Ok, have read up what I could on speedo related issues but have not found a good answer yet to what's happening with mine.

About a week ago it started to bounce, OK I can deal with that, next day it died altogether

So I pull the trans end (4 speed no cruise) of the cable and inspect the tip, looks good, give it a few whirls with the drill (in reverse) and speedo moves fine, no bounce or noise from the cable.

Take out the speedo drive gear, fits tight and damage free, no marring on the teeth, no bore or wear on the receiver end for the cable, still square, looks like new. Reassemble and drive but nothing, nada, honestly officer I wasn't speeding

It seems that the speedo head is fine, with the drill speedo and odo work, cable seems fine or at least will allow it to all work with the drill,
drive gear shows no sign of damage, so what gives?

ideas?

 

I've seen the drive gear (inside the tranny) break, come off the clip, slip forward, backward, every possible combination. Pull the driven gear, look up inside the tranny. The drive gear should be centered in the hole and tight. Gently, GENTLY, try and move it with a screwdriver, see if it spins on the shaft. Check the depth of the driven gear too.

 

Thanks Tim,

Dare I ask how bad the repair is for that? I take it the tranny's got to be pulled.

I'm going to check again, the drive gear did look centered, and on reinserting the driven plastic gear and housing I saw the plastic twist (rotate) to engage, so It seems as if there is contact between them.

On moving it gently with the screwdriver if it spins, does this mean it is off it's mounting point?

Thanks

 

To get to the drive gear the tailshaft cover must be taken off the transmission. This is something that can be done with the transmission still in the car. It involves supporting the trans with a jack and removing the driveshaft and crossmember. It's a bit of a PITA but it can be done in your garage or driveway if you are handy and have the correct hand tools to do the job.

 

Just an idea that just hit me and I've never done this, but how about running the car on jack stands in gear with the speedo cable disconnected and look at the drive gear in the trans while all this is happening to see if you can figure out what's going on?

 

That would work, but I'd be REAL careful. Good stands, make sure it's really solid on the stands.

Anyway, I found a fairly good picture of a Muncie. May give some help/direction. Here's the link:

www.autogear.net-pdfs-munciecat.pdf

 

I wouldn't do this with the car running, it is very dangerous. You can just put the car in gear while in the air and have someone spin the rear wheel and get the same result.

 

75coupered, I've recently suffered the exact same problem you describe and posted a thread about a week ago in an effort to get some answers to no avail. What I have learned is this (and I converted my '70 from TH400 to Muncie M21 last spring)-

Apparently the eBay dude who sold me my less-than-perfect M21 provided a driven gear that was mismatched with my (steel) drive gear. I pulled the cable, checked inside the hole, and the drive gear hasn't moved or crept and is perfectly centered over the opening in the tailshaft housing. Drive gears come in two diameters-.780" and .840", and must be matched to their respective driven gears (which come in two diameters as well) or they either won't work at all or won't work for very long, which was the case with mine. My too-small and partially-engaged steel drive gear eventually wore the teeth off of my driven gear. At first I disconnected the cable and like you ran it with a drill thinking that the (6" too short auto-trans cable) was overstretched and pulled out of the driven gear. It worked fine so I ordered a new manual-trans one, installed it, and got the same result-no speedo. I then ordered a blue and a white driven gear, which I've recieved but haven't yet gotten the time to install. I will first install the .780" diameter white gear (same as what I had before which was reading pretty accurately) and whenever it finally lets go I'll pull the trans back out and install a drive gear that is properly matched to the correct .840" diameter blue gear. I could just put the blue gear in there now but it's 22 teeth vs. 19 for the white one which would really skew my speedo readings a lot. I'll post again to let all know what kind of luck I have maybe Sunday if I can break away from football long enough to get back underneath it.

 

I don't know of anyone that can pull a tail off in the car without the forward reverse Idler gear and thrust washer dropping in the case. Sometimes you get lucky, most times you don't. Whats the point. Yopu have to remove the linkage anyway. Is another 4 bolts going to take up that much time...

1969 or 1970 Muncies are the only units with clip type speedo drive gears. All the rest have pressed on metal gears. I've seen the clips break and the plastic gears rotate erratically, thus the jumping needle. If you have an ST10, the gear is splined to the output.

