I'm in the process of adjusting my TH400 shift points to better match my HP curve but need some parts. I've taken several governors apart and ground the weights to several sizes for testing. The 5 governors I had lying around were all stock and most of them had various strengths of springs installed. What I need is the factory GM part numbers for the various colored springs so I can go buy more for testing. The chevy dealer here can't find that info since he only goes back to '78 and the local trans shops are of no help either since they only have stock components. If anyone has GM part numbers or other sources, they are appreciated! Also, I don't want the $30 B&M kit just to get 3 sets of springs so count out that option. Once I'm done with my testing, I'll post what I've concluded and show how I modified the stock weights and assembled the unit!
it's easy to mod springs if they are close.
post WOT shift points with what you have now, and what you want.
The springs in the grab bag weren't close! I figure it should be easy to get the GM part numbers from a parts manual or trans rebuild book, but I have neither.
With the stock governor, my car was 1-2 shifting at 4800 and 2-3 at 3600 with kickdown in proper working order. I've ground down the small weights a bit and have been changing springs with several diffferent colors to try to get both shift points at around 5500. My peak hp is at 5100 according to G-Tech Pro RR and have read where I need to shift a bit above that due to the large range in gears in a 3 speed. I've read where it's trial and error so need a selection of different strength springs to try to get it right. From what I have found so far, there is no exact formula for getting shift points right. You need to take weight off to get the 2-3 shifts up and if you take weight off, you then have to also change springs to keep 1-2 from getting too high.
I'm going to the library in the next day or so to see if I can find a trans rebuild book that may have the spring numbers so I'll let you know if I get it worked out!
The trans is rebuilt with mods inc. pump improvement, heavy duty sprag and shift kit. The weights and springs primarily determine when the TH400 shifts and I need to adjust that. Been doing it with some success but can't get it exactly where I want it without those GM springs. Thanks for the comments so far!
Not for 3 sets of springs, two of which I already have! There are about 8 different strengths from what I've found. I also want a source for them so once I post my testing results on the forum, I can give GM part numbers so others can easily tune their shift points as well.
For what it is worth.....I am thumbing through my TH400 book by Ron Sessions. He states:
"Although GM doesn't sell governor springs seperately, they are included in shift kits (as you well know).........Any transmission shop should be able to dig up a few of these springs for you."
I checked with a parts guy buddy at a GM dealer, and he too claims that the springs aren't sold seperately.