brake bleeding problems

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Topic author
cone
Posts: 49
Joined: Tue Mar 26, 2013 4:59 am

brake bleeding problems

Post by cone »

The brakes have always been soft on my 87 Grand Wagoneer so I decided to change out the entire system and replace the rear brakes with the disc brake conversion kit from BJ's. I also changed the brake booster, master cylinder and front calipers. The calipers that come with the conversion kit are a Cadillac design and are apparently difficult to bleed properly, the instructions say to gravity bleed them so I tried that. It would take a month of Sunday to do it that way so I also bleed them the conventional way. I get good pressure when the engine is off but as soon as I start the engine the pedal goes to the floor when you pump it. I tested the brake booster and it checks good.After multiple time bleeding the rear brakes and gallon of brake fluid I cap off the front brakes at the master cylinder the check the rears and the pedal was nice and firm with the engine running so I assumed the front ones must be the problem. I swapped out the front calipers for another set and I still have the problem. Put the old master cylinder back on and still have the problem. Removed the New new disc/disc proportioning valve for an adjustable one and changed out all the brake lines and I STILL have the same problem. My question is even though I plugged the port for the front brakes on the master cylinder and the brakes felt good could I still have air in the rear calipers and it doesn't show until I reconnect the front brakes? Have anyone else had issues with these Cadillac calipers?

candymancan
Posts: 3652
Joined: Tue Mar 22, 2016 11:32 pm

Re: brake bleeding problems

Post by candymancan »

Sounds like air is in the system

Have you tried slamming on them really hard many times ? Thats one trick to force the air out of the system.

I would also have the wheels off. And the pistons pushed back all the way with a clamp. Like youd do whenn changing the pads.. and then id put them back on the rotor and if you can have someone step on the brakes and see if the calipers are actually pushing back out or not.

Its either air.. or no air abd pressure isnt getting to the caliper pistons at all somehow.

But try slamming on them a dozen times really hard when the engine is running
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)
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Stuka
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Re: brake bleeding problems

Post by Stuka »

Well, you have certainly tried a lot of things.

Is the new master cylinder intended to go with this setup? If the bore on the master cylinder is too small, it won't move enough fluid. With just the front, or just the rear brakes, it would be fine. But when it has to push fluid to all four, it may not be enough. The result would be the pedal going down too far as it takes a lot more stroke than it would if the bore was larger.

This may not be your issue, but I have run across it before with brake conversions.

Some proportioning valves can also be a pain to bleed. Many have a button on them that needs to be held in while bleeding the brakes. Though I have found this is not always the case if using a vacuum pump to bleed them. Only when using the pedal or a power bleeder at the master cylinder.
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Pevious Jeeps: 1981 J10, 1975 Cherokee, 2008 JK, 2005 KJ, 1989 XJ

sierrablue
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Re: brake bleeding problems

Post by sierrablue »

Let them gravity bleed for like an hour; make sure it doesn't go dry in the master cylinder. Start with the vacuum pump on the wheel farthest from the cylinder, and work your way closer. Make sure if you pump the brakes, you close the valves before you lift off the pedal (unless you have speed bleeders), otherwise lifting off the brake will suck air back into the system.

You may know/have tried all of that. Braided stainless hoses will also make the brakes firmer.

How do the brakes feel when you actually drive it? I mean on our ZJ, you CAN push the pedal all the way to the floor when it's running, fairly easily, but it does have a lot of feel, and if you actually drive it, you will very rarely push the pedal anywhere near that far down. It sounds almost like you have an excessively powerful booster to me.
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candymancan
Posts: 3652
Joined: Tue Mar 22, 2016 11:32 pm

Re: brake bleeding problems

Post by candymancan »

My Zjs both feel like my wagoneer.

I cannot push my zj all the way to the floor. Once it gets halfway its solid unless you mean you put all the weight on it lol ?. You sure your ZJs brakes are up to snuff Seirra ?
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)

sansabarJ
Posts: 152
Joined: Sun Jun 16, 2019 1:40 pm

Re: brake bleeding problems

Post by sansabarJ »

On these disc conversions , (and really any drum brake equipped vehicle converted to disc brakes) , the calipers position of where it's position is as mounted on the vehicle is critical. You need to see if the caddy calipars are oriented with the bleeder screw in the FACTORY POSITION as would be on the Cadillac application . This means the bleeder must be in the correct position for trapped air to be bled out . This is the first thing to check . You will not remove the trapped air IF bleed screw / calipars are not in correct position .You will find online many pictures of the 79 to 85 Eldorado calipers used by everyone . Many not properly orientated on donor vehicle with some even upside down , yes it's true and installed . This is the first thing to be certain of . Now , the caliper piston has to be set properly so once you are installing it over the disc , there is NO clearance between your pad and the disc rotor . The pads should be a rub fit onto rotor while not sticking the rotor from rotation or too tight .
The reason is the Ebrake caliper WILL NOT extend out the piston like the front calipers do . So on fronts, you put it together and pump the pedal after new pads are installed and piston goes out as normal and seats the pad against rotor . This does NOT occur on the rear with this style of caliper that incorporates the internal Park Brake design . If your pads have ANY gap beyond 1/16"maximum , and times that by all 4 pads you will have a soft or lousy pedal . Most kits come with a rotor to go with the particular application IE: wagoneer or Nova or 71 c10 etc as examples. The rotor may not be the same thickness as the original Cadillac rear disc . The answer is to move out the piston by operation of E brake OR rather Park brake lever. The operation of the lever is what pushes out the caliper piston , now yes, you hit brake pedal and piston applies but it WILL NOT push out enough without first adjusting out the piston . It takes a lot to incrementally move the piston out to seat the pads lightly to the disc . You can turn the piston itself with the caliper piston tool , you turn it to extend piston out . This adjustment is again dependent on rotor thickness as you may find the spacing of pad to rotor cannot be obtained as required .
Be mindful of the inner pad notch for inner pad locating pin .
To sum up this whole Eldorado caliper business was a pain in servicing original Cadillac cars with original parts and application .
If the pad to rotor clearance is not correct , you will note the parking brake once applied doesn't even work at all . Final thought is
Gravity bleeding works well and doesn't take an hour unless things are wrong as described above .


SansabarJ

sansabarJ
Posts: 152
Joined: Sun Jun 16, 2019 1:40 pm

Re: brake bleeding problems

Post by sansabarJ »

One other crucial important piece of information is the parking brake MUST always be applied when you stop and park . Or nearly each
time if you forget to set it . This action of applying park brake continues to SET the piston distance outward to the pads . As pads wear the piston will not compensate on its own without brake hydraulic pressure AND parking brake use . In my servicing of all caddy rear calipers 76 up this was number one trouble of failures and stuck caliper piston over time . 40 years of automotive service and repair so I've seen many issues .

SansabarJ
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