I have a built 700R4 in my 79, but I have a small problem. The lockup on the TC is controlled all hydraulically by a kit the previous owner put in it. The TC locks at ~40MPH which is lugging my engine to no extent, and causing me all kinds of problems. He didn't give me the springs or any info on the kit, but I'd like it to change and not lock until ~60MPH.

It all depends on what kit was used...the GM kit came with 3 springs, and some of the aftermarket kits come with 4, or only one...ya never know.
The actual size of the valve will also make a difference in the spring selection. The factory valve will only accommodate a small diameter spring, making it a little tougher to find one that will fit in the sleeve.
It may be best to just get another kit, so you'll have the selection of springs to use...and use the stoutest one in it.
P/M me and I'll see if I can send ya something...


                                                        Click for linkAdams' Apple2008-05-28 10:28:55

The problem is that when a non OD car has a OD put in it, the convertor locks as soon as it goes into 4th gear (OD) and does not unlock untill it shifts out of 4th. This B&M controler will let you lock/unlock the convertor by using speed. If you are going over the set point it will lock and if you slow down it will unlock. Redwingvette2008-05-29 06:07:21

The spring in the lock-up valve accomplishes the same thing. It will lock-up at a particular speed, regardless of what gear it is in.
Too light a spring will have lock-up in 2nd gear, even. My personal preference is for lock-up to come in around 55-60 mph...long after the 3-4 shift. It will also come out of lock-up with a little more throttle, making downshifts/kickdown less likely to be "boggy", or jerky.
There are many ways to have lock-up on the 700s....the 2004R is a bit more involved tho, so the other electrical type kits(such as the B&M kit above) are a better/easier way to go on those.

Several years ago I had that problem, and none of my "experts" ever told me what Joel just posted.  That would have been a perfect solution.  I will save this post for next time.
Thanks, Joel
Larry