8.1L Avalanches

Shaners · January 18, 2002

My buddy just bought a bigblock Av last night and wants to know about the tranny.

I will check the RPO codes when he gets the truck home. I know there are 2 4L80E trannies available. The RPO codes are MN8 and MT1. The MT1 is listed as having electronic controls and that is the only difference. Does anyone know if there is a difference in the tranny (4L80E) that is in my 6.0L truck, and the 4L80E that is connected to the 8.1L in the Avs and Suburbans???

Shaners · January 18, 2002

BTW, I have the MT1 with electronic controls in my 2500HD with the 6.0L. Could it have something to do with the pushbutton 4wd?

ScottS · January 18, 2002

Hey Shaners

I have come to believe that the Av2500's 8.1 is backed by the 4L85E. It is really hard to tell, I have been curious about mine, and can't seem to get a difinative answer. I do however get more 85's than 80's whenever I find a source that lists that type of info.

The printout that I did from GM Canadas build your own site lists the trans as follows...

MN8 4-speed electronically controlled automatic transmission with overdrive

The glovebox code list also shows the MN8 code.

I know this doesn't answer your question, but at least it's a little fuel for the fire. I would be interested to know what you come up with.

Scott

Shaners · January 18, 2002

I am not familiar with the 4L85E but if the 4L80E is a heavier tranny than the 4L60E then it would stand to reason the 4L85E would be heavier yet and would be a good mate for the 8.1L.

Anyone else have some thoughts on this???

Although I still don't know the difference between the MN8 and the MT1. Both are listed as a 4L80E...

Kansas Kid · January 18, 2002

Yes, the 4L85e is a slightly beefed up version of the 4L80e. However, the only reason it can survive in front of a 8.1L (or a Duramax in the future) is torque management. If they let the 8.1 have full fuel in 1st gear it would tear these trannies apart. I personally am gonna guess the M85 is the 4L85e and the MT1 is the 4L80e, but wouldn't put any money on it.

January 19, 2002

My buddy just bought a bigblock Av last night and wants to know about the tranny.

I will check the RPO codes when he gets the truck home. I know there are 2 4L80E trannies available. The RPO codes are MN8 and MT1. The MT1 is listed as having electronic controls and that is the only difference. Does anyone know if there is a difference in the tranny (4L80E) that is in my 6.0L truck, and the 4L80E that is connected to the 8.1L in the Avs and Suburbans???

With the 8.1 isn't the manual trans standard and the Allison the only option?

Shaners · January 19, 2002

My buddy just bought a bigblock Av last night and wants to know about the tranny.

I will check the RPO codes when he gets the truck home. I know there are 2 4L80E trannies available. The RPO codes are MN8 and MT1. The MT1 is listed as having electronic controls and that is the only difference. Does anyone know if there is a difference in the tranny (4L80E) that is in my 6.0L truck, and the 4L80E that is connected to the 8.1L in the Avs and Suburbans???

With the 8.1 isn't the manual trans standard and the Allison the only option?

In the pickups you are right... 6-speed or Allison. In the Av's and Suburbans the 4L80E or is it 4L85E is the slushbox.

chevyzq8 · January 21, 2002

Since the Allison won't fit in the sub's and av's they use the 4L85 which is basically the same tranny, just designed for the 8.1, probably different torquer converter and setup, etc.

tbyrne · January 22, 2002

However, the only reason it can survive in front of a 8.1L (or a Duramax in the future) is torque management. If they let the 8.1 have full fuel in 1st gear it would tear these trannies apart.

I'll let you know after I get rid of the torque management in my 'Burb.

Tom

2002 Supercharged 8.1 Suburban - Project underway now!

2001 Supercharged 6.0 Suburban-15.87 @ 88.41

tfpary · January 22, 2002

Since the Allison won't fit in the sub's and av's they use the 4L85 which is basically the same tranny, just designed for the 8.1,

So the 4l85e is an ALLISON transmission, or did I get confused (again)?

Shaners · January 23, 2002

tfpary,

I think the 4L85 is a beefed up version of the 4L80. The Allison is it's own "Beast".

gandolphxx · January 23, 2002

The 4L85E is definitely not the Allison - needed beefing up to mate with the 8.1L - supposedly the torque management kills power for about .6 secs - the tranny needs about .3 - so I am told - since I have a 6psi supercharger, I am going to be a little careful about pushing the transmission any more than I am. I would be nervous about removing the torque management - but I am not an engineer. I am considering changing the torque converter for a little more aggressive stall speed.

tbyrne · January 23, 2002

Ed Wright can now do programming for the 8.1s so my computer will be there in the morning to take care of the speed limiter and torque management. I'll post results this weekend.

Tom

2002 Supercharged 8.1 Suburban - Project underway now!

2001 Supercharged 6.0 Suburban-15.87 @ 88.41

ClawSS · January 23, 2002

Hey Tom, did this just happen? I talked to Ed late last year and he hadn't done one yet, or had a chance to run the dyno with one.

Still cool news, though.

tbyrne · January 23, 2002

The info they needed from GM came in this morning so my computer left with UPS for overnight delivery. I can't stand the 98 MPH limiter and the torque management really seems to bog the truck down.

Tom