1973 J4000 T18 After Rebuild, Will Not Shift While Running

[Yeller]

Here’s my 2 cent theory lol

The bushing being too tight was pushing the input shaft in enough to keep the intermediate shaft spinning. This would prevent shifting in any scenario.

[tgreese]

We will see.

Manual transmission Jeeps from this era all use the same pilot bushing, PN 3213751. RockAuto says this maps to a Dorman 690042; any parts store can get Dorman stuff easily. Look on RockAuto and the dimensions of this part are given. Suggest you compare with the original part. Typically there is an oil-soaked foam or felt wick behind the pilot bushing, and the step may provide some space for that. Or maybe Dorman supplies a longer bushing as "equivalent" to the original.

Lesson to me is measure everything you can.

[akguy09]

DORMAN 690042
Inside Dia: 0.754"; Outside Dia.: 1.057"; Length: .877"

These were the dimensions given for the Pilot bushing for my Jeep with a T-18.

[Herk]

Keep in mind that an Oilite type bushing is a bronze sponge and will move around quite a bit when pressed into place. So if the bushing is say a .002 interference fit in it's bore, the internal diameter will be reduced by about .002 when pressed into place. So the bushing needs to be "re-sized" once in place. There are then two methods to accomplish this. The production method was to drive a mandrel or "ball mill", slightly larger in diameter than the shaft that will ride in the bushing, is driven into the bushing which expands the inner bore and further swedges the outside of the bushing into the crank in this case. This created the running clearance of the bearing and also locks the bushing into place. The second method is to ream the bore to final size which removes material, enlarging the inner diameter to the desired size but does not further expand the outer diameter. Reaming is more common in the field.

Ok, so how to do this now. Reamers, especially if you are only going to use it once, are a little spendy. If you have access to a lathe, simply make a mandrel the desired size, round the end, and splap it home with a hammer. Bob's your uncle. That's what the factory did. Or, just use the input shaft... I have a universal casting and part preheater on my patio. Says Char-Broil on it and makes great steaks and chicken. The shaft needs to be heated to expand slightly larger than it will be during operation (200F), but keep it under 400 so as not to alter any heat treating.

Long story short, install the bushing into the crank and test fit the nose of the input shaft before assembling the transmission. Also, avoid using any sort of abrasive to cut the bushing as the abrasive will embed and turn the bushing into a hone.

[Finis]

Hopefully you have it figured out, however, make sure you have the pin in place for the shifter. You mentioned vaque shifting.

[Kowpie]

I would like to report back on this issue so that others can learn from my experience. First, I want to thank all who read the post and added their comments. It is our collective knowledge that keeps these beauties on the street and trail. The transmission is back in the truck and happily shifting through all gears as it should.

I had two issues that were the cause of my problems.
#1 As stated before in the post, the replacement pilot bushing was crushed by a step at the bottom of the crankshaft bore. I do not know if this step is supposed to be there or if the bore was not completely machined at the factory? I know now that when a pilot bushing is fully seated flush with the end of the crankshaft (not bottomed out in the bore), the end was crushed on the O.D. just enough to reduce the I.D. of the bushing so that there was no clearance. This in turn caused the input shaft to not release when the clutch was depressed. A replacement bushing was ordered from Novak. This bushing matched the prior bushing in every dimension. After carefully driving the new bushing flush, I inserted the input shaft from my transmission, since it was dismantled, and verified that as before, the bushing I.D. was compromised. As Herk suggested, I purchased a lightly used reamer from Industry Recycles for $22.00 +shipping. A few strokes with the acquired reamer provided the proper clearance.

20221219_075022.jpg

#2 The three shift plates (#5 in the diagram below) supplied with the master rebuild kit that are part of the third/fourth synchronizer assembly were not the correct size for my application. This is something that I should have noticed while assembling and called Novak for verification. The plates supplied were slightly too narrow. The effect of this was to allow the synchronizer (or blocking) rings to rotate just enough to block the needed slide of the third/fourth clutch sleeve for engagement with either the third or fourth gears. This is why I could not shift gears even when matching road speed to engine speed. Since I was in the transmission for the second time and my confidence in correct sizing of aftermarket parts has taken a hit, I ordered the entire third/forth synchronizer assembly (#10 in the diagram below) from Novak for $144.00 +shipping

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T18expl.jpg

It seems that I keep learning valuable lessons...
Like Tim stated specifically above, never assume that just because the parts are in your rebuild kit, or that crank pilot bushing bores are all the same, that they are correct. Measure and double check everything. Below you can see the size difference with the shift plates in the grooves of the third/fourth clutch hub.
Thanks again and Merry Christmas everyone!

[Stuka]

Wow, so two separate issues. Great job and finding them and fixing them. And thanks to all that gave some great input to help him figure it out.

[Yeller]

I'll second the Wow! Thanks for the perseverance to see it through and the update.

[tgreese]

... Don't know specifically, but I would suspect you have the synchro hubs assembled wrong somehow. The blocking rings are always blocking when the main shaft is turning.

Not saying told you so, but I was pretty close.

May I take this opportunity to offer some modestly-wisdom-resembling advice? With manual transmissions, I hesitate to replace anything more than I have to. It seems the main things that wear out in these transmissions are the main bearings (especially the front main bearing), the blocking rings, and the thrust washers. There are specific issues for specific transmissions; in the T-18, you should replace the reverse gate spring in the shift top. I expect you'll find references to those specific problem areas if you search. Otherwise, I'd say do as little as possible.