convert sp400 to th400?

If you had a SP400 that was factory made that way, could you convert it to a TH400? I recall reading some time ago that a TH400 performs much better for drag racing than the SP400.

 

A th400 uses a different input shaft and front pump than a sp400. With a rebuild video like this one VID the change over wil be smooth as silk. At the same time replace the intermidiate sprag. The weak link.
Ray

 

You have it backwards....the SP400 with dual stall conv lets the car accelerate faster off the line and then switch to low stall providing more power to the ground.

 

The nice thing about the TH400 is that it will have the center support snap ring helping with case durability where the '67 trans doesn't have one.

To swap the variable pitch feature to the TH400 you will need:

ST300 or ST400 torque converter
Input shaft
Front pump (with stator solenoid and wiring attached)
Dual prong case electrical connector
Trans case restricting orifice plug (often overlooked)

The restriction in the case is about 0.038" - 0.040", the passage is near 7:00 behind the front pump. This guy used a carburetor jet...neat idea:



Devon

 

I just sold a PAE conversion kit. It had the end of glass fuse for a restriction. I'll have to pm who I sold it to. The jet idea is a good one.
Ray

 

The fuse end cap works just fine too, and it just presses into place...no drilling/tapping required. Mine's drilled to accept an allen set screw with the orifice drilled through.

Devon

 

Ya know, GM still does sell the orrifice plug.. PN 8611710- and then just drill a .038 hole in it..

This will allow you to keep the carb jets and fuses where they belong.. :laugh:

JW

 

Thanks for the feedback. I have been using the SP for street/strip and my 60' times are terrible. I may look into a timer (Poston I think makes one) that switches high/low down the track versus the brake light like I have been doing. That and spem rear suspension work.

 

I bought one of JW's {Jims} SP Kits a mounth or so back. Its going to be installed with the rebuilt 455 this winter. After researching around the net and here, I figured this would be the best rought for a street car and a few runs at the track. I would hope I made the right choice. Also after some checking around JW has the best kit at a great price. It even comes with the wire plug and the correct orrifice.

 

I got the car built already. I think it is a Kenny Bell 2200/1200 that has had some internals upgraded, but I can't say for sure. I am pulling 1.8-1.9 60' with a mid 12 second/107 MPH. I have the south side traction bars and the no-hop brackets on the rear.

 

Hey Devon,

The 67 SP TH400 can have the update center support snap ring installed if you use the later model(thinner) center support, but if the case is already worn from not having the snap ring there you should replace it. Even the early (non SP) TH400s didn't have the snap ring in the case under the center support. As for the parts listed the restrictor plug is for installing a SP, I think Jim was asking about going the other way, to remove the SP the plug should be removed.

Which makes me wonder- Jim,
Does your transmission feel almost like it's shifting gears when you turn the convertor switch on and off? It should, and if you are at a stop and raise the rpm with the brake on the convertor it should go from 1300-2000rpm no problems before the tires spin. If you have a SP conversion kit and don't install the restrictor the convertor stall won't change when you turn the switch on and off (I did that 32 years ago). You have a 69 and 71 model car according to your info, I was wondering if it is a converted trans because the SPs were usually 65-67 or 68? Telling if a trans is SP from the outside is difficult because later models also use 2 prong connectors because of a 3rd gear pressure switch. Look at the stator splines (rear set) in this picture:

The splines on this SP400 are 1/2 the length of a regular 400. And the wire inside the trans should go from the connector up to the front pump, it kind of dissappears above the shift linkage.
I tend to sometimes confuse people by over explaining, so if I need to edit this please let me know.o No: I think the SP should be a better choice in most milder street cars, if it works, unless you go with a later model OD lockup trans.

 

Larry J-

You did a good job of explaining, no need for editing. My transmission is deffinitely an SP400. The high/low is wired through the brake light sensor and when I leave a red light with a slight uphill incline I can clearly feel the lock up to the lower stall.

I am thinking of getting a stall that has a high side of 3000-3600 and I bet that would wake things up off the line:3gears:

 

Are you just using the brake switch for the SP? I would expect you would gain a lot from leaving it on until 30mph.I can't remember what I used to do, but I think I turned it off after the 60' mark to get the best et. But it couldn't hurt to get the higher stall SP because you won't lose much low stall anyways, and probably use it in low stall most of the time.

Have fun Jim:blast: :3gears:

 

Yes, I am using it just off the brake light. I have also tried 1/4 mile passes leaving it low and leaving it high. I did gain on my 60' leaving it on high by about 0.1 seconds. I am thinking about getting one of those PAE or Poston SP timers and getting it to switch low stall about the same time as the 1st to 2nd shift.

On a side note, is Poston still around? Any other manufacturers of the SP timer other than Poston and PAE?