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Old 08-15-2019, 07:00 AM   #1 (permalink)
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TH400 governor

Quick background: My truck is a 1990 K2500 came with a 700R4. Previous owners have swapped in a Jasper 350 TBI and TH400. Truck runs great and is my tow rig. I tow up to 10k bumper pull trailer and haul up to 4k in the bed sometimes. The problem is it short shifts even under full throttle. I know the kickdown switch works and also have adjusted the modulator but it still upshifts at 3000 rpm. At 1/2 throttle it shifts at 2400 rpm to 2nd and 2100 rpm to 3rd. I did unplug the vacuum from the module and got some tire chirping 5000 rpm shifts to check if it was working so I know the problem must be the governor.

I have done some research on adjusting the governor but have been unable to find clear answers. I know that I can buy a governor adjustment kit for $50 but my understanding is that it only has inner weighs and springs. My understanding is that inner weights control the full throttle shifts (the lighter the higher) and the outer weighs control the part throttle shifts. I don't know what the springs control. I also don't want to grind weight off as this is the first time I have done this and certainly don't want to go to far. I also know that there is a bit of trail and error when adjusting the governor. Please correct me if I am misunderstanding any of this.

All the tech and how to that I can find is in relation to drag racing and getting it to shift at 6k. I obviously don't want to do that but I would like to reach my engines peak HP in all gears. I also want to adjust my part throttle shifts up some as when I am loaded heavy I have to stand in it to keep from bogging after it shifts. Since my peak torque happens at 2800 rpm and peak power at 4000 rpm I feel like my shifts should be closer to 3k 1/2 throttle and 4400 full throttle, but would like to keep the 2k shifts when putting around town empty. Any advice on how to achieve this would be appreciated.
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Old 08-15-2019, 10:03 AM   #2 (permalink)
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I might be mistaken here but I think the modulator handles the pressure that the shift happens at (the chirping tires at high line pressure) and the governor weights are what sets the actual RPM under both light and full throttle. Any chance the TH400 came from a diesel truck like military CUCV? The military usually liked to be little cautious about letting people abuse the trucks so it would make sense if it shifted bit lower than the 6.2's max rpm of around 3,600 under load. When you buy a new governor they used to come with instructions on how much to trim to make it shift early under WOT for the diesel.


EDIT: forgot to add if you do buy a kit TCI used to make one that came with different weights and springs that should help you in both WOT and light throttle shifts. It is meant more for the performance world but you are looking for the same thing, slightly higher rpm per shift.

Last edited by 350TacoZilla; 08-15-2019 at 10:14 AM.
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Old 08-15-2019, 11:29 AM   #3 (permalink)
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Quote:
Originally Posted by 350TacoZilla View Post
I might be mistaken here but I think the modulator handles the pressure that the shift happens at (the chirping tires at high line pressure) and the governor weights are what sets the actual RPM under both light and full throttle. Any chance the TH400 came from a diesel truck like military CUCV? The military usually liked to be little cautious about letting people abuse the trucks so it would make sense if it shifted bit lower than the 6.2's max rpm of around 3,600 under load.
I had the thought that this tranny came from a diesel, but wasn't aware that the military used something even slower. The guy that rebuilt this transmission is dead now so I can't find out where it came from. It doesn't really matter where it came the though. I just need to turn it up a bit.
I was aware of these modulator controlling the firmness of the shifts, but also read that it would raise rpm some. Maybe it does on TH350 or 700R4 but I could tell no difference in rpm but went all the way to violent shifts before I backed it down to a firm shift. When I started adjusting it my shifts were so soft I couldn't feel them, only see and hear the rpm change.
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