Do you have to modify the master clylinder or distribution valve for rear disc brakes

[camarossguy2]

Do you have to modify the master clylinder or distribution valve for rear disc brakes?

Like the title says... I had an old rusted blazer with 14bff rear with disc brakes. I thought a i had to modify either the master cylinder or distribution valve on the front cross member to get enough fluid to the rear calipers.... but it was so long ago i cant remember? my old blazer would easily lock up all 4 wheels at the same time.

Anyway, i swapped the axle on to a new blazer and even swapped the distribution valve over, but i still have NO REAR BRAKES, and when i bleed the rears i get maybe 3'''' of fluid in the clear tubing after 30-50 pumps of the peddle.

I searched here and the net for 30 minutes and couldn't find any info on my question... i HATE the "wait 20 seconds" between searches

 

[4X4HIGH]

I still use the stock master cylinder and proportioning valve with my rear disc conversioon and i have no issues.

 

[TDAWG1]

I did nothing to mine and it works Great you should B ok

 

[camarossguy2]

wierd, maybe i need to figure out how to bleed the master cylinder first

 

[4X4HIGH]

wierd, maybe i need to figure out how to bleed the master cylinder first

I just get someone to pump the brakes then hold the pedal while i crack the lines loose at the master, then tighten lines and have helper pump pedal again and repeat until no air comes out THEN move to the wheels (furthest from master first then working closer to master. IE: Right rear, Left rear, Right front, Left front).

 

[mr.smartass]

Yeah I'm also using all stock parts on my '89 k5 with rear discs on a 14bff.

 

[MTMike]

I've got a stock 1-ton MC on my rig and 3/4-ton front calipers on the rear and have no problems.

 

[camarossguy2]

well just tried again... the master cylinder squirts like a jugular, but i cant get more then a trickle at the rear calipers... i guess there might be a clog? i will un hook the rears totally and see if i can blow compressed air through just the lines. also maybe swap out to the other distribution valve since i got two.... btw... what exactly is that thing? (the 4''long thing with all the brake lines in to it and the one electrical connector?) my "brake" light is on, on the dash... never seen that before with the parking brake off...wonder if its related.

 

[4X4HIGH]

The brake light reports low pressure in the system.

Actually, the light indicates that the proportioning valve isn't "centered".

 

[aychdee]

Stock master and prop valve on my '91 and it'll stop 44's on a +45 degree incline no probelm in 4 lo

 

[kevin400ex]

your proportioning valve needs to be recentered or just get a new one. it has a valve inside that will slide over and block off the port when you have a leak, broken line etc. it might be a good idea to also blow out the lines to get any contaminates out of the system.

 

[90'K5]

39.5" tires, disc rear and no changes to any of the system.

 

[doonjumper]

I would change out your porportioning valve. Stock "works" but it dosent allow the proper amount of fluid that the rear calipers require. Im pulling numbers out my arse here, but say that calipers provide 1000lbs. of "squeeze force" with proper fluid volume. Because a stock drum porportioning valve requires less fluid, your calipers may only be creating 700lbs of "squeazing force". Now I doubt "squeazing force" is the correct technical term but.......then again I'm no Barack Obama.....I'm just saying. These guys sell em for like $90 http://www.inlinetube.com/