tranny swap question

[chrpmaster]

I recently bought a 76 C10 with a 350 and auto tranny.  The tranny seems to be geared very low meaning the engine really revs high at highway speeds.  The original owner included the original invoice which said it had a turbo hydra tranny.  My brother has an 82 chevy 4 wd with the 6.2 diesel that had the tranny rebuilt a couple years ago and he offered that tranny to me for free.  It is an automatic with overdrive and really kept the rpms down when traveling down the highway. 

My question is how big of job would it be to swap the trannys?  Would it be just a swap of trannys and maybe linkage or is there more to it?  The 82 is complete and other than the body being eaten up with rust is complete so I can have any extra parts needed.  His wife just wants him to get it out of the yard and take it to the junk yard so I will need to work fast to save the parts I will need.

Thanks
Andy

[TexasRed]

You might check the rear end in that '76, as usually that's what gets changed to get a different gearing. Obviously, a transmission can be modified as well, but I doubt that would be the case as it's cheaper and easier (I would think) to change the rearend. Also, 4wd transmission would require some changing because of the 4wd nature.

[Captkaos]

You would have to tear down a 4x4 trans completely to replace the output shaft (and get a end cover) to install it in a 2WD truck.  If it was a 2WD OD trans it would be an easier swap.  Also, being a diesel, you couldn't use the convert....

[chrpmaster]

Thanks guys for helping me dodge that mess.

How hard is it to change the gearing in the rear end on the 76?  I'm not sure what would have been standard in these trucks.  What model truck should I look for to be the "donor" from the scrap yard?  Or is it better and not too expensive to buy different gearing new?

Thanks
Andy

[cracker0169]

I would pull the diff cover off first and count the teeth on the pinion and on the ring gear and see what exactly your axle ratio is.

[Fordeatinz71]

it's odd that you are complaining about high revolutions at freeway speeds, those trucks often had somewhere around a 2.50-2.80 gear set (normally 2.76 or 2.56) and they were geared that way to PREVENT that.  you could have one of the rare ones that was ordered with a lower gear ratio (higher numerically) and have something like a 3.73 or a 4.10 even. 

you don't have to take off your diff cover to figure out what gears you have.  jack your truck up and support it on jackstands.  chock your front tires WELL and put your truck in neutral.  with a paint marker or white out or something, make a mark on the pinion yoke and the differential housing.  next, make a mark (mentally if you're good at remembering things) on the brake drum and the brake backing plate. 

now, watch your marks as you spin the wheel.  count how many times the pinion spins around past the mark you made on the diff as you watch the wheel.  when the wheel has made one full revolution, stop.  how many times has your pinion rotated?  that is your gear ratio.  i.e.-if it spun around almost 4 turns, it would mean you have a 3.73 rear end or something like that.  you won't get EXACT accuracy like this, but you'll get close enough...

[dumbucket1]

My 76 has a th400 and 4.10 rear gears so the motor is screaming at even 55mph on the interstate

[chrpmaster]

I think mine is like dumbucket1.  I know the original owner was a farmer who had extra heavy duty springs put on at the dealer when he bought it.  They have 8 leafs on them.  Also the rear bumper has been replaced with a heavy duty one.  My guess is he used to to pull grain wagon(s) and haul heavy loads for relatively short distances.  When he sold it he had only put about 48k miles on it.  He sold it to the young guy I bought it from.  It still only has less than 62k miles right now. 

Back to my original question.  How difficult is it to change the rear end gear ratio?  What parts do I need to change?

Thanks
Andy

[zieg85]

Not difficult if you have the right tools and know how.  Parts needed would depend on what gear you have in it right now.  The carrier which the ring gear mounts to will only accept a certain set of ratios.  There are different series carriers.  How drastic of a change do you want?  Do you need just a highway gear and won't tow heavy trailers.  There is a lot to consider. 

[dumbucket1]

Chrpmaster, if thats just a half ton rear end under your truck if you were closer I have a whole rear end with just a 2.70 ish gear ratio in it that I would just give you that would would fix you right up. But I would figure out what gear ratio you have first for sure.

[Fordeatinz71]

swapping gears is easy.  support the truck on jackstands.  remove wheels, brake drums and diff cover.  take out center pin and spider gears.  push in on each axleshaft (one at a time) and remove c-clips.  once the c-clips are removed (c-clips are inside the axle carrier inside the diff) pull each axle out enough to clear the carrier. remove caps that hold in carrier and pull out carrier.  remove driveshaft and pinion yoke and pull pinion gear.  remove ring gear from carrier.  install new gear on carrier (held on with bolts around perimeter) and new bearings.  put new bearings in diff housing and install pinion gear.  put carrier back in as it was removed.  bolt in caps that hold carrier and torque to spec.  there are shims that you will pull out on the sides of the bearings for the carrier.  you will have to adjust these to get your backlash right.  there are a lot of ways to measure backlash, but what i always do is to put some grease in the teeth of the ring.  you want the grease to be touched, but not removed from the teeth.  you are trying to get the pinion to go as deep into the ring as it can without TOUCHING the bottom base of the ring.  once you get the backlash set, put in your axle shafts and c-clips.  put diff cover on, brake drums and wheels.  re-install driveshaft and get truck off jackstands and go for a test run! 


that's pretty much all there is to it...i've had a few shots of tequila so i might have missed some things but i think i pretty much have it.  it's not hard at all really...

[Lt.Del]

i've had a few shots of tequila so i might have missed some things but i think i pretty much have it.  it's not hard at all really...

It's amazing how everything seems so much easier after a few shots!! 

[Fordeatinz71]

lol, yea, i'll go do it right now!  hehe, yea i know it's not "easy" for someone who's never done it, its hard and intimidating.  but once you get into it it's not really that hard...just gotta do some research and get the proper tools and just DO IT

[treny]

I would do what one of them said Ide put the whol rearend out of another 1\2 ton to a 0ne ton and if its a five holer just put your axels in it.. and replace the whole thing alot simpler and easier . Bruce haha Im no mechanic but I can even do that

[Fordeatinz71]

it's honestly a whole lot less manual labor to simply swap the gears, and it's not that hard.  the only rear end that would work and keep a 5-lug pattern is a 2wd 1/2 ton.  so you will be stuck with that unless you wanna upgrade to 3/4 or 1-ton which would be 8-lug and you'd need to swap the front end out too...