3.5L / 3.7L + 6L80e

[CaseyS]

OK, the ideas have been tossed around enough and its time to make a serious technical feasibility study into the possibility of running a 6 speed transmission on the 5 cylinder platform.

Full disclaimer, I have no dog in this hunt as I no longer have this engine, but looking at the technical issues in getting it to run standalone with a diesel, some of those issues will translate here so its worth carrying forward a parallel thread.

This project will not be for the faint of heart and will carry a decent price tag. If this is something that may interest you, read on. The project will need to tackle the following technical areas each with its own set of challenges, and each must be solved independently.

1) adapter plate
2) torque converter pattern and offset matching
3) output shaft conversion
4) transfer case adapter
5) electronics integration

Items 3 an 4 above have been addressed in other builds and solutions are available although #4 may need modification based on differences governed by #1.

 

[CaseyS]

Adapter plate:

So we start with the obvious. Here is a picture of the factory transmission bellhousing

and here is a stock photo of the typical front end of a 6L80e

The very first thing that should be obvious is that the bellhousing patterns are different. Not only that but the starters are on opposite sides. The 6 uses the "standard" chevy bellhousing pattern that has been around for generations and of course the H3 uses a one off pattern that was only used for this engine series.

The 4L60e has removable bellhousings and can easily be converted to a standard chevy bellhousing by removing 8 bolts and swapping the bell. Unfortunately, the bell on a 6L80e has internal parts of the transmission integrated with it, so swapping the bell is not an option. An adapter plate will be needed to mate the two. For those not familiar with the concept, an adapter plate has the engine block pattern locating bolts drilled into one side so the plate can be bolted to the block. Within the adapter plate, mounting holes for the conversion bellhosing are drilled allowing mounting of the transmission to the adapter plate as if it were being bolted directly to the engine block.

Here is an example of an adapter plate made from 3/8" steel for this exact application - atlas inline engine to chevy standard bellhousing.

This is viewed as if you were looking from the transmission towards the engine. Notice the countersunk holes are in the location of the stock bellhousing. The starter is recessed at the 2 o'clock position which is where the starter resides on the atlas block. A special note here, if you notice right to left of the yellow arrow is a hole for a locating dowel and there is one complementary one on the other side. The dowel locations on both the atlas bell and a standard chevy bell are in the same location. This is very significant because by simply locating the two dowel pin holes on a plate of material, the holes for both bellhousings can be transferred to the plate and located and drilled without ever knowing the exact dimensions to the center of the crank or relation to each other.

This is what this plate looks like bolted to an engine with a manual transmission flywheel.

Next up: Why this 3/8" plate won't work and other dimensions that will come into play.

 

[Happy Hummer]

Always like these threads.

 

[08H3]

What's the end goal for this? Frankly on the surface the benefit vs the amount of work and costs involved don't seem to add up.

 

[CaseyS]

There are several parts to the bolt up equation and dimensions that must line up. Part two involves the flywheel height in relation to the block/bell face and the matching measurement to this, the torque converter pad height to bell face. When the transmission is bolted up there should be about 1/8" gap between the torque converter pads and the flywheel. The torque converter is then pulled forward slightly and bolted up to the flywheel. This allows a small axial gap so the notch on the torque converter hub will engage the transmission pump ears without being bottomed out.

Above is a picture of the 3.5 flywheel. Note that the flywheel has a distinct dish to it. The ring gear is set back and the flywheel face is forward (to the rear of the vehicle). If we use the block face as a 0.0" reference, the face of the flywheel is +1.47" out from the rear of the vehicle. Back to the image of the stock transmission, notice how deep the converter sits in the housing. The converter pad height in relation to the bell face is 1.47" + about 1/8".

However, on the 6L80e, the converter sits much closer to the bell face. Stock converter pad height is 1.0" from the bell face.

So, if we were to make the adapter 5/8" thick. Once the transmission were bolted to the adapter, the 6L80e pad height in relation to the block face would be 1.625" The flywheel would still be 1.47" leaving a 0.28" gap to pull the converter forward. This is why the 3/8" thick adapter pictured above won't work, because there would still be interference between the torque converter and the flywheel. We have to not only match the 6L80e bolt pattern, but also space it back far enough that will allow the torque converter to bolt up. An adapter of 5/8" steel plate will fit the bill just nicely. Next up : Not so fast! What about the torque converter pilot.

 

[USMC_TOP]

Great info but I know I wouldn’t put that much money behind these 5 bangers. A 5.3 now that would be real nice!


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[4speedfunk]

I’m lost in “Whyville”.


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[Schwarttzy]

 

[Kick'n Dust]

This is interesting. Just for the sake of conversation keep up the thread

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