6.5TD/Allison?

[More Power]

I get asked about once a month whether the Allison can be used behind the 6.5. I know it'll bolt right up - with it having the same bellhousing bolt pattern and torque converter bolt pattern. So, making the bolt-on connection is easy.... However, the electronics has always been the problem. To my knowledge, Allison hasn't offered a standalone Transmission Control Module (TCM) and the aftermarket announced they were working on one a few years ago, but have not delivered - yet.

In the most recent issue of Diesel World magazine, Chris Neprasch wrote an article about a company called "Destroked" (www.destroked.com (http://www.destroked.com)) that is offering an Allison 1000 5 or 6-speed automatic transmission conversion package for owners of Ford and Dodge diesel pickups.

Their package includes the wiring harnesses, TCM, TPS, and a special module called an "XFC", which substitutes for the Duramax ECM, and allows the TCM to function normally behind an engine it was not designed for.

Like-new used Allison autos have sold for as low as $1800, which makes it competitive with the cost of a 4L80-E rebuild. Upgrading to an Allison would get you an absolutely bulletproof auto with either 5 or 6 forward gears.

Having experimented with the various parts, I know the Allison transfer case adapter has the same bolt pattern as the NP-241 transfer case used behind the 6.5. I'm not sure about output/input splines. The newer NVG-261/263 transfer cases, which was standard equipment on the 2001+ trucks can be adapted to the 90's trucks (I did it).

Jim

[CareyWeber]

How much more or less power loss (parasitic drag) does the Allison 1000 (GM version) have than the 4L80E?

Does the Allison require transmission tunnel modifications or a body lift?

I have wanted to replace my 4L80E with a six speed auto, but I was thinking about the 6L90E. The good this about the Allison is there are more to choose from.

With the six speed Allison do you two in 6th or 5th? Is 5th a small overdrive like 5th in the 6L90E?

Carey

[More Power]

I haven't tried to install an Allison behind a 6.5, but I did install an Allison behind a Duramax in a 90's body style truck. Only minor tweaking of the transmission tunnel was required. It may not require any tweaking behind the 6.5... I believe it'll work. I talked to a couple of GM Powertrain engineers in 1999 who said they experimented with the Allison behind the 6.5 in the 90's trucks, during the early trial period before the Duramax prototype engines were available.

I haven't seen any documentation about parasitic loss through the transmission. Some feel the 4L80-E has more loss than the TH400, and that the Allison has a little more loss than the 4L80-E. But, I don't know for sure.

The 5-speed Allison has a 0.71 OD fifth gear.

The 6-speed Allison has a 0.71 fifth gear and a 0.61 OD sixth gear.

Jim

[Duramaster]

I know this isn't your goal, but what about grabbing the bellhousing adapter off of an old U-HAUL with a 454 and the Allison AT 545 "4 speed" auto trans??? I don't know what the gear ratios are, but it's still an ALLISON auto trans. The newer AT 545's used one electric controlled solenoid in place of the vacuum modulator of the older AT 545's. Maybe someone here can add to this and/ or correct me? :)

[Kansas_Diesel]

You could also try the 4l80e that TCI converted to a six speed it comes with a control unit and paddle shifters,torque conv, wiring harness and tranny cooler

[Robyn]

The 545 will work but most all the older Allisons did not have a park in them.

The 545 is a NON OD box too but instead a simple 4 speed with 4th being 1:1 ratio.

For whatever its worth, I would do a top flight uprate on your 4L80 with some of the latest goodies from Transgo and be done with it.

You will incur far less $$$$$ outlay and forgo the business of converting all the electronics to talk to each other.

Having the extra OD is really not going to give you that much behind the 6.5 thats usable IMHO :)

The 6.5 could use some intermediate gearing (towing applications) rather than a taller OD

The Allison 5 and 6 speed boxes with more OD work sweet behind the DMax's with the extra power they offer.

IMO your $$ outlay will not be rewarded with enough return to warrant.

Now if this is an I want to because it would be Cool then ;) heck, go for it. :D

Just my 2 cents worth

[DaveBr]

OK. This looks like a good thread to ask this question. My truck has 4:10 gears, 2 wheel drive. I tow a lot of weight and it does the job...but when I'm not towing it would be nice if a person had an optional overdrive besides the original that comes with 4L80E tranny. Is this at all possible or should I be throwing out my fantasy island re-run collection? This 6L90E that is mentioned, is this the code name for an allison tranny? I've never heard of it but it sounds interesting.

[DmaxMaverick]

The 6L90E is not an Allison. It is the GM tranny replacing the 4L85E (which replaced the 4L80E).

For an extra OD, look into aux. trannies, such as GearVenders or US Gear. They work very well, but you'll never recover the cost in fuel economy (or anything else, for that matter).

[Robyn]

My 95 DaHooooley has 4.10 gears and will run 20 MPG Hwy.

The 6L90 is a 6 SPEED longitudinal drive and has the 90 rating for its ability to handle load. 60 series (4L60) 80 series (4L80) 3L80 or TH400

Your gains are never going to pay for it.

The package you have will work far better with some exhaust mods, a chip in the puter and a few other additions.

