M20 speedometer gear problem

Hi Guys,
I recently purchased a 70 gs 350 with a 4 speed. I have no experience with 4 speeds but need some help. My speedmeter was not working and I took out the cluster. Ran the cable on a drill and the mph worked. Assuming the gear in the tranny is the problem. I'm looking to where I can get the parts to fix it. Thanks for the help.

 

Sure it's not a Muncie M21?

 

Here is the serial number I saw on it. P9B27A I took the speedo gear out of it and the plastic gears are shredded. I have no clue why but will start by finding a gear for it. Also looking for help on since it just started to not like to go into reverse and third/fourth. Any ideas? shift linkage? Any tips on adjusting?

 

There is a keyway hole in the base of the shifter. Put he shift lever in the postion, which I recall is neutral, so that all the tabs for the arms, which also have keyway holes, line up or come close. Then take loose the set nut and the retaining clip on each shifter arm. Then screw the arm so that it lengthens or shortens it as needed so that it also lines up with the keyway hole in the base. Use a close fitting drill bit to fill the keyway hole in order to check this allignment if you do not have a factory plastic insert.


The correct speedo gear will depend on the size tires that you now have on the car.

 

Thanks for the helps...Very new at 4 speeds but going to try...The one I have is a 17 teeth model. I just put some BFG Radial T/A 245-60-15 all around on it. Got an idea on the number of teeth? Thanks again

 

...if your plastic speedo gear is shreaded, and if the tranny is rebuilt, that likely means that when the tranny was rebuilt, the reverse gear in the output shaft was not put on exactly where it need to be...or they did not replace that gear for some odd reason (doubtful but possible) if so, try a new gear and see if there is a bad noise, and it all works. If no noise and works, problem solved. If noisy and grinding, no worky, it requires disassembly to reposition the metal speedo gear on the output shaft. If not rebuilt, then it is simply worn out and a common part to buy at any gear shop who deals in tranny's. I just remembered the plastic gear is in the tail shaft housing so it would need to come out to repalce this plastic gear

I didn't know there was a relationship to the speedo gear in this instance, but as far as adjusting your shifter or "the brain" to assure all linkage is synchronized with the tranny to the shifter like Jim was talking about, I missed why you asked about it, but a short 1/4" drill bit is the alignment tool if you don't have the actual plastic alignment dowel. With shifter in neautral, you should be able to slide the 1/4" bit through the little 1/2 moon located on the shifter levers through all of them into a hole in the base of the shifter. The shifter would be locked now with this in place. Adjust / align/ tighten one shift gear linkage at a time with trans in neutral like Jim said so you can get the 1/4" bit all the way in so the levers all line up. Use locktite on the nuts that hold the linkage position.

 

Thanks for the input so far. well I recently purchased this car and have been fixing things everyday since I brought it home. Its a 1970 GS 350 / th350 auto converted to a 4 speed car with all original correct parts. We took the car out to run it and make sure the coolant leak was fixed and we started having problems getting it in reverse and 3/4th gears. I will get a 2 new gears and pray for now! It appears to have the factory rear end and its a non posi so I'm thinking it has 3.23 gears based on my books but i have no clue on the drive gear. I was out there tonight and its stuck in 1st and couldn't even get it in neutral. Most bolts on this car were loose and the shift assembly and transmission included and assuming snugging up all the bolts created my problem. I assume I will need yo disconnect all the linkage to get tranny in neutral to start the process. Im hoping I'm correct and its not in the tranny itself and also wish I knew more about these trannys

 

Hi All,
Ok the m20 is definately stuck in gear and im serious in doubt its an alignment issue. we were under the car and got no wear. Any suggestions on what esle could make the tranny do this? assuming its internal now. ideas before I look at dropping this tranny saturday after work? Thanks for the help.

 

Did you tighten the nuts that are on the side cover for the shift linkages? If so I think it is possible to overtighten them and cause them to bind up on the side cover making it either really difficult to shift or lock up completely. Its been a while since I redid my Muncie and I think that was one of the things I found out when I was bolting and adjusting the shifter & linkages. If I remember right there was a specific torque they were supposed to be at. Or it could be something wrong with the shifter itself.

And for the speedo gear, there should be some websites with the info you need on the correct gear. I cant remember where I found the info for mine, but i'll look. And you can buy the speedo gears (both drive and driven) at a GM dealership for pretty cheap.

 

Thanks for the information especially on the side cover. Did not tighten those just the linkage and bolts on the shifter bracket. I don't believe its a shifter problem since when i crawled underneath I could not move the bracket/gear up near the side cover at all. I'm figuring that rules out shifter and makes it internal.