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Hey everyone, I recently swapped my 4.10 gears out for 3.0 gears to improve highway cruising to and from work. As expected, the speedometer is jumping all over the place, so I decided to swap out the driven gear with a 17-tooth gear. I also ordered a new speedo cable to install, as well. However, when went under the truck, I found a speedo cable that screwed onto a housing that screwed into the tail housing and no driven gear inside. Now, I'm not even sure what transmission I have because I've been going by the warrenty plate and assuming that it's a Ford Cruise-O-Matic, but it doesn't any threaded holes for the rertaining bolt to go into to hold the speedo to the housing. I'm posting some pictures to see if anyone has any thoughts on this so I can hopefully get the right parts.
Last year for Ford-O-Matic was 1963. Yours it called the MX Cruise-O-Matic (MX COM). I can see the driven gear in your last picture. Did that come out of your transmission or ??
Seems like all is well. Your speedo wouldn't have been bouncing around if there were no driven gear because there would have been nothing driving the speedo cable.
Okay, but when I put everything back together, the shaft on the speedo cable has nothing internally to spin it. I'm confused because it seems as though something is missing, but I have no idea what.
The center core of the speedo cable spins. The driven gear spins the center core, and the core spins the mag cup in the speedometer head. I can see the center core poking out of the cable in the picture just above your driven gear picture - second from the last.
I should mention that in a good working setup the speedometer core should have a square tip and even though the driven gear looks round at the opening where the cable goes in it becomes a square further down in so you have to make sure the cable is fully inserted into the driven gear. Take the driven gear back out and then take either cable and insert it into the driven gear to get a feel for it. You may have to rotate the center slightly to allow it to slip all of the way into the driven gear by aligning the square core tip with the internal square drive.
You'll need fewer teeth on the new driven gear. Look at your gear and see what it is stamped. It'll show how many teeth it has without even needing to count.
Sorry, that short list is for my truck. With a 3.00 they do have 16 and 17 teeth ones. Looks like you'll need the 7-tooth drive gear which I'd take a wild guess yours currently is 8 or more since it was for the 4.10 presumably.
Okay, thank you. I'll pull it back out and check for stamping. I'll also do the check you recommend above to see if it goes into the square part of the gear. Thanks for all the info.
You are getting into a bit of a sticky wicket possibly. The driven gears in the 3.00 category are not the right style of driven gear. The 3.00 gear looks like it was mostly used with Econoline which had the C4 transmission, so they used a different style gear.
You might need to go with a ratio adapter - just a sample here of what they look like generally. This one at .7555 is about a 3/4 reduction.
Okay, swapping out the driven gear is going down a rabbit hole that I can't get into at this time, so that's going on the back burner. New question: am I able to adjust my shift points on a cruise-o-matic? Looking at the transmission, I can't see where that would be possible. I've been told about a vacuum modulator, but can't seem to see one.
The vacuum modulator looks like some of these examples on eBay. Many, but not all, have a way to adjust them by sliding a screwdriver into the end and adjusting an internal screw.
Right on, thanks TA. I was told you know your stuff and you do for sure. Now, kind of a dumb question, but where might I find the vacuum modulator? When I was under the truck last weekend, I couldn't see it. I'm going to take another look this weekend and see what I can find, but having an idea where to look would sure help. Thanks again.
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