Automatic Transmission - TH400 speedo question




View Full Version : TH400 speedo question


datsbad
07-25-2007, 10:02 PM
I switched from a 4l60 to a Th400, What do I need to do to get the speedo working again?


Vince @ FLT
07-25-2007, 10:15 PM
I have read a couple of threads that guy's have used a front wheel sensor after a 350 or a 400 swap. :search:

GMRACER13
07-25-2007, 11:39 PM
You need a reluctor wheel from your old 4L60E (it's on the output shaft and needs to be pressed off). Machine the INSIDE of it to fit on the output shaft of the TH400 (don't remember the exact size but it must fit tight like it did when it was on the 4L60E shaft). Next you need to purchase an ELECTRONIC speed sensor for a TH400 (this can be purchased at a chevy dealer and was used in some trucks). The final piece is a pigtail with the proper plug end to plug into the new speed sensor (just cut off the factory speed sensor plug on you vehicle's harness and attatch the new plug to the original wires there is no polarity). Your speedo will now work and there is no tunning required as it's using the factory reluctor wheel from the 4L60E.


frcefed98
07-25-2007, 11:41 PM
Yeah but you lose your ABS if you do that, not what everyone wants right?

In the TH400 FAQ there are two part numbers that you have to order from either LS1speed.com or GM directly and you'll be able to get your factory speedo working again.

GM8655291 GM Speedometer Sensor $99.99
GM8655315 GM Speedometer Drive Sensor Rotor $65.99

There you go:D Searching this site is hit or miss so lets just try to help answer questions.

XpEdItIoUs
07-28-2007, 11:02 PM
Anyone know what is need to press it on?

frcefed98
07-28-2007, 11:46 PM
Pics of these pieces too please.

I have what look to be a set of speedo gears pressed onto the output of my TH400?

8a8mfh
07-29-2007, 06:36 AM
Machine the INSIDE of it to fit on the output shaft of the TH400

Just get one for a 32 spline output.

I guess you need to figure out if you have the short 32 spline output or the small diameter long output.
TH400's came from the factory with electric senders on both sizes.

http://www.transmissioncenter.net/HPIM1532.JPG

Vince @ FLT
07-29-2007, 08:01 AM
Anyone know what is need to press it on?

I usually press it on before assembly. I am not a fan of pounding the gear on. The reason for this is because of the bearings and the plastic washers that are inside of the transmission. One guy I worked for had a tool for pressing these on. It would thread into the output shaft and had a sleeve so to speak that would press it on with the use of an additional nut on the bolt. The problem is that not all the 400 shafts have a threaded hole.

GMRACER13
07-29-2007, 09:51 AM
Anyone know what is need to press it on?

I put them on by heating them up first in a toaster oven. If you get it hot enough you should be able to slide it on by hand (wearing thick gloves). Have a punch and a hammer ready just in case it needs some adjustment before it has a chance to cool. If your too slow and it cools down before you get it EXACTLY where you want it and it won't move you can re-heat it with a torch.

GMRACER13
07-29-2007, 09:55 AM
Pics of these pieces too please.

I have what look to be a set of speedo gears pressed onto the output of my TH400?

If your talking about the plastic gears for the mechanical speedometer then you would need to remove that first. It's not pressed on. It has a small metal clip that retains it. Once you remove the plastic gear that's where the metal reluctor wheel goes.

XpEdItIoUs
07-29-2007, 11:14 AM
I put them on by heating them up first in a toaster oven. If you get it hot enough you should be able to slide it on by hand (wearing thick gloves). Have a punch and a hammer ready just in case it needs some adjustment before it has a chance to cool. If your too slow and it cools down before you get it EXACTLY where you want it and it won't move you can re-heat it with a torch.

Thanks for the info, How far do i slide the ring?

GMRACER13
07-29-2007, 09:10 PM
Thanks for the info, How far do i slide the ring?

Untill it's centered in the hole for the speed sensor.

