rear ends

[spiderrey]

I know this has been gone thru numerous times. Is the earlier one better then the later one or vice a versa? Is the only real difference the gearing? Im about to start prepping one to install on my car so that it can come out of the garage, where it has been sleeping for the last two years. Which would better suit my car, its a 70 with a stout 2 liter.
I sold the auto rear end that was in it.

Now I have a standard 79 rear end and two 70 rear ends to chose from.

[Exit98]

Ray,

You're right there are plenty of threads and plenty of opinions on this subject. With the 2 litre I'd vote for the 3:90 over the 4:10. You have plenty of low end torque and at cruise you'll be 350 or so revs down. I switched to a 3:90 on my 76 1800 cc and will never go back. Too bad you sold the AT rear.

Don't know if one is stouter than the other. My 4:10 failed and it wasn't abused. The used 3:90 I put in works fine. If it goes I'll find another one.

[spiderrey]

Thanx for your opinion Doug. The auto rear end took away to much bottom end, but it gave me a crazy top end. Im leaning towards the 3.90 as of now.

[djape1977]

oilder rear end is more durable and if you decide to go that way, 3.9 dif is available for it, as well as LSD

[spiderrey]

Who makes the 3.9 for the rear and the LSD?

[vandor]

Here are the 3.9:1 gears for the earlier rear end:

http://www.autoricambi.us/product/DR9-4 ... 391-Ratio/

Or the complete third member (sorry, no pic):

http://www.autoricambi.us/product/DR9-4 ... 391-Ratio/

I would go with the 3.90 for that setup.
In general I like the early rear ends because they are a lot lighter, and the gears are easier to set up or replace.
But if you already have a 3.90 from a 2L car, use it. You will need the panhard rod that came with that rear end.

On the late style rear end there were 3 different types of gears used - about every 2 years Fiat would make the gears stronger. This would indicate to me that the early ones are failure prone.

Keep the early rears as spares.

[spiderrey]

Csaba, thanx for the info. I recall reading that these gear sets were available for the early setup. But I also recall that there were issues with them. Is that the case. Who manufactures them?

[spiderrey]

Oh, and I have the Panhard rod. Both styles. I have a complete 79 for parts.

[azruss]

I put a stock 71 rear end in an 80 FI. there are several differences beyond just the gearing. The early ones are lighter by several pounds. The brake dust plates are not interchangeable. the early one do not have a wheel centering flange on the axle ends. My guess is there are differences in seals as well. Csaba would know that better than me. Finally, the driveline needs to match the years as well. You can make the early rear ends work with the newer drivelines, but the carrier bearing does not line up properly and I suspect would wear out faster. And, as mentioned, the panhard rod must match the age as well.

[divace73]

Here are the 3.9:1 gears for the earlier rear end:

http://www.autoricambi.us/product/DR9-4 ... 391-Ratio/

Or the complete third member (sorry, no pic):

http://www.autoricambi.us/product/DR9-4 ... 391-Ratio/

I would go with the 3.90 for that setup.
In general I like the early rear ends because they are a lot lighter, and the gears are easier to set up or replace.
But if you already have a 3.90 from a 2L car, use it. You will need the panhard rod that came with that rear end.

On the late style rear end there were 3 different types of gears used - about every 2 years Fiat would make the gears stronger. This would indicate to me that the early ones are failure prone.

Keep the early rears as spares.

I have done exactly this on my 2L FI 3.9 with LSD (ATB really) and it is great (especially considering prior I had a heavy late 132 diff with 3.4 ratio). I have yet to test my track times at a familiar track but it has much more zip and the weight reduction is noticeable. It is a bit of work but well worth it.

[spiderrey]

Things that I already know. Need to use matching panhard rod. Need to use matching drive shaft. I know the backing plates are different because I just took three rearends apart to sand blast and paint the pieces. The early plates are held on by 10 mm bolts, well the late ones are held on by 17 mm bolts. And earlier today I did notice the centering flange on the late axles. See pic. Id like to know the actual weight difference though.

[divace73]

Things that I already know. Need to use matching panhard rod. Need to use matching drive shaft. I know the backing plates are different because I just took three rearends apart to sand blast and paint the pieces. The early plates are held on by 10 mm bolts, well the late ones are held on by 17 mm bolts. And earlier today I did notice the centering flange on the late axles. See pic. Id like to know the actual weight difference though.

Also the rear tail shaft length is different (the nose of the later diffs is longer than the earlier ones.

[vandor]

Csaba, thanx for the info. I recall reading that these gear sets were available for the early setup. But I also recall that there were issues with them. Is that the case. Who manufactures them?

Both of these are Lada parts. This ratio was only available in a Fiat 124 for one year, in the Euro version of the Sedan with the TC engine. Because of this I was never able to find these gears in Italy. However it was a fairly common ratio for Ladas.
Yes, I have seen gear sets that were not made correctly, I actually ended up with a set like that 7-8 years ago, and I did not notice it until I installed them in the third member and was not able to set up the lash correctly. It seemed like the manufacturing on the gear teeth was not finished. Now I have my supplier check each set before they send them out, and I also check them when we receive them.

[divace73]

Yes, I have seen gear sets that were not made correctly, I actually ended up with a set like that 7-8 years ago, and I did not notice it until I installed them in the third member and was not able to set up the lash correctly. It seemed like the manufacturing on the gear teeth was not finished. Now I have my supplier check each set before they send them out, and I also check them when we receive them.

Is there any obvious way of checking, were there any specific markings?

[spiderrey]

Im actually a bit surprised here. I just weighed the early and the late rearend. The early was 81 lbs. The late was about 120 lbs. I figured they might only be 15 lbs between them. Well I started cleaning up the early rear to put in my car. Im going to use pieces from both early rear ends to make a solid one.