Speedo quit working.

[Vbb199]

Doesn't the 89 have a cable driven speedo cable that drives that weird light sensor dealio? Its the sensor that feeds the pulse signal to the ECM, right?

I believe so.

 

[Turbo4whl]

OK, ..... because I just wanna know how it works.


My 89 no longer has a working speedo as of today, and 4th gear also does no lock up anymore.

I'm going to use one of your lines; "Just give the truck to me and you won't have to worry about it"

Here is a guess, since not all '89s have cruise control, is the DRAC in the speedo gauge head?

 

[Vbb199]

I'm going to use one of your lines; "Just give the truck to me and you won't have to worry about it"

Here is a guess, since not all '89s have cruise control, is the DRAC in the speedo gauge head?

That's funny actually lol!

This one does have cruise control. But I don't think this 89 will have a drac module. Maybe tho.

 

[Vbb199]

On the 90 and 91 the drac is behind the dash, under the radio.

 

[Snoots]

Still uses a cable. Its cable driven!!!!!

90 and 91 uses VSS

That seems odd.
Does the cable drive an electronic unit on the back of the speedo?

 

[Vbb199]

That seems odd.
Does the cable drive an electronic unit on the back of the speedo?

Yes. I do believe so.

 

[Vbb199]

Wtf it does use a VSS (or at least what looks like a vss)

But it's a cable driven speedo? Stupid half year ****

You must be registered for see images attach

 

[Vbb199]

So it's got a reluctor ring in the tail shaft, which the vss counts the revolutions...


@Turbo4whl ,maybe you were into something???? The DRAC is in the instrument panel???

 

[Vbb199]

@bucket
Do you have any insight on this?

 

[bucket]

That's just a regular ol speedo cable, with a drive and driven gear in the tailhousing. The VSS mounts to the back of the cluster and has an optical sensor of sorts that reads off of the speedo. Most 80's GM vehicles used the same setup, before electric speedos were phased in.

 

[Turbo4whl]

Here is a guess, since not all '89s have cruise control, is the DRAC in the speedo gauge head?

Lucky guess on my part, except I called the wrong name. DRAC = Digital Ratio Analog Converter

@bucket has the answer as usual.
VSS = Vehicle Speed Sensor

The newest square I ever owned was an '85 Suburban.

 

[Vbb199]

That's just a regular ol speedo cable, with a drive and driven gear in the tailhousing. The VSS mounts to the back of the cluster and has an optical sensor of sorts that reads off of the speedo. Most 80's GM vehicles used the same setup, before electric speedos were phased in.

Alright, so I was correct in what I assumed about it just being a drive/driven gear setup, despite the VSS looking do-hickey In the trans tail.
I knew without a doubt it had a cable driven speedo, I've had the cluster out.

Just wasn't sure "how it worked" in relation to the TC not locking up and now I see. The vss in the speedo reading the pulses sends signal to the ECM for lockup.

 

[Vbb199]

Lucky guess on my part, except I called the wrong name. DRAC = Digital Ratio Analog Converter

@bucket has the answer as usual.
VSS = Vehicle Speed Sensor

The newest square I ever owned was an '85 Suburban.

When I saw the vss looking device in the tail housing, I thought ok... Is this some weird half year stuff....
"drac isn't under the radio like 90 and 91, so maybe Turbo4whl is right... It's got the drac in the speedo"

But now it's all coming together.

Driven/drive gears are for tire/gear setup, vss is just there to count the rotations.


So I just gotta ask, and this is part nobody has answered.


Why the hell does it "look" like a vss is in the tranny tail shaft??? Is that just a cover that's a pre curser to the actual 90 and 91 vss??

 

[bucket]

That's what all the speedo cable bits looked like through the years.

 

[Vbb199]

That's what all the speedo cable bits looked like through the years.

OK, I haven't messed with cable driven speedo's as much as some of the other guys here, so I'm not as familiar with them as the 90 and 91 trucks.

I have more personal experience with the tbi trucks in general, but this was all kinda new to me as far as how it all works.