How To Rebuild A Cub Transmission

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How To Rebuild A Cub Transmission

Postby Bill E Bob » Sat Nov 28, 2009 7:03 pm

My 55 Cub Lo-Boy provided the donor transmission for this article.

Transmission Rebuild Start:

What you see here includes the Countershaft, the Countershaft Front Bearing and Bearing Retainer (with Shims), the Countershaft Gears (1st, 2nd, 3rd and Reverse), the 1st/Reverse and 2nd/3rd Sliding Gears, the Differential unit with Inner Bearing Cones installed, the Transmission Case, the Differential Bearing Retainers with Shims. PTO unit and Gear Shifter unit.

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Rear Mainshaft and Countershaft Bearings Installed:

These were new from TM Tractor. The Spline (main) Shaft Bearing is at the top, the Countershaft Bearing is at the bottom. They are both pressed in from the rear. I used a cheap Harbor Freight bearing and seal installer tool (one of my best buys). I DID note the replacement mainshaft bearing did NOT have an oil hole in the outer race, and any attempts to drill a hole were futile so I decided the aftermarket folks deemed the oil hole unnecessary.

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U.S. General Bearing Race and Seal Driver Set

Checking Differential Bearing Preload:

Definition: Bearing Preload is setting the rigidity of the Bearings by using shims and fastener torques. Rigidity is the amount of flex/spacing between the bearing cage and the bearing race. "Preloaded" bearings are common in automotive and other Differentials (read Cub). In our instance, the amount of preload is set by the following process.

This involves nothing more than a 2' length of nylon cord and a cheap WalMart fish scale. I first installed the differential into the trans case and installed the bearing retainers with shims insuring the correct retainer went to the correct side of the differential. Do this without installing the "O" rings in the differential bearing retainers. Torque the retainers to 45 ft lbs, wrap the cord around the differential, attach the scale and give a steady pull, as the diff turns and the cord unwinds, the scale should read between 1-8 lbs. If not, add or remove shims equally from BOTH retainers to maintain proper side to side diff placement. In my case, since I reused my bearings, there was enough wear to remove a shim from each bearing retainer.

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Countershaft wth Gears and Spacers installed:

Remove the Differential Bearing Retainers and the Differential from the Transmission Case. First install the Reverse Idler Gear. It is the one in the picture in the SIDE of the trans case with its own shaft. The cap screw at the end of the shaft holds it in place. Once removed, you can slip the shaft out toward the front of the transmission and remove the reverse idler. Installation is the reverse process. Make sure the bevel is facing the FRONT of the transmission. Next is the installation of the countershaft with all the gears and spacers. First on, is a spacer, next is reverse gear (Will fit either way), next another spacer, then 1st gear (bevel facing to the REAR of the transmission) then another spacer, then 2nd gear (bevel facing to the FRONT of the transmission) another spacer, then 3rd gear (bevel facing to the REAR of the transmission) then the final spacer, then the front countershaft bearing retainer (with bearing and shims) then the countershaft nut (finger tight).

NOTE: As you are slowly inserting the countershaft from the rear of the transmission, you will be adding the spacers and gears as you go.

GSS-1411 Service Manual Section 6 - Transmission And Differential - Page 2 wrote:Countershaft Spacer Lengths: (from rear to front of transmission)

  • Between rear bearing and reverse gear (beveled edge to bearing) - 0.690 to 0.694 inches
  • Between reverse and first gear - 0.686 to 0.690 inches
  • Between first and second gear - 0.310 to 0.314 inches
  • Between second and third gear - 1.310 to 1.314 inches
  • Between third gear and front bearing (beveled edge to bearing) - 0.848 to 0.852 inches.


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At this point I played with the differential retainer spacers and the countershaft spacers till I got to: TFAR (That Feels About Right) I ended up removing 2 shims from the Left Hand differential bearing retainer and one from the right side. I also removed 1 shim from the front of the countershaft. The manual recommends use of prussian blue and backlash of the diff/countershaft pinion gears. Use of prussian blue allows you to see the mesh pattern of the countershaft pinion and differential gears. You may refer to the GSS-1411 Service Manual for more detail. Backlash is the spacing between the gear teeth as they mesh or "play" in the differential gears/countershaft pinion. GSS-1411 Service Manual mentions 0.003-0.005 which (in my estimation) isn't much. GSS-1411 Service Manual didn't go into detail on how to measure backlash (setting the gear mesh pattern may also take care of the backlash) so I used the TFAR method mentioned above. Removing or adding shims to the differential bearing retainers adjusts preload and can be used to adjust side to side positioning of the differential itself. REMEMBER, once Preload is set, the TOTAL number of shims should NOT change, so adjusting side to side positioning will involve removing a shim from one side and placing it on the other side. More shims on the right side will move the differential to the right and more shims on the left side will move the differential to the left. Removing or adding shims to the countershaft bearing retainer aids in adjustment of backlash. Adding a shim will move the countershaft forward or AWAY from the differential gear, removing a shim will move the countershaft backward or TOWARD the differential gear. Use of all new bearings and races in the rebuild process MAY preclude any adjustments, however, recommended Preload etc. should still be verified.
I then installed the Differential Seals and "O" rings: This involved removing the Differential Bearing Retainers, installing the Seals and "0" rings reinstalling the Retainers and Shims and torquing the capscrews to 45 ft lbs. REMEMBER, keep the shims with each side when installing. By now, you will have realized the Retainers will fit only one way in the Transmission Case.

