Speedo problem please help

[LanceJ]

1990 k5 Blazer, 241 transfer case, stock speedo in dash, odometer working
Background: I was driving on the freeway when the speedo just went to zero. Didnt work for at least six months. On a couple cold nights recently the speedo sprang to life. It worked fine all the way up to 45mph, but then died. Speedo has not been working for at least a week now.

When I turn the key on, I can see the speedo raise up off the perch at zero, but when I drive it doesn't move. When I turn the key off I can see it go back down.

What could it be? VSS in transfer case, DRAC module, Motor in speedo, bad wiring?
Do those symptoms sound familiar to anyone. I searched a bit, but didnt find anything

 

[jeff in co]

Does your cruise work? Any check engine codes/light? If cruise works and no codes, that would tell me you are getting the signal from T-case to your Drac. Then Drac sends signal to cruise, computer, ABS and speedo. If Odometer is working then I would guess that the gauge itself may be bad.

 

[LanceJ]

I didn't put the cruise control back on when i swapped the motor a few years ago. Sometimes when decelerating for a long time without touching the throttle the CEL will come on. #24 VSS circuit. I can turn the key off & back on, the CEL will be off & sometimes not come back on for a couple days. 700R4 doesn't seem to be shifting abnormally...

 

[pblaze725]

Did you disconnect the cable and make sure it spins freely?
Just asking b/c my speedo stopped working, and then worked sometimes.

It was the cable Seizing up.

 

[jeff in co]

If cel, then I would check out the twisted pair of wire from t-case to drac. You could also find another sensor in junk yard and try swapping it.

Just don't know why odometer works but no speedo?

 

[sweetk30]

Did you disconnect the cable and make sure it spins freely?
Just asking b/c my speedo stopped working, and then worked sometimes.

It was the cable Seizing up.

90-91 is electric speedo .

 

[pblaze725]

90-91 is electric speedo .

10-4 thanks for correcting me.

 

[dyeager535]

Does the odometer seem to work 100%?

Odometer and Speedometer use the same feed. If either one works consistently, they are getting the speed signal from the DRAC, and at least that problem is in the speedometer itself.

Wouldn't be a question except you have a VSS code on decel, which is where VSS is mainly used for TBI setups. Since the ECM VSS feed comes from the DRAC too, but on a different pin, that seems to indicate you have two issues, unless the odometer operation is intermittent.

 

[LanceJ]

I thought the odometer was working, maybe it was intermittently. I've watched the odometer the last couple days and it is Not working.

 

[jeff in co]

So I would say a new DRAC would be a start. Hit the junkyard or I believe someone on here was making them with the toggle pin setup (allows you to dial in the speedo accuracy given different gears and tire sizes).

I made my own and the blazer has a more accurate speedo than my 04' Yukon.

 

[dyeager535]

So I would say a new DRAC would be a start. Hit the junkyard or I believe someone on here was making them with the toggle pin setup (allows you to dial in the speedo accuracy given different gears and tire sizes).

It's most likely either DRAC, VSS, or wiring. I don't believe the VSS circuit is fused on a circuit by itself, but need to ensure that however it's powered, the fuse isn't popped.

 

[6872xtc]

The guy to talk to about the adjustable DRAC is sweetK30. He may even have one to sell without a core. I got one from him for my '90 and I like being able to set my speedo so easily!

 

[sweetk30]

shhhh don't tell any one

I have some . have to check what I got .

I think 1 single left . rest are doubles .

they dryed up around here in the yards . . . . thanks to the heavy rust belt.

you send me 1 tho I can swap the fixed pins for the dip switch unit.

 

[LanceJ]

sweetk30, i can send you this drac module, i dont know if it works or not. i would rather have a dip switch unit because im not sure what gear it has in it & its on 35" tires. the drac i have says AGG on it.
i cant figure out how to PM? or find your email?
lancej411@ gmail. com

 

[sweetk30]

I don't have a way to test drac's
that 3 dig code I have no way of knowing .

pm is easy . click my screen name over on left under my avatar pic . start conversation .

 

[LanceJ]

The odometer rolled up 2.3 miles sometime in the last few days. the speedometer didn't move tho.

 

[jeff in co]

I'd try a new DRAC for starters. Easier to do than a Speedo.

Where are you located? If you have access to a junkyard that would be pretty cheap parts to pick up. Speedo being harder to change out due to dash pad removal, etc.

 

[sweetk30]

yep drac clipped in bracket under radio .

 

[LanceJ]

Ive been shopping around for Drac Modules, the prices seem to vary widely. Shouldn't I just buy the cheapest one I can find no matter what the three letters are printed on it, change out the jumpers to an adjustable dip switch unit, and program it to match my gear ratio & tire size?

 

[dyeager535]

Ive been shopping around for Drac Modules, the prices seem to vary widely. Shouldn't I just buy the cheapest one I can find no matter what the three letters are printed on it, change out the jumpers to an adjustable dip switch unit, and program it to match my gear ratio & tire size?

There were a couple of different designs, but I'm not sure that the differences are that critical.

If it's physically the same design, the code on it is meaningless. When they were plentiful, I was grabbing the modules out of the Astro vans. There were way more of those than '90-91 R/V trucks.