front disc brakes locking up!!!!!!!!!

rusty cj · 05-02-2005, 01:07 PM

I looked through all of the threads regarding brakes and could not find anything. I have a 78 cj5 with front discs and rear drums(11 inch). I have replaced the brake lines with stainless steel lines and replaced the master cylinder. I bled the brakes and they work great. will lock up all four tires. But, after you hit the brakes maybe 15 to 20 times the pedal geats imensley hard and the front wheels will not roll. so bad that I could not even move it with them in 4wd. I relievd the pressure with the bleeder screw and they were fine until hitting the pedal a couple of times. I have tried everything that I know of to do. Any help is greatly appreciated.

**Fropleyqk** · 05-02-2005, 01:10 PM

I know with mine, the replacement pads didn't fit perfectly as they should. Did you have a hard time putting the pads in? Also, might want to check on your calipers, maybe theyre sticking. They're a cheap swap. Hope that helps

rjcj-8 · 05-02-2005, 01:37 PM

sounds like your mc is not returning back fully.
If the MC is not able to return to the "rest position" then every time you push the brakes fluid will be pushed to the wheel cylinders/calipers and not allowed to return to the reservoir.

Had a similar situation when i put a power booster on my 8. Had the rod from the booster to the MC about 1/16 of an inch to long. every time i pushed the brakes it would foce more fluid to the calipers/cylinders but not let it return to the reservoir. When i would open the bleeders there was a release of brake pressure then my wheels would spin free again.

Are you using a power booster? If so is the rod from the booster to mc adjustible.
if it is shorten it till it does not make contact with the mc when it is mounted.

If it is manual is your pedel returning all the way up? IIRC on the '78s you had to reuse your push rod from the pedel to the MC, did it seat fully in to the new MC?

**Fropleyqk** · 05-02-2005, 01:53 PM

Very good point. When I got my new M/C from pep boys, it came with a new rod, just FYI

JFM626 · 05-02-2005, 03:15 PM

rjcj-8 has been seconded

rusty cj · 05-02-2005, 08:21 PM

thanks for all the help. Yeah I had the problem with the rod and thought that I solved it. I went through four different m/c and none of them came with the rod. I could not use my old one because whoever owned the jeep before me bought the 10 inch m/c. The rods are different between the two. The 11inch rod sits less in the bore and the bore diameter is larger. I had to grind the rod until it fit like it did in the 10 inch. I also had to make a new washer that goes on the rod due to the larger bore. Do you think that I need to shorten the rod some more or maybe use a skinnier washer? the washer could only be 1/32 bigger in thickness. I don't want to screw the only rod that I have up. Sometimes it is not better to have the 11 inch drums.(HAHA) Thanks for the input though.

rjcj-8 · 05-03-2005, 07:36 AM

a 1/32 could be all it takes to keep the piston from coming back far enough to return the fluid to the resevoir

As for making the rod shorter are you having to push in on the mc piston to get the eye on the post of the brake pedel and/or is it keeping pressure on the piston once it is on?

you could make the rod adjustable by using a threaded rod coupler.
cut the rod, remove about 3/8" of the rod and use a die and thread both ends.

You might be able to go with a MC from an 81 or newer cj, the rod comes with the mc for non power apps, you would have a little more pedel travel though, 1" bore instead of 1 1/8"

At worst you might want to through a little more money at it and find a power brake setup to put in it.

One nice thing though aobut having the 11" drums is that you have the larger calipers and thicker rotors up front that were only on the 78/79 D30s

**dawgates** · 05-03-2005, 08:20 AM

I see all that has been said and done, but no one mentioned the calibers!
Have you replaced or rebuilt them? At all? If not remember your Jeep is twenty seven years old. The calibers should be at least taken apart and cleaned every 30,000 miles or so. About the same time you do a brake job. If you do a lot of water driving (creeks, streams, rivers, lakes) you should service them more often. A lot of dirt and crud gets in behind the dust seal and can cause the piston not to retrack properly.

