inside a TH350 Transmission: Speedometer gears
 

Hey guys - i've tried everything to get my speedo to work in my '75. First off, the speedo worked before my 4 year restoration began. since completion, the speedo does not work. i have tried all the tricks, and the gauge does work with a drill on the cable down by the transmission. AND the gears on the cable looks good... AND the unit on the transmission turns freely and turns the cable just fine...

so, with that being said, i think the only sensible option is to remove the tail shaft and see what's going on in there... i've never done this type of thing and do not know what to expect... any tips? what to look for? any way to set the tailshaft on the bench and get it to all work on the bench?

any tips, advice, web sites, how-to's etc would be appreciated. i have been on plenty of sites that tell you all about the different gears and how to calculate the best option... i just need to know what's going in there... any thoughts?

Re: inside a TH350 Transmission: Speedometer gears
 

http://73-87.com/7387garage/drivetrain/spdgears.htm Best site I've seen.

Re: inside a TH350 Transmission: Speedometer gears
 

If the speedometer "bullet" isnt clocked right it will not engage with the gears.

Re: inside a TH350 Transmission: Speedometer gears
 

tell me more!!!

Re: inside a TH350 Transmission: Speedometer gears
 

When you remove the driven gear sleeve (bullet) you can screw up the install by clocking it wrong. Most of them are egg shaped to accomidate different tooth count gears. Pull it out flip it 180* re install and see what happens.

Re: inside a TH350 Transmission: Speedometer gears
 

Mine is round. It did not seem to matter how it went in the two times I replaced it trying to get it to stop leaking. Maybe mine is different since it is a TH350C. The parts are cheap, as you can see. I would put new ones in when you have them out if you have not replaced them before. :)

http://slonaker.net/images/truck/speedo1.jpg

http://slonaker.net/images/truck/speedo2.jpg

Slonaker

Re: inside a TH350 Transmission: Speedometer gears
 

This is the outer part Im talking about along with SSC's76.

Re: inside a TH350 Transmission: Speedometer gears
 

That explains why the auto parts stores were all trying to sell me an enormous o-ring for mine when I was trying to get it to stop leaking. Mine is only about an inch in diameter, and looks nothing like that. Weird.

Slonaker

Re: inside a TH350 Transmission: Speedometer gears
 

The TH350 uses the smaller bullet like Slonaker posted. It's round, there is no clocking it.

The 700R4 uses the larger housing like Mylilbowtie posted.

75stepside, the drive gear on the mainshaft has a little metal spring clip to keep it in place. The clips sometimes break and allow the gear to slide out of place. If you remove the bullet and driven gear, you can stick your finger in the hole and see if the drive gear is in place and whether it's secure or sliding forward and back on the shaft.

The clips cost a few cents and are easy to replace once you remove the tailhousing.

Re: inside a TH350 Transmission: Speedometer gears
 

I found a picture from the last transmission I rebuilt. This is the drive gear on the mainshaft. Look closely and notice the little metal clip inside the gear. The clip keeps the gear in proper position front to rear, so it locates positively with the driven gear and speedo bullet. Without the clip, it is free to float front and back, allowing it to dissengage fromt the other gear.

http://67-72chevytrucks.com/vboard/a...9&d=1138490381

Re: inside a TH350 Transmission: Speedometer gears
 

The pic I took is from TH-375. I have a TH350 I can take one from If needed. The TH-375 as alot easier to get to than the TH350 I put in my 3/4 ton.

Problem I ran into is the drive gear on my TH350 is that I couldn't get it off. It would only slide closer to the transmission case and not off. I finally got it lined back up to where the driven gear and drive gear mesh good I think. I haven't had anytime to get some miles on it. The 305 in the 3/4 ton retired without a notice and patiently waiting to be fixed.

Re: inside a TH350 Transmission: Speedometer gears
 

Oh I forgot is there a circular spot on that tailshaft for the drive gear clip? Maybe that was why the clip wounldnt stay where it was supposed to be. Or the clip is really worn out. I've never had any problem out of the TH-400s Ive messed with. I didn't want to break the gear off on the TH-350 when all I wanted to do was get the tooth count.