Blackstone Labs Transmission Report

[swathdiver]

I figured out another way to help you fellas spend money on your trucks!

Research revealed that the average life of a GMT-900 6L80 transmission was about 160K miles. So with that milestone coming up I wanted to see if mine was on the same path or not for overhaul or replacement. The least intrusive way was to have Blackstone-labs analyze a sample of fluid for me; so that's what my daughter and I did.

Sample was pulled from a cold vehicle by removing a line from the radiator with a Jiffy-Tite tool and caught the fluid with a quick run of the engine. Half the fluid made it into the container and the rest made a mess. We then guesstimated how much was lost and then topped off and shut the hood. The sample was frothy and purplish in color.

A little background, all of the fluid was changed by my local dealership in August of 2017 at 117,432 miles. Based on the color and internal oil life monitor, I believe this was the first time that the fluid had been changed. At the end of February of this year the mileage was approaching my artificial, 36K mile limit to change all the fluids again. I was wanting to get the truck on an even 50K schedule at 150K but missed it by a little bit. The internal OLM shows in the 70s percentile range right now.

Anyhow, after receipt of this report the fluid will be exchanged again and probably kept on a similar schedule of 36K or so miles.

As always, comments and opinions and advice appreciated.

Who's next?

 

[mikeyss]

I have around 165k on my 6L80, and so far it's not showing any signs of giving up any time soon. I haven't experienced any shift flares I've heard other people describe on these transmissions either. The only thing I can hear is 1st gear whine when my windows are open. I am mostly sure this is normal. When I was a GM tech and the 2014 new Silverado was coming out, the K2 was insulated better than the GMT900 and not much engine noise gets in the cab, but all I could hear was 1st gear singing in those trucks, especially ones with the 4.3 V6.

 

[Doubeleive]

speaking of this, what the local shop told me is the factory converter will give up and then it takes the pump with it, I have been debating having the converter changed and maybe have something with a little stall, what would be good for a naturally aspirated engine? I don't foresee getting a supercharger in the near future unless I come into a big chunk of money.

 

[mikeyss]

Any torque converter with a little more stall than stock will wake it up. I decided when it's time to replace the trans, that'll be when I upgrade to something around a 2600 stall.

 

[gooffeyguy]

What is the factory stall?

2001 Yukon SLT
2012 Yukon Denali XL
2011 Yukon Denali RIP 5/20/18

 

[swathdiver]

...what would be good for a naturally aspirated engine?

What is the factory stall?

Stall speed will vary based on the power of the engine. We have the same 77-JMBX torque converter (17804387) which is a really advanced and stout piece. I think the advertised stall speed was about 1600 rpms behind a 5.3 but my memory of that is faded.

When I looked into high-stall converters a few years ago, I was struck by the older technology being used compared with the ones in our trucks, from the top name brands in transmission performance even. Do your research.

Lots of fellas put the ZL1 - CTS-V converter (24242552) instead for a slightly higher stall speed. Going by memory, which is not always so reliable my wife tells me, this converter behind a 5.3 will yield about 2000 rpm stall speed.

Remember, a higher stall speed means more heat and the clutches have to work a little harder to reduce slippage. When I used to race the Buicks, I worked directly with the converter guys and had them custom made based on my specs as I did not fall for the hype and went converters with those high stall numbers. I learned the hard way that small diameter, 3000 stall converters made the cars feel and look great at launch but actually hindered performance as multiple time slips to proved to the dismay of my wallet and time.

The poor man's way of guessing stall speed is let off the brake and mash the throttle, where the tachometer needle flashes to before slowing down is your stall speed.

 

[Rocket Man]

I thought the factory stall for these was 1800 but I could be wrong. I would do the analysis but my Silverado only has 60k on it and the trans on The Beast only has about 5k on it since the (latest) rebuild.

 

[gooffeyguy]

Stall speed will vary based on the power of the engine. We have the same 77-JMBX torque converter (17804387) which is a really advanced and stout piece. I think the advertised stall speed was about 1600 rpms behind a 5.3 but my memory of that is faded.

When I looked into high-stall converters a few years ago, I was struck by the older technology being used compared with the ones in our trucks, from the top name brands in transmission performance even. Do your research.

Lots of fellas put the ZL1 - CTS-V converter (24242552) instead for a slightly higher stall speed. Going by memory, which is not always so reliable my wife tells me, this converter behind a 5.3 will yield about 2000 rpm stall speed.

Remember, a higher stall speed means more heat and the clutches have to work a little harder to reduce slippage. When I used to race the Buicks, I worked directly with the converter guys and had them custom made based on my specs as I did not fall for the hype and went converters with those high stall numbers. I learned the hard way that small diameter, 3000 stall converters made the cars feel and look great at launch but actually hindered performance as multiple time slips to proved to the dismay of my wallet and time.

The poor man's way of guessing stall speed is let off the brake and mash the throttle, where the tachometer needle flashes to before slowing down is your stall speed.

I don't know much about performance automatic transmissions. My 10 second Mustang has a manual trans (Tremec TKO600 with a SPEC stage 3 hybrid clutch). The wife's low 13 second mustang has the AODE with stock converter and just the shift pressures and shift points adjusted in the tune. It kicks a bit sideways when shifting into 3rd at full throttle. The 4.10 gears help also.... Lol

2001 Yukon SLT
2012 Yukon Denali XL
2011 Yukon Denali RIP 5/20/18

 

[avalonandl]

My trans fluid looks great, have no idea if changed.

 

[George B]

Mine was at 65,000 with no record of being changed. It was purplish colored too. Not any more than a normal amount of fine material sick to the magnet.