Cadillac Owners Forum banner

Whats up with my speedometer?

762 Views 1 Reply 1 Participant Last post by  Night Wolf
Alright, here is a little background information...

Somewhere when the car had ~137k miles on it, no surprise, the tranny started slipping bad. This was maybe 4 or 5 years ago? The speedometer worked great, hardly wobbled too.

Anyway, my mom took the car to a very reputible local (in NY) transmission shop. Well, the 200R4 in the car was not rebuilt and put back in, what happens in, they swaped it out from a 200R4 on the shelf that was already rebuilt. They do this core swap thing to keep busy when there is slow business.... alright, fair enough.

Well, when she got the car back, the speedometer would register 12mph under the acutal speed... this was going on for a long time unnoticed until my mom got pulled over for going 12mph over the speed limit.... on the same stretch of road, back to back (got off both times too...heh)

Then we knew about it, so we took it back to the shop where we had the trans replaced (it was no longer then a couple months afterword) We thought that possibly the trans came out of a different type of vehicle with different size tires and the speedo gear was different.... so... they take the car out and compare it to someone from the shop driving their truck... sure enough, when they were going 55mph the Caddy would say 67mph.

They couldn't understand as they said they don't even touch the speedo gear portion of the trans and that it came from a similar car... So... none the less the change the speedo gear, take it back out and it reads correctly.

That was fine, for about a month or two.... the speedo would slowly get slower and slower, until finally, as it is now, it sits at 0 when you drive. In the past if you were doing 75 or so on the highway it would make its way up around 30mph or so and fluctuate bad.

So that was going on for years, the odo now just turned (1)43k.... so the mileage of the car is kinda unknown... but still, no speedometer.

I thought the cable was bad or something... but one day a few years ago I decided to put the car in neutral while driving (forgot what I was testing) anyway after a second or so, the speedometer actually started working.... and much to my surprise it was reading 12mph over my actual speed limit...

To this day, when the shifter is put in neutral, the speedo works, and reads 12mph over the limit (since the gear was changed) As soon as the shifter is put into D, 3, 2 or 1, the speedo drops fast to 0.


What would cause the speedometer, which is connected by a cable directly to the transmission, to only register in neutral, and not in drive? Also keep in mind when this tranny was first put in the car, the speedo was reading slower then the acutal speed when in drive, but if put in neutral, it would have gave an accurate speed (as evidenced by now reading 12mph over)

My first thought was something wrong with the cable... but... how? when in neutral, the cable works fine, and is pretty steady too.

Then I was thinking, well there much be something binding up at the steering column.... but the speedo cable and shifter never come close to each other.

So finally I am thinking... must be a problem internally in the transmisson... what else would allow the speedometer gear to turn when in neutral, but not in drive?

I will be getting the correct speedometer gear from the '87 Brougham which is now a parts car.... Do you think it could even be a problem with the instrument cluster? I dunno.

It's really stumped me... and I'd like to get the speedo working again... know my speed, calculate fuel mileage... and log miles on the car.... in the past 5 years there has only been 3 or 4,000 miles put on the car (from highway driving with the speedo around 30) when in reality the car probably had close to 50k miles put on it in that time.

I dunno what to do, when I change the speedo gear I was going to shoot some PB blaster inside the trans around the gear to maybe free something up... but still... I'm stuck, I don't know what it could be.

The transmission is otherwise great, shifts great (very firm actually, feels like there is a shift kit in it.... but that isn't bad either) if it was an internal problem with the trans, that would stink... and I can't see myself trying to replace a good transmission. The fluid looks good and the level is ok, I am going to change the fluid and filter anyway, but I doubt that will have an effect on anything. The car has a (large) aux trans cooler on it, which has been hooked up to this particular tranny since it was put in the car.

One other thing that kinda bothers me too is... IIRC, the transmission uses an electronic sensor to lock the torque converter, though it is vaccum shift controled. I remember reading that when the speedometer passes 40mph(?) it tells the torque converter to lock. Well, if thats the case... then the torque converter is never locking up, cause extra wear and a good loss in fuel mileage. Thats another reason why I'd like to get it fixed.
See less See more
1 - 2 of 2 Posts
Man I typed up somg long posts this morning...

basically, when the shifter is in drive, speedometer dosn't work, when shift is in neutral and the car is coasting... speedometer works.
1 - 2 of 2 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.