Brakes Dragging on front....

Brakes Dragging on front....
F

fire3096

Jeeper
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Location
Murrayville, Ga.
Vehicle(s)
1980 CJ-7
I have a '80 CJ7 with v-8. I converted it to disc all around. Put a brake booster on it 2 years ago. Since then it has been under restoration. I have recently got it running and road worthy, Now the brakes are dragging after it has been run for a little bit. Dragging to the point of stopping the jeep without pressing the pedal. The brake booster holds vacum. When this happened i jacked the jeep up and the front wheels were near lock-up, pulled the check valve from the booster, and the passenger side wheel let loose and turned freely. I am going to check the calipers and lube the slides and baybe the piston bore. Other than that I need some ideas on what could cause this...they worked perfect before i started the resto.....(also no changes to the brake system at all, never broke a line!) Give me some ideas cause I am in the dark at this point......:confused::confused::confused:
 
fire3096 said:
I am going to check the calipers and lube the slides and baybe the piston bore. Other than that I need some ideas on what could cause this...they worked perfect before i started the resto.....(also no changes to the brake system at all, never broke a line!) Give me some ideas cause I am in the dark at this point......:confused::confused::confused:
Click to expand...

I'm bet'n thats going to fix it. :chug:
 
One thing not really taught about brakes is residual pressure valves. well ok I will give it up.
Drums require a 8 to 10 pound residual pressure to keep the slave cylinder inflated and working, disc use between 0 and 2 pounds .
So if you do a conversion and do not know such, you may be running a drum brake valve in a disc system.
if you pull the master cylinder there is a rubber looking strange thing inside the area where you start the brake lines, get a needle nose pliers and pull it. now get a aftermarket 2 pound in line valve and cut it in the system, oh you will need a double flair tool but if you are doing brake line work investing 40 clams into such a tool will pay off in the long run as you can now make brake lines wen needed and not Limited to what you can buy in a store. Now the brake drag is eliminated.
Another point you will need to look at is proportioning, a adjustable proportioning valve cut into the rear is a great thing as it will let you tune the new brake system into a system that works to optimum instead of a system that is converted but never tunes and has only the benefits gained with the disc, but losing the performance of a complete tunes system.
In other words, why go 1/2 way when yo spend so much money to do so, another 40 bucks and you have a system that is 3 times the converted and not tuned system.
 
I am trying to understand this, the master cylinder delivers and holds an 8 to 10 pound residual? Then it goes to a proportioning valve which allows the discs to drop all but 2 pounds of residual and hold the 8 to 10 on the drums??
Is there any way to put a pressure gauge on a wheel cylinder/caliper??

BajaEdition said:
One thing not really taught about brakes is residual pressure valves. well ok I will give it up.
Drums require a 8 to 10 pound residual pressure to keep the slave cylinder inflated and working, disc use between 0 and 2 pounds .
So if you do a conversion and do not know such, you may be running a drum brake valve in a disc system.
if you pull the master cylinder there is a rubber looking strange thing inside the area where you start the brake lines, get a needle nose pliers and pull it. now get a aftermarket 2 pound in line valve and cut it in the system, oh you will need a double flair tool but if you are doing brake line work investing 40 clams into such a tool will pay off in the long run as you can now make brake lines wen needed and not Limited to what you can buy in a store. Now the brake drag is eliminated.
Another point you will need to look at is proportioning, a adjustable proportioning valve cut into the rear is a great thing as it will let you tune the new brake system into a system that works to optimum instead of a system that is converted but never tunes and has only the benefits gained with the disc, but losing the performance of a complete tunes system.
In other words, why go 1/2 way when yo spend so much money to do so, another 40 bucks and you have a system that is 3 times the converted and not tuned system.
Click to expand...
 
I understand about the risidual pressure for drum vs disc but thanks for the info, thats very useful info. I have lines directly to the back from the MS with P valve inline. The front is still the same as it has always been minus the dragging. I am going to lube the slides tomorrow I was wondering if the vac booster could be the problem or the push rod between the booster and MS causing it to drag. I was so freaking close to getting to drive it this week...but now, not till the BRAKES are fixed. Its one thing if you cant go, whole nother if you cant stop.....
 
Its one thing if you cant go, whole nother if you cant stop.....

sound wisdom.:cool:
​
 
IO,
ok most residual valves are in the seats of the MC, one for front brakes, one for rear,
that is why when you buy one they have to know what brake options your vehicle have, you need disc fir disc and drum for drum, what they do is to retain so much back preasure in the line.
A proportioning valve limits the pressure passing though it, not holding pressure as a residual valve does. So it only allows say 70 percent through, it is the residual that holds the amount needed to keep the brakes in shape that would do such no matter how much proportioning there is.
DOES THAT MAKE SENSE? like limit going out, stop at a point going back
 
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Fire
how much free space do you have between the push rod and the cylinder, it should be around 6 or 7 mm, if that is not you can get dragging as the piston does not return properly
another cause of dragging is if the rod is not properly aligned, and on conversions sometimes that is a nagging problem.
If you have the correct valves I would suggest going componet to componet to check fit ,clearances and movement. I just did this last year and know the frustration you are going through.:eek:
 
baja, what you are saying is the rod from the booster to the MC should NOT be touching? There should be 5-6mm of play correct?( i did not know this) If I recall i have them touching so that could be the whole problem. It's the little things that get ya, aint it?
 
from the pedal to the piston in non boosters, guess it would be the same in a booster as what happens is when the system heats up the rod expands, if it does not have clearance it will not let the piston fully retract.

http://www.autoshop101.com/forms/brake05.pdf

brake05.pdf
 
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OK, I checked the calipers on my CJ and found that the drivers side was semi-frozen. With a little help from PB Blaster and working the brake pedal and a caliper compression tool. It seems to be working fine. I had the test run around the house and pasture and it seems to be alright, going to make a longer run soon. But you know that saying, "one step foward, two steps back". well the front hubs sound dry while spining them by hand, so its time to get greasy....

Thanks everyone for your input, every bit helps.....God knows I need it!
 
Fire3096, it wouldn't be a bad thing to bleed out the old brake fluid and replace with clean, never allowing the master to drain to dry. I've seen a lot of older cars (drum brakes) with water and pitting, gunk deposits, in the wheel cylinder bores from long periods of inattention to the fluid age and composition. Stands to reason that the same applies to caliper equipped discs.
 
Ok, went on a longer drive to check the brakes. well it took the "two steps back" and started locking up again. $32 later, replaced both front calipers. Another "two steps back", the residual pressure valve is bad cause now i have way to much pedal travel. $53 later, ordered two new valves. So lets see whats happens next, maybe I will lose the fluxcapasitor next. "1.21 gigawatts"
 
Ah the beauty of the brake system
I feel for you
the first time I decided to go and design a new system, and I thought it was just modding a little, I figured how hard can it be. Well it nickeled and dimed me for about 3 months till I got it correct, Brakes are a lot more complicated than they look, and you really end up with a lot of knowledge when finished.
 
1st off I would like to say thanks to everyone who gave input on my situation. I would like to tell everyone that after replacing the front calipers, new residual pressure valves, and replacing brake fluid. my brakes are working great. a few more items to address and my jeep will be done - for now!

Thanks again everyone......:chug:
 
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