Guys,

I have an 88 IROC L98 and the speedometer died over the weekend. Last evening, I decided to have a look to determine how much of a pain it was going to be to replace the head unit or cable (depending on what is broken). I have both the Haynes Manual and the Chilton Manual. They show the cruise control unit in the left-front of the engine bay, near the charcoal canister. The only thing that I can find in that location is the servo valve - no unit...

The cruise unit is not there as pictured in the manual. I found the speedometer cable under the master cylinder, but gave up tracing it because I was in a hurry.

I do know that I have a functioning cruise control unit because I use it...

Note that this car has the RPO for a mechanical speedometer (whatever that means).

Anyone?

 

Keith,

Mine is right there, but it's on an '86 TA:

 

Yeah, that's where the Haynes Manual shows it too...

However, I see that your battery is also there - my charcoal canister is in that location...

Hmmm....

 

Vader's pic shows the cruise throttle servo. There isn't anything connected to the speedometer cable as in days of yore. The cruise is controlled by the ECM using the signal from the VSS on the back of the speedometer. If your cruise works but the speedo doesn't, it's definately the head unit because the cruise wouldn't work if the cable was broken (VSS wouldn't get any signal).

Older 3rd gens still had the speedometer cable driven cruise control govenor - '84 or '85 last year for that (not completely sure which).

The "mechanical speedometer" simply means it is driven directly by the speedometer cable, rather than an electronic sensor on the transmission (VSS) that sends a signal to the ECM, which sends a signal to the speedometer telling it how fast to tell you you're going.

 

five7kid - Thanks. I figured it was something like that (this is my newest car). It was just driving me nuts. Tomorrow I will try out the cruise and see if it works and this should put me on the path.

In the meantime, I assume that you also have the same setup. Does your cable have threads where it "breaks in two" under the master cylinder, then continues to the tranny? That's where mine appears to allow separation into two cables. The problem is that it appears original and is corroded together (PB Blasted to no avail). To make matters worse, it's so tight in there that I'm thinking that I should just cut it and replace it. Since the speedo cable is so tight, I can't pull the instrument panel out to disconnect from the back of the head.

Is this really the cable? Thanks again, both of you.

 

while trying to diagnose, don't overlook the cruise control switches themselves. wire often becomes frayed on the turn signal lever.

 

2v, Keith's problem is the speedo doesn't work.

Keith, my speedo cable is one-piece from tranny to speedo. I had to change it out when I did the swap (because the '82 was the old govenor type and the cables are completely different). All the stuff, including the switch & wiring, is from the '86 donor.

To get the cluster out, I have to pull it back as far as I can (which isn't much), work my hand behind the speedo, and release the cable from the head. Then the cluster will come out, and the cable is lookin' at ya.