Speedometer

[1991silverado]

Wazup everyone. I have a 91 Silverado 2wd and I recently added some 17x11 wheels with a 315/35/17 tires. I noticed that my speedometer is way off. What are y’all doing to fix this issue? TIA. ✌

 

[Drunkcanuk]

Besides getting new wheels and tires that are the same as stock, which obviously is not what you want to do. If you have a 700r4(assuming by your year) transmission, there is a gear in the tailshaft section that drives the spedo, it can get changed out to accommodate different gear ratios and tires.
I believe that's the only way with a 700r4.
If there is another way, someone smarter than me will fix us both up.

 

[someotherguy]

No GMT400's use a cable-driven speedometer. All are electronic. 1988-1991 speedometer is calibrated internally..

Recalibrating 1988-1991 speedometer / dash cluster

(I couldn't find a search result here for this post so I'm copying it over from my old Chevytalk write-up from 2011 - I'll have to break the post into two parts to include all the pictures. Sorry for the super-long book style writing.. I'm trying to give a good understanding of the mod before...

www.gmt400.com

Richard

 

[1991silverado]

Besides getting new wheels and tires that are the same as stock, which obviously is not what you want to do. If you have a 700r4(assuming by your year) transmission, there is a gear in the tailshaft section that drives the spedo, it can get changed out to accommodate different gear ratios and tires.
I believe that's the only way with a 700r4.
If there is another way, someone smarter than me will fix us both up.

Do you happen to know where I can buy this part . ?

 

[1991silverado]

No GMT400's use a cable-driven speedometer. All are electronic. 1988-1991 speedometer is calibrated internally..

Recalibrating 1988-1991 speedometer / dash cluster

(I couldn't find a search result here for this post so I'm copying it over from my old Chevytalk write-up from 2011 - I'll have to break the post into two parts to include all the pictures. Sorry for the super-long book style writing.. I'm trying to give a good understanding of the mod before...

www.gmt400.com

Richard

Is there a way to calibrate the cluster?

 

[Dogged365]

88-91 speedometers are driven by a speed sensor…no gears to change…i would search the site for “ Recalibrating 1988-1991 speedometer/dash cluster “ …. Written by someotherguy…. If you know what your rear end ratio … you could reprogram to the closest tire size in height..315-35-17 are 27.7”closest to that is 205-75-15 at 27.1”

 

[1991silverado]

88-91 speedometers are driven by a speed sensor…no gears to change…i would search the site for “ Recalibrating 1988-1991 speedometer/dash cluster “ …. Written by someotherguy…. If you know what your rear end ratio … you could reprogram to the closest tire size in height..315-35-17 are 27.7”closest to that is 205-75-15 at 27.1”

Will have research on this . Thanks

 

[Drunkcanuk]

88-91 speedometers are driven by a speed sensor…no gears to change…i would search the site for “ Recalibrating 1988-1991 speedometer/dash cluster “ …. Written by someotherguy…. If you know what your rear end ratio … you could reprogram to the closest tire size in height..315-35-17 are 27.7”closest to that is 205-75-15 at 27.1”

When I replaced my exploded 700r4, I remember I had to take the old speedometer gear out and put it in the new one. There is definitely a gear in a 700r4.

https://6772chevytrucks.com/vboard/showthread.php?t=322481

There is a thread I found. Like I said, there may be other ways, including messing with the cluster, but you can get different gears as well.

 

[someotherguy]

I literally linked a post in my prior reply, showing how to calibrate the 1988-1991 clusters. LOL

Richard

 

[Drunkcanuk]

I literally linked a post in my prior reply, showing how to calibrate the 1988-1991 clusters. LOL

Richard

100% right. I was just saying there are other ways, the one post mentioned no gears. Not trying to "start anything" here , just trying to help. I'm glad you posted that, as I was unaware that was a way to do it in those years, I thought it was later years only.