DIY TH350 Governor Calibration

[SkinnyG]

Lots of talk of doing this online. VERY few pictures. Here's what I did to my '77 Silverado....

I finally bought the MSD Tach adapter (8920) to make my tach work with an MSD box, and discovered WOT shifts were occurring at about 3800rpm. I knew it was shifting early, but wow. The cam should be good to 6000rpm (231°@050", 0.470", 108°LSA, 104°ICL, 10.9:1). Gotta change the governor weights.

Governor came out, and I bought a small box of 6d nails. These nails were just a tick too big in diameter, so I drilled the holes #40 so the nails would fit dandy. This is just a baby fart larger. Wonderful manufacturer's tolerances.


OEM Weights are 0.062" thick.


I removed the governor weights and marked them 1/2" from the end, and 1/16" off each side. Ron Sessions' TH350 book says grind no more than 1/2" down, and 3/16" in. I figured I'd do this in stages - it's harder to put metal back.


Then ground them down, and de-burred.

I didn't even install them yet. I decided to get more aggressive.


This is now 5/8" off the end, and 3/16" off the sides.

This brought the shift point to about 4800rpm. More grinding is in order.

I did not change any springs - most folks online have had the best success using the original springs.

[MikeB]

I did the same mod many years ago to the TH350 in my 69 C10. It bumped the WOT shift point to around 4500, as I recall, which was perfect. When/if I wanted it to rev higher, I'd just hold the trans in gear.

[Brent7654]

I used a B&M kit a few years back when I was doing a lot of bracket racing, set it up to shift from 1-2 at 6800.
Was deadly consistent at the track.
I always shifted 2-3 manually as it would depend on the race, but 2-3 shift was slightly lower at full throttle 6500.
Kit was cheap for the results you get. Came with springs and weights and directions for approx shift rpm's...

Brent.....

[cadillac_al]

A nice low buck mod, gotta love it. How does it feel in normal part throttle driving and around town?

[68Timber]

Thanks for the pics, I'd noticed as well guys say it's pretty easy but nobody ever shows a pic of what they did.

[MikeB]

Originally Posted by cadillac_al

How does it feel in normal part throttle driving and around town?

I don't recall anything different under part throttle driving.

Informative article on shift points here: http://yarchive.net/car/transmission.html

[SkinnyG]

Changing WOT shift points from ~4000 to ~5000 had a noticeably affect on part-throttle shifts, probably because of how I have the vacuum modulator set. If I dial the vac.mod back down, there should be no noticeable change.

Soon I will change one weight to a wedge point, and see what it does. If that's not enough, then I will grind the other weight to a wedge point. Then pin points will be next. Then maybe drill holes.

[SkinnyG]

Just a follow-up. It's been over six years now, and I have made no changes to this at all.

[TrailerTrash]

I have been trying off and on to get my TH350 dialed in for the last few months. I used this thread for reference many times until I was comfortable with the process. I appreciate the info you provided.

Mine was shifting at 4,000 exactly. I trimmed a little then I trimmed alot and got to 4800. Then I decided to take one spring out. Dont do that lol. I trimmed even more and it is right at 5,000. I am thinking about tapering the tip and drilling a few holes to get around 5200/5400

It really isnt fun getting that cover off and back on