Differences in factory speedometer internals?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Kaysenmc · 11-27-2009, 11:08 PM

Here's the story.. About a week ago I was going to lube my 87s squeeking speedo cable and removed everything needed to get to the speedo. I always hate trying to unhook the cable from the speedometer head with such little space, so I unhooked the cable at the trans and fed the cable through the firewall for a little more working room. I noticed that the cast aluminum housing looked like it had some really bad casting marks (turned out to be cracks) on it on all sides. I proceeded to unhook the speed sensor (5.5mm bolt, I believe) then the cable, when the cast housing busted into probably 30 pieces. Gears, face, and odometer hit the floor but the part the cable hooks into was still stuck in the end of the cable.
So I have an 84 lwb I have been robbing parts off of and yanked the speedo without the sensor to swap into my 87. My 87's speedo had a gray drive gear that runs (use to run) the odometer, but in the one outta the 84 the same part is light yellow and is shaped differently.
Here's the problem... My speedometer has read slow by ten or so miles an hour (at 65)with my current powertrain setup (tbi 350, 700r4 (I do not know what speedometer gears it has in it) and 3.40 gear rearend (swapped from 2.73)). But now with the 84 speedometer I am reading about 15 mph fast at 65.
Heres the question... are 87 model speedometers a one year only piece (I know the faces will NOT interchange without modification) or are the speedos calibrated for different geared rearends from the factory? Or do I need to swap the speed sensor too? I have searched locally and online but have come up empty...
Thanks in advance and sorry for the long thread!

b454rat · 11-28-2009, 09:21 AM

I never heard of internals being different, I always thought they were the same.

I just looked at the speedo out of my 84, it doesnt' have the VSS on it, but the hole is there to bolt it on, just need a self tapper.

68 TT · 11-28-2009, 09:45 AM

Any pics? The two I have are both gray drive gears.

Kaysenmc · 11-28-2009, 08:07 PM

Well I got to the salvage yard a lil before they closed and all they had was some 100mph speedo's and an 89-91 that had the whole cluster robbed. So, I will keep everyone updated what I can find out

1985-GMC · 11-28-2009, 10:46 PM

Here's a site that has probably anything your looking for dealing with speedometer gears. A little ways down the page they have a ratio adapter that might work for you, give them a call to figure out exactly what you need. Hope this helps.
http://www.transmissioncenter.net/sp...n_______va.htm

11-27-2009, 11:08 PM	#1
Kaysenmc Registered User Join Date: Sep 2007 Location: Marietta, Ok Posts: 246	Differences in factory speedometer internals?? Here's the story.. About a week ago I was going to lube my 87s squeeking speedo cable and removed everything needed to get to the speedo. I always hate trying to unhook the cable from the speedometer head with such little space, so I unhooked the cable at the trans and fed the cable through the firewall for a little more working room. I noticed that the cast aluminum housing looked like it had some really bad casting marks (turned out to be cracks) on it on all sides. I proceeded to unhook the speed sensor (5.5mm bolt, I believe) then the cable, when the cast housing busted into probably 30 pieces. Gears, face, and odometer hit the floor but the part the cable hooks into was still stuck in the end of the cable. So I have an 84 lwb I have been robbing parts off of and yanked the speedo without the sensor to swap into my 87. My 87's speedo had a gray drive gear that runs (use to run) the odometer, but in the one outta the 84 the same part is light yellow and is shaped differently. Here's the problem... My speedometer has read slow by ten or so miles an hour (at 65)with my current powertrain setup (tbi 350, 700r4 (I do not know what speedometer gears it has in it) and 3.40 gear rearend (swapped from 2.73)). But now with the 84 speedometer I am reading about 15 mph fast at 65. Heres the question... are 87 model speedometers a one year only piece (I know the faces will NOT interchange without modification) or are the speedos calibrated for different geared rearends from the factory? Or do I need to swap the speed sensor too? I have searched locally and online but have come up empty... Thanks in advance and sorry for the long thread! __________________ 87 black silverado swb, tbi 350, 700r4, 3.40 gears. 2.5 drop spindles , 2 inches off stock coils, flip kit out back. cragers with radial ta's... ongoing piddle project! 1970 Olds rallye 350, street strip 403/350 3.73 posi. Looks stock/runnin 12's! 86 K5- SOLD!

11-28-2009, 09:21 AM	#2
b454rat Senior Member Join Date: May 2004 Location: Binghamton, NY Posts: 3,454	Re: Differences in factory speedometer internals?? I never heard of internals being different, I always thought they were the same. I just looked at the speedo out of my 84, it doesnt' have the VSS on it, but the hole is there to bolt it on, just need a self tapper. __________________ 2000 GMC CCSB 454/4L80 6” lift SAS 1999 Chevy CCSB 454/NV4500 6” lift 1999 GMC Yukon 350/4L60 4" SAS

11-28-2009, 09:45 AM	#3
68 TT Still plays with trucks Join Date: Jul 2009 Location: Spokane, WA Posts: 3,556	Re: Differences in factory speedometer internals?? Any pics? The two I have are both gray drive gears. __________________ miSSed opportunity - ground up creation of an AWD 1994 454 SS that never was http://67-72chevytrucks.com/vboard/s...d.php?t=795577 69 C10 shortbed stepside 400 small block - built like what a super sport truck could have been 69 K20 lwb TBI 350 4L60E NP208 14-bolt Dana-44 w/disc 68 Camaro SS / RS 500hp 439 inch roller cam big block 4L80E 79 Malibu TPI 350 4L60 w/ Z28 steering & sway bars

11-28-2009, 08:07 PM	#4
Kaysenmc Registered User Join Date: Sep 2007 Location: Marietta, Ok Posts: 246	Re: Differences in factory speedometer internals?? Well I got to the salvage yard a lil before they closed and all they had was some 100mph speedo's and an 89-91 that had the whole cluster robbed. So, I will keep everyone updated what I can find out __________________ 87 black silverado swb, tbi 350, 700r4, 3.40 gears. 2.5 drop spindles , 2 inches off stock coils, flip kit out back. cragers with radial ta's... ongoing piddle project! 1970 Olds rallye 350, street strip 403/350 3.73 posi. Looks stock/runnin 12's! 86 K5- SOLD!

11-28-2009, 10:46 PM	#5
1985-GMC Chevy Enthusiast Join Date: Jul 2009 Location: Canyon Lake Texas Posts: 2,024	Re: Differences in factory speedometer internals?? Here's a site that has probably anything your looking for dealing with speedometer gears. A little ways down the page they have a ratio adapter that might work for you, give them a call to figure out exactly what you need. Hope this helps. http://www.transmissioncenter.net/sp...n_______va.htm __________________ Tony 1985 GMC K2500 restoration Project: Rust, White & Blue 1989 Chevy R3500 CC Cummins & 4X4 swap some day... 1989 Burb (D60, 14BFF, 12V, NV4500, NP205, 37" tires in progress)



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