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Speedo bullet
#1337858 Mon Dec 16 2019 03:03 PM
Joined: Aug 2017
Posts: 7
S
Saluki Offline OP
New Guy
Has anyone adapted a speedometer cable bullet to an SM 420 tranny?

Thanks!

Re: Speedo bullet
Saluki #1337876 Mon Dec 16 2019 04:35 PM
Joined: Sep 2001
Posts: 29,868
ace skiver
Sorry about my ignorance, Saluki, but what is the "cable bullet"

Maybe you are referring to one of the "speedometer gears"?

"Speedometer gears include both a drive gear and a driven gear. The drive gear is located on the transmission's output shaft. The driven gear is positioned in a removable housing that is typically located in the transmission's tailhousing." (from TCXI automotive)?


Tim
1954Advance-Design.com [1954advance-design.com]
1954 3106 Carryall Suburban [stovebolt.com] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [1954advance-design.com] - part of the family for 15 years
Z-series (54/55) GMC 350 (2-ton) COE [1954advance-design.com] - now part of Dave's family
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engine are not "splash oilers" - this is a splash oiler. [chevy.oldcarmanualproject.com]
Re: Speedo bullet
Saluki #1337878 Mon Dec 16 2019 04:45 PM
Joined: Sep 2001
Posts: 29,868
ace skiver
I think I now know what the "bullet" is, Saluki (I did a Google search).

I only know Stovebolt gears - I think the "bullet" is an integral part on one of the original gears?

I think that you need a gear set (drive & driven) that matches your drive-train gear ratio (and your transmission attachment hole). Someone will correct/clarify this, I hope.


Tim
1954Advance-Design.com [1954advance-design.com]
1954 3106 Carryall Suburban [stovebolt.com] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [1954advance-design.com] - part of the family for 15 years
Z-series (54/55) GMC 350 (2-ton) COE [1954advance-design.com] - now part of Dave's family
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engine are not "splash oilers" - this is a splash oiler. [chevy.oldcarmanualproject.com]
Re: Speedo bullet
Saluki #1337880 Mon Dec 16 2019 05:12 PM
Joined: Aug 2017
Posts: 7
S
Saluki Offline OP
New Guy
The bullet is the adapter part that goes into the transmission housing that you hook the speedometer cable into.
Sorry I was not clear. It is a newer version that holds the driven gear. I also saw on eBay (I think) an SM 420 driven gear housing that appeared to have a plastic gear instead of the old metal gear.

IF that is possible I could replace the drive gear and driven gear. I currently have a 4 tooth drive gear and a 13 tooth driven gear that is a bit too slow. So I either change the gears or get an adapter to speed it up.



Last edited by Saluki; Mon Dec 16 2019 05:17 PM.
Re: Speedo bullet
Saluki #1337889 Mon Dec 16 2019 07:05 PM
Joined: Jul 2000
Posts: 962
G
Shop Clutterist
Earlier discussion on this: https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=921081

I'm interested in this subject. I have a piece of paper with the speedometer reading to the actual speed written on it; not convenient but it works.


Gord
----
1954 1/2 ton 235 4 speed
Re: Speedo bullet
Saluki #1337895 Mon Dec 16 2019 07:55 PM
Joined: Aug 2017
Posts: 7
S
Saluki Offline OP
New Guy
I have been using a GPS and I do understand the easiest thing to do is get a ratio adapter. I was just curious if anyone knew of a modification that I might also use.
With the number of 420 trannys out there I thought there might be another option.

Thanks for the link Gord&Fran, I also have a 54 1/2 ton.

If I knew what plastic gear would fit that old adapter, I would also change the drive gear. I could put in an 8 tooth drive gear and a 22 tooth driven gear.



Last edited by Saluki; Mon Dec 16 2019 08:11 PM.
Re: Speedo bullet
Saluki #1337911 Mon Dec 16 2019 08:59 PM
Joined: Jul 2000
Posts: 962
G
Shop Clutterist
There seems to be lots of gears for automatic transmissions and the 4 speeds found in muscle cars. But we have the SM420...

I'm still not settled on the ring and pinion gears in our truck. We might make a change there so I'm not too anxious to get the speedometer reading corrected now. Plus, our speed limits are in Km/h so I'm kind of used to doing conversions in my head.


Gord
----
1954 1/2 ton 235 4 speed
Re: Speedo bullet
Gord&Fran #1338674 Sun Dec 22 2019 05:56 AM
Joined: Feb 2013
Posts: 223
E
Shop Shark
I don't know if they are all the same but my speedometer is adjustable. Kind of trial and error but I was able to dial mine in pretty well.

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