 

Yep, your absolutely right. I forgot that he has a 4 spd., I was thinking Auto and that's how I had to do mine, sorry.

 

Thanks to all for their input so far,

5-speeds and others, when you mention that the drive gears are pressed on, do you mean that the metal gear itself is pressed onto the shaft on which it rotates, or is the gear assembly pressed into some internal receiver?

I guess what I'm asking is if my metal drive gear spins freely, without any movement of the driveshaft, it's freewheeling is there a fix short of removing the trans for this, can pressure be applied in some way to re-engage it, by somewhat pressing it back into place?

Thanks
Bill

EDIT my trans is a BW 4-speed

 

Ok Bill,heres another idea.This happened to my speedometer,it was my cable ,it was the original cable,it was rounded off a little at the cable end and it was actually slipping ,making it jump and not work right.you have to look at the cable end real good,if its slightly rounded off,you need a new cable.

 

OK,
here's what I've got so far.
In the pic of the transmission speedo drive gear opening you can see a better shot of the assembly. There is a plastic (blueish) worm gear that activates the plastic speedo driven gear in the housing to the cable.

The blue worm gear seems to turn with some effort using my finger through the hole. I'm assuming that it is free of it's mounting.

5-speeds mentioned a spline mount, is it correct to assume that the worm gear being plastic has worn through its internal splines if mounted over a metal splined shaft? If so given the location to the tailshaft cover would replacing the worm gear mean removing the cover and sliding on a new one onto the shaft?

Still scratching my head as to why BW or GM would use such a plastic gear inside the trans, not easily serviceable but prone to break by design, I would have expected a metal gear.

Always looking for input.
Thanks,
Bill
\
Billysvette, I looked at the cable end again and am sure that it is fine, it is a metal end and I tested it by removing the driven gear housing and actually using the plastic driven gear (reddish one) to drive the cable by hand, it works fine, if the two ends are not exactly mated the cable end will not insert into the gear, very tight fit. Thanks.

 

Well I think I found an answer to my question regarding how the speedo drive gear is affixed to the tranny. Well gotta think how much my speedo is worth to me.

Repair requires removal of the transmission, removal of tail cover to get access to the main shaft. Removal of the rearmost snap ring and replacement of the gear, likely with another crappy plastic one prone to break yet again from any binding at the cable and or speedo head.

Does anyone make metal replacement gears? This is starting to look like more work than it's worth to me right now, just to know my speed, which of course is never fast enough, working speedo or not

Here's a pic of the assembly and drive gear from corvettemagazine.com:
[IMG][/IMG]

As you can see the gear slides over the splines and held in place sandwitched between two c-clips. Good design, crappy material choice though for the gear.

 

Actually it shouldn't be more than a day's work if you've got a decent place to work on your car. And from looking at your driven gear 8it appears that it's fairly worn too.....for ten bucks it's pretty cheap insurance.

 

What a deet dee dee I am, didn't notice the concave curvature of my driven gear, looking at pics of others like mine I see that the tip of each tooth is straight and flat, mine is'nt, it must be slipping/disengaging at this juncture under load.

I'll get a new one and see if it works, thanks birdsmith for pointing this out. How'd your's go by the way?

 

Thanks to all for your help thusfar.
I replaced the speedo driven gear with a new one as well as the housing, if you have the old aluminum housing, get yourself the new steel one, there was enough combined slop in the driven gear and housing to allow the whole assembly to stop engaging. While I was at it I also replaced the speedo cable, not too bad to feed the new one in.

So now my speedo works again, but it's still bouncing a bit, but this time with a slight click each time heard from the speedo head assembly and now the ODO stopped working

I tried the trip odo reset and that seems to be frozen, I had also tried this before I drove the car when I first found it replacing the cable could it now be stuck and causing the aforementioned clicking?

Any ideas regading a fix short of pulling the speedo head assembly?

Thanks again...

 

It's a good bet that the speedo head is the root of your problems. Too much drag on the cable from the head caused the driven gear to wear. Now that you replaced the gear, the head is really making noise. The odo not working is a tip-off. I'll bet the worm gear in the head is sheared or worn and the source of your click.