Even though you're not having problems with the rear brakes, it would be a good idea to check the rear brake cylinders too.

**Fropleyqk** · 05-03-2005, 08:30 AM

Quote:

Originally Posted by dawgates

I see all that has been said and done, but no one mentioned the calibers!
Have you replaced or rebuilt them? At all? If not remember your Jeep is twenty seven years old. The calibers should be at least taken apart and cleaned every 30,000 miles or so. About the same time you do a brake job. If you do a lot of water driving (creeks, streams, rivers, lakes) you should service them more often. A lot of dirt and crud gets in behind the dust seal and can cause the piston not to retrack properly.

Even though you're not having problems with the rear brakes, it would be a good idea to check the rear brake cylinders too.

I did mention the calipers. I also mentioned that a new M/C from pepboys will come with the proper size push rod, like $25 after the core exchange. Good advice though, dawgates

rusty cj · 05-04-2005, 09:59 AM

I am going to rework the washer and rod on the m/c and let you know what happens. I am kind of knew to the older vehicles and jeeps. Still learning alot. Thanks for all the help.

05-02-2005, 01:37 PM	#3
rjcj-8 Registered User Join Date: Dec 2003 Posts: 116 Profile Gallery Classifieds My Jeeps	sounds like your mc is not returning back fully. If the MC is not able to return to the "rest position" then every time you push the brakes fluid will be pushed to the wheel cylinders/calipers and not allowed to return to the reservoir. Had a similar situation when i put a power booster on my 8. Had the rod from the booster to the MC about 1/16 of an inch to long. every time i pushed the brakes it would foce more fluid to the calipers/cylinders but not let it return to the reservoir. When i would open the bleeders there was a release of brake pressure then my wheels would spin free again. Are you using a power booster? If so is the rod from the booster to mc adjustible. if it is shorten it till it does not make contact with the mc when it is mounted. If it is manual is your pedel returning all the way up? IIRC on the '78s you had to reuse your push rod from the pedel to the MC, did it seat fully in to the new MC?

05-02-2005, 08:21 PM	#6
rusty cj Registered User Join Date: Apr 2005 Posts: 6 Profile Gallery Classifieds My Jeeps	thanks for all the help. Yeah I had the problem with the rod and thought that I solved it. I went through four different m/c and none of them came with the rod. I could not use my old one because whoever owned the jeep before me bought the 10 inch m/c. The rods are different between the two. The 11inch rod sits less in the bore and the bore diameter is larger. I had to grind the rod until it fit like it did in the 10 inch. I also had to make a new washer that goes on the rod due to the larger bore. Do you think that I need to shorten the rod some more or maybe use a skinnier washer? the washer could only be 1/32 bigger in thickness. I don't want to screw the only rod that I have up. Sometimes it is not better to have the 11 inch drums.(HAHA) Thanks for the input though.

05-03-2005, 07:36 AM	#7
rjcj-8 Registered User Join Date: Dec 2003 Posts: 116 Profile Gallery Classifieds My Jeeps	a 1/32 could be all it takes to keep the piston from coming back far enough to return the fluid to the resevoir As for making the rod shorter are you having to push in on the mc piston to get the eye on the post of the brake pedel and/or is it keeping pressure on the piston once it is on? you could make the rod adjustable by using a threaded rod coupler. cut the rod, remove about 3/8" of the rod and use a die and thread both ends. You might be able to go with a MC from an 81 or newer cj, the rod comes with the mc for non power apps, you would have a little more pedel travel though, 1" bore instead of 1 1/8" At worst you might want to through a little more money at it and find a power brake setup to put in it. One nice thing though aobut having the 11" drums is that you have the larger calipers and thicker rotors up front that were only on the 78/79 D30s

05-04-2005, 09:59 AM	#10
rusty cj Registered User Join Date: Apr 2005 Posts: 6 Profile Gallery Classifieds My Jeeps	I am going to rework the washer and rod on the m/c and let you know what happens. I am kind of knew to the older vehicles and jeeps. Still learning alot. Thanks for all the help.