Failed clutch master cylinder: An Autopsy

[beatupjeep]

89 XJ Manual 4.0

On 3rd clutch master cylinder since I've owned it for 5 years, and now this one is bad too.

Took it apart to see whats going on.

No leaks in engine compartment.

Just leaking fluid above the clutch pedal. Can see the drip on the pushrod and dust cap.

Taking it apart I see what looks like corrosion under the dust cap.

Removing the plunger assembly I see and feel scratches in the bore.

I measured the electrical resistance of the bore at several spots, to the outside of the housing, and it was a short every time. This suggests that the bore is NOT anodized and is just soft aluminum. Im not sure what scratches it. There appears to be corrosion where the piston "sits", and also at both ends of the bore internally. Perhaps the steel/iron piston and the aluminum bore corrode when sitting from moisture in the air? Ive seen that happen inside cast iron blocks where aluminum pistons were allowed to sit.

This master cylinder was from autozone, probably part number 12960.

Autozone and oreilly seem to have only the aluminum ones.

Just looking at it, seems like rockauto may have cast iron ones.

I would take cast iron over un-anodized aluminum. Im not 100% sure whats going on here, but it seems like soft aluminum in a situation like this is asking for failure.

Looking at this, it makes me wonder if we could have the housings internally anodized, and then make sure to really clean the plunger assy before installing it, and these would work fine. Something is clearly scratching the bore.

Does anybody know how aftermarket master cylinders are designed?

I would really like to make one for our jeeps, but Id want to throw all the bells and whistles into it.

Does anyone know of a master cylinder design that is bulletproof that we could adapt to the jeep?

http://i242.photobucket.com/albums/ff197/acannell/20150221_152818_zpsjhdu6id7.jpg (http://s242.photobucket.com/user/acannell/media/20150221_152818_zpsjhdu6id7.jpg.html)

http://i242.photobucket.com/albums/ff197/acannell/20150221_152826_zpsrn2izm1e.jpg (http://s242.photobucket.com/user/acannell/media/20150221_152826_zpsrn2izm1e.jpg.html)

http://i242.photobucket.com/albums/ff197/acannell/20150221_152829_zpsamhzx6f6.jpg (http://s242.photobucket.com/user/acannell/media/20150221_152829_zpsamhzx6f6.jpg.html)

[beatupjeep]

Looks like API 1575 31474 is cast iron, from the pictures. Not 100% sure. Its about $35 shipped at rockauto.com. I think I may try it.

[beatupjeep]

This sachs part also seems to look like cast iron..only $29 shipped

http://www.ebay.com/itm/Clutch-Master-Cylinder-SACHS-SH5006-fits-87-90-Jeep-Cherokee-/171617021191?pt=Motors_Car_Truck_Parts_Accessories&hash=item27f52bed07&vxp=mtr

[4.3LXJ]

Bullet proof? Not sure there is one. But there is a much better one. It is designed like the old school single master cylinder. Those would last as long as the brake master cylinder beside them. Jeep went away from that design

[beatupjeep]

Bullet proof? Not sure there is one. But there is a much better one. It is designed like the old school single master cylinder. Those would last as long as the brake master cylinder beside them. Jeep went away from that design

What years was that from?

Also, I am not sure if the cast iron version for the XJ is just fine and has no issues or not. If so then I suppose its good enough, especially since its so cheap. But I'm pretty sure everybody has problems with the aluminum ones.

[4.3LXJ]

There really isn't one of those. You would have to adapt something else in off a Dodge pickup from the sixties

[OldFaurt]

89 XJ Manual 4.0

On 3rd clutch master cylinder since I've owned it for 5 years, and now this one is bad too.

Took it apart to see whats going on.

No leaks in engine compartment.

Just leaking fluid above the clutch pedal. Can see the drip on the pushrod and dust cap.

Taking it apart I see what looks like corrosion under the dust cap.

Removing the plunger assembly I see and feel scratches in the bore.

I measured the electrical resistance of the bore at several spots, to the outside of the housing, and it was a short every time. This suggests that the bore is NOT anodized and is just soft aluminum. Im not sure what scratches it. There appears to be corrosion where the piston "sits", and also at both ends of the bore internally. Perhaps the steel/iron piston and the aluminum bore corrode when sitting from moisture in the air? Ive seen that happen inside cast iron blocks where aluminum pistons were allowed to sit.

