63 gmc gearing

[wc63]

whats up folks,
my question should be fairly simple. i want to change the gearing on my rearend to get better highway mileage. i would like to gover faster than 55mph, but want to keep the truck as original as possible. does anyone know of a good ring and pinion option for a 63 gmc? i dont know what it is for sure, but 60-66 gmc guy says i have a spicer 44 rearend. this should be accurate since the truck is mostly original. any suggestions will definately help.
thanks in advance.

[Captainfab]

It's hard to say without knowing exactly what gears you have now. If you have a manual trans, you most likely have 3.73's I believe the next step up is 3.54 gears which will drop your rpm's down less than 200 rpm's. Tire size plays a part in this too. What size are your tires? stepping up to a little taller tire will help also. I calculated the less than 200rpm difference with 235/75R15 tires which are 28.8" diameter

[slorio]

Rather than changing rear end ratios, have you thought about putting in an overdrive transmission. Typically the overdrives can drop RPM's by 30% in top gear. I used a three speed overdrive from a late 60's GM (T 85N) in place of the stock three speed in my 1966 GMC 1000 series with 305V6. These take a bit of looking to find, but are nice addition that fits the period. I am very happy with this set up. Check out this link below:

http://speedprint.com/deves50/overdriveindex.php

A cheaper alternative is putting a T-5 from an 80's S-10. The inliners.org website has good write ups on this swap.

I hope this is helpful.
Regards,
Steve
New Orleans

[Rap'em Pappy]

I have a 62 GMC with a 305v6, 4 sp, 3/4t 8 bolt. I put a 80 pontiac bonaville 2.73 in. It was from the diesel versions of GM. I just cut the perchs and track rod mounts off. Then rewelded them. At 45 on speedometer, I am doing about 70. I am runing 255x15's. Also a direct bolt in can be done with a 71 or 72 rear end. Then you can get any gear you want. I used 3.08's in my other 60's trucks with v8's. You can find a space saver tire rim that fits 8 bolt and 5 bolts at the yards. You can also convert the front bolt pattern to match.

Save another

[wc63]

wow, thanks to all who replied. i didnt think i had so many options. the rear end swap seems like the easiest thing to do, although, i want to keep the 6 lug pattern. so i have some options to whey. thanks again for your suggestions. hopefully i'll post some pics. next, after i fix the carb. it took a crap on me a few days ago. when it rains it pours.

[62gmc910]

Originally Posted by wc63

wow, thanks to all who replied. i didnt think i had so many options. the rear end swap seems like the easiest thing to do, although, i want to keep the 6 lug pattern. so i have some options to whey. thanks again for your suggestions. hopefully i'll post some pics. next, after i fix the carb. it took a crap on me a few days ago. when it rains it pours.

4X4 1/2 tons have 6 bolt and came with ratios from 4.1 TO 2.73 then you can keep 6 lug might even bolt in ?? I don't know canadian GMC s mostly had coil rears

[TwoFiftyShifter]

A couple other things come into play. What motor and transmission? a 305 V6 and 4-speed creeper would handle a 3.08 rear fine, but a 230 3 on the tree sure wouldn't. If you have the 4 speed i would try a 3.08 rear. You will be able to cruise at highway speeds no problem.

[markeb01]

Originally Posted by wc63

whats up folks,
my question should be fairly simple. i want to change the gearing on my rearend to get better highway mileage. i would like to gover faster than 55mph, but want to keep the truck as original as possible. does anyone know of a good ring and pinion option for a 63 gmc? i dont know what it is for sure, but 60-66 gmc guy says i have a spicer 44 rearend. this should be accurate since the truck is mostly original. any suggestions will definately help.
thanks in advance.

The advice above is right on - it helps if you know what gear set you have, what tire diameter, overdrive transmission consideration, etc. If you do want to keep it close to stock, and do in fact have a Dana 44 rear axle I'd suggest the easiest approach is to just change the gearset. These are very common in Jeeps, Blazers, and some Fords and Mopars. If you currently had a 3.70 or lower, you'll need to change the carrier. A decent rear end shop should have an assortment of used ones available in exchange for the one you have. My 1960 GMC D44 originally came with 3.73's which I had changed to 3.08. Made a world of difference on the highway. There's also a 3.31 available is you don't want to go all the way to a 3.08. As noted above it's important what engine and torque curve you have available prior to selecting gears.

Also unless you're experienced at setting up rear end gears, it's advisable to have a pro do it. Clearances and backlash are critical and best done by someone that has the proper equipment and knowledge.

