Speedometer Problems
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
Likes: 0
From: Inver Grove Minnesota
Speedometer Problems
My speedo hasn't worked for a little while. Like since before I bought it. It has about 1000 miles since it went bad. Anyways it looks like the guy that had it before me disconnected a vacuum hose that runs to a piece of equipment that the speedo cable hooks up to from the tranny then another goes into the fire wall. So I hooked it up but it still doesn't work and when I put the brakes on I have a vacuum leak in my dash ( I can hear it hissing right in front of me) and my engine runs like crap. If I take the hose back off then it is fine. Any sugjestions?
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
That is the cruise transducer. Just turn the cable that runs inside CCW and look at the speedo. It should register a little. That eliminates the stuff inside. Then look at the cable from there to the transmission. You will probably find the transducer bad and the gear in the transmission stripped.
Team Owner
Joined: Jun 2000
Posts: 38,923
Likes: 1,481
From: Southbound
Cruise-In II Veteran
Do you have the '78 assembly instruction manual (AIM)? There may be a filter behind the speedo/tach causing your vacuum leak. If it's there, the AIM should show it along with the proper hose routing to and from it.
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
Likes: 0
From: Inver Grove Minnesota
Yes I do. But I don't want to have to tear out my dash. So I'll just leave it unhooked. I found out that my problem is the gear in the tranny that turns the cable. I took it off and spun it while watching the speedo and it moved.
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
Originally Posted by JustinD
Yes I do. But I don't want to have to tear out my dash. So I'll just leave it unhooked. I found out that my problem is the gear in the tranny that turns the cable. I took it off and spun it while watching the speedo and it moved.
1) Clip fallen out of speedo drive gear in transmission on TH350 trans. Take the driven gear housing off the side of the tail housing and see if the gear on the mainshaft spins. If it does, you have to take the tail housing off and put the clip back.
2) The Cruise transducer may be bad and cause the gear to strip out. If it doesn't work anyway I would remove it and replace the speedo cable with one for a car wothout cruise.
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