Replacing the differential

[aslives]

So my 1979 Spider 2000 has started making an unusual noise. Ran it by the mechanic and after an exam it seems that the differential is going - at least maybe the bearings.

When I rotated the drive shaft I could feel a lumpiness / grinding.

Not my area of expertise but my mechanic says its needs to be replaced or possibly the parts replaced - either way its a $1,500 or so job.

Does that sound right?

[divace73]

So my 1979 Spider 2000 has started making an unusual noise. Ran it by the mechanic and after an exam it seems that the differential is going - at least maybe the bearings.

When I rotated the drive shaft I could feel a lumpiness / grinding.

Not my area of expertise but my mechanic says its needs to be replaced or possibly the parts replaced - either way its a $1,500 or so job.

Does that sound right?

more than likely it the pinion teeth are missing.

Depend where you are, Down here in Australia that would be the cost of a full rebuild with new parts, you could pick up a 2nd unit for much less but may have the same issue down the track. When was the last time you changed the oil?

Assuming you are in the US you have lots of choices, if it were me I'd speak to the guys at autoricambi or mark allison to see what they can do for you

Good luck

[bobplyler]

The differential changed in 1979. You can replace it with an earlier one if you change the panhard rod to the older one. And the ratio will change from (I think) from 3.90 to 4.10/4.30 depending on the year.

[vandor]

The cheapest option is to find a used one close to you. Second cheapest option is to find a used one elsewhere and have it shipped to you.

The earlier diffs had a different ratio, it will make the car very buzzy, you don't want to do that unless you rarely do any highway driving.

[bradartigue]

$1,500 is on the high end for a swap or rebuild. In shop terms thats saying about 10 hours of work and 500 in parts - and these things don't take that long to do in either case. It isn't a horrible price - if you don't like getting filthy then it may be worth the money. Replacing the rear end with a good used unit is something you can do at home - provided you can do the following:

- Remove the brakes
- Unbolt the driveshaft
- Remove shocks bolts
- Remove suspension arm bolts @ the differential

If the used unit has the axles then the hardest part - the axle swap - is taken care of for you. These differentials are held in place by very few parts - heavy duty parts - but very few. You can drop it onto a jack and roll the new one in place in a matter of a few hours if you work systemically (disconnect the brake system completely, then unbolt the driveshaft, then remove the shock bolts, then unbolt the suspension arms) and then reverse the order. Dirty work, I've pressure washed the underside of the cars the day before doing this.

A key "gotcha" that can cause all manner of misery is the brakes lines - make sure that the hard lines that attach to the diff and the rear compensator arm are completely detached before removing. I usually rig up a way to hold the calipers so I don't hang them from the lines but you can remove them if you plan to bleed the brakes again.

[v6spider]

Or just get a used pumpkin . providing the axle bearing s are OK. Just have to make sure the housing is clean..

Rob

[brackie1]

I have a '78 and my rear end went out broke teeth off of spider gear. turns out fiat changed rear end in mid year of '78. they went from a 4.30 2 piece rear end to a one piece 3.90. if you have a 2 piece which is the punkin style rob is talking about it is a 4.30 and a good one is not easy to find believe me I'm there. it is a hit and miss as to whether or not you get a good one. they may say they have been inspected and yeah maybe they are clean but it doesn't mean the gears are lined up properly. believe me I know I just got one which was supposed to have been inspected and yeah it was clean but when installed in whines like crazy when you let off of the gas because gears are not aligned properly and you can't tell by just looking at them. now I have to take it back out and put in purple grease to see where it needs to be an that is no guarantee that it is not worn to a point that it can't be fixed.

Gene
North Carolina

[vandor]

> turns out fiat changed rear end in mid year of '78. they went from a 4.30 2 piece rear end to a one piece 3.90.

Incorrect, the 'one piece' rear end (has a cover on the back) in the '78 is also a 4.30:1 ratio, only in 1979 did it change to 3.90.

You are right, when someone says 'inspected' it might be good to ask what exactly was done to inspect it.

[DieselSpider]

Vicks does have completely new pumpkins for the 78 and older that have been setup with the 3.90 gearsets for better highway manners. They are only $577.73 which is not bad for a totally new unit.

http://www.vickauto.com/newstore/index. ... ts_id=2038

I am seriously considering going to 3.90 since the diesel has a lower redline then a gas engine and I would like to get the rpms down especially on the interstate. Yes it will require recalibration of the speedometer but mines not working anyways so it already needs attention.

[brackie1]

well I can't go with the 3.90 I put bigger tires on and of course that reduces the low end torque and if I went to the 3.90 it would reduce my low end torque even more. I would rather have the low end torque than the highway speed mileage.

[vandor]

We carry that third member for less coin...

[divace73]

well I can't go with the 3.90 I put bigger tires on and of course that reduces the low end torque and if I went to the 3.90 it would reduce my low end torque even more. I would rather have the low end torque than the highway speed mileage.

You may have the 3.9 in there now and with a 2 L I don't think you'll feel the torque loss difference?? I know of people who have a 4.3 and are sick of 1st gear revving out too quickly.

I originally have a 3.4 diff out of an Argenta (you guys didn't get those in the US) which was great on the freeway but no so good for track or zippy street driving. I have since installed an earlier style diff (my car is a 1980) with a 3.9 and ATB diff centre and love it. I to have a 4.44 ratio for the tight tracks but have yet to install it, I imagine I wouldn't need 1st gear at all with a 4.44???

What size wheel do you have,? For eg a 15" wheel with 195/50's is fairly close to the overall diameter of the original setup

A note on inspected, the 3.9 I installed was a completely new ring gear and pinion on a 4.3 dinar pumkin, I was considering staying with the original 4.3 donor pumpkin I had and lucky I didn't, on the back of the pinion there were a few hair line cracks, the teeth on that particular pinion would have stripped in future. Point being there is no way to tell without it all being apart??

keep up posted on which way you decided to go.

[DieselSpider]

Its almost like driving a pickup truck with the 4.30 in it and yes the temptation is to just skip 1st altogether.

[frankcma]

You are better off getting an entire re-manufactured unit from someone like Vicks auto or other selling fiat parts. Its very hard for local mechanic to swap out parts inside without special tools specific to the fiat. Ring and pinion if not set up properly will make noise and prematurely fail. You can then have your mechanic swap out the entire rear or do it yourself ( should be no more than 2-3 hr job at the mechanic). I have experience with this and finally getting an entire rear end worked best.

[Squidders]

Just having a similar issue were the diff was getting progressively noisier and has since failed. I decided to swap out the third member and am keeping the old one as a back up (repairing it later). I purchased mine from autoricambi and had it shipped to Aus. While replacing it I will be swapping out the rear wheel bearings as well as I don't know how long ago they were done. Will also be going from 4.3 to 3.9 as one of the PO's has swapped the diff and axial to to earlier model spider at some point. Will be good to get a better Highway run with less RPM's and better economy.