Speedo cable help on my 72

[Larry.sisk]

I recently installed a 350 engine (1986 model) and an automatic transmission (TH350) now I'm down to hooking up the fuel guage,speedometer neutral safety... The truck had a 327 with a 3speed on the floor which I removed can any of you guys give me some instruction on getting these other things working is it just a matter of finding the right speedo gear etc also the truck has a 6 lug rear end in it ( front has 5 lugs?) I guess that means that the diff or maybe just the axels have been changed , I'm just wondering also how to identify the diff any help on these issues will be appreciated

[MidLifer]

Here's how to figure out your speedo gear:

http://www.tciauto.com/tc/speedometer-gear-calculator/

I'm a gear rower so can't be any help on neutral safety.

[feller]

I am trying to fix this same problem that the PO didn't do right, and it is my understanding that you just have to change the gear that tci calculator seems to be the ticket it even has a tire size spot. I've heard that the gear will just pour fluid out so have a catch pan handy

[Larry.sisk]

Thanks for the info gonna try to figure it out

[TBONE1964]

First question is did you swap your steering column to an automatic transmission style? If so, there should be a neutral safety switch on it. You will need to run the purple wire from the ignition switch to it and from there to the starter solenoid to make the neutral safety switch work correctly. I am not 100% sure how the neutral safety switch is wired on a manual trans truck.

The fuel gauge should work and be wired the same on any 67-72 truck regardless of engine/transmission combination.

You need to do a one mile test to see what you have to start with on the speedometer gears. If you drive a measured mile, then your odometer will advance one full mile if your speedometer gears are correct. If it goes over one mile or does not reach one mile then you need to figure out which gears to use in your tail shaft of the trans. If you are also traveling at 60 mph, then this test should take exactly one minute of time.

Typically changing the gear ratio or the tire diameter will result in the speedometer gears needing to be changed but you have to know what you have for a gear ratio before you can get the correct speedometer gears. If you do not know the gear ratio, then jack up one side and leave one tire on the ground. Use a safety stand. Mark the inside of the tire against the drum or backing plate. Also mark the pinion against the rear end housing. Turn the tire lifted 2 full turns and count the number of revolutions the pinion turned. If the pinion turns 3 and 3/4 turns, then you have a 3:73 gear. If it turns just over 4 turns, then you have a 4:10 geat. If it turns almost 3 1/2 turns then you have a 3:42 and so on. That is if you have a non posi rear diff. For a posi, lift both rear tires and turn the tire, (either side) only one turn instead of two.

If your odometer registers exactly one full mile for a measured mile traveled and you think your speedometer is still not correct, then the speedometer head needs to be calibrated.

The speedometer needle reading will not tell you if your transmission gears are correct. You have to use the odometer and run a measured mile to be sure.

Hope this helps,
Tom

[Larry.sisk]

Thanks TBONE1964. Can't wait to try these things, right now I don't have a speedo cable or the gear so I'm starting from scratch with that ,and yes I put an colum shift auto trans steer colum so I should be able to wire that now thank you for helping.

[TBONE1964]

Originally Posted by Larry.sisk

Thanks TBONE1964. Can't wait to try these things, right now I don't have a speedo cable or the gear so I'm starting from scratch with that ,and yes I put an colum shift auto trans steer colum so I should be able to wire that now thank you for helping.

Never a problem to help out. If you have a local trans shop, they can/should be able to help you with the correct trans speedo gear with the gear ratio and tire diameter that you are running.

Keep us posted on the progress.
Tom

[El Dorado Jim]

Originally Posted by Larry.sisk

I recently installed a 350 engine (1986 model) and an automatic transmission (TH350) now I'm down to hooking up the fuel guage,speedometer neutral safety... The truck had a 327 with a 3speed on the floor which I removed can any of you guys give me some instruction on getting these other things working is it just a matter of finding the right speedo gear etc also the truck has a 6 lug rear end in it ( front has 5 lugs?) I guess that means that the diff or maybe just the axels have been changed , I'm just wondering also how to identify the diff any help on these issues will be appreciated

In West Sacramento https://local.yahoo.com/info-2176534...est-sacramento this place can install an adapter at the transmission where the cable hooks up to it, and put the correct gears in it to get your speedometer to read correctly, will be around $100.00 bucks,they have done a couple of trucks for me.....

[Larry.sisk]

Man it's nice to get such good help thanks everyone when I can I'll post some pics of where I'm at with this 72 short fleet pre build , I want to poor boy it and get it on the road then start stock piling some parts and chit for the real build although it will never be like truck of the tear or anything , thanks again

[EARNHARDT#3]

If you have a smartphone (with free speedometer app) or a GPS you can always check your MPH with that as well.