The are about a million GM 10L80 ten speeds out on the road today, and they are starting to come out of warranty. A very common issue with these units is a pump noise complaint. In this edition of Fun With Transmissions we are going to check out what causes this issue and how to take care of the noise using Ford parts.
Once it is determined that the noise is coming from the transmission, the pan can be dropped, and the pump can be removed to inspect the pump drive gear and the transfer gear (Figure 1). The gear may be chipped or wobble on the bearing. Once inspected, the transmission can be removed so we can remove the front support to inspect the gears further.
Now, with the unit on the bench and the front support on the bench. We can remove the front cover snap ring and the 7mm bolt to remove the front cover. With the cover out of the way, we can remove the pump drive gear and the thrust washer driven by the torque converter. Since the gears are being replaced, we can toss them and the washer.
Here is the weird part about removing the transfer gear and bearing. While researching for this article I could not find one bolt in the shop that would fit this gear! I looked everywhere! So I took the front support, with the transfer gear attached down to the bolt store. Turns out the threads in the gear are a 7mm X 1.50 thread pitch. Even the bolt store did not have this in stock, so they had to order it. Most, if not all of the stuff we work on is even numbered: 4mm, 6mm, 8mm, etc.
Use the bolts to remove the gear by screwing the bolts through the gear. This will press the bearing off the support (Figure 2).
In another situation, the gear fell right off the support (Figure 3). In Figure 4, we fit a .004” thick feeler gauge between the bearing and the gear!
THE CAUSE
The whole 10-speed, 60, 80, 90, and 140 lines from both Ford and GM are a collaboration between the two automakers. The 10R80 and the 10R60 use many of the same parts and can be changed between the two units. This includes the P1, P2, and P3 planets, the CDF Drum, and the front support.
The major difference in the front support between the two is the pump gears. GM wanted a quiet set of gears, so they used helical-cut gears. Ford went with straight (or spur) cut gears. The problem with the helical cut gears is the side force the gears put on the bearing. The small roller bearing and gear setup does not handle the side load of the helical cut gears.
Thanks to my friend Bill Anthony at WIT for sending me the mathematical equation to figure out the amount and direction of the sideload.
THE FIX
What we can do to correct this issue when a 10L80 comes in the door with pump noise is to replace the old helical cut gears with Ford’s straight cut gears. The straight-cut gears have zero side load, which makes it much easier for both the bearing and the gear.
Ford’s gears are also cheaper to replace. From your local Ford dealer, the gears are priced as follows: (prices are retail) The driven gear is about 38$, the transfer gear is about 42$, the drive gear is about 6$, and the new transfer gear bearing is about 7$. All of this coming in at less than 95 bucks! What a deal!
If you choose to stay with GM OE parts, the front support, which comes with the drive gear, the transfer gear, and the transfer gear bearing, is anywhere from 450 to 700$, depending on where you call. Purchasing a complete front support from GM is the only way to get new gears. The gears are not sold separately.
CONCLUSION
ATRA has always been about using the right part for the right job. Doing so takes out the guesswork should something go sideways with the job. In using the Ford parts in a GM application, we see using the right parts for the right job because the front supports are identical, the drive gear is driven the same, and both converter hubs are the same, with both manufacturers. The transfer bearing and gear are identical in dimensions; finally, the pump-driven gear is identical in dimensions (Figure 5).
It’s important to know that when you replace the GM gears with the Ford gears, do not use the washer. The GM gears have a step that Ford gears do not. The washer takes up that space from the step. The Ford gears have a step up, and DO NOT use a washer. (Figure 6)
Go ahead and use those straightcut gears in a GM application, and keep having Fun With Transmissions!
