Clutch master cylinder replacement

**Mean Max** · 03-15-2009, 02:36 PM

I replaced the clutch master cylinder in my neighbor's '89 YJ 2.5L today. Here are step-by-step instructions on how I did it, with pics.

First, I verified I had the right part, which came from Auto Parts Fast at RockAuto for $53.03 delivered to my door in 3 days. I didn't want to start the repair unless I knew for sure that I had the correct part in hand.

Here is the clip that holds the M/C pushrod to the pedal assembly. Remove the clip & pull the pushrod off the pedal stud.

Next, remove the hydraulic line from the old M/C (this one was an 11MM wrench size) and then remove the 2 nuts (these were 13MM) from the studs to remove the M/C from the firewall.

Install the new M/C & attach & tighten the nuts back onto the studs. If it doesn't feel like it wants to line up right away, you may have to look under the dash & make sure the pushrod is on the correct side of the pedal.

Finally, reattach the hydraulic line onto the M/C, then reattach the pushrod to the clutch pedal stud. Then fill the reservoir with fresh DOT 3 or DOT 4 brake fluid.

Now the M/C install portion of your repair is complete. All that is left to do is to bleed the system.

I'll give you a little tip here. If the hydraulic system is leaking, but doesn't have a lot of air in it you might get away with just bleeding it at the master. This particular Jeep fell into that category. The bleeder screw looked a bit shaky on this one, and after I bled it at the M/C it had a pretty good pedal. Obviously, the preferable method would be to flush the whole system, but I really didn't feel like "rolling the dice" on breaking the bleeder off, or damaging the slave cylinder.

The plastic M/C's (and some metal ones too!) found in newer YJ's use a roll pin to hold the line on. This makes it impossible to do a true "bleed" at the M/C. In that case, I fill the reservoir with the roll pin still out & the line loose. The M/C will "gravity bleed" a bit & reduce the amount of air in the line. You may still have to attempt to bleed the system at the slave cylinder with these types of systems. Use the following bleeding instructions but bleed at the slave cylinder bleed valve.

We bled it out by slowly pumping the clutch pedal 3-4 times using only about 1/2 of the total pedal travel. On the 3rd or 4th stroke my assistant would hold the pedal down while I cracked the line fitting on the M/C loose to release the air. After a few times of this, we started using full pedal stokes. The reason I used partial strokes at first, is because I'm trying to avoid pushing air farther down the line. Once a good firm pedal was achieved, I topped up the reservoir & cleaned up any spilled brake fluid and then went for a test drive. It was all good!

Hope this helps!

Max

w9kh_kevin · 03-15-2009, 02:43 PM

Awesome write-up. They should put it permanently in the tech write-ups.
Just wondering how you knew it was the clutch master and not the clutch slave. I had a 90 YJ that the slave went out on, so it was much more work. Younger and less experienced then, so I let a shop do it.

**Mean Max** · 03-15-2009, 02:49 PM

Quote:

Originally Posted by w9kh_kevin

Awesome write-up. They should put it permanently in the tech write-ups.
Just wondering how you knew it was the clutch master and not the clutch slave. I had a 90 YJ that the slave went out on, so it was much more work. Younger and less experienced then, so I let a shop do it.

Thanks!

I knew the master was bad because I had diagnosed it earlier & found this.

Max

Burnerman · 03-15-2009, 02:59 PM

Nice W/U. It's all the same on the plastic M/C except you can't bleed the Master only. The plastic ones use a roll pin that holds a quick connect plastic line in. You'll have to bleed it at the slave. Check the condition of the bleeder and spray it with PB and get it loose before you swap the M/C. I don't think you'd wanna have this to look forward to getting loose....

**Mean Max** · 03-15-2009, 03:03 PM

Quote:

Originally Posted by Burnerman

Nice W/U. It's all the same on the plastic M/C except you can't bleed the Master only. The plastic ones use a roll pin that holds a quick connect plastic line in. You'll have to bleed it at the slave. Check the condition of the bleeder and spray it with PB and get it loose before you swap the M/C. I don't think you'd wanna have this to look forward to getting loose....

Thanks!

