Tahoe 6-Speed T56 Conversion

[digitalfiend]

I will never have a daily driver that is an automatic if I can help it. It is my strongly held personal belief that this mod is a requirement as it fixes the biggest flaw of the NBS Tahoe: an automatic transmission. I did an auto-to-manual swap on my last vehicle (2003 Toyota Tacoma) so this is just a natural progression of making this Tahoe to be MY TAHOE.

With that said, I have to pay credit to where it's due. I'm standing on the shoulders of giants by doing this to my Tahoe because this conversion was not my original idea. The biggest reason I decided to buy a Tahoe is because of vanillagorilla's thread over at performancetrucksDOTnet that covers his Official A4 to M6 (T-56) Thread . vanillagorilla's thread covers all the necessary information, so I'm not going to go too far into the build detail. My aim is to show that the conversion is possible in an NBS Tahoe, show what it costs, then point out what I had to do that wasn't a direct bolt-in.

Parts

• $2300 T56 GM/LS1 rebuilt to withstand 750 foot pounds of torque
• $220 lightly used LS flywheel/clutch/pressure plate
• $160 abused & used LS T56 Bell Housing
• $35 Arp-330-2802 Flywheel Bolts
• $24 Arp-134-2201 Pressure Plate Bolts
• $25 Grade 10.9 M10x1.5x40 Fasteners
  For Bell housing to engine & transmission to bell housing
  From McMaster
• $176 Slave/Master/Hydraulic-Line CC649034 (Rockauto)
• $4 Brake pedal pad 15706041 (Rockauto)
• $47 Shipping (Rockauto)
• $18 Pilot Bearing (O'Reilly Auto Parts)
• $135 used crossmember from a 2003 Silverado with manual transmission
• $75 used clutch pedtal from a Silverado
• $52 Throwout shim kit (TICK Performance)
• $300 HPTuners (used)
• $100 HPTuners credits for my single vehicle
• $130 Driveshaft shortening (1") and balancing
• $0 used t-shirt for prototype shifter boot
• $20 Genuine leather for shifter boot

My Process At A High Level
Items in red are not direct bolt-ins

• remove the old tranny/flywheel
• install the pilot bearing
• install the flywheel/clutch/pressure-plate onto the engine
• install the bell housing onto the engine
• remove the entire center console (temporarily)
• cut the hole in the floor for the shifter
• install the transmission onto the back of the bell housing
• cut the hole in the firewall for the clutch pedal
• install the clutch pedal and master cylinder and run the hydraulic line
• cut the brake pedal to be the size of a manual brake pedal
• buy or fabricate a shifter arm, then install
• buy or fabricate a short throw shifter, then install
• alter the center console to allow a spot for the shifter
• buy or make a shifter boot, then install
• reinstall the center console
• measure the driveshaft then have it shortened or lengthened then balanced
• install the driveshaft
• rewire the park/neutral switch to be in drive so that the speedometer and cruise work, and that the Tahoe will start
• wire up the reverse lockout into the brake pedal switch
• wire up the reverse lights
• correct the speedometer with HPTuner
• retune the throttle flollower with HPTuner so that the throttle falls faster and makes shifts smoother
• remove error codes due to the manual transmission being removed with HPTuner

Pros

• When I don't hammer the gas pedal and bang through the gears after every stop light I see an increase of 2MPG across the board
• IT'S FUN TO DRIVE THIS WAY
• You get to command your Tahoe when and how to shift. Since the 4L60e is compter controlled this means there's one less computer in control of my destiny. SCREW YOU SKYNET!!!
• The truck is instantly more responsive thanks to not having a torque converter any longer
• This was the way this truck should have come from the factory.

Cons

• There is a lot of work involved to make this happen. For me this was a labor of love, so it was just another fun mod to do to my Tahoe...others may see this differently.
• There's quite a bit of cost involved with this mod. If you don't need a new transmission and/or you're not sure you'll own your Tahoe for a long time then this mod is not for you.

This transmission shifted fine...but I strongly dislike automatic transmissions, so it's got to go:

Here she is, 750 foot pounds of torque handling beauty:

Here's the master cylinder, hydraulic line, and slave cylinder:

Here's the shifter before the installation of the short throw kit:

Before:

After:

Todo Items

• Finish tweaking the custom short throw shifter
• Tweak the custom shifter arm so that the shifter is in the sweet spot for my comfort
• Create a refined shifter boot in real leather
• Wire the clutch pedal to interrupt the cruise control
• Wire the clutch pedal to interrupt the starter when not depressed
• Ditch the stock 3.73 rear end gear and install a 4.10 gear

Things I'd Do Differently If I Did It Again

• Use a SPEEDWAY Clutch remote bleeder line
• Use a new bell housing. The used one I bought had three bolt holes stripped, so I had to ream them out and thread them to use M12X1.5 fasteners. With this added cost I saved less than $20, and bell housings cost $200 new.
• Budget for a stronger clutch because the weight of the Tahoe is a little too much for the clutch to last long term.

