broken firewall

[jerry b]

Last week i posted that i was having clutch problems with my 84 cherokee. I was told to look for a crack in the firewall where the clutch master cylinder is mounted and sure enough there was a 3" crack right where the mounting bolts goes through the firewall. This is causing the firewall to flex so the master cylinder is moving and my clutch will not disengage. Thanks again to the person that pointed me in the right direction. Now i need help fixing it. I am wondering if anyone else has had this happen and the best way to fix it.

[JDPascal]

I see three choices here

How's your fabrication skills....or ?

Best to take the components off the fire wall first for the first two.

1. Weld up the crack. MIG or TIG is best but gas/brazing would work too.

2. Fabricate a plate out of 16 gauge metal to go over the existing firewall location. Make it 3-6" larger all around the master cylinder mount and pop rivit/screw it to the firewall for more support. If you put it inside under the dash you would have better natural support when the pedal is pressed but it's likely more difficult to get it in place. On the engine side of the fire wall, it would be more obvious but if you used some aluminium checker plate it would look more custom made and not so much a repair.

3. sell it as is..............



JD

[Saudade]

If you pursue JD's option 2, you should use a small drill and drill out each end of the crack. The hole will distribute the stresses and prevent the crack from growing.

You should use some silicone as well to stop any water penetration.

Good luck!

[JDPascal]

Thanks for the addition Saudade. Brain is going west on me --- should have remembered that.....

[jerry b]

I am thinking very deeply into my repair options cuz I only want to do this once and I was thinking that if I put the metal late on the outside of the firewall that might affect the travel of the master cylinder however slightly. I am thinking inside the cab is my best option. This is really going to suck.

[Saudade]

No problem JD. I know you knew that. Sometimes I leave out steps that seem like second nature when I tell people similar stuff.

Jerry, check the rod to the pedal and see if there's an adjuster you can use to make up for the increased distance. I don't think the 16 guage plate JD suggests would really make that much difference.

[JDPascal]

jerry b

I think that Saudade is right that the 16 gauge would not likely make a difference.

You could try it and see but like Saudade said, even before that, look at the clutch swing assy and see if there is a stop adjustment or a rod adjustment that would let you make up for the thickeness if it did turn out to be a problem....

With the 16 ga. plate you are only looking at about 0.051" thickness. That is double the thickness of the 22 ga. usually used in body sheetmetal. You could likely get away with 18 ga. at 0.040" thick too..... That is around one turn of an adjuster bolt with coarse thread to make up for the difference.....

ain't makin stuff fun!!!!! Love it!!

JD

[jerry b]

It turns out i had two problems, which always sucks. The crack in the firewall which i repaired by drilling holes at the ends of the crack and reinforcing it on the inside of the firewall. Also the plunger that connects the pedal to the master cylinder appears to e slightly bent. Not quite sure how that happened. But i think the combination of the two is what made it quit working. Im just glad i dont have to pull the tranny. Thanks for the input.

[Saudade]

Ah, the old bent plunger that connects to the master cylinder trick.....

Glad you caught that!