These items will repay themselves as well as gain performance and power as well as mileage

Robyn

[DaveBr]

OK - just checked out gear venders price and $3000.00 is a little steep. I would like to try 3:73 gears just for the heck of it and see how many RPM the tach drops. Anybody know what the difference would be?

[6.5 Detroit Diesel]

Figure out your rpms at 100 kms, (should be around 2,000), and divide by your gear ratios. Figure out the difference. I did once but can't remember. It isn't that much of a drop though.

[THEFERMANATOR]

http://www.grimmjeeper.com/gears.html

You can go to this site and plug in wha trans, gears and RPM's as well as speed and see the differences each will make. It also has 2 different columns so you can do 4.10 in one and 3.73's in the other and see EXACTLY what will change and how much. Roughly a 200 RPM drop at 65MPH or about 105 KMH.

[JohnC]

About 200 RPM in OD at highway speeds. The member's area of the Web site has a link to an RPM calculator.

Or: New RPM = (old ratio/new ratio) X old RPM

[DaveBr]

Thanks for the info everyone. Much appreciated.

Dave

[cdndiesel]

Food for thought. I just got the latest issue of Diesel World and in it they had a small new products write up on a 6spd version of the 4L80e from TCI . Seems that might be a good alternative to the GM 6L90e($$$$) or converting to an allison. No prices were mentioned so I have no idea if it would be a viable choice or not. good to have more options though.

[DaveBr]

I checked TCI's site and couldn't find the 6sp 4L80E. It sounds good if my tranny ever gives up and I needed a replacement. I could get it past my wife as general maintenance.

[trbankii]

I couldn't find it on TCI's website either, but I did see this article awhile back: http://www.motorator.com/blog/gm/tci-6-speed-automatic-transmission

[JohnC]

Isn't the 6 speed trick just engaging the OD pack in first and second as well as 3rd? (So it's a splitter...)

[THEFERMANATOR]

Isn't the 6 speed trick just engaging the OD pack in first and second as well as 3rd? (So it's a splitter...)

That's how JET used to do it, but they discontinued there kit about 2 years ago.

[trbankii]

I sort of wondered how you "converted" a transmission to add more gears...

From the press release:

The TCI (http://www.tciauto.com/) 6-X Six Speed Automatic Transmission gives you six forward gears (3.08, 2.34, 1.60, 1.30, 1.00, 0.75) for quicker acceleration and increased fuel economy at cruising speeds.

From the 'net, it seems that standard is 2.48, 1.48, 1.00, and 0.75. So, if it was just a splitter, wouldn't the "standard" gears show up as well?

[DaveBr]

I was hoping for a better OD ratio than the stock tranny but in towing applications this looks very interesting.

[JohnC]

I was hoping for a better OD ratio than the stock tranny ...

If you have 6 speeds to choose from, you can go to a longer rear axle and get the same effect.

[DaveBr]

You are right John. Sometimes the obvious eludes me. I wonder what the project 6.5 Jim built would've done in the 10,000 lb. pull off aginst the 99 Ford with this tranny in it.

[More Power]

I checked TCI's site and couldn't find the 6sp 4L80E. It sounds good if my tranny ever gives up and I needed a replacement. I could get it past my wife as general maintenance.


DaveBr;
You are right John. Sometimes the obvious eludes me. I wonder what the project 6.5 Jim built would've done in the 10,000 lb. pull off aginst the 99 Ford with this tranny in it.

GM also produces a 6L90-E, which is an evolution of their very good 4L80-E. GM installed the 6L behind their larger gas engines in the luxury SUV's.

A second OD would be a big help to 6.5 owners who need 4.10 gears to tow, but want better highway fuel economy and lower engine rpms when not towing.

I'm told that an Allison soaks up more power than the 4L80-E, which might not be too big a deal behind a built 6.5.... just like the 4L80-E soaks up more power than the non-OD TH400. The Project 6.5's best 0-60 times came with the TH400, but I wouldn't trade the 4L80-E's OD for a little more power.... ;)

Jim

[moondoggie]

Good Day!

"For an extra OD, look into aux. trannies, such as GearVenders or US Gear. They work very well, but you'll never recover the cost in fuel economy..." Maybe...it depends on what you pay for the Gear Vendors. I bought mine used from a DP member for $500. Even though my total cost ended up being ~ $2000, it did indeed pay for itself. I guess there was at least ONE benefit of the really high fuel prices, eh?

"...or anything else, for that matter)." There's more reasons than fuel economy to make such a change. My 95 pickup, with 4L80-E, 4.10 gears, stock exhaust, & Gear Vendors Aux. OD (0.78 ratio) is VERY quiet. If Scotty beamed you into my truck at highway speed, there's no way you'd know you're in a diesel. (I got tired of hearing my vehicle somewhere in my mid-twenties).

Do you want to know if such a modification will pay for itself or not? Why guess? Go to the Member's Area (http://www.thedieselpage.com/password.htm), & near the bottom is Brian Johnson's MPG Payback Calculator Excel Spreadsheet (I can't figure out how to link directly to it - sorry!).

I found my exactly the truck I wanted, my recently-purchased 93, by doing a Google search. If time isn't an issue, you might just come up with exactly what fits your needs. If you search around, you might find an aux OD (auxillary overdrive) that makes sense.

Blessings!