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Mainshaft and Shifter Forks are next:

First, I left the Shifter Fork Shafts in the Transmission Case. They will both slide to the rear of the Case and remain out of the way during the rebuild. If you want, you can remove the plugs from the front of the transmission case and completely remove the Shifter Rods (if you wish). I installed the Front Mainshaft (spline shaft) Bearing with the Bearing Shield to the rear of the Transmission Case and the open side of the Bearing to the front of the Transmission Case.

Next, the Retainer/Seal unit is slid onto the mainshaft (flat side to the front or protruding side toward the mainshaft bearing. As the Mainshaft is slowly slid into the Transmission, you will want to first slide the shaft through the 2nd/3rd Sliding Gear, (gear orientation may be noted in the picture) then the 1st/reverse sliding gear. (apologies for NOT showing the gear clearly in the picture, but the TOOTHED part of the gear is toward the REAR of the transmission).

Next is installation of the Shifter Forks. 1. install the Spring and poppet Ball into the proper spot, slide the Fork onto the Shaft and slide the Shaft forward while holding down the ball and spring so the Shaft will slide over it (I used a small pin punch to hold the poppet ball in place till the shifter shaft was slid into place. REMEMBER, make sure the fork is engaged in the proper Sliding Mainshaft Gear before installing. Left Side Fork for 2nd/3rd Slider, Right Side Fork for 1st/Reverse Slider. Tighten down the Shifter Fork lock bolts.

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Next, shift the Transmission into 2 Gears (Right Side Fork to the rear and Left Side Fork to the front. This will lock the Countershaft so you can torque the Countershaft Nut to the required 90 ft lbs. Install the Cotter Key and install the Cover and Gasket over the front of the Countershaft. Torque the bolts for the Countershaft Cover and Mainshaft Bearing Retainer. (Mainshaft Bearing Retainer 20 ft lbs, Countershaft Cover to 45 ft lbs (I stopped at 40).

NOTE the Mainshaft Bearing Retainer orientation in picture.

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I then installed the PTO Assembly and the Transmission Shifte. I first installed a new Spring, Pin and Spring Retainers on the Transmission Shifter. While I had the Shifter out, I built up the ball end of the Shifter with weld and ground it down to fit. I then installed the Shifter into the Shifter Tower. Before installing the Shifter unit, I made sure the Transmission was in Neutral. The PTO was next. The bearing was good, so I just replaced the seal. (Oops, almost forgot--I did install a new PTO Shaft Bushing in the Mainshaft BEFORE installing it into the Transmission. Next, I installed the PTO Shifter Shaft into the transmission Case. Since the Felt Seal for the shaft is NLA, I used 2 "0" rings for the seal. (suggestion from one of the forum members). I then installed the PTO unit following the "How To" for that procedure. I then bolted down the Gear Shift unit and the Tab for the PTO Shifter and I was essentially finished. (I DID use Gasket Sealer on ALL Gaskets to further insure no leaks BTDT :oops: )

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And there you have it!!


NOTE: ALL references to LEFT/RIGHT orientation are from the operators seat facing forward.

Many thanks to Ralph at Ralph's Cubs who provided a Reverse Idler, Reverse Gear, Shifter Forks and the Mainshaft. Thanks also to Tom & Lynn at TM Tractor who provided all the needed Gaskets, Seals and Bearings.

I was the photographer, so any and all bad shots are of my own doing :oops:

Please note: There are several GOOD how-to's for various aspects of the above: Rudi's Tranny Repair 101, George Willer's Cub Shifter Repair and Improvement and the PTO installation How-To's.
Last edited by Bill E Bob on Tue Dec 01, 2009 9:48 am, edited 6 times in total.
Bill E Bob
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