Speedo Cable-non standard engine/transmission

[ken mcculloch]

So my M37 had a conversion done to it before I bought it. I have a Chevy 350 with a Muncie SM465 transmission. The truck does not have a speedo cable installed, only the casing is there. My question... should I be able to simply by a cable that will fit the SM465 tranny? I assume I do not want an original cable as the trans is now different?

 

[greeno]

I don't know...but I'd love to see pics of a 350 in an M37.

 

[ken mcculloch]

I will have to get some pictures of the engine bay but here are a few of the truck itself.

 

[ken mcculloch]

Here are a few shots of the engine compartment. Mike Hewitt did a nice job of loading the 350 in there with ample room left over to work.

I'm still looking for some help with regards to my question about the speddo cable question.

Thanks, Ken

 

[greeno]

So you want to use an M37 speedo connected to your tranny? It will take some maths in order figure out what the correct gear will be for that tranny and speedo head combination. I know different gears are out there; but don't know what specific gear you'll need.

 

[ken mcculloch]

greeno,
the speedo I have is made by AutoMeter, not original. It is my understanding that the M37 cable has a larger square end that enters the tranny? Since I do not have the original tranny, but a SM465, the question is can I just get a "standard" off the shelf cable that will fit into the SM465?

I realize that I may need to re-gear the tranny to get an accurate speed reading due to the tire size, but that may have already been done. I won't know until I can get a look at what gear may be already installed. I just don't want to buy an M37 cable to have it not fit.

Does this make more sense?

thanks,

 

[clinto]

Several points:

Sometimes a "custom" speedo cable has to be made-SM465 compatible end on one end, M37 (or AutoMeter uin your case) compatible end at the other and a specific length. I believe some speedo shops can create such things, but I have no first hand experience with this.

If you can not get the correct math in the SM465 speedo pinion, speedo shops can provide what is effectively a gearbox that goes in between the tranny and the cable that speeds up or reduces the cable to make the speedo correct. I.E. the speedo is 11% fast, so there's an 11% underdrive gearbox that slows the speedo cable down the appropriate amount.

 

[ken mcculloch]

Thanks Clinto,

I guess I will need to talk to a speedo shop to see if I can a custome made cable. I appreciate all the input so for.

thanks,

 

[FarmerRob]

Maybe take your autometer gauge to your local parts store, have them show you an SM465 speedo cable and see if it will fit your gauge. I'm almost sure that I actually have an SM465 cable in my garage but they're cheap, so it would probably be faster and easier to just hit up your local autozone. If they need a vehicle to look up and you don't know what your parts came out of, try a 1980 Chevy K-10 pickup. That's what I had and it should get you in the ballpark.

 

[ken mcculloch]

Thanks FarmerRob, great help. That sounds like an easy enough solution. I guess I would also need to know the length of the cable needed? I have seen reference to M37 cables being in the neighborhood of 88" and 100"? I assume the length difference may be if it is in a cargo vs. ambulance?

 

[FarmerRob]

That's a good place to start but unless everything in the drivetrain is exactly the same length and in exactly the same relative position (highly doubtful), then it's still going to be "by guess and by golly". That being said, having a cable that's too long is better than having one too short. You can always re-route to take up extra length. If it's too short, Speedo Cable Stretchers are expensive and hard to find.

I would start with a stock chevy cable and go from there (if the gauge end is right). The beauty of getting off-the-shelf parts is that you can return them!

 

[rosco]

You need to know the tire OD, gear ratio, and the kind of Speedo, you will use. Heavy truck shop can do this, and build a complete unite, including the outside cable. Included will be a small gear unite, the cable runs through. They will adjust the gearing to compensate for the variables. Here in Fairbanks, Power & Transmission, 907-456-2230, has done several for me. They are 1st class!.

Note: Best to just run a tape around the outside of your tire.

 

[Roller]

So my M37 had a conversion done to it before I bought it. I have a Chevy 350 with a Muncie SM465 transmission. The truck does not have a speedo cable installed, only the casing is there. My question... should I be able to simply by a cable that will fit the SM465 tranny? I assume I do not want an original cable as the trans is now different?

What transfer case are you using? The original speedometer cable attaches to the transfer case, not the transmission. If you are using the NP200 transfer case and it is in the stock location, the stock cable should work.

Frank

 

[ken mcculloch]

Frank,

I really love it when a plan comes together but I hate it when I realize that all the pieces of the puzzle were right in front of me but I only looked at the pieces as individuals rather than a whole.

I have only hade my M for a few weeks & have not had the chance to do any real work on it yet. I have only had time to “look” it over, make some notes on items to be dealt with & research if/where I can get the parts needed to fix the issues it has.

With that said, here are the things I saw that led me to my original question…

1. Speedo is not working…look behind the dash panel… speedo cable is not connected to the speedometer… HMMM, there is no cable in the casing so even if it were connected it wouldn’t work… guess I need to get one… ASSUMED that the cable was attached at the transmission… not the factory transmission in my M so I need to get a cable that attaches to the current transmission.

NOW that it is after the fact, here are the pieces I that I didn’t put together before I asked my original question…

1. Why in the world, if the cable is attached to the NEW, not stock transmission, would the speedo cable casing be so **** big? It looks nothing like the ¼” dia. “normal” speedo cable casing on civilian vehicles that I have seen?????
2. Why would there be different length cables for the M (cargo vs. ambulance?) and why would I need an 80-100” cable just to reach the transmission which is basically located at my feet??

How the plan came together…

Last night I was reading the TM on how to adjust the parking brake & in doing so I am seeing the cable leading to the transfer case… DUHHH… the speedo cable CAN’T go to the tranny as this is a 4x4 system, & YES, I have the stock T-case so a stock M cable is what I am going to need.

Then this morning I see your response & BINGO…

Thanks so very much for the confirmation on what I though was a “stroke in process” due to my own confusion.

Ken