Differential going?

kjp · #1 (**permalink**) 07-28-2003, 09:54 AM

Getting a vibration and some noise from the back end when braking, and sometimes when accelerating. I checked the brake system, and replaced any questionable components, so there shouldn't be any problem with them.

Sounds almost like a clunking, grabbing type noise with some vibration felt coming up through the seat. This symptom mainly occurs on braking, does not matter if I am in gear or coasting in neutral.

When acclerating, it sometimes feels like something is grabbing for a second or two until I am moving over 10-15MPH .

I have a '77 Spider with what should be the limited slip 4.56 rear. I changed out the oil in the diff, but no difference. Also looked like I didn't get the full 2.5-3.0 Pints out of the diff when I drained it, but cannot see any leaks. Am I looking at a bead bearing, or a fried limited slip assembly? Is it easier to rebuild or replace the entire axle?

Thanks.

Keven · #2 (**permalink**) 07-28-2003, 02:38 PM

Ken,

Sounds like you have a warped rear rotor.
Replace both, its not very expensive.

It is hard to remove, you need a very large
puller. Might be able to rent this tool from
a auto parts store like Napa, Kragen, etc.

Good luck.

kjp · #3 (**permalink**) 07-29-2003, 06:28 AM

Rotors were my first thought also. So, one of the first things I did was replace the rotors as part of the testing process. The old ones didn't look that bad though, but could use a very light resurfacing. I'm keeping them as spares since they both are still within operating specs. Same problem with the new ones as the the old ones.

I also replaced the brake pads while I was working on the rotors and tested the calipers for proper operation and they checked out OK.

The good guys at Centerline advised me to check the driveshaft and it's connecting points - rubber donut, intermediate bearing, and U-joints. And just in general to make sure everything was bolted down and attached correctly.

Guess I'll be spending some more quality time under the car this evening.

kjp · #4 (**permalink**) 08-07-2003, 06:20 AM

Well, after checking all the U-joints, rubber donut, etc. on the driveshaft - it all looked OK. I changed out the oil in the differential with one of a higher viscosity, and the problem is less noticeable. Something is amiss inside the axle assembly somewhere. Now comes the fun part of fixing it.

Questions -

Simpler or cheaper to swap out axles or repair it?

If I find a good later model 4.10 unit to replace my stock 1977 4.56 unit, is it a straight bolt-in process?

And is it possible to get any of the gearing from the transmission of the donor car that turns the speedometer cable? Just concerned about speedo accuracy here, if such a part exists in the Alfa tranny.

Thanks.

**italcarguy** · #5 (**permalink**) 08-07-2003, 07:25 AM

you might save money by replacing it with a used rear end. all depends on how much you pay for a used one and how much your mechanic wants to rebuilfd your current one.

yes, its a direct bolt in unit.

**Roadtrip** · #6 (**permalink**) 08-07-2003, 08:38 AM

Don't forget to check the rear transmission mount. If that's soft or broken, it can cause wear and noise on other components. Sure hope it's not the axle. That's a PIA to find and fix. I think there was a thread earlier on axle swaps and Anthony informed us that the old non-LSD axle parts are not interchangable with LSD. Be sure you look on the bottom plate on the axle to be sure someone isn't trying to sell you a non-LSD by mistake.

Does it make any difference in noise, vibration, or grabbing as you turn left or right and unload the respective wheel?

kjp · #7 (**permalink**) 08-07-2003, 09:13 AM

I have the LSD in my '77. The diff assembly matches the photos posted elsewhere on this site.

I have only noticed the noise/grabbing on slow acceleration (sometimes), and on braking. Noise still exists when braking with transmission engaged or coasting in neutral.

The mounts looked 'OK', but I will doublecheck.

I will have to try the either wheel test later on today. If this is the case, would it be a wheel/axle bearing on the affected side?

Thanks.

kjp · #8 (**permalink**) 08-13-2003, 12:38 PM

OK - same noise when turning either way. On load - most noise/vibration when de-accelerating, some on acceleration, but not much. Thicker oil 80-120W in the diff has seemed to quiet it down a good bit compared to the normal 80-90W.

I have a chance to pick up either a used '79 or a '86 rear end. Both are LSD. Different axle ratios, 4.56 and 4.10.

The 4.10 should give a bit more top end, how can speedo accuracy be maintained with the 4.10 if I go that route?

Thanks,

othercarsaford · #9 (**permalink**) 08-19-2003, 05:58 AM

You may have already correctly diagnosed your problem, but I had a problem before with a '67 Duetto that manifested itself very similarly to your problem. It felt like the driveshaft had fallen off and might be wiggling around on the pavement. Try taking off the rear disks and making sure that the handbrake springs and pins are intact and properly positioned. It turned out for me that the internals of the handbrake assembly in the driver's side rear disk had broken and were "swimming" around in the handbrake drum and binding up from time to time. It was a mess, but after replacing the components, the problem was gone. Might be worth a look.

emr5503 · #10 (**permalink**) 08-23-2003, 09:01 AM

Roadtrip wrote "Be sure to look on the bottom plate on the axle.... "
What are you looking for? I was unaware there was any external way to tell if it was LSD.
Ed

**Roadtrip** · #11 (**permalink**) 08-23-2003, 11:11 AM

Yes you can. Check the following pictures:

http://alfacentro.com/tech/diff.html

emr5503 · #12 (**permalink**) 08-23-2003, 11:50 AM

Thanks ! Tried to find it on their site to read any discussion, but couldn't. Any suggestions?
Ed

kjp · #13 (**permalink**) 09-09-2003, 08:01 AM

After some hours on my part and the assistance of my local shop, it is determined that one of my U-joints was bad. One end of one joint was seized up. Very hard to tell from my perspective at home without a lift!

The problem now is finding good replacement parts. Mechanic ordered a pair through Ricambi, both of them came in the wrong size. Possibly for a different model? We were puzzled at this one, since Alfa made the same U-joint for Spider/GTV for a good number of years from 1970 on up to the end in the 90's.

Second batch he orders comes from another West coast distributor, and these do not fit exactly either. In fact, one of the two did not even turn and move properly.

Third time we get them from International, one of the two fits, while the other one does not. So now a fourth call is put in, again to International to find a match. I expect to hear back today if this one is a winner.

Anybody else having problems getting parts that fit as they should? We are thinking that a bad batch of these things are floating around in our suppliers stockrooms.

Going on two weeks without a drive in my Spider and getting antsy .....

**Roadtrip** · #14 (**permalink**) 09-09-2003, 08:57 AM

I find it hard to believe that your driveshaft has non-standard U-joints on a 77 model. Alfa U-joint yokes are fairly soft and can bend quite easily in addition to getting buggered journal edges . . . . if a hamfisted mechanic (or most likely PO) trys to use a hammer instead of a press to remove and replace them. I'd be willing to be that one of your yokes is bent.

kjp · #15 (**permalink**) 09-09-2003, 09:51 AM

That is exactly what I am hoping has not happened. especially the journals themselves being out of round or expanded in the past (to put it mildly) by previous parties.

Everything else seemed to check out OK - the yokes did not seem bent, nor the driveshaft. It also balanced up OK.