73-87 Chevy _ GMC Trucks > Instrumentation

Non working speedo

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Chevygold:
On the first drive of my truck I noticed that the speedo doesn't work, one of the jobs I had to do before I could drive the truck was to change out the tranny, original was TH350 replaced with a used TH400 as the original only drove in reverse!
I fitted the speedo cable with the adaptor from the TH350 assuming all would be good, I have no idea whether the speedo worked before the original trans failed, I tried fitting the cable direct to the tranny without the adaptor but still nothing, what I noticed when I had it apart there was a lot of end float on the shaft inside the housing where the adaptor fits, is this normal?
If I spin the cable with my drill which way should I spin it to test the speedo? BTW the adaptor is sound, output turns when I turn the input shaft.
Thanks
Graham

Chevygold:
Sorry forgot to say '76 C10 Cheyenne Longbed 350 with TH400

frotosride:
A few things to check, make sure that the drive rod (kinda looks like the internal drive rod of a weed eater) isn't rounded and that it isn't too small for the adapter female socket that drives it (driven gear).
The adapter out of the tranny, when looking directly at it, spins clockwise. So when looking directly at the speedo cable it should spin counter clockwise.
If everything above checks out, and speedo turns then it is probably the drive and/or driven gear for the speedo output in the tranny. The bullet that houses the speedo driven gear ( this is where the speedo cable attaches to) may be worn out and allowing the driven gear to move away from the drive gear and thus no speedo. Performance automatics (PA) actuall makes these bullets out of steel as replacements if you find that to be an issue or just want to stop it from happening later.
The only other option is if the speedo doesn't move. The cable could be broke, disconnected from the speedo, or the spedo itself is bad. You can take the gauge cluster out (not necessary but helpful for first timers) and drive the truck back and forth, watching the speedo cable to see if it's moving.
Last but not least, when you do get the speedo working it will likely be off depending on the final drive ratio (ring and pinion) and tire height of the TH400's original vehicle versus yours.

Chevygold:
Thanks frotosride,
Thats the exact info I needed, from what you've said I think it could well be the drive gear moving out of mesh but I'll go through the cable etc. hopefully it's not the speedo head as I prefer things I can fix!
Graham

Chevygold:
OK spun the speedo cable today and the speedo is good so it looks like it's the drive, can I take out the "bullet"without loosing fluid from the tranny?
Graham

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