TH400 governor adjustment

IndianaDundee

Member
Joined
Aug 27, 2019
Location
Greeneville, TN
I have a 1990 K2500 that is my tow rig. It has a new engine and rebuilt transmission from a previous owner. It runs good but the only problems is it shifts at 2800-3000 rpm even at WOT. It isn't a problem when empty but when pulling a heavy load I could use some more power to the pavement. It came with a 700R4 that had died and the previous owner swapped in this TH400. I already checked the kickdown switch and adjusted the modulator so I know they are good. I did unhook the vacuum from the modulator to check it and was rewarded with a tire chirping 4400 rpm 1-2 shift. I know this 350 TBI engine makes peak torque at 2800 rpm and hp at 4000 and has a 4500 rpm redline. My half throttle shifts are at 1500-2000 rpm. So I think adjusting the governor is my best bet.

The problem I am having is all the info I am finding on this topic seems to be drag racing related. I get that it takes a bit of trail and error to dial it in so I don't want to grind away some metal and find that I have a 7000 rpm shift point. I know I can get a kit for $50 to adjust the governor and the lighter weights raise the shift points. But it only has the inner weights and springs. What do the outer weights and springs control? How do I adjust the part throttle shifts up? I want my half throttle shifts to be at 2500-2800 rpm and my full throttle shifts at 4200-4400 rpm. Should I just buy a new governor? Or do they all use the same governor regardless if it was a diesel or sports car?

Can someone please point to a good source of information? I ask the same question over on Pirate with very little response.
 
Any vacuum leaks to the modulator? How many modulator adjustments did you make?

I, too, was running into shifting problems with a TH400, but I just sold the truck it was in, and I never got it sorted out. I'm more here for answers as well.
 
The outer weights control your part throttle shift points. Inner weights are for the WOT shift points. Less weight will give higher shift points. I've never seen a kit that offers different outer weights since most are only concerned with WOT shifts. You can grind off material from the outer weights to raise your part throttle shifts, but if you take too much you will have to replace them. Better yet, buy a spare governor to modify, then adjust as necessary.

It sounds to me like that was possibly behind a 6.2 and still has the diesel governor in it, judging by what you're saying about the shift points. You might want to try a red-stripe modulator for some more adjustability.
 
I already have a red stripe modulator and adjusted it up to completely violent shifts then backed it down one full turn at a time (seven total) until I got firm but tolerable shifts. I could never tell a difference in rpm unless I left it unplugged and then it was redline shifting. I will double check the vacuum line for leaks but I am under the impression that TH400 shifts are controlled by the governor where TH350 and 700R4 are more dependent on the modulator. But honestly I don't have tons of experience with autos even though all three of my current tagged vehicles are autos. In the past I have driven mostly manual (even pulled a TH350 to put in a SM465 in my Blazer) but after an accident and surgery to put my left leg back together, I don't think my knee will hold up to heavy clutch usage. I just want my tranny to make full use of the powerband available.
 
Scooter402 said:
The outer weights control your part throttle shift points. Inner weights are for the WOT shift points. Less weight will give higher shift points. I've never seen a kit that offers different outer weights since most are only concerned with WOT shifts. You can grind off material from the outer weights to raise your part throttle shifts, but if you take too much you will have to replace them. Better yet, buy a spare governor to modify, then adjust as necessary.

It sounds to me like that was possibly behind a 6.2 and still has the diesel governor in it, judging by what you're saying about the shift points.
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I had the same thought of it coming from a diesel, but have not been able to confirm that they are different. I had the thought that the outer weights may be part throttle shifts but does that mean the springs control the difference between part and full throttle shifts?
 
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IndianaDundee said:
I had the same thought of it coming from a diesel, but have not been able to confirm that they are different. I had the thought that the outer weights may be part throttle shifts but does that mean the springs control the difference between part and full throttle shifts?
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Yep, the governors for diesel and gas engines are different. The difference in part and full throttle shifts are quite a combination of things. The vacuum signal to the modulator, the position of the weights in the govorner, wheel speed (also controls weight position) and the springs as well. You can make changes to the weights and leave the springs alone and still see results. If you do plan on modifying your current governor instead of swapping or using a kit (which is totally fine, I would do the same) I'd get a kitchen scale to make sure each pair are as close as possible to matching in weight. Take a few grams of mass off at a time. Obviously the outer weights are supposed to stay a good deal heavier than the inners.

Or, if you see a good deal on a gas TH400 governor, you might try swapping that in first.
 
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