Transmission Overhaul series

[Chuck W.]

I am in the process of replacing a damaged transaxle case, and with the assembly out of the mule, I thought it would be easier to take good photos and do an article on the process. Hope it helps.

PART 1

Here's the transaxle assembly mounted on my engine stand. I will remove the left and right axle housings later.


First step is to remove the output shaft "nose cone". Remove the 4 nuts and washers, and be sure to keep up with the shims. I tie-wire them to the housing. This is also the easiest way to replace the output shaft seal.


Now, use a chisel to bend up the sheet metal lock behind the shaft nut.


And use the 5120-601-2224 wrench to remove the shaft nut.


Now you can remove the bearing retainer from the cover. Be sure to keep up with the shims as before, and look for a thin thrust washer on the shaft behind the bearing, don't loose it. It might be stuck to the back of the bearing, so be sure you find it.


Next, remove the two bearing covers.


and the two bolts and washers from the ends of the two shafts. I reinstall the bolts without the washers for the next step.


I use these two homemade pusher tools to force the two shafts through the bearings. Remove the cover nuts and washers and slowly thighten the pusher tools until the cover starts to move. There are two dowels in the cover and you may need to gently pry the cover round these dowels to get things moving. Go slow and take your time.


Once the shafts are through the bearings, the cover will come off.


The bevel spur gear can be simply pulled from the case.


Now you need to remove the plug, spring and poppet ball from the high-low shifter rail.




With the spring and poppet out of the way, you can remove the entire pinion shaft and shifter fork from the housing. Now you can see why I am replacing this case!


Your case should look like this, without the big hole in the bottom, I hope!


PART 2 will deal with the removal of the main gear shaft, counter shaft and reverse idler gear. Stay tuned.

[Chuck W.]

PART 2

I hope this does not become confusing, please remember that I am using photos from 4-5 different transaxles, so don't be confused if things look a little different from one photo to the next, and a few of the photos are staged with empty cases.

At this point, I went ahead and removed the left and right axle housings. There are shims behind the right axle housing, so keep up with them as before.


Now, cut the safety wire on the 2-3 shift fork lock screw and remove the screw.






The two shift rails have springs and poppet balls just like the high-low range shifter, so remove the two plugs in the case above the shifter rails and remove the two springs and balls. The M274 and M274A1 mules only have one plug, so the 2-3 shift rail poppet ball and spring can only be removed after the shift rails are removed. There is also an interlock slug between the two shift rails, so the 1-R shift fork must be in the neutral position before the 2-3 shift rail can be removed and the fork removed.


At this point, you will be tempted to try to remove the main gear assembly, but it won't quite come clear, and this is the point where gear teeth are easly broken!

Did I mention that the engine will have to be removed? You will need access to the flywheel side of the transaxle case.

Remove the throwout bearing return spring, the throwout bearing and the fork, then remove the 4 nuts and washers around the input shaft retainer.


Carefully seperate the throwout bearing carrier from the bearing retainer and remove it.


There is a snap ring around the shaft that must be removed before the bearing carrier can be removed.


Now you can slide the input shaft foward enough to give you room to remove the mainshaft assembly from the case.

With the main shaft removed from the case, you can drive the cluster gear shaft out from the engine side of the transaxle and then remove the cluster gear and the two thrust washers.




Use the same basic procedure to remove the reverse idler gear shaft, gear and thrust washers.


Now you can remove the other shift fork and rail, and don't forget to remove the interlock slug between the two shift rails. I use a small magnet to remove it through the 1-R poppet ball hole.

The case is empty and ready for a lot of cleaning. In my case, since the housing was cracked, I removed all the usable studs and the case went into the aluminum scrap pile!


Part 3 will show the reassembly, but I've got a lot of cleaning to do first!

[Chuck W.]

PART 2a

I spent some time today working on the new case. The replacement is from an A5, so it was necessary to drill and tap 3/8" x 16 holes for the mounting studs for the rear axle steering bellcrank. There's more info on how to do this in the thread, "Four Wheel Steer Kit Installation". Check the USMC Forest Green paint on the case!


I also did some cleaning and test fitting of parts.


So, now I am waiting for some seals and gaskets and I'll be ready to put this thing back together. As the TM's say, "Reverse above procedure to re-assemble!"

[Chuck W.]

PART 3 ASSEMBLY

While I was waiting for the shift shaft seals, I went ahead and installed the reverse idler gear and the cluster gear. Simple, gear, thrust washer on each end, and the shaft. Just make sure the tangs on the end of the shafts are aligned as shown before you drive the shafts into the case.


As far as the shift shaft seals, I have started installing them as the manual shows, inside seal facing out, outside seal facing in. I usually find them with the two seals facing out, but apparently that is wrong.


Next, install the shift interlock slug into the space between the two shift rails. I use a small magnet.


Now you can install the R-1 shift fork and shaft. Be sure to safety-wire the retaining screw.


Inspect the synchronizer on the main shaft, make sure the three shift plates and two springs are in the proper position.




Don't forget the blocking ring that goes on the input shaft. I stick it on with a little grease. This is the area we will be looking at later in PART 3a


It's nice having the transmission on the bench where I can lay it on it's side to install the mainshaft. In the frame, it really takes two people. Make sure the R-1 shift fork is installed into the groove in the gear collar.


