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clutch master cylinder qoustion

xjbubba

NAXJA Member # 1524
My OEM clutch MC is showing signs of leaking around the boot---again!
Happened a number of years ago, causing untold havoc with my electrical system.
Anyway, back then ended up buying a replacement from local Jeep dealer. Didn't pay any attention to bore size, just bought one for an "88 Laredo, 4.0, with Peugeot trans".
Did notice that my pedal has to be on the floor, literally, for the clutch to fully disengage.
I've since installed a Chevy with an NV4500 trans, along with an external slave cylinder with a 7/8 bore; I still need to go to the floor for disengagement.
Now that I need to replace the MC again, I wanted to determine my options, considering fitment and bore size; I'd like to get as close to 7/8" as I can.
I've perused a number of on-line suppliers, and get mixed info on bore size for the '88. I was not aware that more than one size existed.
Some examples of what I've found: Dorman CM39645; 1.063 (1-1/16) and made out of plasic. Dorman CM106439; .813 (13/16). From NAPA, NNC39645; 7.75MM (Huh? that's .305, or less than 5/16). From Kragen, CM113830; .8675 (11/16). From Rockauto, a number of different suppliers with no sizes given, and a couple that duplicate the above info.
Can anyone shed any light on MC bore sizes for the '87-90 XJ?
 
I first went with a Howe about 10 years ago. You can get rebuild kits and they are cheaper than the Autozone variety. I did a bit of fab to use the old connection to the pedal and adapt to the new MC. I bought a coupler nut and a jam nut that fit the MC, then cut off the end of the old MC rod. I then brazed the coupler nut to the old end. You end up with an adjustable brake pedal.

The reason I changed MCs was that I blanchard ground my flywheel. The factory setup has no adjustment for different flywheel thickness, as witnessed by their statement you can't resurface a flywheel. I went up a size in the bore diameter to compensate for the longer throw of the slave.

It worked flawlessly and I could adjust my pedal height to my liking.
 
Re: clutch master cylinder question

Appreciate the insights--I'll take a look at the Howe units.
However, I'm puzzled by the various bore sizes advertised as direct replacements for an '88 XJ. I had assumed there was maybe 2 different sizes--one for the 2.5L and one for the 4.0L. The adds for each MC state the same MC is for both engine apps.
I measured the travel of my MC today--~1.25 inches. My clutch-arm only moves 3/4 inch. This tells me either my MC is less than my slave cylinder, which is 7/8 (.875), or I still have air in the system. However, I'm not experiencing problems disengaging the clutch. I just don't like having to hit the floor to ensure disengagement.
Any ideas, or experience with variances in OEM MC's?

Old_man--do you remember which Howe MC you bought? And,was there any mods to the fire-wall required?
 
Re: clutch master cylinder question

Appreciate the insights--I'll take a look at the Howe units.
However, I'm puzzled by the various bore sizes advertised as direct replacements for an '88 XJ. I had assumed there was maybe 2 different sizes--one for the 2.5L and one for the 4.0L. The adds for each MC state the same MC is for both engine apps.
I measured the travel of my MC today--~1.25 inches. My clutch-arm only moves 3/4 inch. This tells me either my MC is less than my slave cylinder, which is 7/8 (.875), or I still have air in the system. However, I'm not experiencing problems disengaging the clutch. I just don't like having to hit the floor to ensure disengagement.
Any ideas, or experience with variances in OEM MC's?

Old_man--do you remember which Howe MC you bought? And,was there any mods to the fire-wall required?

I can only give you my take on this.

A manufacturer will try and use existing components in as many applications as possible. That said, after the 1984 introduction of the XJ only the original OEM supplier (and there may have been more than one at a time) was making a MC for the XJ, A**uming that the 1984 XJ MC wasn't already in use on another vehicle. As demand grows other manufacturers join the party and make XJ MC--the considerations are: will it mount properly, and will it provide enough hydraulic pressure and piston travel?

So that is my take on things. Also, some minimum wage data entry dude is putting those specs on websites. Don't A**ume that everything posted or printed is correct.
 
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