This master cylinder was from autozone, probably part number 12960.

Autozone and oreilly seem to have only the aluminum ones.

Just looking at it, seems like rockauto may have cast iron ones.

I would take cast iron over un-anodized aluminum. Im not 100% sure whats going on here, but it seems like soft aluminum in a situation like this is asking for failure.

Looking at this, it makes me wonder if we could have the housings internally anodized, and then make sure to really clean the plunger assy before installing it, and these would work fine. Something is clearly scratching the bore.

Does anybody know how aftermarket master cylinders are designed?

I would really like to make one for our jeeps, but Id want to throw all the bells and whistles into it.

Does anyone know of a master cylinder design that is bulletproof that we could adapt to the jeep?

http://i242.photobucket.com/albums/ff197/acannell/20150221_152818_zpsjhdu6id7.jpg (http://s242.photobucket.com/user/acannell/media/20150221_152818_zpsjhdu6id7.jpg.html)

http://i242.photobucket.com/albums/ff197/acannell/20150221_152826_zpsrn2izm1e.jpg (http://s242.photobucket.com/user/acannell/media/20150221_152826_zpsrn2izm1e.jpg.html)

http://i242.photobucket.com/albums/ff197/acannell/20150221_152829_zpsamhzx6f6.jpg (http://s242.photobucket.com/user/acannell/media/20150221_152829_zpsamhzx6f6.jpg.html)

The problem is this...
The body of the master cylinder is aluminum, the piston is steel. If you don't completely purge all the old brake fluid and replace it with fresh clean fluid, it will have water and other contaminants in it that will cause Galvanic corrosion. Basically any even slightly acidic liquid in the master cylinder will create an electrical current between the aluminum and steel. this will make a green mess and will etch the aluminum. finding a cast iron master cylinder will fix it. BUT if you clean all the parts before assembling the aluminum master cylinder with alcohol, make sure there is NO BRAKE FLUID on the dry side of the piston rubber cap, you might just get good service from aluminum master cylinder. The key is, no fluid between the steel and aluminum parts, the clutch side dust seal MUST be put on the master cylinder to keep out all moisture!

And remember Mr. Phelps, If you or any of you crew should be captured or killed, the secretary will disavow any knowledge of your existance...

This message will self destruct in 5 seconds... Good Luck Mr. Phelps...

Poof!

[beatupjeep]

okay its confirmed..I received my $30 shipped master cylinder off ebay and it was cast iron. I messaged them first and confirmed it was cast iron before buying it.

Apparently its brand new (not reman) too.

this is the one I got:

Clutch Master Cylinder for Jeep COMANCHE Wagoneer Cherokee | eBay

I should note I messaged some other listings that looked like cast iron and they said they were NOT. So I would message first and confirm before buying..who knows how quickly these people turn over the stock and whether or not the housing material is even called out in the part number (maybe aluminum or cast iron are considered "interchangeable").

Im going to take it apart and clean/inspect it before re-installing it.

For the record, the listing says:

Condition: New Part Brand: Aftermarket Replacement
Interchange Part Number: MC342,417-00114,53004467 Manufacturer Part Number:
AM-42235383
Warranty: Yes

and it says it has a 10 year warranty.

Also, it lists fitment as only 87-90 cherokee and comanche, and 87 wagoneer

[beatupjeep]

I took apart the brand new cast iron master cylinder..and there was a deep scratch on the piston (not the bore).

It was about 1/4" long, lengthwise, along the rear piston outer circumference, which is the surface that rides along the bore (or may touch the bore possibly? maybe not im not sure..the rubber seals may keep it floating..but I wouldnt be surprised if it touches occasionally). It was sharp and easily feelable with your finger (not your nail, just your finger).

I carefully covered the piston assy with a wet paper towel, and filed the scratch smooth.

otherwise the assembly looked clean and ready to go.

I would think the piston is steel, and therefore harder than cast iron..that scratch probably would have done some serious damage...

Hopefully that clears the way for some additional life