5 speed transmission rebuild update (5th gear fell off)

[Steve St.Laurent]

For those that aren't aware I lost my 5th gear about a week and a half ago on my '98. 5 24v. At ~60,000 miles I had the mopar split 5th gear nut fix installed (as a preventative measure - didn't have any problems, and the gear was tight) when I had a new clutch installed and at 100,050 5th gear backed off the transmission. I lost my 5th gear driving unloaded at 60 mph cruising along - just after a 2,000 mile trip towing my 8,500 lb 35'TT to and from Maryland plus two days of drag racing!



I took the truck apart, down to the 5th gear with the help of Lsfarm (AWESOME shop Greg - thanks for the use of it and your help, not to mention the loan of your minivan - as painful as it is to be seen in it and live without my baby ) and was hoping to just put 5th gear back on. What we found was that the smooth part of the mainshaft was hammered badly and that the gear could easily slide on and off the mainshaft (should be a press fit). Not wanting to do a temporary fix I decided I'd either have to rebuild the trans or replace it. I had one possibility of getting a trans with ~1,500 miles on it and researched that - it had already been parted out. I also considered having the trans rebuilt by someone else (money is very tight here right now) or doing it myself. After researching all the options available and reading the service manual many times over I decided to rebuild it myself. Time will tell if this was an intelligent decision or not ! My truck was still at Lsfarm's house and he was out of town so Doc Tinker met me there and helped me pull the transmission (about an hour since everything else was already off - thanks Doc).



Today I tore the transmission down to pieces and found that it looks brand new on the inside with the exception of the 5th-reverse syncro. I'll be examining the bearings with a magnifying glass over the weekend to be sure. The magnet inside the case had a build up on it but it was EXTREMELY fine particles of metal that were so fine that they felt like grease (normal wear IMO) and not that much of it (especially consider 100,000 miles of abuse).



I had planned on rebuilding the transmission completely - but after seeing the insides decided otherwise. I'll be ordering the new fully supported mainshaft and new 5th gear on monday along with the 5th gear/reverse syncro, and new seals. Assuming I don't find anything over the weekend with the magnifying glass on the bearings I'll put them back in - they look brand new to the naked eye. Things may change before I get it all back together (or maybe soon thereafter) but thus far I don't see anything in this rebuild that any halfway competent shadetree mechanic couldn't handle him/herself. I'll be writing an article on the whole saga with pics for a future mag.

 

[jsimpson]

Can you replace the fifth gear synchro with just the tailshaft out?

 

[MikeBeggy]

Steve, I did the same thing with mine and upon reassembly found the mainshaft thrust setting was not in spec. I had to wait another 3 days for 5$ worth of bearing shims. I think that normal mfg tolerances for the new shaft reguire some changes to thrust washers to properly set the end play.

 

[Steve St.Laurent]

jsimpson - no, you have to remove the mainshaft from the case and take the gears off the shaft in order to get to the syncros. You wouldn't want to replace just that one without looking at them all anyway IMO. I expected to see the 3rd gear sycnro looking bad since that is one of the problem spots in the transmission I've heard. Also, I have ground 3rd gear twice when drag racing (trying to shift too fast). But it looked perfect.



Mike - thanks for the advice. I had planned on checking the mainshaft end play upon reassembly. Was it $5 for a selection of shim's or was that just for the specific shim you needed? If it's for a selection of shim's I'll just order those now.



-Steve

 

[SOOT]

Good to hear it was only minor damage, and it is an easy rebuild.



Are there any special tools needed to do the rebuild?

 

[Scot]

I would replace the brass when I tore it down if I were you. Back during my mis-spent youth, I rebuilt a T-86 in a Jeep and did not know that you MUST put the synchro back on the gear it came off, even though they are the same. Evidently they wear to fit. I did not find twice to be twice as much fun.

 

[MikeBeggy]

Steve, they sell an assortment pack with 8 or 10 shims. . I was able to mix and match to get the correct endplay.

 

[Steve St.Laurent]

Nothing that I've seen MMclain. There are bearing races that need to be driven out but there are slots in there to drive them out with normal tools. Of course then there are races that need to be driven back in by race drivers (I call those normal tools - can be rented). Worst case you could tear it down by hand and take the few pieces you needed removed/reinstalled to a local machine shop for that if you need to do a complete rebuild. The individual components can be removed from the trans yourself though and then the hard parts taken to a machine shop. You do need a dial indicator with a magnetic base to set the end play on the mainshaft and countershaft (if you remove the countershaft - I haven't as it didn't seem necessary after looking at the rest of the trans). Those tools could be rented as well. Honestly there's nothing in the trans after tearing it down that IMO any shadetree mechanic couldn't handle themselves as long as they were meticilulous with tear down and layed out the parts carefully for the reassembly. I layed out the parts on my bar with the face down part of each piece facing towards the rear of the transmission. Took pictures of the transmission as I took it apart, and of the parts and pieces laid out on the bar in case of a catastrophy. The only part I don't have off yet is the first gear on the mainshaft - when they say you need a HEAVY DUTY snap ring plier they aren't kidding - that sucker is MAJOR heavy duty - again this tool can be rented which I will be doing before my parts get here.



FYI - All of this info is based on my current data which is before I try to put my trans back together. I will update this info as I get the trans back together and actually test it on the strip as well as daily driving and towing. Keeping my fingers crossed!!



-Steve

 

[SOOT]

Thats good to know.



When I get the time, a place to do it and a second vehicle I might tear mine down.



I have torn down a 10, 13, 15 & 18 speed Eaton Fuller & Meritor Rockwell. Talk about HEAVY man those gears are really heavy. The main shaft with the gears on it weighed like 60LBS:--)