66 Differential problem (maybe)

[Gary Schisler]

I finally put my 66 out on the road today and it ran well. If you have seen any of my posts, I have rebuilt the brake master cylinder, rebuilt the stainless brakes, and worked on the rebuilt carb. Everything works as it should and the car just hums. What a great way to start the day.

Now, here is the question. While driving at highway speeds the car will sometimes just sort of shimmy sideways a little bit, as if a gust of wind hit the car or if you happen to run in one of the ridges or valleys that the heavy trucks create on asphalt highways. The only problem is there wasn't any wind and the roadway is realtively new concrete with no ridges and valleys. It almost feels as if this is coming from the differential. I don't know why I say this, but after seven years of ownership, I can usually tell when something "just ain't right". Is this a symptom that any of you have had or are experienced with? The differential is the one system component that I have not rebuilt or torn apart to put in new seals. I did drain the differential and refill it about 4-5 years ago, and I also put in the special positraction additive. Any ideas here? Thanks, Gary

[Bill Clupper]

Re: 66 Differential problem (maybe)

Check to see if the stub axles coming out of the differential are still securely located by the spring clip that retains them in place. the clip can become unasttached, or break, or the end of the stub axle can be worn down to the point where the retaining groove is lost. either problem will give you the feeling you describe. The problem is, you have to pull the rear cover off to fix the problem.

[Bill Clupper]

Re: 66 Differential problem (maybe)

Check to see if the stub axles coming out of the differential are still securely located by the spring clip that retains them in place. the clip can become unasttached, or break, or the end of the stub axle can be worn down to the point where the retaining groove is lost. either problem will give you the feeling you describe. The problem is, you have to pull the rear cover off to fix the problem.

[Joe L.]

Re: 66 Differential problem (maybe)

Gary-----

I agree with Bill; the first thing that I'd check would be stub axle end-play. Whether or not the c-clip has departed, if there exists any perceptible "in-and-out" movement of the stub axle, it's time for replacement. Once the stub axles start to wear and the heat-treated portion is worn through, wear accelerates dramatically. In order to check the stub axles you will need to remove the half-shafts from them and, usually, this means removal of them from the car.

Other possible causes of your problem are:

1)Incorrect rear wheel alignment, especially toe-in/out;

2)Deteriorated trailing arm forward bushings;

3)Missing or loose trailing arm shims;

4)Excessive rear spindle bearing assembly end play or worn bearings;

5)Deteriorated or incorrectly installed differential "snubber" bushings(located where the differential forward bracket mounts to the frame crossmember). There are two of these bushings---an upper and lower.

[Joe L.]

Re: 66 Differential problem (maybe)

Gary-----

I agree with Bill; the first thing that I'd check would be stub axle end-play. Whether or not the c-clip has departed, if there exists any perceptible "in-and-out" movement of the stub axle, it's time for replacement. Once the stub axles start to wear and the heat-treated portion is worn through, wear accelerates dramatically. In order to check the stub axles you will need to remove the half-shafts from them and, usually, this means removal of them from the car.

Other possible causes of your problem are:

1)Incorrect rear wheel alignment, especially toe-in/out;

2)Deteriorated trailing arm forward bushings;

3)Missing or loose trailing arm shims;

4)Excessive rear spindle bearing assembly end play or worn bearings;

5)Deteriorated or incorrectly installed differential "snubber" bushings(located where the differential forward bracket mounts to the frame crossmember). There are two of these bushings---an upper and lower.

[Gary Schisler]

Re: 66 Differential problem (maybe)

Thank you for your responses. I had read about the clip that holds the stub axle in, breaking off or failing. I had pretty much eliminated the trailing arms, since they are all new replacement units. In addition, last week, I double checked the bolts and shims to insure that they are secure. In addtion, after the trailing arm replacement, I had a complete four wheel alignment that was done an old timer who has been doing this for many years. The car has never tracked truer than it does today.

Is the car still safe to drive this way for short or long trips? I am pretty much a mild driver with this car. In addition, once I remove the half shafts to check the play on the axle stubs, can I have the clips re-installed (assuming the end of the axle has not deteriorated) or new axle stubs installed with the differential still on the car?

[Gary Schisler]

Re: 66 Differential problem (maybe)

Thank you for your responses. I had read about the clip that holds the stub axle in, breaking off or failing. I had pretty much eliminated the trailing arms, since they are all new replacement units. In addition, last week, I double checked the bolts and shims to insure that they are secure. In addtion, after the trailing arm replacement, I had a complete four wheel alignment that was done an old timer who has been doing this for many years. The car has never tracked truer than it does today.

Is the car still safe to drive this way for short or long trips? I am pretty much a mild driver with this car. In addition, once I remove the half shafts to check the play on the axle stubs, can I have the clips re-installed (assuming the end of the axle has not deteriorated) or new axle stubs installed with the differential still on the car?

[Joe L.]

Re: 66 Differential problem (maybe)

Gary----

Unfortunately, it is not possible to replace the stub axles or the stub axle c-clips with the differential unit in the car. If this turns out to be your problem, you will need to remove the differential for further service and repairs.

It sounds like you've got most of the other possible problems that I mentioned covered. However, I'd still check the "snubber" bushings if they haven't been replaced recently. If it turns out that you have to remove the differential, that's a convenient time to replace these, too. As a matter of fact, the differential should never be re-installed in the car with used "snubber" bushings.

[Joe L.]

Re: 66 Differential problem (maybe)

Gary----

Unfortunately, it is not possible to replace the stub axles or the stub axle c-clips with the differential unit in the car. If this turns out to be your problem, you will need to remove the differential for further service and repairs.

It sounds like you've got most of the other possible problems that I mentioned covered. However, I'd still check the "snubber" bushings if they haven't been replaced recently. If it turns out that you have to remove the differential, that's a convenient time to replace these, too. As a matter of fact, the differential should never be re-installed in the car with used "snubber" bushings.

[Paul E. Young]

Re: 66 Differential problem (maybe)

I have one suggestion that might save on disassembly time. I once had a positraction that had the same symtoms. I changed gear lube and added some positraction additive and it went away. I assume that the clutch package in the differential was sticking some way. Good luck. Paul 5962

[Paul E. Young]

Re: 66 Differential problem (maybe)

I have one suggestion that might save on disassembly time. I once had a positraction that had the same symtoms. I changed gear lube and added some positraction additive and it went away. I assume that the clutch package in the differential was sticking some way. Good luck. Paul 5962

[Philip C.]

Re: 66 Differential problem (maybe)

Hi Gary This might sound funny, try changing the rear end oil, make sure you use more than one tube of additive and posi lube.Get as much old oil out as you can.I use a thin line ( plastic )and cause a syphen and let it drain over a day or so till it stops.good luck Phil

[Philip C.]

Re: 66 Differential problem (maybe)

Hi Gary This might sound funny, try changing the rear end oil, make sure you use more than one tube of additive and posi lube.Get as much old oil out as you can.I use a thin line ( plastic )and cause a syphen and let it drain over a day or so till it stops.good luck Phil