 

[1sickz71]

talk about something out of the ordinary lol good for those whose truck are supercharged or has other mods a friend of mines went through 3 trannies within months apart due to his supercharger

 

[95escahoe]

Looks great

Sent from my HTC One X using Tapatalk

 

[dcarver]

How does the short throw feel in a truck as opposed to a small car? Reason I ask is I've only driven cars with a short throw and trucks and jeeps with the long shifter

 

[yukondoit]

This is awesome, I would love to this mod in 02.
Makes me glad I have the 5 speed manual in my 94 Yukon.

 

[08grey]

750 lbs of torque. I wanna see a burn out video. Nice work!!!

 

[Gzes]

looks damn nice. yep i hate dd autos aswell

 

[yukondoit]

750 lbs of torque. I wanna see a burn out video. Nice work!!!

+1, we need a video

 

[Goodinblack]

Dang. Nice.

 

[Wake]

Very cool...

I must be getting old though, I'm pretty content with an automatic on my commute. I drove stick shift on my 100 mile commute for 3 years and I've had enough of that. LOL.

I still have my 6spd Corvette for my fun car when I feel like rowing through the gears, so I haven't totally walked away from manual gear selection.

Four speed automatics were a great improvement over the previous 3 speeds but were pretty fragile and they're antiquated now when you see what's out there.

My STS-V and my Audi A6 have 6 speed automatics in them and those two extra gears really make a difference. I had a Mercedes with a 7 speed auto for a month as a loaner car and even with a four cylinder the car was always in the right gear for what I needed from it. I believe Mercedes is working or has an 8 speed automatic now.

Your conversion is definitely a clean job from appearances, glad it work out for you.

 

[digitalfiend]

Thanks for the feedback y'all...

talk about something out of the ordinary lol good for those whose truck are supercharged or has other mods a friend of mines went through 3 trannies within months apart due to his supercharger

Yep...now I can look into a turbo or supercharger upgrade without worrying about the transmission grenading.

How does the short throw feel in a truck as opposed to a small car? Reason I ask is I've only driven cars with a short throw and trucks and jeeps with the long shifter

The short throw feels AWESOME. I've driven a couple mustangs that had aggressive short throw shifters and it feels exactly the same way. I held off posting this until after I got the short throw mod done because the stock T56 shifter is not designed to be used in a Tahoe and desperately needs to be upgraded. Unfortunately, I went a little overboard with it though and the throws are a little too short. I think I'm going to do a new one that's only a 1.5" extension instead of the current 2" extension on the inside of the shifter...this should help strike a happy medium of the throws being just right. The current 2" setup is totally functional, but it's just not as tame as I'd like it to be.

750 lbs of torque. I wanna see a burn out video. Nice work!!!

+1, we need a video

You two are crackin' me up. Just to be clear, the tranny is *rated* at 750 foot pounds...I'm still at the stock levels of output on the 5.3 engine that came with my Tahoe. However, despite the engine being stock, this mod really brings the truck to life and I can abuse it like a sports car when I feel up to it. When I upgrade the rear gear to a 4.10 I'll post a burnout video or two.

Very cool...

I must be getting old though, I'm pretty content with an automatic on my commute. I drove stick shift on my 100 mile commute for 3 years and I've had enough of that. LOL.

I still have my 6spd Corvette for my fun car when I feel like rowing through the gears, so I haven't totally walked away from manual gear selection.

Four speed automatics were a great improvement over the previous 3 speeds but were pretty fragile and they're antiquated now when you see what's out there.

My STS-V and my Audi A6 have 6 speed automatics in them and those two extra gears really make a difference. I had a Mercedes with a 7 speed auto for a month as a loaner car and even with a four cylinder the car was always in the right gear for what I needed from it. I believe Mercedes is working or has an 8 speed automatic now.

Your conversion is definitely a clean job from appearances, glad it work out for you.

Thanks Wake! I'm still young and stubborn enough that I don't mind driving the manual. And yes, the extra two gears make a huge difference.

 

[BirchyBoy]

I'm not familiar enough with models, but the T-56 seems to be built for sports cars based on Wikipedia. I wonder how it would be for towing a trailer. Have you put any thought into that?

 

[Rivieraracing]

Talk about a cool idea, would love to have a stick shift in the denali!

 

[digitalfiend]

I'm not familiar enough with models, but the T-56 seems to be built for sports cars based on Wikipedia. I wonder how it would be for towing a trailer. Have you put any thought into that?

