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#1 super6al

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Posted 14 January 2021 - 01:45 PM

Hi All

1275cc A+ carb cooper - I decided to change my diff from a 3.1 to 3.44 & wish I hadn't bothered.

All was well & good until I bolted the crown wheel to the diff case & realised the fibre washer was still stuck to the oid crown wheel - doh!

So I removed it again & then when I torqued the bolts (60b ft-seems a lot for what it is) one of them has pulled a thread. The bolt is fine, its the casing thread thats gone. No idea why, I'm confident my torque wrench is accurate & its the first time I ever this happened (with a torque wrench).I can only think its fatigued after 3 refits.

Options I can think of are,

1) Ive re tapped & could torque to a lesser value with thread lock. Others would be torqued to spec.

2) Fit a longer bolt  - std are 3/4" long & I could fit 1" & maybe 1 1/4"

3) Helicoil with an M10 bolt.

The last option is to scrap the case & start again (I'm not keen on that idea)

While I'm on, I fitted lock tabs but not keen as the bolts bite & leave metal shards. I have read on here some people now use threadlock

Any views on the option or any other ideas.

Alan 



#2 absx2

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Posted 14 January 2021 - 01:53 PM

Do you mean the diff cage https://www.minispar...ic/DAM6027.aspx

Give Guessworks a call and use threadlock on your new cage.


Edited by absx2, 14 January 2021 - 01:54 PM.


#3 super6al

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Posted 14 January 2021 - 03:24 PM

Yes thats the one. Haynes call it the diff case but cage is what I would say.



#4 Cooperman

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Posted 14 January 2021 - 05:54 PM

If the crownwheel bolts were ovr-torqued by a previous mechanic, it could be that the threads were weakened.

The only way to do the job properly is to heli-coil the bolt hole using a 3/8" UNF Heli-Coil. Then fit and torque up to the correct torque.

thread-lock is better than those steel straps, but make sure the threads and bolts are completely grease free.

Because of the location and the possible effecs of having a bolt come loose it is best to do a proper repair rather than try to bodge it.



#5 Spider

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Posted 14 January 2021 - 07:28 PM

There is 2 different figures for these Bolts. The Early cars up to about 72 - 74-ish used a higher grade bolt and the figure was 60 ft/lb. After the change in Bolt Spec, this was reduced to 48 ft/lb. I'll see if I can dig out both types later and post them up here so they can be ID'ed.

 

I gave up on the Locktabs a while back as I found them too soft and so with a bit of time, the Bolts would loose much of their initial torque. I Locktite them in with 243.

If you decide to Helicoil your Cage / Case, you'll box yourself in going to M10 as you won't get an M10 bolt through the Crown Wheel. Go 3/8" UNF and use a long series Helicoil. You'll also need to drill and tap for this dead square, there's no room for error. The holes in the Crown Wheel are a neat fit to the Bolts and these are used as Drive Pegs, this is why you won't get (or shouldn't be able to) an M10 Bolt through the Crown Wheel. Because these are such a neat fit, if the Thread in the Cage / Case is slightly off square, you won't get the Bolt in. Definitely do-able, but some care and precision is needed.

 

I gotta say, while I do like to save as many parts as I can (there are only getting thinner on the ground), I'd most likely just replace the Cage / Case with another. You should be able to pick up a good used item for not much money, if you were close by, I'd happily give you one.



#6 super6al

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Posted 14 January 2021 - 10:17 PM

Thanks all

Prior to myself the diff has never been apart so I can rule out a previous mechanic over tightening. Just wondering about Mokes point & should the torque spec be 48 lb/ft (although presumably the diff cage design was never changed?). I agree about the tabs being soft & compressing. 

Looking at the cost of a helicoil kit v a second hand cage, I'm inclined to replace the cage & rebuild it again with threadlock.

Alan



#7 GraemeC

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Posted 14 January 2021 - 10:39 PM

A second hand diff cage shouldn’t be hard, or expensive, to get - many people swap them out for 4 pin (or other performance) diffs



#8 KTS

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Posted 14 January 2021 - 10:43 PM

£12 on guessworks website

#9 Clip

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Posted 15 January 2021 - 07:06 AM

You won’t be sorry when you get the 3.44 diff in and running. It’ll seem like you’ve picked up another 10hp. 



#10 super6al

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Posted 15 January 2021 - 08:35 AM

You won’t be sorry when you get the 3.44 diff in and running. It’ll seem like you’ve picked up another 10hp. 

 

Clip, thanks for that comment you have just re fired my enthusiasm !! It was definitely flagging after what will be the 3rd rebuild on something that started out as a quick bush & bearing refresh.






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