� GEARSSeptember2007

of How Ford and Chevrolet Put the Lapelletier Geartrain to Work

The Lapelletier geartrain is head-ed your way. The Lapelletier (pronounced: La-pelt-e-ay)

geartrain has been around for sometime now; it was first used by ZF in 2001. While you may have yet to experience this type of geartrain, you can bet it won’t be long before one makes its way onto your bench.

The Lapelletier geartrain, as used in these transmissions, consists of:

• A front planet with the sun gear fixed to the front pump.

• A planetary gear set fixed to an input drum.

• A ring gear attached to the input shaft.

This assembly is used to drive a Ravigneaux gearset in the back of the transmission. What Mr. Lapelletier figured out was that if the planetary gearset in the back of the transmission is turned at one speed and the sun gear is turned at another speed — usually slower — the combination creates an overdrive ratio. This overdriven ratio is slightly lower than the one created by holding the sun gear and driving the planet.

The important thing to understand is that the combination of the single planet being driven faster than the sun gears, which are being driven in reduc-tion, is what creates the different ratios.

It may take a while to get the hang of this new concept and it will be much easier with the parts on the bench in front of you so you can get a feel for how the reduction and overdrive takes place. For a complete explanation on how the Lepelletier geartrain works, check out Dennis Madden’s article in the November/December 2006 issue of GEARS Magazine.

In this edition of Fun with Transmissions, we’re going to compare the major similarities and differences between the Chevy 6L80 and Ford 6R60 geartrains. There are many oth-ers that use this geartrain, but for now, these two models will probably be the

by Bill Brayton

FUN WITH TRANSMISSIONS

Figure 1A Figure 1B

6R60 6L80

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GEARS September 2007 �

most common. Primarily, we’ll examine the differences in how these carmakers drive the sun gears at a different rate than the planetary gearset.

One of the bigger differences between the two manufacturers is the terminologies they use. GM seems to have the best approach by giving the components the names of the ranges they are used in. Ford uses the same names it’s always used through the years: forward clutch, direct clutch, intermediate clutch, etc.

Starting from the front of the trans-missions, both units have a sun gear that’s splined to the pump (figure 1). And they both have the input planet splined to the forward, or input, drum (figure 2).

The GM name for this drum is actually the 1-2-3-4 and 3-5- Reverse drum, which is cool because that’s when it’s working. But to save space for this article, we’re going to call it the input drum, as the only gear it isn’t applied in is 4th. The major difference in these drums is the GM drum has the 3-5 clutch built into it (figure 3). This clutch drives the large sun gear in 3rd, 5th and reverse. The 1-2-3-4 clutch drives the small sun gear in all the other ranges.

Here’s where the two transmissions really split in design:

The Ford forward/input drum uses the forward clutch to drive the small sun gear for 1st through 4th gears, through the sun gear hub and shaft (figure 4). Next, the direct clutch hub is splined to the forward drum. Ford applies the direct drum, which locks the large sun gear to the forward/input drum for reverse, 3rd and 5th gears (figure 5).

How Things Stack UpWhen it comes to the front planet

assembly, it’s interesting to see the dif-ferent ways the two automakers design the same part. The Ford planet has a snap ring arrangement to secure the planet and sun gear to the forward drum. The 6L80E uses a much simpler spline arrangement to hold the gear to the input drum (figure 6).

So far, we haven’t heard of any failures with either of these planets. At the time of this writing, the Ford front planet lists for $400 from the dealer; used planets are unheard of yet — but

Figure 2

Figure 3

Figure 4

6R60 6L80

3-5 Clutch

� GEARSSeptember2007

stay tuned. The input shaft/overdrive drums

have some differences in construc-tion, but both function identically. The clutches in this drum are splined to the intermediate shaft. This shaft drives the rear planet at the same speed as the tur-bine shaft when the clutches are applied (figure 7).

The back halves of these two units are again very similar, with just a cou-ple of differences.

The 6L80E has a much larger cen-ter support than its Ford counterpart. The back half of the 6L80E houses the low/reverse clutch pack, along with the low one-way sprag assembly. The low sprag is splined to the planet (figures 8 and 9).

Figure 5 Figure 6A

Figure 7

A Side-by-Side Comparison

Figure 6B

Figure 8 Figure 9

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� GEARSSeptember2007

The 6R60 uses a different approach to the low/reverse clutch pack. Unlike the 6L80E, the 6R60 has no low sprag. The steel plates in the low/reverse clutch pack are splined to the case, and the low/reverse clutches, which are splined directly to the planetary gear-set, are applied whenever the transmis-sion is in the first or reverse ranges. This eliminates the need for the low sprag, and also means the transmission will provide engine braking whenever the transmission is in first gear (figures 10a and 10b).

The only aspect of the planetary gearsets shared between these two transmissions is they both have a small and a large sun gear (figure 11). On the 6L80 planet, the sun gears are captured by a pressed-in roller bearing that rides on the center support. The 6R60 planet is splined to the low/reverse clutches. What this means is, for the first time in a Ford transmission, the low/reverse clutch is now a shifting clutch; that is, the clutch is applied and released when

the transmissions shifts into or out of first gear.

The Lapelletier geartrain is here to stay. GM is using it in many of its late model, rear wheel drive applica-tions. The 6L45, 6L50, 6L90 are all using this geartrain. Ford is planning on releasing several variations of the 6R60. The 6R75 and the 6R80 will take the place of the 4R70W and the 4R75W.

While it may be a while before these transmissions hit your bench, it’s always good to be prepared for when they do arrive. As always, knowledge is power, and being prepared will not only keep you and your technicians ahead of the game, you will be better prepared to have Fun with Transmissions.

Figure 11

A Side-by-Side Comparison

Figure 10A

Figure 10B

6R60 6L80

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