The Stovebolt Site Forums The Shop Area Driveline Spedometer cable R&R questions 55 C3100, manual trans, 235

Hi All,
It has been a while since I last visited here, so I hope I am still welcome

I have been immensely enjoying my 1955 Series 1 C3100, 235-6 ,three on on the tree, and I think I lost the speedometer cable tonight. I have heard some squeaking last few times out that got louder as I went faster and virtually disappeared when I was at idle. Well, I noticed the sound stopped and both my stock spedo and odometer are no longer registering my driving speed or mileage - Spedo stuck at 0, odometer stopped moving. I suspect the speedometer cable has decided to permanently retire and before I attempt this repair. I would appreciate advice form those who are familiar with this procedure. I have some questions

1) Other possibilities than the speedometer cable? - (before cable break, spedo was consistently 7-9 mph less than actual and Odo matched GPS)

2) The spedo cable looks reasonably east to access on tranny, but my nemesis, reaching behind the dash makes me a bit apprehensive here - I have been trying to reach behind there for a while now and i cant figure out how to reach anything - Can I change this cable at the dash end without pulling gauge cluster?

3) I have asked this in the past, but any suggestions on pulling the cluster out of dash to make access easier? - that actually would also help my burned out dash bulb replacement - I can't see how to even remove the chrome bezel

4) anything else I should be aware of or look out for on the cable swap?

thanks to all who respond

Joe (Detroit, MI. area)

Joe, most folks can unscrew the cable at back of the speedometer. First thing is get a good look at it and to that end try this; find a board about 4' long and 12" wide or so. Then lay one end in the floor of the truck, the other end is supported with a chair, 5 gal bucket or what ever is handy. You can now lay comfortably on you back and look under the dash with a light making it easy to see the speedometer cable and plan your attack.

Swapping the cable out is easy and several online vendors have em. NAPA may be a good source if that's an option.

Before you buy a new cable, disconnect the old one at both ends, attach a small drill motor to the tranny end of the cable and have someone spin it while you watch the speedometer end. Hopefully it won't spin meaning a simple cable replacement will solve the problem.

Also, lots of reading available on how to best service the speedometer. Me, (despite advise to the contrary) I occasional squirt a bit of WD40 into the back of the speedometer head. This quiets things down and smooths out the jumpy needle. I did replace the cable a couple years ago and 4,000 miles later all's still good.

Good Luck, RonR

When installing new cable, drag it through some wheel bearing grease or some such to lube the whole thing.

Ed

Hi Ron
Thank you for your suggestion - I never thought of a ledge to make it a bit easier to reach underneath - I also have a burned out instrument bulb that I have not been able to replace because of same reason - I must confess though, I am struggling visualizing the setup you describe above - Do I read it correctly that you suggest laying on end in the truck ( middle of cab for example and hang other end out the truck and support it with something to make a ramp or similar? - That sounds like a great idea - did I read that correctly?

Also, to Ed - Thank you for the reminder - the squeaking I haed the last 10 miles or so before the thing broke certainly shouted something is in need of lubrication

Joe, yes you are visualizing it correctly. Only downfall is if you are full grown and don’t fit between the front edge of the seat and the door jamb.🛠

LOL, @ 6’ and a wiry 165lbs I feel full grown and fit just fine. Am I hearing that fitting between the seat back and steering wheel doesn’t guarantee fitting under the dash?

Just a note, as you are installing the new cable attach the cable to the transmission FIRST and then fit the new cable thru the firewall and up to the back of the speedometer. The transmission end of the cable is too large to fit thru the holes in the firewall. I KNOW because I just replaced the missing cable on my 54 3/4 ton.

Joe, you might also try removing the speaker cover and ashtray assembly to give you an easier way to stick your hand and arm back in there. Don't forget to disconnect your battery ground cable as it's very easy to dislodge the ammeter wire and cause a commotion. And band aids aren't a bad idea either!

Hey all,
Thanks for the suggestions - I have a new related question now - I was taking a closer look at the transmission end of the cable, and to my surprise, the spedo cable does not go directly into the transmission housing but goes to another unit in line that also has same type of connector (knurled thread ring) to the rear of the tranny housing. Perhaps it is some kind of adapter to get cable rpm correct for the 1/2 ton? Does this sound familiar to any of you? - Also, I have noticed several spedo calbes listed for my truck, with the shortest being listed as 63" (might have been 68" - don't quite remember) - anyone know the correct length? ( 1955 C3100, 235 inline 6, std 3 speed trans) - I am at a bit of a pause here. I sure hope it is only the cable - I also examined the possibility it is the spedo gauge itself that has ceased to function - Only thing I can find are more modern replacement sets for 600-800 bucks ( although that is a complete 2 gauge set with all new senders that theoretically fit in the existing dash holes)

Update on my non functioning speedometer problem

Hi All,
I finally got to test a few things tonight and I no longer think I have a bad speedo cable or speedometer. I ran two tests tonight

1) Disconnected the speedo cable at both ends and had a helper site in the drivers seat with a clear view of the end of the cable that goes into the speedometer, while I attached a drill to the transmission end - I then started to slowly turn the transmission end of the cable and my helper reported the other end was also turning - it kept turning through various speeds and continual test as well - this indicated to me that my existing speedo cable was not broken as I thought

2) Test #2 - I reconnected the speedo cable to the back of the speedometer and left the tranny end connected to my drill. I then turned the drill at various speeds while my helper watched the speedo - the speedo needle moved to more mph as the drill was sped up and held stead when drill was held steady ( as possible) - this indicates to me that the speedo itself is working - needle was not jumping wildly or making any weird noises

These two tests taken together indicate to me that my cable and speedometer are not broken - This now suggests either the adapter the speedo cable hooks into, or the tranny itself - I have no idea how to test either one. I do see the adapter has a threaded fitting the same in size as the speedo cable and that the adapter can rotate freely about 20-40 degrees while securely fastened down. I notice also that there appears to be a slot in the adapter and some kind of key that looks like it might go in the slot - the key and bolt holding it were tight however as my next thought was maybe that key came loose

So , I need some suggestions here - I was thinking of taking off the adapter and taking it apart or buying a new one - but that is a wild guess at this point - I don't see this adapter for sale in any of the old truck vendor catalogs yet - How would I test it and anyone know where I might buy a new one if it is the culprit - I don't want to think of the other possibility here in my mind - something in the tranny housing ( speedometer gear) is not working or broken - she drives fine, shifts fine

Any help would be appreciated

Joe

Take the adapter off and see it turns at both ends by slipping the shaft in. These are common. It might also be that the cable is too short, do you have any history of it working in the past?

Ed

Hi Ed
Thanks for the suggestion - I do have history of it working - Speedo and odometer were working for last 4 years and just quit a week ago - I did hear a clicking sound starting late last year right before I put the truck away for winter. The clicking sound sped up with the vehicle and slowed down when the truck slowed down. I thought it might be the speedometer itself, but my tests last night showed the needle assembly still works when I spin the speedo cable manually

Also, I have not been able to find any source for the adapter unit that looks anywhere the same as what I saw - I also have the service manual for my truck and it only discusses the use of adapters for non standard size tires and rims - The speedo was about 8-10 mph off since I have owned the truck and I just attributed it to the speedometer itself being old and a bit stiff