That's correct, the '91 & newer master cylinders use a roll pin to attach the line to the master cylinder. Here are some pictures generously contributed by JF member Opihi59 that give an excellent view of how the pin attachment system works, and how to use a small diameter punch to remove the pin.

Many thanks to Opihi59 for providing these excellent pics & allowing me to use them here!

Max

Burnerman · 03-15-2009, 03:17 PM

NP.. I just tried to loosen that bleeder on the old slave and it snapped right off flush with the adapter. I guess the older models used a metal line and brake line type metal fittings...

**Mean Max** · 03-15-2009, 08:46 PM

Quote:

Originally Posted by Burnerman

NP.. I just tried to loosen that bleeder on the old slave and it snapped right off flush with the adapter. I guess the older models used a metal line and brake line type metal fittings...

My '91 has a fairly decent bleeder on the slave. I've had no issues bleeding the system there a few times. But some of them (like this '89) have a pretty shaky looking setup for bleeding at the slave.

And I'm not sure when the M/C's changed from threaded flare fittings to the O-ring & roll pin setup occurred. This is an '89 (like yours is, except that it's a 2.5L) that has the threaded line at the M/C, and my '91 has the roll pin. Apparently it was around that time?

Max

Hoobly_Goob · 03-16-2009, 03:54 PM

I've never bled the system before, I've found the bleed valve, but there seem to be two places a wrench could fit....which do I turn?
Also, I can't seem to get the roll pin outta the dang MC.

**Mean Max** · 03-16-2009, 04:04 PM

Quote:

Originally Posted by HooblyGoob

I've never bled the system before, I've found the bleed valve, but there seem to be two places a wrench could fit....which do I turn?
"HOLD" the wrench fitting that the line goes into from the slave, "TURN" the wrench fitting closest to the end, that's the bleeder valve.

Also, I can't seem to get the roll pin outta the dang MC.
Are you using a flat-tipped punch, just slightly smaller in diameter than the roll pin?

I plan on adding some pics to the write-up that demonstrate how to remove the roll pin and show some detail on the slave cylinder bleeder.

Max

Burnerman · 03-16-2009, 04:14 PM

Quote:

but there seem to be two places a wrench could fit....which do I turn?

In the pic I posted the bleeder is the tiny little nipple on the end. You need a 9/16" wrench on the larger "body" and a 1/4" wrench on the bleeder. The roll pin just needs to be tapped out with a flat ended punch of a slightly smaller diameter. I tapped it out then used a pair of dykes to pull it out. That pic is from the slave that was in my son's 93 YJ..

Selafane · 03-28-2009, 12:50 AM

sorry if this is a stupid questions, but how do you find out what the bore size is.

do you just measure the hole in the firewall?

Burnerman · 03-28-2009, 04:54 AM

Bore size?
Bore size would be the diameter of the cylinder inside the M/C.

Urb4nTr0ll · 04-22-2009, 02:32 PM

Great article. Thanks for the many tips!

**Dwatts5250** · 04-22-2009, 03:38 PM

im assuming that write up will apply to the 4.0 6cyl as well? Ive got a 94, but im not sure it needs to be replaced, the clutch goes down and the shift works, but sometimes the first gear gear alil bull headed and i have to start off in 2nd gear to go anywhere.
alotta times its like that after i drive alot and the jeep is hot.

**Mean Max** · 04-22-2009, 03:41 PM

Quote:

Originally Posted by Dwatts5250

im assuming that write up will apply to the 4.0 6cyl as well? Ive got a 94, but im not sure it needs to be replaced, the clutch goes down and the shift works, but sometimes the first gear gear alil bull headed and i have to start off in 2nd gear to go anywhere.
alotta times its like that after i drive alot and the jeep is hot.

Yes, it's exactly the same on the 4.0L Jeeps. Your '94 will have a roll pin holding the hydraulic line on the master, instead of the flare nut fitting like in the '89 that I did the write-up on. That type of fitting is discussed in the thread.

Max

P.S. Thank you for your sig line, I too am a proud veteran who is also still in the National Defense business as a civilian these days.

I "donated" my knees to the USMC as a young man, but I refuse to attempt to collect disability compensation. I'm glad to have done it, and I'd still offer my life to the citizens of this great country if I could.

SEMPER FI!!!