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ron73

Reinforcing the diff area on a 4A

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Hi - I have to have my diff rebuilt (again, after 3k! - but that's a separate subject). It's on the ramp, and I'm told it's a great time to "reinforce" the diff area. Honestly, I've owned the car for 30 years and haven't heard about this. I don't race it, or drive it hard. The car has overdrive, and American spec, so I have higher gearing. Honestly, I'd rather spend the cash on something like new tires. Any thoughts here? Yes, I plan on keeping the car..

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Ron hi have a look at http://www.mossmotoring.com/a-weak-differential-mount-fixing-a-common-tr6-problem/

 

this should give you an idea of what they are talking about

Edited by Graham

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Hi Ron,

you can't edit the title bar (nor can I apparently). Don't panic though it is in the 4/4A forum so 2+2 = $$$$

 

If you have had the car for many many years and driving a good number of miles then I would suggest have a look all around the bridge are where the diff sits

and look for any cracking. Also look or feel on top of the bridge around where the diff pins stick through and detect any cracking.

If it is not cracked I would leave it alone.

However if you find cracks around the pins then repair is necessary.

 

Why has the diff failed so soon after a previous repair.?

 

Roger

 

PS - just seen Graham's post. The TR6 has 50% more power going through the same structure.

I still think you can leave it alone.

Edited by RogerH

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post-11421-0-63392500-1488018660_thumb.jpgRon.

 

I strengthened mine.

 

Clear pictures here of the process etc plus articles and suppliers.

 

http://tr4a.weebly.com/chassis-strengthening-kit-welding.html

 

http://tr4a.weebly.com/ctm-chassis-strengthening-kit.html

 

http://tr4a.weebly.com/chassis-strengthening-kits-from-others.html

 

I also added a couple of extra lengths of box steel between the diff bridges.

I saw this mod on a website and thought "Why not" as I had it all exposed and it was easy to do at the time.

A picture of this is in this post.

I will put detailed pictures of the modification on one of my chassis pages later today as I realised it was not on my website.

 

Best wishes

 

Paul.

 

 

 

 

 

 

 

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Thanks, As the diff is out I think - as I've had the car a while - I might as well just do it to be sure going forward. A smaller part of a larger bill.

 

The diff failed due to a poor rebuild I guess - it was 10 years ago, but only 3k on the clock from the diff rebuild (and it was original with 116,000 on it!). I went back to the garage who had outsourced it. They said the guy had moved to Norwich and - as it was 10 years later (I have all receipt invoices, mileage etc) it was probably too late to hope of getting anything back. So I have to do it again:(

 

The garage said they would help me in the future with a better labor rate.....

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I think once you see the pics of what boxing-in is done you can easily cut some ~2mm thick sheet using cardboard templates, no need for some kit.

Make sure you strengthen the flat section around the pin...on mine these pins pulled thru (rather than the whole section coming away from the chassis)

I suggest drilling access holes so you can wax inside...us 4A owners know how boxed sections can rust...

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I think once you see the pics of what boxing-in is done you can easily cut some ~2mm thick sheet using cardboard templates, no need for some kit.

Make sure you strengthen the flat section around the pin...on mine these pins pulled thru (rather than the whole section coming away from the chassis)

I suggest drilling access holes so you can wax inside...us 4A owners know how boxed sections can rust...

.

 

You said it Dave, there are areas of the 4A Chassis where there are holes in the sides but no holes in the base to let water out so first big puddle and it fills up and stays there, until the bottom rusts through and lets it out!

And some areas are boxed in completly, no vent holes at all!!

 

Chris

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Honestly, I've owned the car for 30 years and haven't heard about this. I don't race it, or drive it hard. The car has overdrive, and American spec, so I have higher gearing. Honestly, I'd rather spend the cash on something like new tires. Any thoughts here? Yes, I plan on keeping the car..

Ron -

 

It's a design weakness on the car. My preference, were I in your position,

would be to reinforce the weak areas while you have a good opportunity.

 

Are you CERTAIN you have a higher gearing (i.e. not 3.7)

 

In any event, you don't need to drive an IRS TR hard to experience

a problem with the diff bridge mounting. You have been lucky so far.

 

AlanR

Edited by TR 2100

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I've decided to do the strengthening so that's being done now; while it's up I'll ascertain the gearing. I do remember being offered a newly rebuilt diff (and trying it out) in London but the gearing was different - yes it could do a "smoother" top end but it "lugged" at low speed. I preferred a faster shift with more revs, as my diff gave. So trying to stay original.

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And yes, I have the 4.1 gearing. It's much friendlier at slower speeds and works a charm when paired with the overdrive. I was given a 3.7 to "try it out" and thought - well, this is OK if I didn't have overdrive but you really have to rev to keep from stalling driving around a parking lot, say. At least, that was my impression. Smoother ride, better mileage with 3.7 etc etc - well, I like my 4.1....I don't over-rev the engine anyway...

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Last question - any idea how many TR4A's were equipped with the 4:1 differential at the factory? Mine was - just wondering how many others?

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Very rarely, 3.7 was standard.

Stuart.

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