XpEdItIoUs
07-29-2007, 10:01 PM
What atf are you guys using on your th400?

frcefed98
07-29-2007, 11:27 PM
Thanks for that info GMRACER13. I'll check em out a lil closer. When I say a set..there are two sets of helical gears one in front of the other. I took the tailshaft housing off to see what was on the output shaft and thats what was there:confused:

LOL what a pain this has been.
J:D

8a8mfh
07-30-2007, 01:09 PM
Thanks for that info GMRACER13. I'll check em out a lil closer. When I say a set..there are two sets of helical gears one in front of the other. I took the tailshaft housing off to see what was on the output shaft and thats what was there:confused:

LOL what a pain this has been.
J:D

I've went through an old hardparts suppliers warehouse and looked at at least 200 th400 tailshafts. I grabbed a bunch of short 32 spline shafts for use with a 4" tail housing.

A lot of them had a STEEL SPEEDO GEAR.
The easiest way to get these off is with a cutoff wheel.
The gear you see cut into the shaft up by the case is to drive the governor.

frcefed98
07-30-2007, 03:58 PM
Yep thats whats in there alright....guess i'll be getting the dremel out and doing some precision cutting:dark: Both are steel gears:( Cut off the first gear only right?

crazyfokker
07-30-2007, 04:27 PM
what would it hurt to leave the speedo unhooked??? mine wasnt hooked up for two months.

XpEdItIoUs
07-30-2007, 06:41 PM
Nothing just your speedometor won't work.

Dirty 30
08-11-2007, 10:22 PM
This should be addressed in TH400 FAQ thread! I didnt know this shit was pressed on there and ive been here 1 hour trying to take it off lol :(

Stuarta
08-12-2007, 08:15 AM
One of the gears is for governor drive, the other is speedo.
The governor drive is cut into the shaft.
Measure the depth of the speedometer gear from the end of the output shaft before removal and install the new one that same depth.

Dirty 30
08-12-2007, 03:23 PM
whats the purpose of the governer?

lethal93ta
08-12-2007, 05:08 PM
I gave my speedo reluctor and pick up to the trans shop and they put it in when they built it.
http://www.streetlethal.net/trans/IMG_2966.JPG
http://www.streetlethal.net/trans/IMG_2967.JPG

8a8mfh
08-12-2007, 06:45 PM
whats the purpose of the governer?
It's basically a valve with weights on it that alters shift points as vehicle speed varies.
Transmissions with manual valve bodies don't need them.

Dirty 30
08-12-2007, 11:44 PM
It's basically a valve with weights on it that alters shift points as vehicle speed varies.
Transmissions with manual valve bodies don't need them.

Can it be removed or something to raise shift points? When i run WOT from 1st to 2nd the tranny shifts by itself but too early, like 4,500 rpm. But from 2nd to 3rd it does let me shift at any RPM.

8a8mfh
08-13-2007, 06:22 AM
Can it be removed or something to raise shift points? When i run WOT from 1st to 2nd the tranny shifts by itself but too early, like 4,500 rpm. But from 2nd to 3rd it does let me shift at any RPM.

Yes, if you have a th400 remove the cover held on by four bolts toward the rear of the trans on the passenger side. You can make the inner weights lighter to raise shift points or buy a governor calibration kit.
Make sure the vacuum modulator is connected to a manifold source, not a ported source.

Dirty 30
08-13-2007, 06:32 AM
Yes, if you have a th400 remove the cover held on by four bolts toward the rear of the trans on the passenger side. You can make the inner weights lighter to raise shift points or buy a governor calibration kit.
Make sure the vacuum modulator is connected to a manifold source, not a ported source.

What if I pull it out completely? If not, im guessing i can grind some material off to make it lighter? I have the modulator hooked up to the top of my intake (on my truck).

Thanks!
-Jesse

Stuarta
08-13-2007, 08:56 AM
Once you have cover off the governor just pulls out.

There are no timing marks.
It does not matter which way it goes back in.
Other than gear end first.

john kilgore
08-13-2007, 09:06 AM
if you have not connected the electric passing, the trans DOES NOT know you are at full throttle. just put 12v to it through a switch and l think you will be amazed good luck

8a8mfh
08-13-2007, 09:55 AM
From what I've experienced governor problems usually cause both shifts to be too early or too late.

So if you determine it is a governor calibration problem you can cut the nails off and remove the inner weights, grind a little off the sides, and reinstall using finish nails of the same size, crimp the finish nails with vise grips. It will look original, only difference is the factory used hardened nails.