Now you can install the input shaft. You'll have to keep turning it until the blocking ring aligns, but you'll feel it when it goes into place.


Install the bearing carrier with a new gasket, and then install the snap ring on the shaft.


Next, install the "nose cone" with a new gasket. Install the 4 nuts and washers.


Next, you can install the 2-3 shift fork and shift rail. You'll have to be sure the R-1 shift rail is in the neutral position, and the easiest way to do this is to go ahead and install the poppet ball, spring and plug for that rail. Be sure to safety-wire the retaining screw.


Now you can go ahead and install the 2-3 shift rail poppet ball, spring and plug.

[Chuck W.]

PART 3a - Adjusting the main shaft clearance.

This is a procedure that I learned from Bill Watson, and it's very important, don't skip it, or your transmission may lock up with you at some point down the road!

First, I install this cut-down cover gasket.


Then, I install this modified cover. The cover has been cut down so that only the main shaft rear bearing is left. The bearing holder is installed with a gasket, and the inside of the bearing has been honed out so that it is a slip fit onto the shaft. This makes it easy to remove and install during the shimming process. I install the bolt and washer into the end of the shaft and install the cover bolts and tighten everything up as it will be in the finished transmission.


Now I use a mirror and a feeler gauge to check the space between the blocking ring and the input shaft.


The red arrow shows the gap that I am looking at.


If this gap is too big, it's possible for the shift plates in the synchronizer to become wedged into the gap between the blocking ring. When this happens, the shift collar will become hung and there is no way to fix it without going into the transmission. This usually happens when someone tries to "speed-shift" between 1st and 2nd. The clearance is adjusted with shims between the bearing and the gear.


This main shaft needs about .040" of shims to remove the excessive gap. I don't have enough shims, so now I'm waiting for an order from McMaster-Carr.

Stay tuned, next time we will finish this puppy up, we're on the home stretch now!

[Marty, SoCal]

Chuck, If that case is normally worth something besides scrap value, you could have the hole Heliarc welded shut. I've seen alot worse looking holes and cracks perfectly patched, then ground down and shaped so as to be invisable as a patch by a skilled aluminum Welder/Fabricator. I have a good local guy in SoCal that does that type of work, Jim Shirley, at Shirley Design, in Huntington Beach, CA. I've watched him TIG up broken fins on an aluminum motorcycle cylinder, file them back to shape, then a bead blast them, they looked perfect when he was done, all on the bike! He's also repaired broken off ears of aluminum engine case halfs on my buddy's Quad racer. There's probably a good welding shop in your area, too.

Hope this helps!

[Chuck W.]

Thanks, Marty! If this had been an A2 or A5 case, it probable would be worth fixing, but being a plain M274, it's really not worth the trouble.

PART 3B

After installing several combinations of shims, I decided on .040".


The shims go on the end of the mainshaft, behind the bearing.


It's hard to tell, because I forgot to move the shift collar out of the way, but I have a much smaller gap now between the input shaft and the blocking ring. I don't want to close the gap completely, so I left about .030" clearance.


Once everything looks good on the mainshaft, it's time to install the pinion shaft and shift rail into the case.


Followed by the spur gear...


Followed by the large and small thrust washers.




Next, the bevel spur gearshaft is installed into the case...


Next a new gasket and then the cover...


Next, the two bearing carriers, with new gaskets..


and now the two bearings and their retaining bolts and washers.


I've got to tighten everything down and seat the bearings into the retainers and onto the shafts before I do the final install of the retainer bolts with Loc-Tite, then I can install the two covers with new gaskets, but it's starting to look like a mule transaxle!

Next time, we'll check the pinion depth and install the pinion bearings and retainer.

I probably won't be back before Thanksgiving, so Happy Turkey Day, everybody!

[Austringer]

Perfect timing on the article. I"m in the process of rebuilding mine. What are the roller bearing numbers for the transmission. Want to see what it would cost to replace them.

Thanks
Jason

[Chuck W.]

Jason, not sure which bearings you need, but the two on the bevel spur gearshaft and the one on the end of the main shaft are the same, and the number is MRC 2055.

[Austringer]

Do you have a cross over number, I can't find the bearings using rockauto.com or Napa.

Thanks
jason

[Chuck W.]

PART 4 - Finishing things up

For the most part, if you have not changed any major assemblies, you can install the pinion with the same shims that were there. In my case, since I had changed the case, I thought I better check. I borrowed Bill's pinion depth setting tool.


This tool goes into the right side of the transaxle, and the lever rides on the end of the pinion.


Follow the instructions shown in the TM and printed on the tool to use a feeler gauge to determine the correct pinion depth.


I was able to determine that the thickness of the orignal shim pack was correct.


The inner shim pack was installed after giving each shim a light coat of RTV, then the nut and lock were installed onto the shaft.


Followed by the outer shim pack and the seal carrier "nose cone".


I installed the ring gear carrier with the old shims and then the right axle housing with a new gasket and then the left axle housing.



At this point, we are ready to install the transaxle back into the mule and fill it with oil.

I hope this serie has helped.

[Chuck W.]

This should clarify the point I was trying to make about the differences in the shift rail poppet ball access plugs on early and late transaxle cases.