I am in the middle of a 4 wheel disc brake conversion.Here is my problem---I have a front disc brake set up that I put on the front--I bought this from a member here.So I am confident that it is in working order.I put a disc brake set up off a firebird on the rear. I didnt have the calipers for the rear so I took the backing plates to advance auto parts and we matched the plates to calipers. The calipers that matched were the same as front calipers from a 72 monte carlo. I have replaced all the rubber hoses front and rear. And the main rubber hose on the back. I have put on a new master cylinder. WhenI adjust the rod to the master cylinder to get good pedal --the brakes are locked up---When I adjust the rod to where the wheels will turn the pedal goes to the floor ????? I have bled all the air out of the lines--I even used an air bleeder on it to make sure there is no air in the lines.Im at wits end trying to figure this out. A buddy of mine called speedwaqy and a tech guy there said to do away with the proportional valve and run lines directly to the front calipers And put an adjustable proportional valve on for the rear. I thought this sounded crazy but I thought I would see what you guys think. I know ther is someone here who knows how to fix this problem.So HEEEELLLLLPPPPPP----thanks in advance---Danny

danny & i are doing this project , after i left his shop today i thought & thought nore about this problem one thing danny did not mention is the pedal will go 3/4 ways to floor ,car has brakes,but here is the kicker once brakes are applied ALL 4 CALIPERS REMAIN LOCKED WITH SPONGY BRAKE PEDAL!! i feel like we have porportial valve problems???i was the one who called speedway i can see tech guys point of view to a certian extent!! i hate to start butchering on dannys brake lines until i have too !! i work on street rods & antique gm cars everyday for a living done disc brake conversions on the muscle car era stuff many times never seen this happen! i do know on the vettes if your emergency brakes is not adjusted right your ear calipers will not work right !! normally i use a complete conversion from f body gm cars which is what danny has the deal though is dannys seller sold him a disc brake conversion off of a 82-92 camaro rear end but there are two different ones one set will accept the front calipers of of a body gm`s which we done i see no difference except emergency barkes his seller got two sets mixed up & sent wrong backing plates so i went to parts store to match somthing up !! that is how the front brake calipers got involved!! i have put every rubber hose new on this car a new master cylinder only thing left is the porp. & steel lines i know lines are good they are not leaking any where i feel like the root of the problem is the fluid is getting distrubited to all 4 calipers but not correctly i feel like the porp valve ( orginal 67 drum valve) is not functioning like it should on a system like this! if someone has had this problem i am all open for comments, thanks Jason

Danny, I had all four wheels lockup on
my 65 after driving a while. It ended up
being my power booster had a crack inside.
hope this helps. bob

no power booster we went manual route all rubber lines are new

I agree it is more than likely the prop valve. You need one for a 4 wheel disc setup. You might look for one from a late 2nd gen Trans Am or Z28.

The prop valve is different..these guys should have any thing you need..Sorry about getting tied up in bench racing ;)
http://www.mpbrakes.com/
TROY

Back to bench racing :D :D

Can you be more specific (parts wise) on the setup you are trying to get to work?

That may help us out with getting to the root of the cause for your problems.

Joe

I agree with the guy at Speedway. My conversion, although still in the works has no prop valve. I drive it everyday with the fronts already done in this configuration. Stops great. I'm sure once I get the rears on I will need to run an adjustable valve to the rears.

I run an adjustable valve on the rear. I like it, I turn it all the way one direction to do burnouts, and just count the turns back to where it stops best :D

what master cylinder do I need to run?? some people have told me the original for 4 wheel drums is ok--some have said front disc master cylinder is best and others have said 4 wheel disc master cylinder only????? I dont mind buying what I need --I just hate all the trial and error crap---thanks again---Danny

I would use a master cly off a 4wheel disc car. Auto zone has them for corvette's. Make sure hole in the back where the pin goes matches the one you take off.
Also you can "gut" the proportioning valve turning it into a manifold.

I would use a master cly off a 4wheel disc car. Auto zone has them for corvette's. Make sure hole in the back where the pin goes matches the one you take off.
Also you can "gut" the proportioning valve turning it into a manifold.

I used a 4-wheel disc master cyl.

Ask for one from a 68 corvette with NON-POWER 4-wheel discs. This will bolt directly to a chevelle disc-brake power booster, so you can still have power brakes.

Worked for me! smile.gif

I am going manual disc --will this still work in place of my stock master cylinder?? and also I know you said you used an adjustable proportional valve for the rear--what did you use on the front??

It will work as long as the hole in the back match up. Just go to parts store and match one up.
You dont need anything on the front to proportion. You might want an ajustable on the rear.

that is what i recomended doing at begining while i was installing these brakes for him ,but i could not really make him understand that it would work plumbing straight into the front wheels this i what i told him i would do if car was mine , i told him i would come out of front master cyl. resivor down to a tee go front left wheel & then right left wheel & then come out of back brake master cyl. resivor down to a adjustable rear porp. valve & then plumb onto rear brake line this is only my opinion but i would either want access to my adj. porp valve either slightly under seat or tucked away by console somehow that way(knob through floor board), a person could do their tweaking during actuall driving time for this reason most save all of that time driving car getting out poping hood adjusting time & time again until you get it right!or hey if you are a car show a want to burn a little rubber you can shut the brakes plum down serving almost the same principal as a line lock!! if the valve is under the hood or car it may take 25 trips down the road before you get it like you want it if if you adj. valve is positioned through floor pan about a mile or so you can have system adjusted to your driving needs that is only my opinion

You dont need to put in a bunch of plumbing (tees...) just gut the prop valve and you are set. All the lines will bolt right back in the stock location.

this was vintages suggestion after a tech at speedway suggested this to him--I just did not know about by passing the master cylinder all together. This is going to be a driver--not a race car--so putting the adjustable proprtional valve in the console or under the seat would not be worth all the time and trouble.I really appreciate all the effort you guys have put in answering my questions. Vintage is a new member and he asked me if anyone here would try to help and I told him that the guys on team chevelle were the most knowlegable people there are on the workings of a chevelle.Thanks again for your help---Danny