85 Suburban TH400 to 4L80E swap
 

I am preparing to change the TH400 in my 85 2WD C20 Suburban 454 to a 4L80E transmission. Does anyone have experience with what needs to be done for the crossmember?

Re: 85 Suburban TH400 to 4L80E swap
 

How to here: http://67-72chevytrucks.com/vboard/s...d.php?t=574800

Re: 85 Suburban TH400 to 4L80E swap
 

No details in that thread about the cross member modifications.

Re: 85 Suburban TH400 to 4L80E swap
 

I think he said he used the stock cross member with the 4L80E mount.

Re: 85 Suburban TH400 to 4L80E swap
 

when I put an 6.0l/4l80e in my 86 Suburban (originally a 350/th400) I used Dirty Dingo mounts. all I had to do was re-drill the cross member holes in the frame around 1.5" back. but the cross member its self needed no modification. The 4l80e trans bushing bolted right to the cross member.

Re: 85 Suburban TH400 to 4L80E swap
 

I am starting this swap project. I have the transmission and torque converter complete and ready to install. Transmission is fresh overhauled with a shift kit, manual speedometer output housing with gears and deep aluminum pan.

I will try to update with progress and pictures as I work on it and make progress.

Re: 85 Suburban TH400 to 4L80E swap
 

Moved the transmission crossmember back to line up the front crossmember bolt holes with the rear bolt holes in the frame and the mount on the transmission lines up perfectly. Drilled new rear holes in the frame using the crossmember as a template and bolted everything up. Transmission and torque converter are now installed and bolted in.

Re: 85 Suburban TH400 to 4L80E swap
 

Driveshaft shortened 3-3/8 inches and re installed. Cooler lines from TH400 moved back 2-3 inches and re bent to fit 91-96 4L80E case.

Re: 85 Suburban TH400 to 4L80E swap
 

Installing the TCI Transmission control unit and TPS sensor this weekend, That just leaves the shifter linkage and speedometer cable left to finish up.

Re: 85 Suburban TH400 to 4L80E swap
 

Finished up the installation and drove it several times pulling my boat. Really satisfied with the results. Tinkered around with the controller settings to get a good shift feeling. And the Lockup converter settings based on MPH and TPS percentage. Mileage is much better what used to take a full tank is now down to about 3/4 tank for a vacation trip.

Pictures of the transmission with the TCI deep aluminum pan and the Mechanical Speedometer tail housing so I can use my original speedometer. Low stall torque converter for the 454.

Re: 85 Suburban TH400 to 4L80E swap
 

Good to hear it. Any idea how much the entire conversion ran? I know the controllers can get pricey.

Re: 85 Suburban TH400 to 4L80E swap
 

Pictures of the cross member moved back 3.75" with a 4L80E mount.

Re: 85 Suburban TH400 to 4L80E swap
 

The complete conversion can vary depending on what you do for a transmission and converter, Year of vehicle you are putting it in for Speedometer use, Cross member modifications and Controller with TPS if needed.

The Transmission controller I used was a TCI TCU unit #302820 which cost $614.00, TCI Remote TPS for the Carburetor cost $142.00 and the cable bracket to mount the remote TPS cable to the carb is TCI part #376700 and cost is $23.00.

Re: 85 Suburban TH400 to 4L80E swap
 

Driveshaft shortened 3-3/8" the difference in case length between the TH400 and the 4L80E Transmissions with the bolt on yoke

Re: 85 Suburban TH400 to 4L80E swap
 

Engine RPM at 65 MPH with 235/85/16 tires with the TH400 was about 2700, with the 4L80E and the converter locked the RPM is about 1950. What a difference a .75 Overdrive and a Lock Up Torque Converter make.

Computer cable plug on side of transmission.

Re: 85 Suburban TH400 to 4L80E swap
 

Lookin good! Who sells the speedo tail housing?

Re: 85 Suburban TH400 to 4L80E swap
 

Thanks for an excellent how-to and pics. Any plans for fuel injection?

Re: 85 Suburban TH400 to 4L80E swap
 

I sent a PM to you about the Speedometer conversion kit that we offer.

Re: 85 Suburban TH400 to 4L80E swap
 

Thanks for the compliment.

No plans for fuel injection at this time. It would be a nice update if I ever decide to do it.

Re: 85 Suburban TH400 to 4L80E swap
 

Picture of the shifter linkage. Moved frame bracket back putting front bracket hole in rear frame hole and dropping down about 1/4". Lengthened shifter rod down from column by 2".

Re: 85 Suburban TH400 to 4L80E swap
 

Is it possible you could send me that info also?

Re: 85 Suburban TH400 to 4L80E swap
 

I sent a PM to you about the mechanical speedometer conversion for the 4L80E.

Re: 85 Suburban TH400 to 4L80E swap
 

Nice write up, I have been thinking about the swap with my 454 swapped c10 if you could please send me that info also! Thank you!

Re: 85 Suburban TH400 to 4L80E swap
 

I sent a PM to you about the speedometer conversion.

Re: 85 Suburban TH400 to 4L80E swap
 

Any reason not to post the speedo conversion info here ? I am interested too. Do you sell the kit ?