Hello everyone and thanks in advance for any advice.
I'm trying to finish up an auto TH400 to t56 manual transmission swap, and now that I have it almost back together, I'm finding some stuff I must not have done right.
Since I had to remove the dash to get the pedal assembly out, I also tried to rebuild the speedometer because the odometer didn't work.
My speedometer did turn the needle to show the speed just fine before I took it apart. (but a bit wiggly)
When I took it apart, the black plastic worm gear that turns the odometer gears was stripped, and the odometer roller numbers were corroded so they didn't turn freely on the odometer shaft. The frozen odometer numbers (rollers) are what stripped the black plastic worm gear. I have removed the corrosion on the odometer number shaft, freeing them up to move the way they were intended, and replaced the worm gear with a metal one (they only kind available I found.) Now the speedometer goes in the opposite direction when i turn the cable clockwise, and doesn't go up at all when I turn the cable counter-clockwise.
The worm gear issue doesn't seem related to the the gauge not telling the speed correctly, from the diagrams I've seen.
Is it possible to install the first worm and magnet (where the speedo cable connects) backwards?
Any advice is appreciated.

I hope everyone can see the see clip below.

 

I had a similar issue with my speedo a few years ago. I needed to replace the first worm and magnet along with the second worm gear.

Your problem might be an "assembly" issue. I think you have the needle/cup on the wrong side of the stopper. I don't specifically remember the configuration, just that you could install it together and have the needle/shaft on the wrong side.

You should be able to take the needle and physically move it in the correct motion and the spring should return it back to the stop.

 

Thanks for the tip!
I'm taking it all back out tonight, and will take a closer look at the needle/cup.
I spent way too much to have the F-body t56 tail-housing modified for mechanical speedometer to not get this working. I'll try to take some pics in case anyone else runs into the same thing, and of course bench test it before i put it back in.

 

Since your speedo is likely coming apart again, if you can find a 1,000 RPM motor source to spin the speedo, you can check it's accuracy. The magnetism in the first worm magnet gets weak over time. The spring is adjustable to compensate if it's not too weak.
1,000 rpm = 60 MPH (I needed to calibrate mine after repair)

 

Thanks, this is great info!
Any chance you have pictures of how to adjust the spring?

 

See photo, simply rotate the arm, tightens or loosens the spring tension.

Also in the photo you can see where the "finger" limits the cup/needle. Easy to assemble with the tab on the wrong side of the finger. Likely what's causing your current problem.

 

I don't know where I would be without you kind fellows.
I took my dash back out and checked out the orientation of the speed cup and retainer, and that was exactly the issue!
Thank you so much!

Before

Funny thing though, I had to flip the little tab on the other side of the retainer cup compared to your picture above..

After, correct
With the trip meter gear in place, I couldn't totally remove the retainer, but I didn't have to. Just removed the 2 flat head screws, lifted the retainer a little, then rotated the speedo cable a little to move the speed cup tab on the other side. Seems to have worked!

I used a drill to spin the cable and watch it turn the needle in the right direction and odometer moving as it should.
Prior to doing this fix, I drove the car around for several miles to test out the other aspects of my t56 swap, so I'll also check the accuracy with a rpm meter. I hope that didn't damage the bushing or anything else in the speedometer.
While I was turning the cable with a drill, the speedometer only went up to about 25 mph (before it seemed pretty close to accurate).
I have to think my drill was spinning faster than 1000rpms.
Are you sure 1000 rpm = 60 mph on the gauge?

I hope my experience, AND ALL THIS GREAT ADVICE, can help someone else in the future who may try to rebuild their speedometer the same way I did.

 

I'm sure 1,000 rpm = 60 mph, set mine up that way and it's dead on. Here is another discussion on the subject that will give you some more info.
https://www.corvetteforum.com/forums...dometer%20head.

Looks like you're well on your way to being a speedometer expert. Removal & replacement of the speedometer is a challenging job, you're doing great!

 

Well, I confirmed my speedometer is reading accurately according to the 1000rpms = 60 mph
I was expecting more from my drill, which was actually turning only 460rpms, which showed about ~27 mph on the gauge.
I would have thought after all these years it would need some adjustment, especially after being run backwards for several miles on the shake down test of the new t56. Pretty cool!

Barry, your test set up looks more precise than mine. I just bought one of these for $20, and put a piece of white tape on the drill chuck while turning the speedometer cable connected to the speedometer. It worked well enough for my purposes considering the mechanical gauge is pretty wiggly anyway.


Wow! To think I was considering removing the transmission again to reverse the orientation of the new retrofit speedometer drive gear on the tail shaft.
Thanks again for all your help!

 

Good to hear that you were successful. Your RPM tool looks to be a very handy thing to have. My test setup was made up of scraps of things laying around. The RPM digital gauge was a $10 item. The AGPtec would have saved me a lot of time.