T-84 Input Shaft - thrusting problem

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
privatebrian
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T-84 Input Shaft - thrusting problem

Post by privatebrian » Mon Oct 16, 2017 5:02 am

I'm rebuilding a T-84 and ran into an odd situation with the input shaft. While holding the output shaft in place, and rotating the input shaft clockwise (facing the front of the trans) the input shaft moves/thrusts toward the rear of the transmission, as if it were "threaded". Likewise, rotating ccw, the shaft thrusts toward the front of the trans, like it were threaded with right-hand threads, but of course it is not. First I changed the 13 roller bearings with a new set, but same result. I measured the male end of the output shaft and it is not tapered. The female "bearing race" in the input shaft does not appear to be tapered either. I'm actually holding the output shaft in a vice, and the results are very consistent, the input shaft moves about 1/16" per revolution. The lateral movement can be overcome with force, but it is causing me problems with the blocking rings engaging.
I'm wondering if anyone has run into this, and if replacing the input shaft is the answer...??
THANKS!
Brian


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Re: T-84 Input Shaft - thrusting problem

Post by Joe Gopan » Mon Oct 16, 2017 5:30 am

The M.D. Bearing retainer along with the proper thickness snap ring will control that.
Is the M.D. Bearing used?
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Re: T-84 Input Shaft - thrusting problem

Post by privatebrian » Mon Oct 16, 2017 5:53 am

I'm assuming M.D. means main drive, and yes my input shaft bearing has a snap ring that is held against the trans case by the front bearing retainer. But there is some room for movement there, maybe 0.010"-0.015", so when I rotate the input shaft I still get sticking of the blocking rings on the input shaft taper. I have about 0.020" of movement in the blocking rings in the "static" condition.
I am observing this phenomenon outside of the case, with just the two shafts "connected" by the roller bearings in the joint. What I am trying to understand is why there is thrusting at all, when they should just rotate...
Thanks, Brian

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Re: T-84 Input Shaft - thrusting problem

Post by privatebrian » Mon Oct 16, 2017 6:06 am

Ben - I may have misunderstood your question... I believe the main drive input bearing is NEW. In fact I believe everything in the main drive is new, input shaft, output shaft, bearings and needle bearings. I bought the transmission as "rebuilt", I am just going through it to tweak it until it feels good to me. Right now I'm not happy with how it sticks when spinning in neutral.
I have a video I could send if you pm me.
Thanks again.

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Re: T-84 Input Shaft - thrusting problem

Post by Joe Gopan » Mon Oct 16, 2017 7:58 am

Those 13 Pilot Bearings inside the M.D. Gear have nothing to do with M.D. Gear end play.
Best to have the gearbox and the components in question on a bench right in front of the inspector where a trained eye can actually perform hands on inspection and use precision measuring tools to verify manufacturers and visually look for flaws.
These gearbox discussions have good intentions but can result in distractions and "friendly" arguments that go on for days.
Last edited by Joe Gopan on Mon Oct 16, 2017 8:06 am, edited 1 time in total.
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Re: T-84 Input Shaft - thrusting problem

Post by Chuck Lutz » Mon Oct 16, 2017 8:02 am

Remove the front bearing retainer and measure the depth from the face of the retainer to the first lip where it "retains" the snap ring. It would seem that in addition to the possibility that the front of the case opening is enlarged and the retainer isn't "retaining" the snap ring....the bearing is allowed not only to rotate but to move in and out of the case.

1) The gasket up front should not be any thicker than 0.014" which is what Ron's gasket kit is as opposed to over-the-counter gasket kits which are much thicker.
2) If the front bearing retainer does not capture the snap ring TIGHT against the case it will turn as yours does.
3) What is the measurement I asked about above?
4) If you have access to other front bearing retainers with a shallower measurement, go with them.
5) The front bearing retainers used on WGs are not uniform in depth to hold the snap ring. If you can find a GPW front bearing retainer it will work for you as they are all pretty uniform and of the correct depth.
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privatebrian
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Re: T-84 Input Shaft - thrusting problem

Post by privatebrian » Mon Oct 16, 2017 8:15 am

Thanks Chuck. I'm at work and won't be able to make measurements until this evening.

However, forget for the moment about holding the input bearing in place with the snap ring and retainer...
My original question -
With just the two shafts, OUTSIDE of the case, holding the output shaft in a vice, I can spin the input shaft and it moves laterally, consistently.
I just want to know if anyone else has seen this, and what could cause it. Seems to defy physics.