Good comment about the sports cars...great question about towing too...I overthink most things so of course I thought of towing!

Normally, yes, the T-56 is built with a rating of 300-400 ft pounds of torque and intended to be used in a 3000-4000 lb car. With that stock rating I wouldn't try towing much at all.

However, the T-56 with some internal upgrades similar to the one I'm running should give a lot of capability to tow. Personally, I don't regularly tow anything, but I'm comfortable that my Tahoe will tow anything I will be throwing at it. There has been *some* discussion of this in the original performancetrucksDOTnet thread. In this post from the conversion thread, TurboGibbs writes:

"FYI - I just towed 8500 lbs for 3 hrs at 75-85 mph on hilly terrain with an LS7 clutch and a LS1 T56.
I guess it is a good towing trans too!"

The biggest thing to watch for once you have an upgraded T-56 when it comes to towing is the clutch...don't put a basic stock camaro clutch in one if you're going to tow a lot of weight. If you're going to tow a lot of weight then you should invest in an upgraded clutch, like an LS7 or aftermarket clutch. In fact, you should plan on running a beefier clutch anyways because of the difference in weight of a Tahoe compared to a camaro. I went with a basic used clutch just to get my project off the ground and I'll be upgrading the clutch to something stronger if/when it dies.

These transmissions have been used in everything from camaros to vipers to corvettes. It's definitely possible to snap the input or output shaft of a *stock* T-56 by launching ******* slicks with nitrous...but that is also why companies like Tick Performance have different levels of upgrade/rebuild packages that are rated to handle from 450 to 900 ft lbs of torque.

If you really want to go balls out and run an extreme turbo/supercharged/nitrous setup through a T-56 then you could always go with a rebuild package or upgrade to the T-56's big brother the T-56 Magnum. I almost went with a Magnum but I decided against spending the extra money for a Magnum after I realized the great availability of used T-56 trannys, repair parts, and strengthened upgrade parts.

 

[M Hankel]

Awesome job man!! Funny I found ya on PT today in searching for parts for my own T56 swap lol.... I was going to mention, depending on your tire height you could definitely go with a deeper rear gear than a 4.10. I ran 4.10 gears in my camaro as a daily driver and also freeway commuting 120 miles a day without a problem and that was with a short 26.5" tall tire. I'd go with a 4.88 at least if your tire is around 30".

Play around with this calculator and you'll see what I mean. You will thank me later.
http://www.ringpinion.com/Calculators/Calc_RPM.aspx

Mike

 

[Chevy305]

I love to see these conversions! I despise my auto too and hope to do this swap soon. I read that thread over on Performance Trucks a little while back and its great for a 2wd but I'm 4wd so that complicates it a bit for me. I want to run a NV4500 and ditch my autotrac tcase for maybe a 241 or similar.

How's the shifter placement? Is it awkward with the armrest down or is it more comfortable?

Sent from my Galaxy "LS3"

 

[hoe]

Op you did a nice project kudos for that. But honestly the 4l80e is a better stronger transmission Than that. You did nothing wrong at all at stock power levels. Some hd silverados are stuck shift. But the 1tons etc were 80e auto trans. A used 80e with a shift kit can rollout 800# easy and hold 600hp fairly easy too. That's sorta hwy I went 80e. Plus turbos spool faster with auto.

I'm looking for a corvette. And I'm looking to put a 80e auto into it.

 

[M Hankel]

Op you did a nice project kudos for that. But honestly the 4l80e is a better stronger transmission Than that. You did nothing wrong at all at stock power levels. Some hd silverados are stuck shift. But the 1tons etc were 80e auto trans. A used 80e with a shift kit can rollout 800# easy and hold 600hp fairly easy too. That's sorta hwy I went 80e. Plus turbos spool faster with auto.

I'm looking for a corvette. And I'm looking to put a 80e auto into it.

The word "better" is one hell of an exaggeration when comparing the two transmissions. Built T56's have lived behind 8 sec capable cars so I'm not sure why you chose that description. Every trans can break at some point. If you read his first post he didn't do the swap solely for strength but because he enjoys "driving" a vehicle with a clutch. For a select group of people an automatic is very boring and disconnected from the vehicle, myself being one of them. I personally hate having an auto constantly hunt for the correct gear, giving it gas and wondering if its ever going to downshift etc. With a manual trans you always know what to expect in any condition. I will also be looking forward to a 5-6 mpg increase on the highway.

Mike

 

[Chevy305]

^^^^ Well put. Auto transmissions just feel lazy to me. I want be engaged in the driving experience and have full control over my vehicle. No auto transmission can anticipate the road ahead like I can.

Sent from my Galaxy "LS3"

 

[01ssreda4]

Nice work.