Rear axle - Repair or Swap out

[kgfiske]

Hi all,
I need some advice. I have a 78 Spider with the early style rear axle in it. I
am running a strong 2.0L engine with good number of performance mods on it. A
number of years ago, I swapped out the original 4.3 pumpkin with a 4.1 pumpkin
from a Fiat Coupe. Over the past month or so, the diff is starting to make some
nasty 'popping' sounds if I put the car in reverse and back up somewhat
aggressively. This makes me believe the old 4.1 diff is about to cash out.
I've been wanting to replace it with a lower ratio 3.90 unit for some time and
this situation is definitely prompting some more immediate attention.

So, it seems to me that I have two options, simply installing a new 3.90 pumpkin
assy into the existing axle, OR getting my hands on and swapping out a later
style 3.90 rear axle assembly/panhard rod and shorter rear drive shaft. I could
probably do the latter option more economically, but with the first option, I
would have the peace of mind of having a brand new assembly in place.

I would be interested in what the general thoughts are about the pros and cons
of swapping to the later style axle versus sticking with the earlier version.
Is one 'tougher' than the other? Either way, I want to end up with a 3.90 ratio
rear end.

BTW, if I do opt to swap out a later axle assembly, I will be looking for one if
anyone has one available within say a 400 mile driving radius of Akron Ohio.

Thanks folks,
Kelly Fiske
Medina, OH

[RoyBatty]

My choice would be to get the assembled 3.90 unit from Auto Ricambi, along with new pays to change out the outer axle bearings.

[kgfiske]

Thanks for the reply, I have decided to stick with my existing rear axle and change the pumpkin itself.

[Exit98]

When the rear went on my 76 I put in a used 3.90 from a parts car. With some excellent help from the NJ guys it was an easy job. I love the 3.90. When and if it goes out I'll just put another used one in. The Maryland guys (John Erskind) usually have a few around.

But there are pros and cons to all our choices.

[paintdudeluke]

somebody here talked about dropping in an RX7 rear axle with posi and disk brakes. I like that idea. A little welding on the housing, but not a big deal. Nice upgrade.

[MrJD]

The issue there is bolt pattern. It'd be really easy to get a random healthy rear end, but getting the bolt pattern to match...

I have to assume the hubs would have to be welded up and re-machined by a pro. then you get onto brake pressure distribution...

[divace73]

Stay with what you have, you have far more option...if you want LSD type action with the earlier pumpkin diffs then there is always the ATB option. I've done it in my car and love it.
It may be a bit of a cost for US folks but it was well worth it for me. http://www.ladaworld.com/product_info.p ... ucts_id=47 the chap Stig is great to deal with

All up I have a new 3.9 pinion and ring gear put on to a new ATB centre and it cost me almost AUD$1000 In total. I realise that me be a cost of a car in some places, but mine originally cost me $15k over 10 years ago as they are rare here.
If you want to see it in action just click on my you tube link below and see the latest video.
Just an option out there