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TR4/4A TR4A IRS Differential Mounts

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Zimmycobra

Zimmycobra

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Is it possible to replace the differential mount rubber without removing the differential completely? I am thinking that I can unbolt the axles and then just lower the diff until I can get the mount rubber out, replace with the new poly mounts and then raise it back up and reconnect everything. (I would use a floor jack to support and raise/lower the diff.)

Am I crazy or will this work? Thanks.
 
Pretty tight, diff is heavy and awkward, might be worth a shot. You should be able to take the four bolts each off the axles and driveshaft, leave them in place and drop it down. Good time to inspect the mounts, especially the right front which is prone to failure.
 
I replaced not only the rubber bushing mounts, but the axles, too. Just last year. Gosh, sorry I can't say for certain, but I really do not think you can do that. It's actually quite easy to disconnect the axles, and with a floor jack beneath the diff, and a real buff wife balancing it so it won't rock off the jack, I'd think that approach might be best. I just can't imagine those axles swinging down far enough to swap out the mounts that way, but good luck and sorry I can't say for certain.

Hey, don't want to scare you, but a buddy of mine and I welded reinforcing plates all over my 4A diff mounts partly just as a precaution and partly because, despite the immaculate appearance, even my beauty had a hairline crack in one the the box housings the long pin bolts from the front bridge pass down through. It's the old story of once you start, you can't stop . . . . There are some old posts about this.
 
By the way, I hope you don't need to even think about this fix, but here's a picture showing where I boxed in those two front brackets, after first welding slats front to back across the inside of the brackets and against the pins, to reinforce the pins. In other words, they were strengthened two ways, inside against the pins, and then the brackets, themselves, by boxing them in. I just cut forms from mild steel and fit them for welding. Then I also repeated that for the rear bridge, though the front one is the problem.

Box-In.jpg
 
Zimmy, there are eight bushes, one lower and one upper on each of the four studs. You won't be able to get the front upper bushes off the studs unless you drop the diff completely off all four studs, and at that point just angle it back and down to slide it out. I think you'll save yourself some grief, and reduce the risk of damage or injury, if you simply remove the diff rather than try to work around it.
 
As KVH mentioned, those diff mounts are prone to cracking. I've seen it countless times on all the IRS TRs. Careful inspection of the brackets is a must. I would think that getting the diff out of the way would be the only way to do that. Also, even if the brackets are OK, my personal opinion is that putting in poly bushings, because they are harder then the original rubber, would only prove to hasten the failure of those brackets. I certainly wouldn't be putting in the poly bushings without reinforcing those brackets. BTW, there are parts sold for that because the problem is so prevalent. See this page from TRF that, besides listing the reinforcing parts, also has a tech note on the problem...https://trf.zeni.net/TR6bluebook/101.php
 
I just want to add one other thought. On mine, I might have sworn out an affidavit that my brackets weren't cracked. They looked perfect. The two front ones are where the worry is. Then my buddy used an air grinder with one of those brush adapters to take off the paint. One had a visible crack and the other was questionable.
 
If you are inspecting for broken mounts, be sure to check the frame crossmember that the pin is welded to. It is very common to find cracks around the pin. The cure requires removing the body or cutting an access hole in the shelf, drill&filling the cracks, and welding a plate to the frame and replacing the pin.
Berry
 
Thanks everyone for the advice and help. I was able to change the mounting bushings without a total removal. I disconnected both axles but left the driveshaft connected. By using a floor jack for support, I was able to lower the diff and have just enough room to change the rubber mounts. Got it all back together without any difficulty at all. Thanks for the support. All mounts looked as good as I could tell and we are going to hope for the best. I will keep an eye on them for sure. The old rubber mounts had several cracks in them from old age and lack of use (not driven in about 30 years).
 
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