Rear Disc Brake Help - JeepForum.com

 
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post #1 of 7 Old 07-14-2013, 11:06 AM Thread Starter
gup
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1985 CJ7 
 
Join Date: Jan 2012
Location: Hudsonville
Posts: 19
Rear Disc Brake Help

Issue
• After trying to bleed brakes and getting fluid at all wheels. The rear calipers don’t move at all. Is there something I am missing that would stop these from moving? I just received the axle with these brakes from a local shop that built the axle for me and need advice.

Jeep information
• 1985 CJ7 – Chevy 350
• Stock front Disc brakes
• 8” Dual Diaphragm Power brake booster unit.
• Master cylinder, 1” bore
• Stock proportioning valve

New additions
• New Rear Disc Brakes (Calipers/Discs/Pads from 1998 Ford Explorer)
• Ford 8.8 axle cut to width.
• Braided lines from Calipers to Steel lines then to rear brake hose.


1985 CJ7 - Chevy 350 - Edelbrock 4 brl Offroad - Hedman Headers - SM456 4 Speed - Ford 8.8 Rear Axle 3.31 Gears - Yukon Grizzly Locker - Rear Disc - 8” Dual Diaphragm Power booster - Twin Stick - Fiberglass Tub - Total Lift 5.5" (2.5" Suspension, 2" Body, 1" Shackle) - 35 x 12.50 Baja Claws.
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post #2 of 7 Old 07-14-2013, 11:16 AM
jeepwhore
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1984 CJ7 
 
Join Date: Jun 2006
Location: Kamloops
Posts: 3,951
Rear disc conversions seem to be hit and miss. Some have no problems, some have nothing but. Could be you need a residual valve. Might want to search the forum. There are several rear disc threads that might have a solution for you.

'84 CJ-7: Yota axles (spartan locked front, e-locked rear) 4" BDS, 1" Daystar & 3/8" shackle lifts, 35" X-Terrains on steelies, YJ Tub & family roll bar, heater blower upgrade, 4.2L w/MC2100 & Team Rush, Warn 8274. Rebuilt 4.2/4.0 hybrid, AX15 and twin sticks/clocking ring waiting to go in.

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post #3 of 7 Old 07-14-2013, 03:28 PM Thread Starter
gup
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1985 CJ7 
 
Join Date: Jan 2012
Location: Hudsonville
Posts: 19
Thanks JH. (couldn't bring myself to calling you your full name)

So is a "residual valve" the same as a porportioning valve? And by looking at them there are tons of options. Is it advisable to go after market and adjustable?

1985 CJ7 - Chevy 350 - Edelbrock 4 brl Offroad - Hedman Headers - SM456 4 Speed - Ford 8.8 Rear Axle 3.31 Gears - Yukon Grizzly Locker - Rear Disc - 8” Dual Diaphragm Power booster - Twin Stick - Fiberglass Tub - Total Lift 5.5" (2.5" Suspension, 2" Body, 1" Shackle) - 35 x 12.50 Baja Claws.
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post #4 of 7 Old 07-14-2013, 03:48 PM
BESRK
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1980 CJ5 
 
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Location: Newport News, VA
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The residual valve is actually inside the master cylinder. It simply maintains a set amount of pressure in the rear brake system (IIRC, it's about 10lbs for a typical drum brake). The residual valve is there to help apply some pressure to counter the rear brake shoe springs when they retract. It minimizes the distance the shoes need to travel before they engage in the drum. That helps keep a nice firm brake pedal with "comfortable" travel.

On a typical rear disk setup, the brake pads don't have any sort of spring system trying to retract them.. usual residual valve for a disk setup is about 2lbs.

I'd verify that your getting pressure in the rear line coming out of the master cylinder. If so, next point of blockage would be the proportioning valve. Maybe crack the rear line coming out of the proportioning valve while someone depresses the brake pedal. If you have pressure at the proportioning valve, next stop is back at the rear axle lines and calipers.

Also, if you let the master cylinder go dry, you may have to bench bleed it to get good pressure/flow from it again.

'80 CJ5 w/AMC360, T176, D44 w/Detroit 4.56, RE 4" YJ lift and 35s..


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post #5 of 7 Old 07-14-2013, 04:00 PM
waterdowg
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Join Date: Mar 2009
Location: nj
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Quote:
Originally Posted by gup View Post
Issue
• After trying to bleed brakes and getting fluid at all wheels. The rear calipers don’t move at all. Is there something I am missing that would stop these from moving? I just received the axle with these brakes from a local shop that built the axle for me and need advice.

Jeep information
• 1985 CJ7 – Chevy 350
• Stock front Disc brakes
• 8” Dual Diaphragm Power brake booster unit.
• Master cylinder, 1” bore
• Stock proportioning valve

New additions
• New Rear Disc Brakes (Calipers/Discs/Pads from 1998 Ford Explorer)
• Ford 8.8 axle cut to width.
• Braided lines from Calipers to Steel lines then to rear brake hose.
How did you bleed then?
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post #6 of 7 Old 07-14-2013, 06:13 PM Thread Starter
gup
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1985 CJ7 
 
Join Date: Jan 2012
Location: Hudsonville
Posts: 19
So hopefully I can answer the questions you guys gave me while trying to help me. About 3 momths ago I purchased and installed the following:

http://www.ebay.com/itm/74-86-JEEP-C...item4174dea341

I then bench bleed it prior to installation. It helped but I had drums that were bad on the back so I assumed it was just that. Then I did the axle swap with disc brakes on the rear.

I bleed those starting with the farthest wheel. Helper pressed the pedal while I released the bleeder letting air out...repeat all wheels while refilling the resevoir between.

1985 CJ7 - Chevy 350 - Edelbrock 4 brl Offroad - Hedman Headers - SM456 4 Speed - Ford 8.8 Rear Axle 3.31 Gears - Yukon Grizzly Locker - Rear Disc - 8” Dual Diaphragm Power booster - Twin Stick - Fiberglass Tub - Total Lift 5.5" (2.5" Suspension, 2" Body, 1" Shackle) - 35 x 12.50 Baja Claws.
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post #7 of 7 Old 07-15-2013, 08:17 AM
dg6772
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1986 CJ7 
 
Join Date: Feb 2011
Location: Muskegon
Posts: 2,047
Does the m/c have 2 equal reservoirs? Are you sending enough fluid to the rear brakes, as discs use more fluid than drums do.

Dave in Muskegon
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