Remove differential without removing rear axle on a 1979 1980 Spider

[MartinK]

Hi there,
New to the forum. Recently bought a 1980 carbureted Spider with an awful whining noise at higher speeds and depending on load.
Obviously the differential, but I could not find if it is possible to remove the differential from the car without removing the rear axle.
Any help would be appreciated...

[18Fiatsandcounting]

It's not possible. A question, though: Do you have the later style differential, the one with the rear cover with bolts around it? That replaced the earlier "pumpkin" style differential in late 1978 or so. If you have the later style, you can drain the oil, remove the rear cover, and inspect the insides. Look for anything loose, any metal debris (which is not good).

Some quick things to check: Enough oil in the differential, and the right kind (80 or 90 weight EP oil)? Front input shaft to the differential is not loose? While under the car, see if there is any play in the input flange, which would indicate a bad pinion bearing.

Whining noise can be caused by bad rear wheel bearings, so you might need to remove the axle anyway.

-Bryan

[MartinK]

Thank you very much for your reply!
Yes, I do have the later style with the rear cover.
I did check and change the oil, no overly amount of debris in the old oil.
The flange I will still have to check, but then my question would be if the noise is so strongly depending on acceleration and deceleration at higher speeds (from about 50mph) and really whining loudly, could it still be a bearing?
And do you have some more details about why it is not possible to remove the differential without removing the entire rear axle from the car? I could not just pull both drive shafts and then take out the differential?
Thanks for your help, Martin

[18Fiatsandcounting]

And do you have some more details about why it is not possible to remove the differential without removing the entire rear axle from the car? I could not just pull both drive shafts and then take out the differential?

Ooops, sorry, my mistake, I thought you meant remove the differential without removing the two axle shafts. Yes, you can remove the differential with the rear axle still on the car, but the two axle shafts do need to come out. I'm mostly familiar with the earlier differentials, where you remove the axle shafts and then the front case (the "pumpkin") unbolts and comes out towards the front. I imagine the process is similar for the later differentials, although my recollection is that the differential "innards" remove from the rear once you unbolt them.

Cheers,
-Bryan

[MartinK]

Ok, thanks, although the next step would be to know HOW do you remove it?
Are special tools required?

And then of course I would like to know where to get a replacement or how to repair?

Any help would be appreciated.

[18Fiatsandcounting]

I'm not going to be much help here as my only experience is with rebuilding the early-style differentials. But, I believe for the later model differentials, you drain the oil, remove both axle shafts, remove the rear cover, and you should see two saddles on either side secured by two bolts each. Remove the 4 bolts. At this point, the differential may slide out, but I've also see reference to a spreader that is used to ever-so-slightly spread the saddles apart (only 0.5mm or so) so the differential will slide out. That spreader would be a special tool.

I guess you'd need to look into this more, or at least get a better answer than mine. There are shops that rebuild rear axles, so the easiest thing might just to be to drop the entire rear axle and take it to such a shop.

You other option is to find a good used rear axle with a good differential. But, I'd make totally sure that the noise is really a differential issue and not something else. Properly set up, filled with oil and not abused, differentials normally last a long time without issue. Pinion seals and rear wheel bearings do fail over time.

-Bryan

[MartinK]

Once again, thank you very much.
Amazing that on the entire www I cannot find anyone who has ever taken out the differential from a 79 or younger Spider.
After your reply I have decided to first get a proper diagnose. Cannot come before October 12, but I will keep you updated.
Martin

[18Fiatsandcounting]

Amazing that on the entire www I cannot find anyone who has ever taken out the differential from a 79 or younger Spider.

Now that you mention it, that seems true. I've also heard that the 1979 and onward differentials are set up using shims, so you need a whole collection of those to get it set up right. 1978 and older had adjustable features to set up things like bearing preload. It still is a bit of an art, though.

Pro-Tip: If I disconnect the driveshaft from a differential input, I put marks on the flanges so that I can put it back together the same way. The same is true for the two U-joint couplings. Apparently the driveshafts were balanced at the factory, and putting the driveshaft back together 180 degrees out can cause vibrations. Usually around 35 to 40 mph with a second harmonic at 70 to 80 mph. I've never tested the next harmonic at 140 to 160 mph...

-Bryan

[Nut124]

I have worked on my -78 diff, which is the early style.

If I were faced with your dilemma, I'd consider locating an early rear axle at a junk yard, inspecting it and swapping the entire rear axle. Successfully rebuilding the late diff in the car is no easy task.

[ORFORD2004]

Successfully rebuilding the late diff in the car is no easy task.

Not that hard if you know what you are doing. The hard part is crush sleeve and rotational torque of the pinion. I used 3...
I now have winding sound coasting witch mean too much backlash. So, i will have to play with shims to put gear closer but it will be next summer.