Tahoe 6-Speed T56 Conversion

[ccreddell]

Any progress yet?

 

[Nick161024]

looks good

 

[crazycoupe]

I bet the mileage is way better

 

[992dr]

Any updates?

 

[TheAutumnWind]

Love this

 

[digitalfiend]

Any progress yet?

Hi ccreddell...the swap is done. I've been enjoying this swap for two years since when I posted this in February of 2014.

looks good

Thanks!

I bet the mileage is way better

The mileage is better when I can keep my right foot out of it and not shift at red line from every stop. Driving it with the 6-speed is way more fun than should be allowed. If I work really hard and leave my lead foot at home then I can see upwards of 18-19 mpg on the highway. Otherwise, when I drive it like a bat out of hell (within reason) I routinely see 15-16mpg per a tank...but even this includes some nasty rush-hour stop and go traffic.

Any updates?

Sure, I'll share some of what has transpired within the last two years since I did the swap:

My dad is an 1/8th mile bracket racing veteran and when he visited in August of 2014. We took my Tahoe out to the San Antonio Raceway drag strip for a test and tune night just to see what it would do. At the beginning of the night my ET's were in the high 16's. With his coaching I was able to break into the 15's on street tires. I didn't win a single race, but I repeatedly killed at the starting line with my reaction time - I'm really proud of this since the other guys were almost all driving automatics. I'll remember that night with my dad for the rest of my life.

Last year the GM plastic clutch pedal bracket broke. It's the part that mounts inside the cabin on the firewall and the clutch hydraulic master cylinder mounts to it through the firewall. I can't understand why anyone would make a clutch pedal bracket from plastic - I'd like to leave a flaming bag of poop on his or her doorstep for such a flawed design. I sucked it up and bought a new one from GM to get me back on the road. It will be the LAST plastic clutch pedal bracket I ever buy. I'm fabricating a new one from metal that I cut on my CNC plasma table. It will have a couple nice nice tricks to it that GM decided to not provide. Once it's ready for resale I plan on becoming a sponsor on performancetrucks DOT net and on here and selling them to Silverado and Tahoe guys.

I have made a few changes to the short throw shifter. It's better than my original version, but it still uses some of the original worn out shifter parts. It has some room for improvement, but I'm very happy with it.

Last year the used clutch started slipping pretty bad on hard acceleration. I upgraded to a Diamond Clutch Stage 2 Comp clutch. While it's better than what I had it's still not "the right" clutch for this setup. For my next clutch I'll be calling one of the leading clutch manufacturers directly and telling them my application so they can match up a clutch that will work better.

On a related note, my favorite way to abuse parts is to drop the clutch. It's really ******* the clutch and tranny, but it's pure entertainment. If dump the clutch at 3000 RPM from a rolling start it'll cause both tires light up for a brief second...then they hook and the Tahoe takes off. It's TOTALLY ******* parts...but it's TOTALLY fun. It's not the sole reason I've had problems with the clutch...but it is a major contributing factor. I do this very rarely nowadays.

I also changed the exhaust again last year and replaced the gutted mustang mufflers with a set of cherry bombs - INSTANT increase in power from idle to redline! The straight-through design is plenty loud enough while being calm enough to not get me a ticket yet...and the wife still rides in it! I still want to install a set of cutouts so I can get open headers on the freeway because there's nothing like announcing yourself with open headers when someone does something stupid in front of you.

I've almost perfected launching from a dead stop and staying solidly in the power band. It's not a 6-second demon, but it'll gently pin you back in your seat while having room for my wife and three kids.

 

[Martinjmpr]

This is very cool - I often wondered if someone ever figured out how to stuff a MT into a NBS Tahoe or Suburban.

Looks like yours is a "street" setup. So now what I'd like to see is a 'Burb or XL 4x4 with a 5 speed MT and a manual shift T-case, just like in the old days! Has anyone done THAT?

 

[992dr]

The mileage is better when I can keep my right foot out of it and not shift at red line from every stop. Driving it with the 6-speed is way more fun than should be allowed. If I work really hard and leave my lead foot at home then I can see upwards of 18-19 mpg on the highway. Otherwise, when I drive it like a bat out of hell (within reason) I routinely see 15-16mpg per a tank...but even this includes some nasty rush-hour stop and go traffic.

Sure, I'll share some of what has transpired within the last two years since I did the swap:

My dad is an 1/8th mile bracket racing veteran and when he visited in August of 2014. We took my Tahoe out to the San Antonio Raceway drag strip for a test and tune night just to see what it would do. At the beginning of the night my ET's were in the high 16's. With his coaching I was able to break into the 15's on street tires. I didn't win a single race, but I repeatedly killed at the starting line with my reaction time - I'm really proud of this since the other guys were almost all driving automatics. I'll remember that night with my dad for the rest of my life.

Last year the GM plastic clutch pedal bracket broke. It's the part that mounts inside the cabin on the firewall and the clutch hydraulic master cylinder mounts to it through the firewall. I can't understand why anyone would make a clutch pedal bracket from plastic - I'd like to leave a flaming bag of poop on his or her doorstep for such a flawed design. I sucked it up and bought a new one from GM to get me back on the road. It will be the LAST plastic clutch pedal bracket I ever buy. I'm fabricating a new one from metal that I cut on my CNC plasma table. It will have a couple nice nice tricks to it that GM decided to not provide. Once it's ready for resale I plan on becoming a sponsor on performancetrucks DOT net and on here and selling them to Silverado and Tahoe guys.

