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Old 02-05-2014, 09:10 PM
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70SS454 70SS454 is offline
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Default Speedometer stoped working

My speedometer recently quit working. I have a 1970 chevelle ss with a Muncie 22 4 speed. I have a new speedo cable that does turn the speedometer (I tested it with a drill attached to the cable on the transmission end). The red drive gear also looks fine. However the worm gear in the transmission looks to have broken off. I have attached a picture of the plastic gear on a metal shaft inside the transmission that I took through the hole for the drive gear. Is it broken and can it be replaced without pulling the transmission and breaking it open? Maybe by a transmission shop?

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Old 02-05-2014, 10:09 PM
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I think you are looking at pulling the trans to fix that. To change the drive gear inside the tranny, I believe the tail shaft housing has to come off.
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Old 02-06-2014, 07:34 AM
BillsCamino BillsCamino is offline
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I don't think you'll have to remove the trans from your car...just take out the driveshaft, unbolt the mount and remove the trans tail housing...supporting the rest of the trans with a jack.
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Old 02-06-2014, 06:27 PM
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Quote:
Originally Posted by BillsCamino View Post
I don't think you'll have to remove the trans from your car...just take out the driveshaft, unbolt the mount and remove the trans tail housing...supporting the rest of the trans with a jack.
Bill you probably are right, but working under a car trying to see in is a pain. I like working where I can see what I'm doing, Lol.
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Old 02-06-2014, 08:09 PM
BillsCamino BillsCamino is offline
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What??? No lift??? Oh, that is so dark ages...
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Old 02-06-2014, 08:24 PM
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I called several trans shops today. I got all different stories. Some said you only need to pull tail cone while it's on the car, some said you have to remove transmission, and some said you have to break open transmission to fix it.
It sounds like you both think that you only have to pull tail cone and not break open the trans. I think some shops are just trying to make some extra$$$. The one that says it can be done while it's in the car wants $175.
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Old 02-06-2014, 10:19 PM
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Quote:
Originally Posted by BillsCamino View Post
What??? No lift??? Oh, that is so dark ages...
Lol, I would love to have a shop with a lift.
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Old 02-06-2014, 10:36 PM
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I did a little research and this is what I found when others had that same gear problem. At least you know what it might take to fix it.

"If you have to remove the tail shaft housing, get an overhaul manual before you start because reverse gear is in the tail housing and certain procedures must be followed or IIRC you'll end up disassembling almost the entire trans. You have to stand the trans on its nose before removing the tail housing. Use blocks of wood or ?? to support the case while allowing clearance for the input shaft. Or cut a hole in the workbench like I did. "

Here another one I found.

As already mentioned, that gear is NORMALLY a press fit. But, you say that you have a plastic gear, which tells me that you have a 69 (plastic gear and retaining clip). The other years used a steel gear that is pressed onto the shaft. You will have to remove the tail housing to do this operation. Getting the tail housing off is no big deal, but getting it back on can be! The reverse shifter shaft is retained by a small tapered pin. Use a punch and drive out the pin FROM THE BOTTOM. Then grasp the reverse shifter shaft (if it has a threaded hole, insert a bolt and pull on it) and pull out on it. It will only come out about 3/8in. Remove the five bolts and remove the tail housing. BE CAREFUL THAT YOU DON'T SEPERATE THE MIDPLATE FROM THE MAIN CASE!! ALSO, ONCE YOU REMOVE THE TAIL HOUSING, DON'T PUSH THE REVERSE SHIFTER SHAFT BACK IN. A SMALL BALL WILL FALL OUT AND IT CAN BE A REAL PAIN TO GET IT BACK IN!! After removing the tail housing, take that plastic gear off of the shaft and throw it as far as you can------------------------or incenerate it! Then install a steel gear. There are two sizes with eignt teeth for your tranny, you want the larger gear which is 1.84in diameter. This gear will be compatable with the small plastic speedo gears which go into the fitting on the side. The plastic gears are still available from Chev, the steel gear is not. The plastic gears are 3987917, 3987918, 39879019, 3987920, 3987921, 3987922 (17 to 22 teeth). As mentioned, you can just drive on the steel gear with a length of pipe. ALSO, AS MENTIONED, IT MUST GO ON AT A SPECIFIC POSITION!!! Simply measure from the front surface of the tail houising back to the center of the speedo fitting hole, then measure the same distance from the rear of the mid plate to the location on the tail shaft. Then drive the steel gear onto the shaft the same distance.
To re-install the tail housing, I find it easiest to do by placing the tranny upright (if you have a big enough vice, place it in the vice and clamp around the outer diameter of the front bearing retainer). If the shaft for the reverse idler gear came out with the housing, remove the reverse shaft (it just pulls out of the tail housing) and install it through the idler gear (there should have been a smooth thrust washer that goes up against the reverse idler gear), making sure that the pin in the shaft is in the verticle position because it lines up with slots in the tail housing. Shift the reverse shifter shaft forward. Install a new gasket with sealer on both sides (or if you wish, you can just use RTV, I prefer a gasket). Insert the reverse shifter fork into the shifter shaft. Lift up on the sliding reverse gear and place something like a screwdriver handle between reverse gear and the mid plate. Slip the tail housing down over the tail housing and shine a flashlight up into the housing to see when the fork lines up with the flange on the reverse gear. When it is lined up, push in on the shifter shaft to engage the shifter fork with reverse gear. Remove the screwdriver handle and push the tail housing on down all the way. Sometimes this requires some juggling of the tail housing to get it all the way on. Button it all back together. I don't know what the correct torque is on the five bolts, but for the past 40yrs that I've been building Muncies, I just tighten the crap out of them.
I shouls have mentioned that since you have the tail housing off, now would be a perfect time to replace the rear bushing (if it appears to be worn) and especially the rear seal. The bushing has to be driven out of the tail housing and a new one driven in. Just pry out the old seal and tap in a new one (seal and bushing are available at the local auto parts store, same seal and bushing as a turbo 350).

