: 68 caddy deville convertable BRAKE ISSUES

01-08-13, 08:25 AM
Hi all, heres my problem, i have a 68 deville vert , someone has installed an air suspension system in it on all 4 corners , they also changed out the front drums to disk brakes, the problem i am having is the rear brakes seem to lock up intermittantly after applying them , sometimes they lock up sometimes they dont . i found that the master cylinder wasnt the right one for front disk , so i changed that out, but this problem still persists , does anyone have any idea what the problem could be ? thanks for your help

01-08-13, 10:36 AM
Maybe the proportioning valve below the master cylinder? I presume you've looked at the rear brakes to make sure no wheel cylinder seepage and that the brake shoe hold down hardware is in good shape?

01-08-13, 10:42 AM
I dont believe there is a proportioning valve in the system, doesnt that just send more pressure to the rear brakes than the front , is it really necessary? we did check the rears and all looked good

01-08-13, 11:15 AM
Because it was a 4 wheel drum system before it might not have a proportioning valve. Every disc/drum car I've seen has one.

01-08-13, 11:26 AM
You have to have a proportioning valve the original system was designed for drums. There is a different amount of pressure required to insure proper brake function. Add one and you will fix problem.

01-08-13, 11:41 AM
Okay, i'll give the proportioning valve a try, but i cant see how that will prevent the rears from locking up . Isnt the function of that valve to send more pressure to the rears than the front ?

01-08-13, 11:48 AM
Log onto www.mbmbrakeboosters.com to read their info. on proportioning valves. Or do a google search " what does a brake proportioning valve do" great info. The MBM web site has a video on updating a drum brake car to disc brakes. It shows what a proportioning valve does and how to mount it.

01-08-13, 11:59 AM
i just googled it and guess what ? It says it prevents rear wheel lock up !! thanks for the input guys , obviously my mechanic doesnt know as much as he thinks he does !

01-28-13, 08:20 AM
well, i had a proportioning valve added and it did indeed solve the problem ! I cant believe the mechanic i used didnt know this , he is a very talented individual that has years of experience . Anyway thanks guys , i kinda knew in the back of my head i needed it but was talked out of it by this guy. Live an learn!

01-28-13, 10:44 AM
Thank you for posting the fix!

01-28-13, 10:48 AM
thanks for re educating me !