91 4l80/241 diesel into a 85 5.7/700r ?

[GreaseDog]

Converter for the diesel will not bolt to his flw wheel. Stall speeds are different aswell.

stroll over to FSC and ask oldred95... pretty sure he's running a 350 with a set of ported Vortecs and an LT4 Hot cam... and a stock diesel converter in front of the 80E.

Yes the 4L80E has a higher first gear ratio, 248:1 and anything less then 4.10's WILL create to much slippage and heat causing failure. It's the same goes with tire sizes (final drive ratio)

guys have been running TH400s for years with higher than 4.10 gear, and the same 2.48 1st gear, with big tires for years... when was the last time you heard of a TH400 as a weak trans because of its higher 1st gear?

 

[oneluckypops]

stroll over to FSC and ask oldred95... pretty sure he's running a 350 with a set of ported Vortecs and an LT4 Hot cam... and a stock diesel converter in front of the 80E.
guys have been running TH400s for years with higher than 4.10 gear, and the same 2.48 1st gear, with big tires for years... when was the last time you heard of a TH400 as a weak trans because of its higher 1st gear?

Not saying it is a weak transmission, Its not but it needs the correct final drive ratio just like EVERY other transmission, I have seen alot of TH400 fail due to bigger tires and high gears.

Seems like everyone goes in the reverse order when it comes to mods, Big tires, then big motor, then a transmission, and never do anything with the gears. IMO that is totally bass ackwords of what should be done.

IMO mods should be in this order,
1. Gears
2. Transmission
3. Tires
4. Motor
Seems like most people think to run big tires you have to have BIG power, That is not true, as long as you start from the rear and work your way forword.

 

[HotRodPC]

I'll agree you should WANT somewhat of a lower gear with a Th400 since with that 2.48 first gear, it doesn't take off the fastest, but Th400 can handle some abuse without a doubt. Look at my 84C20. 3.21 wussy gear, 31in tire and that trans lasted over 150K in a truck that towed a small trailer and welding rig most of its life. Granted with a lower gear, it have gone well over 200,000 miles. And remember, this trans failed due to a broken roller clutch. Had it had the dogbone sprag like it does now, it may have gotten over 200,000 anyway. The intermediate and low/reverse clutches had lots of meat. It was the Forward and Direct clutch drums that fried cuz of the failure. I've got the upmost faith in a 400 to stand up to some hell and abuse. Second in line woudl be the Th350 aslo in need of the sprag upgrade.