple of people that have done this as well. I did it and my brakes worked well, the peddle just didn't feel right. As said above it also depends on the size of the brake calipers you used during the disc swap.
 
JEBSR said:
I have heard a a couple of people that have done this as well. I did it and my brakes worked well, the peddle just didn't feel right. As said above it also depends on the size of the brake calipers you used during the disc swap.
Click to expand...
I just used 1/2ton calipers.
 
I have a 60/14 setup. Using a 1 ton MC (PN 101534 77 K30 4x4 1 5/16” bore) The fronts run to a T, then out to each wheel. The rears have a Wilwood adj prop valve in them for tuning. Brakes work well and I'm confident in them. This is on a 76 K5.

One thing I had to do once to get the peddal right was to screw in the brake rod (about 3 turns) under the dash to get the piston to move more fluid. The wierd thing was I burned up my front brakes real quick after a couple rides. I screwed it back down to normal and replaced the brakes and the brakes were great still. My suspicion is that my rotors have a decent lip on then indicating some good wear and my pads were gettting thin too- These two components might have required more fluid movement then the MC was able to give until I screwed in the rod.- Or I possibly had air in the MC. I'm still running the factory booster.
 
that is the same MC that i'm using, the 101534. i don't use the stock proportioning valve for the rear. i have them directly hooked up.
 
ok i havent checked this for like a week, but last night i went out and got a master cylinder from a P30 that had all 4 discs... turns out its a hydro-boost master cylinder and i have to return it... THE CRAZY THING IS, my currnet MC has a 1 5/8'' bore which is larger than the 1 5/16'' bore everyone else seems to be using..... My MC is the composit master cylinder with a large and a small resivoir.

SO, if I go get that K30 MC with a 1 5/16'' bore would it do me any good??? I dont think it will... Does anyone know how large of a bore the 73-76 corvette MC is?

Or can anyone tell me why my larger bore MC can't handle the discs?? BTW i think its a fairly new MC
 
I am running a 10b/14bff and did the disk brake install with the non eldo caliepers. I had to bleed it really really good but ended up with an outstanding pedal and the rears will lock up fine. I have hydroboost though. Everyone ends up with different results but I think you are on the right path. you might need to get an adjustable prop valve just to tune it in.
 
my rear calipers have a 3 5/32'' piston, i think that just may be the problem... too big haha. too bad I cant take them back cuz i already ground them down to fit 15'' wheels.
 
YZEATER said:
i think you measured wrong. a stock one should be around 1 1/8" dia.
Click to expand...
Are you talking about the calipers or the MC? That size caliper would be for a small car.
 
Blue85 said:
Are you talking about the calipers or the MC? That size caliper would be for a small car.
Click to expand...

I am talking about the MC size, and I'm really sure its 1 5/8''. It is the composit one, ie; the one with plastic resivoirs and an alluminum master cylinder housing. I don't know for sure if it is the original one.

I have been doing more research, and I found a formula to calculate the master cylinder size needed... unfortunatly the formula is pretty incomplete and very hard to follow. It's in the "Chevy & GMC Performance Handbook" by Jim Allen. If anyone knows the formula and could give me the complete version of it that might help.

So here is a recap, I am running a MC with a bore of 1 5/8''. I have four 1979 front disc brake calipers from a K20 chevy witha piston size of 3 5/32''. I still have the stock proportioning valve, and I dont think I have a risidual valve(couldn't see one anywhere).

I didnt buy anything from TSM but emailed them last night with some questions and the only thing they told me was too bleed the brakes again... haha so I assume they mean gravity bleed them. Does anyone think I should gravity bleed, or was regular bleeding good enough? btw my bleeder is already positioned up.

One other note, I am considering getting 1970 eldorado calipers if I cant get anything to work, the main question I have here is, WILL 1970 FRONT K20 ROTORS WORK WITH 1979 ELDORADO CALIPERS????? Or do I need smaller, or different calipers?
 
My dad just got done swapping the rear 13" drums for front rotor/1976-78 Eldo calipers.

Stock everything else, he has pedal/brakes, and it doesn't hit the floor. Bleed with the truck off. Our method (need two people) seemed to work good...put a hose over the bleeder, and submerge the end of the tube in a bottle of brake fluid. Make sure the hose is good, or it may split and let air in at the fitting. :)

Remove the master cylinder cap, and then open the bleeder. You should see bubbles being pushed out as the hose fills with fluid and expels air/fluid via gravity. Once it stops pumping air out (it will be a constant stream of bubbles, then nothing) make sure the reservoir is full, and press the pedal to the floor. (slow pedal though, or it will spray fluid from the MC all over) Once it's to the floor, seal the bleeder, let the pedal up, and repeat. We noticed NO difference pumping the pedal before bleeding or not. Bleed it like this a couple more times AFTER you get no more bubbles, then do the other side.

FWIW, the master cylinder reservoir is on the front in his, and the rear piston size has nothing to do with the forward reservoir, since they use two different pistons, and can be entirely different sizes. I'm not saying they are different sizes for certain, but since there are seperate pistons front/rear, they can be.

There are like 3 different master cylinders listed for the 1985-88 trucks, but the aluminum one I believe was used with the light duty stuff, such as the Blazers etc. My '83 had that one, and I believe it was stock.
 
i was talking about the MC. make sure your calipers aren't hanging up. i thought i had 2 good ones for the rear and they were froze. you will probably have to go thru alot of brake fluid bleeding them.
 
YZEATER said:
i was talking about the MC. make sure your calipers aren't hanging up. i thought i had 2 good ones for the rear and they were froze. you will probably have to go thru alot of brake fluid bleeding them.
Click to expand...


They are brand new calipers so I shouldnt have that problem.

Also I just ordered an adjustable proportioning valve from summit, I'm just ganna give the rears as much fluid as I can, then work back from there!
 
a proportioning valve only cuts down the amount of fluid that goes to the front of back.
 
YZEATER said:
a proportioning valve only cuts down the amount of fluid that goes to the front of back.
Click to expand...


I know, but right now I am running the stock proportioning valve, wich is severly limiting the amount of fluid my rear calipers are recieving. With an adjustable proportioning valve on the rear line I can make it full open and then trun it down if my brakes are locking up in the rear... (in theory this will work for me haha)

So I'm ganna have my front lines hooked directly to the MC and my rear line will have an UPV running wide open to start with, so it will be like having a direct line with no PV at all. If I am still not pumping enough fluid, I have desided to get that k30 MC some people have mentioned on here.
 
i have my rear lines running direct with the p-valve blocked off for the rears. i was trying to eliminate any problems. mine's trail only so it doesn't matter.
 
Good News!!!!!! I finally got the chance to work on my truck today, and I had bought a APV and some fittings, but then desided to put a different MC on first just in case thats all I needed. I used MC PN 101534 1977 K30 4x4 1 5/16” bore and it works perfectly after bleeding the system!!! I was out tearing up the streets tonight and my braking power is tremendous. I am kinda glade I went with those very large calipers in back now!

Thanks for all the input from everyone!!
 
You must log in or register to reply here.

Latest Posts

Top Bottom