TH400 governor...Standard item?

[Asmoday]

Is the governor assembly used in the M1009 TH400's just a standard governor assembly?

If so anyone familiar with the Sonnax units?

Thanks....!

 

[Asmoday]

So after some searching I came up with some puzzling info. The TM lists the Trans governor part number as a 8629227, 2520-01-151-3857. When I search this NSN number I also get a GM part number of 8679975 which I believe is probably the part number used in the M998. This part number also comes up as available still from GM.

When I searched more on the 8679975 part number...it comes up obviously as a AC Delco number as well but it says that this part number fits gasser applications, 262, 305, 350, 454 as well as the 6.2L diesel applications. ????

I thought that the governor in the M1009 TH400 trans was specific for diesel applications due to the lower RPM shift points necessary with the diesel engines.

But...according to the application sheets as well as some Sonnax application chart info it appears the governor is standard. Confusing...

What gives...??? All you transmission gurus please chime in.

 

[doghead]

I'm no Guru but, I think the mechanical governor only sets the shift points in a WOT(wide open throttle) situation.

The vacuum modulator controls the shift points during normal driving situations.

 

[Jersey4x4]

When I just rebuilt my TH400 the gov itself was the same part number for the gas to diesel but there was paperwork in the box to modify the weights for the diesel and for the corvette. It was no big deal just used a die grinder to cut on the line. This was a replacement part from the transmission supplier. I may still have the old one if you need one. I have to look to see if it is in the recycle bin still or not to be sure. It still was free I just replaced it because I could. From what I was always told the Gov controls deceleration downshifts when not on the throttle and also minor shifting upon acceleration along with the vac modulator (which should be a red stripe for the diesel) and passing gear is controlled electrically by a valve on the valve body activated by the switch inside the cab next to the go peddle.

 

[doghead]

Well, just a Google search away, I found this.

In TH-350, TH-400, and 700-R4 automatic transmissions, a governor controls part and full throttle up-shifts. Think of the governor as a hydraulic speedometer, which tells the transmission when to shift up based on vehicle speed. The governor turns in direct relation to the output shaft rotation, and therefore vehicle speed. Inside the governor is a valve that opens and closes to "govern" the upshifts.
There are two sets of rotating weights in the governor. The heavier, outer weights act at low vehicle speed and the lighter inner weights take over at higher speeds, especially during full throttle conditions. Centrifugal force acting upon the weights controls the opening and closing of the governor valve itself. The valve controls governor pressure delivery, which in turn controls upshifts.
When there is enough centrifugal force upon the weights to open the valve, line governor pressure overrides the shift valve spring, and the shift occurs. Changing the inner weights on the governor allows you to adjust the rate of this line pressure versus vehicle speed balancing act, and optimize full throttle shift points to your vehicles power to weight ratio, rear end gear ratio, and so on.
Since the governor came set from the factory for whichever vehicle the transmission originally came in, you may or may not be getting the most out of your setup. This is especially true if you have changed rear end gear ratios.
The B&M Governor Recalibration Kit allows for raising or lowering of transmission shift points relative to vehicle speed. Keep in mind that the governor has no effect on the crispness or "hit" of the shifts. Modifications to shift characteristics must be made by modifying the valve body with a shift recalibration kit.