Thanks

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Re: T-84 Input Shaft - thrusting problem

Post by Chuck Lutz » Mon Oct 16, 2017 8:57 am

Since the tip of the main shaft rides on the 13 roller bearings in the end of the main gear....if there is lateral movement the something is wrong:
1) lost a couple roller bearings or they collapsed into the void in the main gear
2) the tip of the main shaft is out of spec (measure it)
3) the tip isn't inserted all the way for some reason

Now....there are far too many shoddy parts being sold for the T84 and this too may be an issue....
Chuck Lutz

GPW 17963 4/24/42 Chester, PA. USA 20113473 (USA est./Tom W.)
Bantam T3-C 1947

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Re: T-84 Input Shaft - thrusting problem

Post by Joe Gopan » Mon Oct 16, 2017 9:47 am

Those 13 Pilot Rollers are held in position in the M.D. Gear by a small wire snap ring. What does happen is that a roller will fall out of place if the main shaft is pulled out too far from inside the M.D. Gear and will block the Main Shaft from going all the way into the M.D. Gear.
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Re: T-84 Input Shaft - thrusting problem

Post by privatebrian » Mon Oct 16, 2017 12:42 pm

Thanks everyone -
1. All 13 rollers are in place, and the wire snap ring is in place. (I changed the entire set of 13 and problem did not change.)
2. The nose of the main shaft fits SNUG in the rollers. Almost no play, it takes a little force to drive the shafts together. Guessing 3-5 lbs of force.
3. The problem persists in or out of the housing.

I wish I could post the video of it moving, it would make things so much easier to understand...

Brian

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Re: T-84 Input Shaft - thrusting problem

Post by privatebrian » Mon Oct 16, 2017 1:18 pm

Thanks!
I do have good Vernier micrometers and will take measurements tonight and post everything tomorrow.

I suppose that since there are an odd number of bearings, that inferring the inside diameter of the input shaft by subtracting twice the diameter of the roller bearings from the measured ID would be in error (slightly). I may be able to get a good idea of the ID of the opening tangent to the 13 rollers using AutoCAD, I'll give that a try as well.

Brian

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Re: T-84 Input Shaft - thrusting problem

Post by Joe Gopan » Tue Oct 17, 2017 1:18 am

And a reminder to Brian, a Vernier Micrometer is not as accurate as a Micrometer Caliper.
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HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
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privatebrian
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Re: T-84 Input Shaft - thrusting problem

Post by privatebrian » Tue Oct 17, 2017 4:58 am

Bantamj - THANKS VERY MUCH for taking the time to get measurements for me.

My measurements are:
Roller (average of 13) = 4.758mm (0.18731") which is 0.003mm (0.0001") larger than yours.
Bore of the Input Shaft = 24.765mm (0.9750") which is 0.045"mm (0.0018") larger than yours.
Nose of the Main Shaft = 15.151mm (0.5965") which is 0.013"mm (0.0005") larger than yours.

Calculated clearance between parts = 24.765-[15.151+(2*4.758)] =0.099mm (0.0039") which is about 37% more clearance than you are showing.
Which leaves me puzzled.

Earlier in the thread, someone asked for the gasket and bearing snap ring thicknesses and the recess dimension in the retainer:
Bearing snap ring thickness = 0.0644"
Retainer recess = 0.060"
Gasket material = 0.022"-0.023" (too thick which is allowing movement of the input shaft bearing.)

Brian

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Re: T-84 Input Shaft - thrusting problem

Post by privatebrian » Tue Oct 17, 2017 5:33 am

Thanks again Bantamj -
I am very confident in the measurements for the nose and the bearings.
For the input shaft bore, I had to use two tools; first I used a pipe caliper also called an inside spring caliper, opened to fit the bore with just slight drag. Then I measured the distance between the tips of the pipe caliper with a vernier micrometer. There could be some error in that.
I work at a large manufacturing company and have access to the machine shop tools. I may be able to borrow a fowler gauge or an inside micrometer to repeat the bore measurement.

Thanks, Brian

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Re: T-84 Input Shaft - thrusting problem

Post by privatebrian » Tue Oct 17, 2017 5:36 am

Here is another thought - could the bore could be out-of-round causing tightness in only one position (?). Is the input shaft plated with chrome or something else? could the plating thickness vary causing the bore to be out of round?

Brian


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