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TH400 speedo question

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Old 07-25-2007, 10:02 PM   #1
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Default TH400 speedo question

I switched from a 4l60 to a Th400, What do I need to do to get the speedo working again?
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Old 07-25-2007, 10:15 PM   #2
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I have read a couple of threads that guy's have used a front wheel sensor after a 350 or a 400 swap.
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Old 07-25-2007, 11:39 PM   #3
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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.
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Old 07-25-2007, 11:41 PM   #4
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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 Searching this site is hit or miss so lets just try to help answer questions.
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Old 07-28-2007, 11:02 PM   #5
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Anyone know what is need to press it on?
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Old 07-28-2007, 11:46 PM   #6
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Pics of these pieces too please.

I have what look to be a set of speedo gears pressed onto the output of my TH400?
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Old 07-29-2007, 06:36 AM   #7
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Quote:
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.

Click the image to open in full size.

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Old 07-29-2007, 08:01 AM   #8
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Quote:
Originally Posted by XpEdItIoUs
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.
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Old 07-29-2007, 09:51 AM   #9
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Quote:
Originally Posted by XpEdItIoUs
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.
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Old 07-29-2007, 09:55 AM   #10
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Quote:
Originally Posted by frcefed98
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.
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Old 07-29-2007, 11:14 AM   #11
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Quote:
Originally Posted by GMRACER13
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?
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Old 07-29-2007, 09:10 PM   #12
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Quote:
Originally Posted by XpEdItIoUs
Thanks for the info, How far do i slide the ring?
Untill it's centered in the hole for the speed sensor.
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Old 07-29-2007, 10:01 PM   #13
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What atf are you guys using on your th400?
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Old 07-29-2007, 11:27 PM   #14
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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

LOL what a pain this has been.
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Old 07-30-2007, 01:09 PM   #15
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Quote:
Originally Posted by frcefed98
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

LOL what a pain this has been.
J
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.
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Old 07-30-2007, 03:58 PM   #16
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Yep thats whats in there alright....guess i'll be getting the dremel out and doing some precision cutting Both are steel gears Cut off the first gear only right?
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Old 07-30-2007, 04:27 PM   #17
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what would it hurt to leave the speedo unhooked??? mine wasnt hooked up for two months.
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Old 07-30-2007, 06:41 PM   #18
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Nothing just your speedometor won't work.
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Old 08-11-2007, 10:22 PM   #19
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This should be addressed in TH400 FAQ thread! I didnt know this **** was pressed on there and ive been here 1 hour trying to take it off lol
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Old 08-12-2007, 08:15 AM   #20
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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.
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Old 08-12-2007, 08:15 AM
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