and another

ITS NOT A TAILSHAFT!!!!!!!!!!!!!!!!!!!

IT IS A TAIL HOUSING, OR MORE CORRECTLY, AN EXTENSION HOUSING!!!!! BUT IT IS NOT A SHAFT!

THE TAIL SHAFT IS THE PART INSIDE THE TAIL HOUSING THAT THE DRIVE SHAFT YOKE IS CONNECTED TO!!!

IF YOU'RE GOING TO CALL THE TAIL HOUSING A TAIL SHAFT, THEN WHY DON'T YOU CALL THE MAIN CASE A FRONT SHAFT OR MAIN SHAFT??????????????????????????

Now, to answer you question. If the 18 tooth gear has not been having any problems , then you can change that plastic gear with a 17 through 22 tooth gear and all will be just fine. YOU DO NOT HAVE TO CHANGE THE GEAR INSIDE THE TAIL HOUSING JUST TO CHANGE THE GEAR THAT GOES IN THAT HOLE! Simply remove the speedo gear adapter from the tail housing, slip out the plastic gear, insert a different gear and put it back in.
There are 2 different gears that are used on the tail shaft (remember, the tail SHAFT is inside the tail HOUSING). One gear mates with the 17-22 teeth plastic gears and the other gear mates with the 22-25 teeth gears. The gear for the 17-22 teeth gears is the larger of the 2 gears and the 17-22 teeth plastic gears are smaller. The gear for the 22-25 teeth plastic gear is a smaller gear and the 22-25 teeth plastic gears are larger than the 17-22 teeth gears (there are TWO different 22 teeth plastic gears). You cannot mix these gears, they won't work together. If you use the big (22-25 teeth) plastic gears with the big gear on the tail shaft, the plastic teeth will be chewed up. If you use the small plastic gears (17-22) with the small gear on the tail shaft, they won't engage each other enough and will eventually won't work at all.
The gear inside the tail housing (the one on the tail shaft) is a steel gear that is pressed onto the shaft (except for 69 Muncies, they were a plastic gear that was retained by a small clip). In order to change the gear on the shaft, you need to remove the tranny from the car, remove the tail housing from the tranny and use a puller to remove the speedometer gear that is pressed onto the shaft.

Find someone in your are area that knows munice's transmissions. If you don't have someone, I can make a call to a friend who rebuilds these transmissions and ask him what it will take to fix the problem you have.
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Last edited by shadowgray396; 02-06-2014 at 10:46 PM.
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Old 02-07-2014, 07:11 AM
BillsCamino BillsCamino is offline
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Good job Ray. I honestly didn't think there was that much involved.

70SS454...I noticed you're in Lucas, TX...not too far from OKC. I've got a good friend that lives in Mustang, OK that is an absolute genius when it comes to Muncie trannys. And he's a Super Chevelle guy to boot.
I can put you in contact with him if you're interested...
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1967 Camaro SS -5.3L LS w/4L60E & 4.11 12 bolt
2019 Cadillac XT5 3.6L V6 w/310 HP & 8 speed AWD
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Old 02-07-2014, 08:42 AM
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I bet his name is Tom with a straw hat .
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