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Unread 09-08-2011, 07:28 PM   #1
black954
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1978 CJ7 
 
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Location: winfield, IL
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yj power brake swap problems

I searched and couldn't really find exactly the answer to my problem. I have a 1978 CJ7 that originally had manual brakes with discs up front and drums in the rear. I installed all new brake components, wheel cylinders, shoes, hardware, calipers, pads, SS inline tube brake line kit, Russel braided SS brake hoses. I reused the stock proportioning valve and had custom lines made to go from the stock frame mounted proportioning to the 1995 YJ power brake master and booster. I used the stock YJ master, booster, firewall mount, and pushrod. I bench bled the master and then bled all the brakes starting at the passenger rear, driver rear, passenger front, and driver front. I rebled the master and rebled all the brakes again with zero bubbles and still no brakes. The pedal goes to the floor and if you pump them, it will kind of work but still pedal to the floor. I've tried pinching off the vacuum to the booster and still the same. Any ideas? I measured the length of the stock manual pushrod coming out of the master and it was the same as the YJ pushrod sticking out past the booster. It seems like alot of people had to lengthen theirs, could this be the culprit?

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Unread 09-08-2011, 07:38 PM   #2
mopar346
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Get some old brake lines and disconnect the Jeep lines at the master cylinder and then use the old lines to create plugs for the master. By doing this you can bleed the master off and see if you get a pedal, if you do then the problem is down steam and start adding sections of the braking system until you hit a snag or get a pedal with the whole system in tact. If you cant get a pedal with just the master then the problem in up stream whether it be a bad master or a rod issue. A rod issue in my mind might create a low pedal but it would still be solid. I have seen short rods literally pull the piston out of the master and get air in the system that way. I have also seen air trapped in the lines even when you get good fluid at the bleeders, I like to gravity bleed them first and then pump and release bleed.
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Unread 09-08-2011, 07:59 PM   #3
black954
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a friend suggested the same same and he has plugs to use. i will pick them up tonight and try that tomorrow, I'm still curious about the pushrod length though.
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Unread 09-08-2011, 08:02 PM   #4
lucdog
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Your probaley going to have to lengthen the push rod from the pedal to the booster. Also the push rod coming out of booster in the YJ booster, is adjustable, it should be just touching the plunger on the MC.

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Unread 09-08-2011, 10:16 PM   #5
ComancheCounty
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Just did this same mod on my brother's 84' CJ7. He had the same non powered disc setup and we installed a JY YJ MC and booster. The rods were not the same length, nor were the ends that attach to the brake pedal. We measured the CJ rod several times to be accurate, then cut off the YJ rod end and welded the CJ end on to connect to the existing CJ brake pedal.

We had a problem with air in the MC. Solved it by using the left over MC hard lines and bending them where they would bend up and back into the MC reservoirs. We pumped the brakes until the master was bled, reattached the MC to distribution block lines, bled the system rear to front as you did, then we finally had good brakes.
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Unread 09-08-2011, 10:35 PM   #6
black954
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Quote:
Originally Posted by ComancheCounty
Just did this same mod on my brother's 84' CJ7. He had the same non powered disc setup and we installed a JY YJ MC and booster. The rods were not the same length, nor were the ends that attach to the brake pedal. We measured the CJ rod several times to be accurate, then cut off the YJ rod end and welded the CJ end on to connect to the existing CJ brake pedal.

We had a problem with air in the MC. Solved it by using the left over MC hard lines and bending them where they would bend up and back into the MC reservoirs. We pumped the brakes until the master was bled, reattached the MC to distribution block lines, bled the system rear to front as you did, then we finally had good brakes.
The ends are a little different, but it bolted on fine. I will have to check the length of the rod and modify it accordingly
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