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What the heck? Replaced transmission mount, now exhaust bangs crossmember

NotMatt

NAXJA Forum User
Location
Wenatchee, WA
I've got an 87 Laredo with a 4.0 in it and the dreaded BA10 transmission. I just recently noticed that the front motor mounts were shot, so I got some new ones and replaced those. Once I did that, I could hear this thumping noise every time I took off from a stand-still. It would go away once I was up to speed, just a momentary "thump-thump-thump". So, I figured maybe the transmission mount was bad too, so I pulled that and replaced it as well.

Now, whenever I start the truck or let it idle I get a constant thump-thump-thump, and when I take off it gets worse. I had someone start it up while I looked underneath there and it appears that the exhaust is now banging on the crossmember something fierce (it's hitting right where it passes through the crossmember).

Has anyone else with a BA10 had this problem? Why the heck is this happening all of the sudden? I unbolted the crossmember the other day and tried to see if there was any wiggle room in it so I could shift it over out of the way, but the holes are only slotted on one end, and even at that, if I could shift it out of the way, it would shift the whole transmission mount and thus the exhaust at that point as well, so it wouldn't help at all.

I bought my mount from the dealership, so I don't think it would be an issue of crappy-fitting aftermarket stuff, and it looked identical to my old one (except for the new rubber of course), down to the size and distance of the exhaust mount as well.

Any ideas? I'm about ready to just pull the stupid crossmember off and put a big notch in it for the exhaust and then plate it over... I don't think it's the best idea, but the noise is really pissing me off.
 
same thing happened to my '90 with an ax-15. put in m.o.r.e. motormounts and no probs. then I thought better do the tranny as well. didnt want poly so I bought a stealship one. it looks identical,but lets the exhaust hit the front of the crossmember. I wonder if the rubber is softer and is compressing more? of course the dealer said I'm the only one that has ever complained!
 
Mine did that with a 91 4.0/AW4 after replacing the engine & trans mounts. I took it to the redneck muffler/tire shop nearby and all they did was use a transmission jack under the exhaust pipe to bend the rod that goes into the rubber mount up at the point where the exhaust goes through the crossmember. It did not appear to be an exact science. They only charged $5. I guess it had sagged or the trans mount was slightly different or something.
 
Yeah, I'm sure I got it on there right as the nutserts for the skidplate are in the rear.

Anyway, I fixed it. I took the crossmember off and heated that section with a torch and banged a nice half-moon into it and no more problems! Probably not the perfect way to fix it, but it worked and I'm happy.
 
If a lot of people are having this problem after changing the tranny mount it makes me wonder if the dealers are selling a pos mount! right now I'd like to take mine back and get the m.o.r.e. poly mount just to see if it lets the exhaust bang as well or performs as spectacularly as my bombproof motor mounts.
 
I agree the factory mount looks like a joke compared to the MORE mount. I am actually putting a new factory mount on next week. I have a 2 month old MORE on there, but the vibes for my DD are too much. Frigging everything rattles! The vents, the door lock, etc. I can't stand it, so I decided to go back with factory. That MORE is one huge chunk of poly. One thing I have done to stop the knocking(prior to the new mount) was to shove a few large flat washers under the rubber "box" that the exhaust mount on the x-member slides into. Mine was sitting right on top of the cross x-member. A few washers did the trick. With the MORE mount, though, that thing has a good inch of clearance.
 
had the same problem (87xj)

take the crossmember off, put a double layer of rubber (slice of tire tube etc...) under the trans mounting and put it back on. 15 min fix, works perfect.

good luck
 
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