I am running a SP 400 that was professionally built. It will not upshift under full throttlei t ahsnt since I bought it. I have swapped out the governor, vac diapghram and rekitted the transmission with a TransGo shift kit. All with no success. Putting a stock governor out of an electra just lowered the partial throttle shift points. I have tried disconnecting the kick down switch (made things worse). If I apply full throttle in 3rd it will downshift and the engine will rev to the limiter 6200 rpm and stay there. If I back off the throttle it will upshift, but will downshift once I apply full throttle again. I am at my wits end and Im about to install a full manual valve body. Does anyone have a suggestion as to what may be causing me all of this grief? I ran a 13:22 with a screwed up transmission. Leave it in drive or try to shift manually its all the same........Please help!!!!!
With a correct manifold hookup, at WOT vac would be close to zero, which is what tells the transmission you're at Wide Open Throttle. Ported vac is a different story, hence my question. Do you know if the governor valve is moving freely throughout it's normal travel? Devon
That is a good question. I swapped out the gevernor and it didnt solve the problem. I suppose I have 2 bad governors but it seems pretty unlikely. However is it possible that somthing inside the transmission is limiting the governors travel???
Yep, the gov valve can fully or partially hang up, gov feed tubes can be plugged or crossed. Do you have a decent trans reference manual? Try "How to Work With and Modify the Turbo Hydramatic 400 Transmission" by Ron Sessions. Devon
Steve, have you tried replacing the downshift solenoid? Can you hear it click if you apply 12 volts to it? If it is stuck in the open position, the trans won't upshift at full throttle, and simply disconnecting the electrical connection might not fix that.
Larry, with the detent valve in the solenoid stuck open, he shouldn't have part-throttle upshift either, right? Devon
I had not thought of that. I assumed that it was downshifting because I was actuating the downshift solenoid. So it may be that the downshift solenoid is always activated/stuck and it is upshifting when I lift off the throttle because ??????? I got lost there. even if the downshift solenoid was stuck, shouldn't it upshift eventually when the governor gives the signal. Full throttle upshifts occur when the solenoid is activated anyway, right? Sorry, Im trying to think my way throught this theory, it seems plausible,.
Ideally Steve, the governor should have the last word on upshift at WOT. I'm still picking my brain to remember how much influence the modulator circuit has, especially since this tranny's been "professionally built"...the early SP trannys had some peculiarities, especially with mixed parts. Devon
OK, add a fully or partially stuck modulator valve to your list of things to check. Simply trying a known good modulator might not hurt either. Devon
To my understanding (and I'm no trans expert), it's like a tug of war between the governor, modulator and detent valve position, as to where the shift occurs. Removing your foot from the throttle makes vacuum shoot right up, and that may be enough to make it shift. You could have a shift valve stuck in the valvebody also.
Good idea... I'm not one either, and in fact the last time I rebuilt mine (yes it took me more than once) I ditched the modulator and welded up the governor...all manual now. Devon
I am strongly considering installing a full manual valve body. This is a last ditch effort to get the transmission to work right. If I have to remove the pan again I think Im swapping in a manual valve body.
Is there a way to modify my transmission to full manual operation with out installing a reverse valve body? The manual reverse valve bodies I have seen appear to require modifications to the internal components of the transmission. I would like to be able to manually downshift/upshift the transmission but I really dont want to have to pull the transmission from the car.
The good news is the answer is "yes", I've done it. The bad news is that it's been forever and I lost most of my notes in a house fire in 1996. What I do remember: Governor weights are welded, I believe in the completely closed position. Modulator is gone and a modulator plug is in its place. My other mods were to raise line pressure, disable accumulator circuits, add the 34 element sprag. Let me do some more research to make sure I don't steer you down the wrong path somewhere. I used the advice of a hydramatic engineer who was an engineer in the mid to late '60's, he gave me this info as well as advice on raising the variable pitch high stall. Let's see what else I can dig up. For some reason I'm thinking there's something I'm leaving out regarding the manual conversion. Devon
How are you activating your sp solenoid? I am wondering if the wire to the kickdown solenoid could be crossed with the sp solenoid. If you disconnect both wires and it wont upshift then you would need to look elsewhere.o No: Maybe governor gears are worn.
The SP solenoid is activated by the brake lamp switch. Its working fine. And please remember I have has this problem through 2 completely different governors. In retrospect I dont think I have swapped the modulator out though.
I have the same trouble with my sp/th400. Only mine worked well for several years before doing this. I am getting ready to pull the trans and check the roller clutch as someone on this board recommended. I also have gone through all the other stuff somewhat easy to get to. I might get into it next week if I can get the disc brake conversion done on the 54Chevy. I'll post my results when I get them.
