AXLE CODES:

[Stewart G Griffin]

PT.3 Continued:

Well, it's seems inevitable that i would have take the tailhousing extension cone off so i could see exactly what speedo gears i got so i would have some sort of reference.

But i can't get the driveshaft out:



i tried tapping the ear things on the driveshaft (figure a's) with a 5 lb hammer to try to move the shaft foward, but to no avail.  The wheels are chocked, the trans is in neutral, and, as you can see, the two u-joint retaining straps are off.  This is an 8.5 inch 10 bolt differential if it matters.  i've removed the shafts on a monte carlo and malibu (very similar to the truck) with no problems.

Any suggestions?

[VileZambonie]

I don't understand why you are taking the tailshaft off to check your speedo gear? Just remove the clamp and pop it out. To get the u-joint seperated from the yoke just pry against the pinion nut with a prybar or large screwdriver against the trunion.

[Stewart G Griffin]

...... don't understand why you are taking the tailshaft off to check your speedo gear?

i need to find out what speedo drive gear as well as driven gear i got.  i suspect that the trans was replaced with another one out of a car or truck with lower diff gears which is why my speedometer reads slower than actual speed.  The previous owner didn't want to mess with it (figure out the correct speedo  gears).  i can sort of  understand why.

[VileZambonie]

All you need to know is the driven gear just pull it out and see what you have. Check these links out

http://www.bgsoflex.com/speedo1.html

http://www.transmissioncenter.net/speedometer_calibration_______va.htm

[Stewart G Griffin]

Yeah............i'm still not quite sure i'm following you;  First, i thought that TH-350's came with different speedo drive gears---the one on the output shaft.  So, that means if i do plug in what i know about my setup----tire size, rear diff gear and speedo driven gear, into those calculator links,  this might not mean i will know what drive gear i got?  And, i thought you need to know that one to get your speedometer reading correctly.

[VileZambonie]

I'm not getting what you're asking. The drive gear should be standard. The driven gear will have a different # of teeth to match the pitch of the drive gear based on rear axle ratio. If you know your axle ratio and tire size most dealers can tell you which driven gear you need without pulling anything apart.

[Stewart G Griffin]

Ok, are you basically stating that all TH-350C's installed in 1/2 ton pickups came from the factory with the same speedometer drive gear?  And, they (the factory), only changed the speedometer driven gear dependant on which rear differential gear came with the truck (i.e., 2.73, 3.08, 3.73 etc.) in order to get the speedometer to read correct?

[VileZambonie]

No but if IIRC there were 3 sizes per pitch. It's been a while since I had to recalibrate one but regardless you don't need to pull the tailshaft housing off. All you need to do is see which driven gear you have and call a competent dealer to help you find which setup you need or use the link I posted above. There's no point in pulling it apart if you know you need to change it anyway.

[Stewart G Griffin]

Ok, i think i will try that.  Much less work anyways.

[Captkaos]

There are only 3 drive gears available, 15 = gray, 17 = red and 18 = blue. If you pull the driven gear out you should be able to tell what color it is.  then you can use this to calculate which new driven gear you need...
http://73-87.com/7387garage/drivetrain/speedo.htm

[Stewart G Griffin]

Ok, something "interesting" happened today; A) i went to the dealer to try to determine what speedometer gears are stock for my application so i could get a baseline.  It is beginning to appear that i do, in fact, have the right drive and driven speedometer gears.  So, if anyone is interested, for an 83 truck with 2.56 rear and 195/75 15's the driven gear is the blue 20 tooth #3987920 and the drive gear is the purple, 10 tooth #6261785.

B) the other thing i discovered is that on TH-350 long tailshafts, you can actually see the drive gear after you pull the driven gear out----with a flashlight.  These aren't the best pictures, but you can just see the "purplish" (hopefully) drive gear in there:
 


C) But what i discovered is that since i do not have the stock size tires (P195/75 15's), i have 235/75 15's, perhaps this is what is causing the speedo to read slow.  Originally i did not think there was much a difference between the two since it was only 40 millimeters.  But that is over 2 inches.

So, in your opinion, do you feel that 2 inches difference between tires could throw the speedo off by 10 mph slower reading?

P.S.  Capt., i think you are getting the 700's drive gears confused with the 350's.  i appreciate the help though.

[VileZambonie]

Why did your truck have 195s? The stock tires were 225/75R15 or 235/75R15.

What's printed on the placard?

[Stewart G Griffin]

Yes,  believe it or not, the stock tires for an 83 1/2 ton custom deluxe are 195/75 15's.  The decal on the driver's side front inner fender well says so. (i will try to find the RPO code) Also, i confirmed it at the dealer. As if the 235/75 15's that i have on there now don't already look lost in there---imagine how the 195's would look like?  But that's another thing i like about these trucks---plenty of space for huge tires.

[VileZambonie]

Are you sure that's not just listing the spare?

[Stewart G Griffin]

Yes, i'm 99.8% sure these are the baseline stock tires for this truck because:

1) The dealer had a listing in their speedo gear chart that lists this tire as the base tires.

2) The spec decal on the left front innerfenderwell lists these as the "standard tires."

3)  The owners manual lists these as the base tire (which by the way, apparently 1/2 ton trucks also use passenger car tires?)

i think the prev owner upgraded to 235/75's but didn't switch speedo gears.

P.S. this is not a silverado, it is a very spartan (but loveable) custom deluxe.