Ford  Top Loader Three Speed Transmission

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Potential Problems with Transmission Popping Out of Gear

This is practically the number one complaint on early Ford (1939 and newer) three speed transmissions. The most common symptom is that the trans is popping out of 2nd gear under deceleration. This action generally occurs while in second gear and the driver lets off the gas (reducing power to the driveline) and will happen most frequently as the vehicle is going down a hill in second gear.

Because the 1932 and newer transmissions had the helical cut gear teeth for second gear, there is an axial thrust load on the gearset. In other words, the gears tend to push themselves toward the front or the rear of the gearbox, depending on the driving conditions. What happens is that the connection between the second gear (7102 in the drawings) and the synchronizer sleeve (7106 in the drawings) moves apart under deceleration. The splines inside the sleeve will disengage from the synchro teeth on the gear. There is a small amount of spline-to-tooth engagement (about 1/8" from front to rear) so a relatively small amount of slack in the transmission parts will allow that disengagement movement.

There are multiple reasons for this slack and the rebuilder must evaluate each possibility for any contribution to the problem. Let's look at each point and how it must be addressed. These transmissions are typically 60 to 70 years old with many miles on them. They may have been poorly maintained over their lifespan. They may have been abused by various drivers over the years. They may have had inadequate or improper rebuilds during their life, so finding the root cause may involve more than one single issue.

The 1932 to 1938 type transmissions used an early version of a synchronizer assembly. Some details relating to the endplay of second gear will be different from the 1939 and newer type.

• Worn Second Gear: The 7102 second gear (located on the mainshaft) has 30 small synchronizer engagement teeth. These teeth will have parallel sides of about 1/8" apart, and have a pointed tip that faces the synchronizer sleeve. As the gear wears, there will be a loss of tooth width and the pointed end will become rounded off. This leaves less tooth to grasp and hold into place. Also, the internal bronze bushing used on most of these gears will eventually wear to the point that the gear can rock slightly on the mainshaft, tipping some of the synchro teeth even more out of alignment. This bushing was manufactured into the steel gear and was never sold as a service part. If the bushing or the synchro teeth are well worn, the gear must be replaced. Some variations of these gears were made with an exact ground and finished inside bore, and did not come with a soft bushing insert.

• Worn Synchronizer Sleeve: The 7106 sleeve has 30 internal splines that engage the small synchro teeth on second gear (and also on the main drive gear when the trans is shifted into 3rd gear). These splines may also become worn where they grab the engagement teeth on second gear. A fresh 7106 sleeve with a better fit of the splines would be called for.

• Excessive Endplay in the Gearset: Mainly, this involves movement of second gear on the 7061 mainshaft, but also includes movement of the mainshaft in the gearbox case. When second gear and the synchronizer assembly are installed on the mainshaft, their movement is limited by the shoulder at the front of the spiral splines on the mainshaft, and the lock ring (7059) placed in its groove just in front of the synchro hub. This movement is supposed to be limited to 0.004 to 0.008" and is checked with a feeler gauge after the two components (and any required spacer washers) are fitted in place. It is best to keep this clearance (or endplay) to the minimum 0.004" as much as possible. Various spacing washers are available to limit this endplay.
  

• The transmission input shaft (7017 main drive gear) and output shaft (7061 mainshaft) are controlled to their exact locations by their ball bearing, the snap ring on each bearing, and the front & rear bearing retainers (7050 and 7085). When the mainshaft (which carries second gear) is allowed to drift toward the rear of the gearbox, the 2nd/high shifter fork is going to hold the synchro sleeve (7106) in its normal position.....and the drifting action will carry second gear and the mating synchro teeth further away from each other. There are two details to watch in controlling this problem. First is the correct snap ring (7070) on the rear ball bearing. This retaining ring is supposed to be 0.075 to 0.077" thick. A used ring should never be reinstalled on a bearing as the ring will be worn in its inner face (where it fits into the groove of the bearing). Many aftermarket suppliers of snap rings do not have the correct thickness for this ring. Be sure to use a new ring of the correct thickness here. Also, the front (7051) and rear (7086) retainer gaskets should not be excessively thick or the gasket will hold the bearing retainer away from the case, allowing the ball bearing to travel toward the rear. The correct gasket thickness should be approximately 0.014 to 0.016" thick. A simple test for shaft endplay is to push-pull the shaft with your hand.....after you have installed the shaft with its bearing, snap ring, and bearing retainer in place. On closed drive transmissions, you will have to install the universal joint on to the mainshaft. You have to grab the front half of the U-Joint to push-pull the shaft assembly. Any visible movement front-to-rear, which you will be able to feel and perhaps see, will indicate the possibility of excessive endplay. Recheck the assembly and fit of everything to determine the problem.
  

• The 1932 and newer three speed transmissions generally had an oil baffle (7080) located on the back end of the mainshaft (7061) just ahead of the rear ball bearing. It is important that the correct baffle is in place as it also positions the mainshaft on its final assembly position.

• Worn Shifter Fork: The 2nd/high shift fork (7230) can be badly worn at the fork tips. This is usually evident by a curved wear pattern at the point where each tip fits into the fork groove of the synchronizer sleeve (7106). The fork can also be worn in the upper slot where the shifter lever makes contact with the fork for front-to-rear shifting action. In either case, if a new or good used fork is not available, you will have to weld up the worn areas to restore them to the original dimensions, and carefully grind or file the welding to make as smooth a fit as the original.

• Worn Shifter Lever: In the case of the toploader three speed transmission, the shifting lever (7210) has a small nub about 2" up from the bottom tip, which is the actuating portion for the 2nd gear shifting fork. As with the fork, a welded repair will work if a new or good used lever is not available. The nub is 0.501" in diameter. The normal wear will occur at the 3 o'clock and the 9 o'clock positions on this nub.
  
  In the case of a side loader transmission, check the adjustment of the two shifter rods as one or both might not be placing the transmission fully into a gear position. Set the shifter lever (at the steering column) in neutral and secure it there. Remove the shifter rods at the ends with the adjustable clevis. Place the gearbox shift levers into their respective neutral detent positions. Re-position each shift rod onto its own shift lever..........adjust the threaded clevis to raise or lower the rod until it aligns and fits into its lever without having to push or pull it into place. Tighten the clevis lock nut and repeat the same adjustment on the other shift rod. Replace any worn bushings in the shifter rods if needed.

• Other Things to Check: There can be other factors contributing to the popping out problem. In no particular order, consider these potential issues:

• Badly worn (or even missing) pilot bearing, allowing the input shaft & gear to wander out of alignment

• Gearbox case not bolted tightly to the engine bell housing, or something keeping the gearbox out of alignment to the engine.

• Broken caged roller bearing (7118) in the back pocket of the 7017 main drive gear, allowing the 7061 mainshaft to drop out of alignment.

• Incorrect rear bearing retainer. Some early truck retainers do not come with the retaining ring cast into the retainer, and have been mistakenly used in place of the correct B-7085  retainer and B-5099 plate that is supposed to be used on the 1932-36 three speed rear supports.