I have made a few changes to the short throw shifter. It's better than my original version, but it still uses some of the original worn out shifter parts. It has some room for improvement, but I'm very happy with it.

Last year the used clutch started slipping pretty bad on hard acceleration. I upgraded to a Diamond Clutch Stage 2 Comp clutch. While it's better than what I had it's still not "the right" clutch for this setup. For my next clutch I'll be calling one of the leading clutch manufacturers directly and telling them my application so they can match up a clutch that will work better.

On a related note, my favorite way to abuse parts is to drop the clutch. It's really ******* the clutch and tranny, but it's pure entertainment. If dump the clutch at 3000 RPM from a rolling start it'll cause both tires light up for a brief second...then they hook and the Tahoe takes off. It's TOTALLY ******* parts...but it's TOTALLY fun. It's not the sole reason I've had problems with the clutch...but it is a major contributing factor. I do this very rarely nowadays.

I also changed the exhaust again last year and replaced the gutted mustang mufflers with a set of cherry bombs - INSTANT increase in power from idle to redline! The straight-through design is plenty loud enough while being calm enough to not get me a ticket yet...and the wife still rides in it! I still want to install a set of cutouts so I can get open headers on the freeway because there's nothing like announcing yourself with open headers when someone does something stupid in front of you.

I've almost perfected launching from a dead stop and staying solidly in the power band. It's not a 6-second demon, but it'll gently pin you back in your seat while having room for my wife and three kids.

Man, I wish I saw this earlier haha. Its only been a little over a year and a half

Sounds like your dad is a pretty awesome guy and even better coach. Nicely done.

How's the project going? Are you working with Atomic for the bracket? I think you using a different name on PT.

You should post up some pics of the interior with how the shifter sits now.

Man, it must be a blast. I'm completely jealous hahaha. Been dying to get back into a manual trans.
What's the full weight of your Hoe?
What kind of clutch would they match you up with?
Dumping that must be a shocker and surprise quite a few people. That must be a blast.

Lookin forward to hearing your updates.

 

[adriver]

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.

Obviously this was about having something different than that. Your post makes it sound like he did all this because he couldn't find an automatic trans that was strong enough.....???? All three NBS Silverado sizes came with an optional manual transmission: The 1/2 ton/1500 got the nv3500/5spd behind the 4.3 v6 and the 4.8 v8. The 3/4 ton/2500 got got the nv4500/5psd behind the 6.0. The 3500/ONE TON had the zf-s6-650/6spd behind the 8.1 and 6.6 diesel.


​

Hi ccreddell...the swap is done. I've been enjoying this swap for two years since when I posted this in February of 2014.

Last year the GM plastic clutch pedal bracket broke. It's the part that mounts inside the cabin on the firewall and the clutch hydraulic master cylinder mounts to it through the firewall. I can't understand why anyone would make a clutch pedal bracket from plastic - I'd like to leave a flaming bag of poop on his or her doorstep for such a flawed design. I sucked it up and bought a new one from GM to get me back on the road. It will be the LAST plastic clutch pedal bracket I ever buy. I'm fabricating a new one from metal that I cut on my CNC plasma table. It will have a couple nice nice tricks to it that GM decided to not provide. Once it's ready for resale I plan on becoming a sponsor on performancetrucks DOT net and on here and selling them to Silverado and Tahoe guys.

I have made a few changes to the short throw shifter. It's better than my original version, but it still uses some of the original worn out shifter parts. It has some room for improvement, but I'm very happy with it.

Any other problems that came up that might have been associated with the swap? and more importantly, did you ever end up making any parts that would help with this? ​

 

[digitalfiend]

Latest updates...

The swap outlived my 2004 Tahoe - a nasty hail storm several years back totalled it into a golfball that looked a little bit like a Tahoe. I put the same T56 parts into a 2005 Avalanche for a short while but parted with the Avalanche as I really like the Tahoe platform. Before selling it I converted it back to an auto and kept all the stickshift swap parts. Within the last 18 months I purchased a 2003 Tahoe in Austin. It's transmission was slipping in 4th gear but I got it for a song at $1500. As I drove away and got onto interstate 35 to head from Austin to my home in San Antonio 4th gear gave out completely. Soon after that 3rd gear gave out. I drove it back from Austin in 2nd gear on side roads with my girlfriend following me. As soon as I got it back I swapped the T56 into it. I also put a 5.13 gear in the rear end only to realize (yet again) that one of the weak points of our 10-bolt rear ends is the spider gears when one of the spider gears split into several pieces. I upgraded to an Eaton TrueTrac and donuts on dry pavement are loads of fun.

As of today, the transmission is needing an overhaul. For me this isn't surprising since I drive it hard and it's in a heavier vehicle than it was designed for. I need to replace the 5.13 gears because the shrapnel from the exploded spider gear damaged them slightly so that they're noisy and I'm tired of the loud noise - I have all the replacement bearings and gears and I will overhaul and break in the new parts before a summer road trip. The Monster twin disc clutch I'm running seems to be in great shape. This morning the Tilton 3/4" bore master cylinder seems to have failed. I'm waiting on a replacement to ship from Wilwood and I'll get that swapped in either tomorrow or Monday and I'll follow up if there is any interest in this thread.

I'm going to do the transmission rebuild and keep on going because I still love my Tahoe and very frequently use the middle and third row seating along with it's towing capacity to haul the kids and our dirtbikes to the track.