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Old 07-05-2018, 11:05 PM   #1
jocko
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Gear Vendors behind a 90 K2500 w/TH400 - speedo question

I'm "assuming" the speedo is electronic in a 90 K2500 (someone help me here) - and if that's the case, has anyone hooked a GV o/u drive up behind the t-case and how did you provide a speedo signal? If it's mechanical, then no worries - but I can't remember which your the mech speedometer cable gets ousted for electronics... I thought it was early 90's, but I don't recall a speedo cable on a 92 I had (but it was a long, long time ago) - so figured I'd ask. Thanks
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Old 07-06-2018, 08:47 AM   #2
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Re: Gear Vendors behind a 90 K2500 w/TH400 - speedo question

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Originally Posted by jocko View Post
I'm "assuming" the speedo is electronic in a 90 K2500 (someone help me here) ...
Yes it is electronic.
On a 1990 the DRAC module is built into the instrument panel.

The DRAC (Digital ratio adapter controller) is also referred to as the “vehicle speed sensor buffer”.

The DRAC conditions the alternating currant signal from the vehicle speed sensor to a square wave signal so it can be used by the vehicle electronics.
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Old 07-06-2018, 09:42 AM   #3
95 S_Trucker
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Re: Gear Vendors behind a 90 K2500 w/TH400 - speedo question

Wouldn't the gear vendors go between the transmission and transfer case?

You would have serious problems if it was mounted after the transfer case. Your front drive shaft would turn at a different speed than your rear drive shaft.

There is a VSS(vehicle speed sensor) mounted in the tail shaft of the transfer case.
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Old 07-06-2018, 03:59 PM   #4
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Re: Gear Vendors behind a 90 K2500 w/TH400 - speedo question

Thanks Chevy tech - Can the VSS be relocated from the t-case to a GV o/u output?
95 S - it has to go behind the t-case, usually a direct mount, and can only be used for 2WD.
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Old 07-06-2018, 04:39 PM   #5
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Re: Gear Vendors behind a 90 K2500 w/TH400 - speedo question

Early TBI vehicles use 40 pulses per drive shaft revolution.

The shaft would have to have a 40 tooth square cut “Tone Wheel” or the VSS will not work.

There are vehicle speed sensors that are made to run off an speedo drive cable connection. Some GM vehicle even used that arrangement from the factory. All the links I had saved on this topic are very old and no longer work. I just don't have the time to search for a photo of what you need.

EDIT:
Some GM F body cars came with a VSS that ran off the cable drive but I do not remember if they produced 40 pulses per revolution.
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Last edited by ChevyTech; 07-06-2018 at 05:00 PM. Reason: Add more
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Old 07-06-2018, 06:28 PM   #6
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Re: Gear Vendors behind a 90 K2500 w/TH400 - speedo question

Quote:
Originally Posted by ChevyTech View Post
Early TBI vehicles use 40 pulses per drive shaft revolution.

The shaft would have to have a 40 tooth square cut “Tone Wheel” or the VSS will not work.

There are vehicle speed sensors that are made to run off an speedo drive cable connection. Some GM vehicle even used that arrangement from the factory. All the links I had saved on this topic are very old and no longer work. I just don't have the time to search for a photo of what you need.

EDIT:
Some GM F body cars came with a VSS that ran off the cable drive but I do not remember if they produced 40 pulses per revolution.
An outfit called "Jags That Run" actually sold a VSS sensor that ran off the speedo cable. I had the intention of using a TBI engine in my old car at one time but those plans changed. I still have that setup somewhere in my garage. Wouldn't a better economic plan to swap out the T400 for a 4L80E be a better and cheaper idea?
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Old 07-06-2018, 07:34 PM   #7
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Re: Gear Vendors behind a 90 K2500 w/TH400 - speedo question

Copy all gents, thanks for the help. I can do the searchin, just wanted a little vector before I added thrust.
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Old 07-06-2018, 11:15 PM   #8
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Re: Gear Vendors behind a 90 K2500 w/TH400 - speedo question

Quote:
Originally Posted by Mr_Rich View Post
An outfit called "Jags That Run" actually sold a VSS sensor that ran off the speedo cable. I had the intention of using a TBI engine in my old car at one time but those plans changed. I still have that setup somewhere in my garage. Wouldn't a better economic plan to swap out the T400 for a 4L80E be a better and cheaper idea?
I agree with this guy a 4L80 with controller is a nicer combo for driving unless you can get the GV cheap.
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Old 07-06-2018, 11:23 PM   #9
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Re: Gear Vendors behind a 90 K2500 w/TH400 - speedo question

This is a truck I was looking at buying, am right on the dang fence, ha. It's a C6P, would like to keep its original TH400, but you both raise a good point, 4L80 might be a better route - similarly tough transmissions, just one with o/d. I normally live in the 67-72 world... Would a 4L80 swap require moving the t-case (I guess I assumed it would and that's why I hadn't really considered it)? In 67-72 world, o/d swaps are usually accomplished by moving the engine fwd an inch or two, so just curious how easy a swap it would be to stuff the 4L80 into a 90. Thanks guys.
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Old 07-07-2018, 12:20 AM   #10
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Re: Gear Vendors behind a 90 K2500 w/TH400 - speedo question

I can probably measure the cross-member on my K1500 and compare it to my K2500. I think the 700R4 actually has a close measurement to a T400. I'm kind of curious now.
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1989 K1500 Chev. EC
Original owner; some of the aftermarket parts I've installed are Borla headers, Hypertech chip, Edelbrock water pump, and a Stillen rear disc brake conversion kit.
2009 Hummer H3T 3.7L 5M.
1997 K2500 Chev. EC 7.4L/ 4L80E
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Old 07-07-2018, 11:35 AM   #11
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Re: Gear Vendors behind a 90 K2500 w/TH400 - speedo question

It looks like the 4L80E trans cross-member is two inches further back on my K2500 than the cross-member on my K1500 truck with the 700R4.
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1989 K1500 Chev. EC
Original owner; some of the aftermarket parts I've installed are Borla headers, Hypertech chip, Edelbrock water pump, and a Stillen rear disc brake conversion kit.
2009 Hummer H3T 3.7L 5M.
1997 K2500 Chev. EC 7.4L/ 4L80E
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Old 07-07-2018, 09:53 PM   #12
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Re: Gear Vendors behind a 90 K2500 w/TH400 - speedo question

Thanks very much Mr Rich!
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