1955 Speedometer not working in the car but does on bench

[buickbrothers]

I've rebuilt the speedometer which was locked up and won't turn. I has a second speedometer which I robbed the base housing from and swapped with the original housing on my cars speedometer that the drum sits in. I have bench tested it with a drill and the new speedometer cable and my red line drum now operates and displays the speed my drill can output. I install in the car - nothing. Anyone ever seen the transmission speedometer gear not working? It seemed fine when I rebuilt the transmission and checked it. Good gear teeth with no wear pattern and it spun freely. How do I determine if the speedometer gear is the problem since the cable and speedometer both work on the bench? Do I have to drain the transmission to pull the gear and once out - how do it test it? Are there any know issues on the after-market speedometer cables - like the tang is not long enough for the transmission gear end to connect properly? Bought the new cable from oldbuickparts. Thanks.

[37_Roadmaster_C]

With the speedometer having been locked up I would suspect that the square drive inside the speedometer gear in the transmission could have been rounded out or like you mentioned, the cable core may be short.

[avgwarhawk]

Also, the cable may have broken inside the cable covering.

[buickbrothers]

The cable is new and not broken as I used it for the bench test. Any thoughts on pulling the speedometer gear out of the tail and how to bench test all three together (gear, cable and speedometer connected end-to-end)? Do I need to drain the transmission fluid to pull the gear? 

[EmTee]

If you remove the speedometer drive gear from the transmission a visual inspection should be enough to determine whether it is still serviceable.

[KAD36]

 

On 6/5/2024 at 12:48 AM, 37_Roadmaster_C said:

With the speedometer having been locked up I would suspect that the square drive inside the speedometer gear in the transmission could have been rounded out or like you mentioned, the cable core may be short.

^—- +1.   
 

Dopey question -  has the speedometer end of the cable been observed being turned by the transmission before you connect it to the head?  And if so, if you put a very little bit of tension on it while the car is wheels up in both D and R with needle nose pliers or holding it with a paper towel or newspaper does it hold tension and still rotate? And with the core aligned and fully seated into the transmission gear does it look like a reasonable amount of core left to align and fully seat into the speedometer head?

 

Do not hold the core with a cotton towel to see if the transmission gear will apply some tension on the cables core unless you have patience and a good set of tweezers.  Ask me how I know….

 

Edited June 7 by KAD36 (see edit history)

[buickbrothers]

Hi KAD36. I'm working on this today so will let you know what I observe and the result. Was sidelined on getting the clock working. I finally have a working clock!

[buickbrothers]

Update. I was able to get the speedometer gear out of the transmission tail - a few #@!$ words later. It's a 19 tooth which matches the book for my series 70 Roadmaster car/ 3.4 to 1 axel ratio. The problem is that the tang of the old speedometer cable snapped off and was embedded in the cable receiving end of the gear shaft preventing the new cable tang from fully inserting. The gear spins freely and the gear teeth are all good. I was extremely blessed that I was able to get the old tang out in less than a minute. I talked to Wille (old tank) and we expected the wires to have welded it in, but it came out clean. I have reinstalled the cable on the car and the speedometer is working now. It still seems that this after-market cable is shorter internally as I pushed the internal cable to ensure it was fully contacting the speedometer gear at the transmission end before connecting to the speedo housing. I haven't done a test drive since I have the top of the dash out. I'll let you know if anything comes up, otherwise, all good for now! 

 

Headed toward side glass and front/rear windshields next. Trying to start closing her up now that all the dash parts are working.   

[EmTee]

Glad you found the problem.  Hopefully there wasn't anything more to it than the cable itself binding and breaking.  The fact that you had the speedometer operating on the bench without issue is a good sign. 

[KAD36]

Good job - The redliner speedometer always fascinated me since a kid.  How did you approach adjusting the accuracy?  Or perhaps it was good and didn’t need any?  Have had to fiddle with mine numerous times - it reads about 0-5 high depending on how the spring constant changes over temperature or so it appears.  Used to be almost 10 high.  Seems like I have to keep chasing it down as it weakens.

Edited June 9 by KAD36 (see edit history)

[buickbrothers]

Validating the speed calibration is a next step. When I rebuilt the speedometer, I set the spring at what I believe was its original level as a baseline. I plan to use a speedometer app when I road test to determine actual GPS speed vs displayed speed on the speedometer. I'm sure mine will need to be adjusted because I'm running radials and smaller tires currently. Per Wille tire size/type (bias vs radial) has an impact on the speedometer correctness. If they were readily available, swapping speedometer gear from my current 19 tooth to 20, for radials, would also be better. I'll report back on how it first measures and how it does after I adjust. Just learning as I go and passing on some points from Willie.     

[KAD36]

Some additional points - how the magnet sits in the drum can be adjusted, the drums pivot point pressure needs careful attention to avoid “stiction”, and if you need to increase spring tension slightly I’ve had good luck slipping a piece of hollow wire insulation over the end of the coil spring that is bent and rests against the stop tab to provide a little more wind up.  In fact, have used strips of masking tape on the piece of insulation to change the spring tension by very small incremental amounts.  Having gone from L78 15 bias plys for 25+ years (bigger tire and it still read high and the gear is correct) to 225 radials, can attest to those induced differences per Willie’s experience.  Sharing the above parameters for awareness as they also can be used to improve accuracy, not sure what a real speedometer shop would adjust, but you can trial and error dial it in pretty darn close from my shade tree experience.  On a bench I ran it until the odometer was reading a mile a minute then tried to dial in 60 mph as my initial starting point, then adjusted from there at some different set points and finally fine tuned in the car.  Did not try for 100 mph as a set point - just sayin.  
 

Perhaps changes in the magnet strength and spring over time are different so it’s difficult to balance it out any more, who knows, would be nice if there were new ones.
 

Good luck and thanks for the updates.

[old-tank]

3 hours ago, KAD36 said:

not sure what a real speedometer shop would adjust

 

3 hours ago, KAD36 said:

Perhaps changes in the magnet strength

They induce or extract magnetism.

[buickbrothers]

Update. I road tested the speedometer yesterday and it worked well. It's off by about 10 miles per hour per GPS which I expected it to be off with my smaller tires. I don't think I will do anything about making calibration adjustments since I plan on getting the correct tire size at some point in the future and I would have to change it again. In Texas, you go with the flow/speed of traffic anyway or they will run you over even if the flow is 10 miles greater than the posted speed limit - lol. Thanks for all the education on this. I'm just happy I have it and the clock working so I can close the dash up now!