Drive Train Question:

I own a 1962 m38a1. The vehicle has been making a vibration when accelerating in 2nd gear as if the u-joints were bad. After replacing the u-joints, the vibration is less but still exists. I noticed that there is a lot of free play in the differential. Question: #1) How much free play should exist in the differential?
Thanks for your help!

 

Rotational, usually some slop. That said, you should be able to grab the pinion yoke and there should be no slop except rotational. Usually, a pinion bearing going south is more evident on deceleration when the wear lets the pinion go rearward too far. Likewise, there should only be rotational movement in the transfercase companion flange.

My experience with too much backspace is it rarely imparts a vibration unless it gets pretty severe. Just that dubious (guessing) 10 to maybe 15 degrees of rotation.

You did note whether the driveshaft was in-phase-trunions parallel at both ends?

 

Check transfer case drum brake.

 

Thank you for your input - the slop I observed is rotational, and it does seem to be at least 15 degrees or more. I need some help understanding the driveshaft being in-phase, can you explain that further?

 

I never considered the brake drum as being a possible source of the vibration. I will investigate - thanks!

 

Ok, after using this site's search engine and a youtube explanation of u-joint technology I think I understand the term "in-phase". The driveshaft was never completely disassembled so the yokes should still line up with each other.

 

That doesn't mean that a previous owner hasn't mis-aligned them some time in the last 60 years.

 

Presumably your front driveshaft is rotating too, unless you can unlock the hubs. Are you considering that as a source of the vibration?

Check the slip-splines for wear on both shafts, but in my experience the fronts seem to get sloppy first.

Also you could simply compare the front diff pinion to the rear to estimate your pinion "slop."

 

So do you not get the same vibration in first and third?

 

The front hubs are manual locking and the transfer case is in 2wd so I don't think the front shaft rotates. The vibration only comes in the high rpm / high torque end of second gear. There is no vibration if I "Baby" second gear.

 

Weeds need to be cut back 50' from all buildings in LA county by May 31st. So weed whacking has jumped to the front of my priority list. I will just have to tolerate the vibration a little longer. Nothing in this life is perfect

 

Put the transfer case in neutral and run the second gear up high rpm and see if you still have it.

 

Here is the rest of the story: The transmission finally locked up in 2nd gear, so I tore the transmission apart and found a broken main shaft. The tip of the shaft that extends into the input shaft had sheared off. I also replaced the clutch assembly and found the pilot bushing had unusual wear.
I hope this helps someone else who may be experiencing the same problem.

 

The pilot bushing probably took a beating from an input shaft not properly supported by the mainshaft.

Thanks for following up!

 

That's a weird place to break.

 

What carnage. Wish you had pics.

So, your slop in the differential is probably within specs then?