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TR4/4A TR4A IRS Front and Rear Differential Bridge Pins


Luke Skywalker
Country flag
When those threaded pins that hold the differential, quite stout, actually fail or break, can't they be replaced by carefully cutting them off and welding a new threaded extension?

I've not seen that done, but it seems like a possible fix, and maybe more practical than removing the body of car and dropping a new pin in from the top (assuming anyone would do that).



Darth Vader
Has anyone actually had the pins themselves break? I thought the usual failures were initially the lower part of the bracket would crack where the pin goes through it and if left untreated, then the pin would tear loose from where it was welded to the top bridge.



I believe HerronScott is correct. My bracket cracked side to side from the pin. I certainly feel like it could have caused the pin to crack loose at the top bridge as there is not much to hold it there if unsupported at the bottom. I did the "fixes" with both bracket side supports and extra reinforcement welded at the top of the bridge. Also did the fixes on the front suspension at the same time. I have had a failure at the front on a previous car that was within a couple of minutes of probably costing me my life. So I don't want to mess around with things that could have bad consequences. But my car is disassembled so fixing these items was much easier.


Luke Skywalker
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Yes, the main issue is where the pin enters the bracket. It is common to see those brackets with hairline cracks. Mine, for instance, looked perfect until we hit the brackets with a wire brush. We then boxed them in with cross members for added protection.

However, the pins do fail--at the top of the bridge and at the bottom where the threads can be stripped. I've seen some awkward fixes with stripped pins, and I was just curious how difficult the "fix" might be.


Mine was more than a hairline crack and I believe that finding it and correctin g it was critical. Mine was like most it was the front right mount that failed Don't skip on safety. I've now owned two TR4A IRS's and both have had cracks at the bad places. But we know of these weaknesses front and rear and suppliers do to and provide the necessary parts to fix these.


Country flag
Side note - generally speaking welding upside down in that location unless you have a proper lift is not a laugh riot.

I boxed in my TR6 and TR4a and it was not the most fun I've ever had.


Darth Vader
well I just boxed in mine on my TR6 and what I found was the welding portion, although a pain, was the easy part, cleaning all the grease off was the hard part,

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