Need speedo help, its way off
Thread Starter
Melting Slicks
Joined: Jun 2001
Posts: 3,031
Likes: 1
From: Republic of Texas
Need speedo help, its way off
My 1991 ZR-1 had 4.10s in it when I got it. As I am not a drag racer, I soon tired of those gears so I swapped complete rear axle assemblies with a friend of mine's LT4. We also swapped the speedo gears from the transmission. His speedo is right on, mine is way off, around 15% slow. Any ideas? Is there a chip setting I need to change too? I thought it was just the gear. The gears are not different from '91 to '96 are they? Could my gear be seated wrong causing it to skip?
TIA for any help.
TIA for any help.
Thread Starter
Melting Slicks
Joined: Jun 2001
Posts: 3,031
Likes: 1
From: Republic of Texas
Re: Need speedo help, its way off (91mongoose)
I started playing with a spreadsheet that shows speed per RPM in each gear with various rear ratios and discovered that my car's speedo still thinks its got 4.10s. I changed the gear in the tranny (the car I swapped with has a correct speedo), could it be my prom? I didn't think that the prom had anything to do with the speedo.
Thread Starter
Melting Slicks
Joined: Jun 2001
Posts: 3,031
Likes: 1
From: Republic of Texas
Re: Need speedo help, its way off (91mongoose)
I put the gear and sender from my spare tranny in and I get the same thing. It's not the prom, I tried that and confirmed it through the service manual as well. The gear that came out when the 4.10s did was a different color (not dark green) and it corrected my friends speedo to work with the gears. Why am I not having any luck?
Anybody?
Anybody?
Burning Brakes
Joined: Oct 2001
Posts: 945
Likes: 24
From: NORTHRIDGE CALIFORNIA
Re: Need speedo help, its way off (91mongoose)
I just did the reverse swap. Bill Boudreau from ZR51 told me how. Got the 2 replacement gears from LPE
for about $140. There are 2 gears to swap: the plastic drive gear on the drive shaft(thick,round), and the
plastic driven gear (cone shaped) in the side housing off the tail piece. I removed the yoke/drive shaft,
and the side housing, and did not remove the tail piece, just looked through the side opening. PITA to deal
with the retaining clip for the drive gear, but doable. Summary- there are 2 gears to change.
for about $140. There are 2 gears to swap: the plastic drive gear on the drive shaft(thick,round), and the
plastic driven gear (cone shaped) in the side housing off the tail piece. I removed the yoke/drive shaft,
and the side housing, and did not remove the tail piece, just looked through the side opening. PITA to deal
with the retaining clip for the drive gear, but doable. Summary- there are 2 gears to change.
Thread Starter
Melting Slicks
Joined: Jun 2001
Posts: 3,031
Likes: 1
From: Republic of Texas
Re: Need speedo help, its way off (95ZR1)
Thanks. I did the swap yesterday. I have a spare transmission so I took the gear out of it, made it easy to see what I was up against before crawling under the car. My speedo is still off, though. It now reads 10% slow instead of 20% slow.
