Speedo failure

[Peer81]

Hello everybody,

I have a speedo failure and what to know what could be the problem.
Thing is, I have a new speedo, new upper and lower cable, old cruise controller transducer.

Speedo works fine on steady and little acceleration, but when I put the pedal to the metal the speedo goes to zero. I put grease on (or in) the upper and lower cable so I was thinking maybe it is slipping back from the speedo. But the upper cable is locked into the speedo and I unlocked the upper cable and the CC. Tried to pull the inner cable back but it was locked (I could only move it for 1/4 - 1/2"). First time I did this I reinstalled the upper cable into the CC and it worked till the next acceleration. Anybody an idea?

Greetings Peter

 

[Vettehead Mikey]

Mine did that many years ago. It was the driven gear inside the transmission just plain worn out. Easy fix.

 

[Peer81]

Thanks, now you say it, the speedo wasn't steady but I was thinking that was stock (after driving it again after 6 or 7 years). I'll look at the driven gear, like you say, not to difficult.

Greetings Peter

 

[Peer81]

I took out the driven gear and it was worn out like you said. Thing is, it's a 700R4 (or 4L60) from a 90 Corvette. The drive gear is a red 17 teeth gear, but I can move it a little forward and backward, is this normal? My driven gear (still needed to see if it was the right one) was/is a 42 teeth gear.
This website: Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4
says that the driven gear needs to be matched to the driven gear housing, that is the problem is I have the wrong housing for a 42 teeth gear?

Greetings Peter

 

[Peer81]

The problem continues...

I put in a new driven gear today. No effect! :ugh
The I did what I did before. Took the upper cable out of the cruise controll. I could move the inner cable up and down a little (about 1/4 to 1/2 inch) but I couldn't get it furter out. Then I pushed the inner cable up (to the speedo meter) and assembled the upper cable back into the CC. Went for a little drive and the speedo WORKED! But within 2 minutes the speedo was dead again. Same thing, upper cable disscontected at the cc, pushed the inner cable up, connected very thing and again the speedo worked for about 1 minute.

So my question, what is locking the upper cable "in place", and could I alter this to keep it locked higher up?

Greetings Peter

 

[Rex S]

Does your car have a transducer? It's a small box like deal with 1 cable running from the transmission to the box and 1 cable coming from the box to the speedo that controlls the cruse controll. If so it is going bad.

 

[LLC5]

The problem continues...

I put in a new driven gear today. No effect! :ugh
The I did what I did before. Took the upper cable out of the cruise controll. I could move the inner cable up and down a little (about 1/4 to 1/2 inch) but I couldn't get it furter out. Then I pushed the inner cable up (to the speedo meter) and assembled the upper cable back into the CC. Went for a little drive and the speedo WORKED! But within 2 minutes the speedo was dead again. Same thing, upper cable disscontected at the cc, pushed the inner cable up, connected very thing and again the speedo worked for about 1 minute.

So my question, what is locking the upper cable "in place", and could I alter this to keep it locked higher up?

Greetings Peter

If you are sure both your inner cables are good, then it is probably a bad transducer. I have replaced many in the past for inoperative speedometers.

 

[Peer81]

Thanks everybody,

The transducer was already not working properly (7 years ago before the body off) So I was thinking about replacing it anyway.

Greetings Peter

 

[Peer81]

BTW. Is there some connector so I can connect the upper cable with the lower cable and bypass the cruise control (until I have the new transducer)? Because I can't find them...

Greetings Peter

 

[LLC5]

BTW. Is there some connector so I can connect the upper cable with the lower cable and bypass the cruise control (until I have the new transducer)? Because I can't find them...

Greetings Peter

There were couplers available to bypass the transducer, but it has been so long that I can't remember where they came from. You may want to call a few dealers and see if any of the older parts people might remember them.

 

[78IndyPace]

Is there some connector so I can connect the upper cable with the lower cable and bypass the cruise control (until I have the new transducer)? Because I can't find them...

You have 3 choices as far as I know:

1. Replace the 2 speedo cables with the single cable for a non-cruise control Vette, or

2. Replace the cruise control transducer, or

3. Repair your cruise control transducer.

I know of no instructions on how to do a transducer repair, but the unit is pretty simple. I took mine apart a couple of years ago and cured a bouncing speedometer needle and slowly increasing speed while the cruise was engaged. The spinning disk inside had slipped a bit on its shaft and was rubbing slightly on the sensor assembly. I carefully tapped the spinning disk a bit toward the rear until I could no longer feel or hear the rubbing when I spun the input from the transmission using the tang of a small file.

Other guys have had success with disassembling and cleaning the transducer to cure various problems. You have nothing to loose by taking it apart and checking it out, and it might save time and $$.

Good luck!
Jerry

 

[Peer81]

Hello Jerry,

Thanks for the advice and I'll go for option 3
I'll take it apart and see what the service manual says about it!

Greetings Peter

 

[Peer81]

I found the problem!

The new upper cable was the problem. The inside cable was to "short" to stay connected to the speedo. Or correctly said, on the side the cable goes into the CC it goes from round to squared. The squared side was to long so when spinning it could slide deeper into the CC and on the other side it disconnected from the speedo.
I put the old one back in and everything works fine again.

Well, only my CC has a little problem, it slowly deaccelerates so that is something to look at.

Greetings Peter

 

[TimAT]

Check the cruise control system for vacuum leaks. Slow decel could be the diaphragm that's connected to the throttle linkage leaking, or it's bleeding off vacuum. Usually the transducer will sense the slowing speed and compensate, but it's possible. It could be the transducer is doing as it should and giving all the vacuum it can but it's not taking effect.

 

[Peer81]

Thanks Tim, I'll check the diagram with a vacuumpump - meter.

Greetings Peter

I'll check the

 

[Peer81]

Checked the diagram with a vacuumpump - meter today. And for 15 minutes it holds a steady vacuum and holds the throttle in the same position. So no problem there.

Greetings Peter