[jbgroby]

If you have the DANA 44 rearend it's probaly a 3.92 which you can change out to a 3.23 and THAT makes a world of differance. I was topping out at 65-70 and she was really screeming 3100 rpm with a 305 V-6 . I dropped in the 3.23 and now it hardly breaks 2100 RPM.

I got everything I needed from Precision Gear (on the net) see pictures.

http://rides.webshots.com/album/570438270cjSEvE

Jake

[xratt]

I'm kinda going thou the same deal with my '66 C10 with 3.73 rear gears. Thanks to Markeb01 for the info he sent me already. I went to the Driveline shop near me looking for a rebuild with 3.08 gears, and of course. Nothing they have will fit my truck. As I was told by Mark, they would have to change the carrier. Well no one makes a carrier anymore for the 12 bolt GM 8 7/8 rear end I have. Now this is according to the first shop I talked to. The guy did say he would check out back to see if you had any end rear ends he could scalp parts from, but he would have to get back with me after the holidays. I have one other shop near here to check with. Florida Power Train, I'm assuming to get similar results, but I'm, going to try anyway.

I'm running a 305 V8 sbc, with a 350th.

If I hit a dead end with rebuilding this rear end. I guess I'm going to end up swapping it out with a 80's truck rear end. Not what I wanted with it being wider. My truck sits real low, on bags. But this is my daily driver and I rack up some miles with lots of highway driving too. Not to mention any car shows within driving range.

So far at the junk yards I'm coming up with 80's truck rear ends with what seems to be 3.43 gears. Going rate at one place is $100-$150. I'm still wanting 3.08 gears. So getting the newer rear end and then having it rebuilt is looking a little out of my price range. So I might be saving up a bit if it comes down to this.

I've read lots of post and advice on this for a while. It would seem cut and dry on what to do. But I'm still not sure.

[Captainfab]

Well someone is blowing smoke up your a$$. There are 3 or 4 companies that make limited slip and locker carriers for the truck 12 bolt. You can see some right HERE Those new ones may not be in your price range, but used ones can be found on ebay, Craigslist, etc. The GM truck 12 bolt was used from '63-'81 ( I used to think it was thru '79) in both 2wd and 4wd. So there were a larger number of these produced over the years, and should not be too hard to find what you need.

Also it isn't always about obtaining the lowest cruise rpm's. It is more important to get your engine in it's 'sweet spot' rpm wise where it is most efficient. Finding that may require some research into factory combinations, and asking others what works for them. That's where this forum comes in real handy.

Originally Posted by xratt

I'm kinda going thou the same deal with my '66 C10 with 3.73 rear gears. Thanks to Markeb01 for the info he sent me already. I went to the Driveline shop near me looking for a rebuild with 3.08 gears, and of course. Nothing they have will fit my truck. As I was told by Mark, they would have to change the carrier. Well no one makes a carrier anymore for the 12 bolt GM 8 7/8 rear end I have. Now this is according to the first shop I talked to. The guy did say he would check out back to see if you had any end rear ends he could scalp parts from, but he would have to get back with me after the holidays. I have one other shop near here to check with. Florida Power Train, I'm assuming to get similar results, but I'm, going to try anyway.

I'm running a 305 V8 sbc, with a 350th.

If I hit a dead end with rebuilding this rear end. I guess I'm going to end up swapping it out with a 80's truck rear end. Not what I wanted with it being wider. My truck sits real low, on bags. But this is my daily driver and I rack up some miles with lots of highway driving too. Not to mention any car shows within driving range.

So far at the junk yards I'm coming up with 80's truck rear ends with what seems to be 3.43 gears. Going rate at one place is $100-$150. I'm still wanting 3.08 gears. So getting the newer rear end and then having it rebuilt is looking a little out of my price range. So I might be saving up a bit if it comes down to this.

I've read lots of post and advice on this for a while. It would seem cut and dry on what to do. But I'm still not sure.

[62gmc910]

Originally Posted by Captainfab

Well someone is blowing smoke up your a$$. There are 3 or 4 companies that make limited slip and locker carriers for the truck 12 bolt. You can see some right HERE Those new ones may not be in your price range, but used ones can be found on ebay, Craigslist, etc. The GM truck 12 bolt was used from '63-'81 ( I used to think it was thru '79) in both 2wd and 4wd. So there were a larger number of these produced over the years, and should not be too hard to find what you need.

Also it isn't always about obtaining the lowest cruise rpm's. It is more important to get your engine in it's 'sweet spot' rpm wise where it is most efficient. Finding that may require some research into factory combinations, and asking others what works for them. That's where this forum comes in real handy.

thats pretty much what I was gonna say

[xratt]

Thanks for your help too, Captainfab. Used your advice many times on this build. Ive got more research to do then.