400-700nitemare

[trukrtrash10]

89 tbi 5.0, th400. i have made the swap from th400 to 700r4. i got trans from local trans shop,(1) trans guy said in order for it to work correctly in my truck w/out the pwr connection to the 700 he would have to install a hydraulic kit in valve body to eliminate need for 12v pwr source, (for whatever pwr conn does).
(2) have no speedo now. (elec) same trans guy said my now 700 has mech speedo output shaft and will have to be pulled and taken back apart to be replaced w/ electronic speedo shaft.
after installation it seems to shift out fine but cant really tell when it shifts into od, have no tach but thats another topic.
So to the expert 700r4 trans tech is statements (1) and (2) correct?
is there another option to regain speedo?
at what rpm should i be in od?
thnx, tt10

 

[Tzfbird]

He is not right or wrong on either IMO. There is always more than one way to go about most things.

I was going to do this swap on my 90. I picked up the ACDelco 40-tooth reluctor to put on the output shaft in order to run the speedo. All the trans guy needed to do was remove the plastic drive gear and press on the steel reluctor. To do it without risking damage to the internals, yes it would be a good idea to tear-down and do it with the shaft removed or else swap shafts as he said.
As far as the TCC (converter lockup), I don't know if the truck has the correct brake switch but it might be as easy as switching out the brake switch and running +12 to the correct terminal and then from there to the 4-pin connector on the transmission. There are 3 wires in that connector. Purple which is +12 from the brake switch, LT BLU and TAN/Blk from the ECM. I downloaded a diagram off SilveradoSierra.com which has both diagrams for the TH400 and 700r4. The TH400 shows a kickdown relay which the 4-pin TCC pigtail is connected to. The kickdown is the same as the TCC meaning that when you apply heavy throttle, the transmission will kickdown from 3-2 or 2-1, likewise the TCC will turn off (converter unlock). Depending on the year of 700r4 it has internal pressure switches which the TCC signal is run through in order to lockup the converter. I know there is a 4th gear switch, so the transmission has a constant +12 whenever the brake is not pressed and the converter will wait to lock until it reaches 4th gear. The converter will then unlock when either commanded by the ECM or the brake pedal is pressed.

Sorry if that is a very technical and confusing description.
I never looked but I'm assuming that somewhere on the truck (probably engine bay firewall) is a relay you need to disconnect and the correct connector to run the 700r4. Whether the wires are the right length is another story. Hope that helps. If you find anything please let me know as I spent quite a few hours tracking this information down but I never followed through as I found a different truck with less rust.
The RPM for a given gear is dependent on the governor in the transmission which is turned by output shaft speed, in other words vehicle speed which again is based on differential gear ratio.

 

[trukrtrash10]

thanks for reply, very thorough just what i was looking for.

 

[Tzfbird]

I was under my truck switching the parking pawl bracket around and noticed that the 4-pin/3-wire connector is there right next to the transmission. It plugs into a female connector and goes back into the wiring harness by the firewall and comes back as the 1-wire to the kickdown solenoid. So, I'm guessing you can just unplug that and right into the 700r4 with no wiring needed. I'm not 100% sure but my guess is that the TCC unlock from the ECM is used as a kickdown in the case of the TH400. The only thing I'm unsure about is the signal from the brake switch because that would cause the Th400 to kickdown if the brake is pressed, however that doesn't happen so there's something else going on with that particular part of the TCC electrical.

 

[TylerZ281500]

no you cannot, 700r4 uses a tv cable not a kickdown. to get kickdown youll have to full manual do so which sounds like the trans has? or you get a wiring kit from bowtie overdrives to have it operational.