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i have a th400 i put in my 88 chevy half ton the pickup had the 700r4 in it before, this transmission worked great in the pickup i pulled it out of. i put it in this one now it slips terribly in D and in 1st and 2nd it will slip some when u get on the gas, i have a 700r4 to th400 transmission kickdown harness on it would that have anything to do with it slipping also i put in a new vacum modulator

tylerj, This is gonna be the

Submitted by Big Block 409 on Wed, 01/11/2012 - 16:07.

tylerj,

This is gonna be the worst kind of problem to fix, because I wasn't there to supervise, manage, and or observe the transmission swap and installation. On the other hand the fact that you’re a diesel mechanic helps. Don’t get insulted or defensive, but I gotta ask you how long you've been a diesel mechanic? Again I gotta ask you this because this is an online forum and I don’t know the first thing about you, and I don’t have your truck in front of me to test. If it makes a difference, I’m 76 years old, and have been a MASTER my entire adult life. I started in this business when I was 14. Put it down long enough to enlist in the MARINE CORPS, and volunteer for SNIPER SCHOOL and volunteered for the front lines at NAM. There I became an awarded sniper via an impressive amount of kills. The actual number doesn't matter, because I'm not here to embarrass anyone, and again as proud as I am, I AM NOT boasting or anything like that. I just wanted you to know a little something about me. So back to your truck. Like I said the fact that you are diesel mechanic makes resolving this problem that much easier. In terms of the basics that pertain to the installation/swap you did, and in terms of the shifting basics that plagues the TH400, what have you ruled in or ruled out so far?

i have only been turning

Submitted by tylerj69 on Wed, 01/11/2012 - 17:00.

i have only been turning wrenches for about 5 years with 2yrs of school before that. well i ruled out any vacum issues and the modulator, i was wondering if the electric kick down would cause it to not work properly. i have everything hooked the same way it was in my other pickup. the other pickup is identical just a year newer and everything worked fine till the motor went south

Tyler, (You said) i have

Submitted by Big Block 409 on Thu, 01/12/2012 - 05:46.

Tyler,

(You said) i have everything hooked the same way it was in my other pickup.

Well that's good, but did it ever occur to you that the kick down has to be:

ADJUSTED after it's hooked up?
Did you adjust it?
Have you checked the adjustment?

Here's a link that tells you how to adjust the kick-down Just in case you don't know how to adjust it.

http://blogs.hotrod.com/hot-rodautomatic-transmission-98.html

its not the adjustable type,

Submitted by tylerj69 on Thu, 01/12/2012 - 18:03.

its not the adjustable type, th400 does not have the tv cable it is electric on these

Sorry for the brain fart

Submitted by Big Block 409 on Thu, 01/12/2012 - 19:41.

Sorry for the brain fart there Tyler, forgot for a moment we're dealin with an electric kick down here. Have you given any thought to the possibility of a broken sprag inside the torque converter? The converter loses all torque multiplication when the sprag breaks. Could have broke in the process of the swap.

Tyler, My last answer was

Submitted by Big Block 409 on Fri, 01/13/2012 - 05:17.

Tyler,

My last answer was based on the fact that you’re mechanic with some experience, and the fact that the transmission was working correctly in the vehicle it came out of. My answer was also based on the fact that the BASICS that pertain to the kick down have been ADDRESSED. Since you are a mechanic I feel that I shouldn't have to go into such obvious detail, but is the:

700R4 to TH400 transmission kick down harness (and related wiring) in good condition and installed correctly?

Is the kick down switch itself is good?

There is enough vacuum going to the modulator?