Swapped Rears.....speedo Way Off...help

[nejeff]

Just completed swapping rears from a 72 Custom 10 (307, 3 speed) into my 72 Super Cheyenne(350, auto) and the speedo is now running fast, unsure yet of how much but looks like about 10 mph at least.

Also I seemed to have bumped things up enough that the center support bearing thing( unsure what you call it) is whining real bad. Took a look and can move it all around with my hands easy. What is the name of the piece so I can call Oreilly's

Thanks guys for your help

[flyinbass]

nejeff,
I have a 1970 Longhorn fleetside with a 350/350 and a 1-ton rearend. I replaced the third member (was a limited-slip) for a possi-track rearend. The engine ran fast, the transmission shifted quickly and I was going about 25 mph. The speedometer read about 75mph. The third-member was from a truck with a manual transmission and is geared lower than one out of an automatic (in my case anyway). I think the "center support bearing thing" you refer to is the 'Carrier' bearing for the two piece driveshaft in longbed trucks.

Regards,
Gary R70

[nejeff]

Thanks alot Fly! Found the carrier bearing at Oreilly's.

[rodnok1]

the easiest fix is to take your truck out on the expressway and go mile marker to mile marker and check your speedo read out. i.e. actual mileage 1 mile, speedo reads 1 mile 3 tenths. Take this info and your old gears and holder(as it may change) to a good trans or speedo shop. They should be able to give you correct gears based of your info. Good luck

[COBALT]

Yeah, you need a different speedo gear in your transmission. if you unscrew the cable you'll see that the plate should come off and allow you to turn the speedometer gear out of the transmission. Its driven by a worm gear off of the output shaft. Knowing what to replace it with may take some doing...