Dirty 30
08-13-2007, 11:05 AM
if you have not connected the electric passing, the trans DOES NOT know you are at full throttle. just put 12v to it through a switch and l think you will be amazed good luck
Thanks!
Im guessing the switch would be a WOT micro switch to the pedal? (i have DBW throttle body)

bjamick
08-13-2007, 11:15 AM
Yeah but you lose your ABS if you do that, not what everyone wants right?

In the TH400 FAQ there are two part numbers that you have to order from either LS1speed.com or GM directly and you'll be able to get your factory speedo working again.

GM8655291 GM Speedometer Sensor $99.99
GM8655315 GM Speedometer Drive Sensor Rotor $65.99

There you go:D Searching this site is hit or miss so lets just try to help answer questions.

So thats all thats needed to get the speedo to work?? I've got a TH350 but i want ABS but im wanting the speedo to work also :(..

Dirty 30
08-13-2007, 12:16 PM
on my 03 truck, the abs and (brake!) lights came on. Now that i swaped the speed sensor and rotor, the lights went away and the speedo works.

lethal93ta
08-13-2007, 04:08 PM
So thats all thats needed to get the speedo to work?? I've got a TH350 but i want ABS but im wanting the speedo to work also :(..


a TH350 and TH400 use diffrent parts, the output shafts are diffrent sizes.

bjamick
08-13-2007, 04:10 PM
a TH350 and TH400 use diffrent parts, the output shafts are diffrent sizes.
Dammit :bang:.. So can someone help me out a lil :hijack:

What will i need to make the TH350 work. W/O spending $250.

lethal93ta
08-13-2007, 04:12 PM
when I was looking to put a TH350 in mine the trans shop was just going to use my factory sender and pick up off my 4l60. then I decided to just go with a trans I know Im not going to blow.

this is the sensor out of a 93 4l60 it should work in the same hole a th350 has. its the same size as the pick up for the Th400 I got, it would fit in the th400 hole but i needed a pick up to work on the bigger th400 output so I went with the reluctor wheel on there. I dont know how the pick up is for the 4l60E but depending on how its made you might be able to use that, when I get my blazer back ill have to look how the speedo is.
http://www.streetlethal.net/speedo/1.jpg

8a8mfh
08-13-2007, 07:05 PM
Dammit :bang:.. So can someone help me out a lil :hijack:

What will i need to make the TH350 work. W/O spending $250.

Well if you have a short tail th350, it's as easy as swapping out the chevy tail housing with it's 3/4" speedo hole and getting a BOP (Buick, Oldsmobile, Pontiac) th350 tail housing, these have a 2" speedo hole, same as 700R4's and early 4L60E's.

So if you have a short tail th350, get a BOP tail, reluctor wheel and sender off a 700, 4L60E. And thats it.

bjamick
08-15-2007, 10:25 AM
Well if you have a short tail th350, it's as easy as swapping out the chevy tail housing with it's 3/4" speedo hole and getting a BOP (Buick, Oldsmobile, Pontiac) th350 tail housing, these have a 2" speedo hole, same as 700R4's and early 4L60E's.

So if you have a short tail th350, get a BOP tail, reluctor wheel and sender off a 700, 4L60E. And thats it.
I have a 9" tailshaft, bc i wanted to use the stock driveshaft :(.. I know some places sale a whole tailshaft with the modifications already made so the Stock speedo sensor will just plug right in. I think they are like $250 though :(

HAMRHEAD
08-28-2007, 03:31 PM
Can anyone tell me what the two wires go to? I assume one is to the speedo but is the other one a power, ground, or what? And which wire is what? They are both gray and I can't find any markings. This is for a th400 and am connecting a Autometer speedo.

Thanks.

lethal93ta
08-28-2007, 04:22 PM
yous just put one to ground and the other to the signal wire on the speedo dpnt matter witch eather will work. the sensor just acts like a switch its on and off thats it.

HAMRHEAD
08-28-2007, 04:46 PM
Thanks!

psi3000
03-22-2013, 02:19 PM
You guys are going to kick yourselves after i post this. Check it out....
http://www.summitracing.com/parts/rpc-250-4153
I just found this, I think i might try it out with my build.
Its a converter from the mechanical to the electronic pulse for the th400 and i think the th350 as long as they use the same output cable size. let me know what you think of this guys.

Jimmy_d
10-20-2013, 06:43 PM
Did that work?