YuriSouder
New member
how do i replace the master cylinder in my 94 wrangler straight 6?
how do i replace the master cylinder?
- Thread starter YuriSouder
- Start date
It shouldn't be too hard to actually bolt in (you simply unbolt the old one and bolt in the new one), then fill it with fluid. The hard part comes in bleeding the brakes (getting the air out of the lines). The idea is that brake fluid doesn't compress, but air does, so if you have air in your brake lines, and you stomp on the brakes, instead of compressing the brake pads, the air in your lines will compress, and you don't stop.
To bleed your brakes, start in the back of the Jeep. Pump your brakes about 15 times, until the pedal gets firm (this is a job for your girlfriend, because you'll be working on the brakes at the back of the jeep). While she has the brake down firm, put your closed end wrench on the bleeder valve, then slip a piece of clear tube over the bleeder valve. Make sure to use the right size wrench, as those guys are easy to round off.
Open the valve - fluid will shoot out (hopefully into the tube), and her foot will hit the floor. Close the valve (this will suck fluid out of the master cylinder and into the lines), have her pump the pedal, hold to the floor, then open the valve. do this about 10 times, then top off the master cylinder. The idea is the flush all the fluid out of the lines, and get good new fluid in them, the whole time not letting any air back in (hence the tube). You'll have to do this probably 10 to 20 times per wheel, and it will take time, but it's not hard.
To bleed your brakes, start in the back of the Jeep. Pump your brakes about 15 times, until the pedal gets firm (this is a job for your girlfriend, because you'll be working on the brakes at the back of the jeep). While she has the brake down firm, put your closed end wrench on the bleeder valve, then slip a piece of clear tube over the bleeder valve. Make sure to use the right size wrench, as those guys are easy to round off.
Open the valve - fluid will shoot out (hopefully into the tube), and her foot will hit the floor. Close the valve (this will suck fluid out of the master cylinder and into the lines), have her pump the pedal, hold to the floor, then open the valve. do this about 10 times, then top off the master cylinder. The idea is the flush all the fluid out of the lines, and get good new fluid in them, the whole time not letting any air back in (hence the tube). You'll have to do this probably 10 to 20 times per wheel, and it will take time, but it's not hard.
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shvlhd666
New member
It is easier if you bleed the master cylinder before you install it on your Jeep. To do that, you will need a master cylinder bleed kit which can be purchased at your local parts store. i.e. Thexton 346 Master Cylinder Bleeder Kit
Screw in the nipples and attach the lines per the instructions. Clamp the M/C in a vise and fill with brake fluid.
You can also install it on your Jeep to do this. This works better if there are 2 people involved. One to pump the pedal and one to watch the fluid.
Clamp the M/C in a vise and fill with brake fluid. Using a medium sized phillips head screwdriver, push the piston in and release as many times as necessary until no more air is present in the fluid. Use moderate pressure when pushing in the piston. You don't want to jam the piston at the bottom of the bore. Put the cover on, remove the nipples and install on your Jeep.
This will make bleeding you brakes a lot more easier without having to push all that air out of the M/C and down through the brake lines.
Screw in the nipples and attach the lines per the instructions. Clamp the M/C in a vise and fill with brake fluid.
You can also install it on your Jeep to do this. This works better if there are 2 people involved. One to pump the pedal and one to watch the fluid.
Clamp the M/C in a vise and fill with brake fluid. Using a medium sized phillips head screwdriver, push the piston in and release as many times as necessary until no more air is present in the fluid. Use moderate pressure when pushing in the piston. You don't want to jam the piston at the bottom of the bore. Put the cover on, remove the nipples and install on your Jeep.
This will make bleeding you brakes a lot more easier without having to push all that air out of the M/C and down through the brake lines.
Last edited:
LVRockCrawler
New member
good tip shvlhd - its commonly called "bench bleeding" and can be done with some tubing and a screwdriver (or something to work the piston) run the tubing from the nipples up and into the bowls and pump it till all the air bubbles are gone ... = learned that lesson the hard way yrs ago - a friend showed me how to do it after i c/o'd a master on an old car and couldnt get the brakes to bleed out....
SteelHeadz
Super Moderator
Also make sure that you dont get the fluid squirted in your eye. not saying it happened to me from my personal experience, im not mentioning names (cough)me. Bleed the brakes starting from the calipers closest to the Master Cylinder to the Farthest.
Cazador65
New member
I've always started with the caliper farthest from the M/C, RR, LR, FR, FL.
Also- after bench bleeding, it is possible, with the right help, to open a bleeder, press the brake pedal down & hold, Close the bleeder and release the pedal, this step is repeated several times and sends a true stream out each time the pedal is pressed. Pumping the pedal and holding prior to opening works though. I have gotten brake fluid in my eyes, and flushed them quickly, it gets the red out.
Sand Scorpions rrip & tear-
I've always done rear brakes first as well. Now that doesn't mean that I've been doing it right though...
I've rounded off and broke my share of bleeder valves, and in my younger days I would save money by re-using brake fluid
But in all seriousness, what's the theory in starting from the front? Is it just easier to push the air though the shorter lines, instead of starting with the longest?
I've rounded off and broke my share of bleeder valves, and in my younger days I would save money by re-using brake fluid
But in all seriousness, what's the theory in starting from the front? Is it just easier to push the air though the shorter lines, instead of starting with the longest?
I have always started with the farthest from the m/c and worked my way closer also. Another method I have used after bench bleeding the m/c is "gravity bleeding", open the bleeder valves and don't push the pedal, just let them drip for a while. Then close all bleeders and pressure bleed.
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