Differential Confusion

[72 Cheyenne K20]

I went to NAPA today to try and find a replacement for my Free/Lock hub knob on my 72' 3/4 ton. I don't think the guy has laughed that hard in a long time. Anyway, I started talking to him about different diffs for front and rear. I haven't really thought to much about them yet but wanted to ask what the options were. I have a d44 in front and non posi 10 bolt in back. I looked at some posts today and I saw one that said that 10 bolt rears were not introduced until the mid 80's. Is this true?I also wanted to ask any preformance differences between d44 & d60 for the front and 10 bolt, 12 bolt, 14 bolt for the rear?

Thanks, Scott

[JIMs70GMC]

Ok the 10 bolt(eaton) that would be in your truck is not the same as the corperate 10 bolt. Your 10 bolt has a round cover and drop out center section refered to by RPO numbers: H052 and H072. The 12 bolt was in 1/2 ton trucks. 14 bolt was introduced in 1973 not available in our trucks, though a 1 ton 14 bff will bolt in and only require moving the shock mounts. Forgot some dana 60 rears made it under the rear of some 3/4 ton 4wd trucks mostly the GMCs.
The spicer hub you need is not made anymore, it's an external hub. Everything now are internal. Post a wtb on the parts board, the dials came in 3 different covers blue(our trucks), yellow and red(ferd).

Performance, where to begin..... The highest gears for an eaton(our axle) is 4.10, only traction aid is a, not made anymore, detroit locker refered to as the no-spin on the option sheet. That's it.

You'd have more option with a newer axle.

Our front (dana44) w/ 8 lugs was the biggest available until 1977 w/ the 1 ton 4wds came w/ a dana 60. Comparision 8.5" ring gear to 9.75" ring gear. Axle are 40% bigger, u-joint are over 100% stronger. W/ a dana 60 front you can run 44" tires. max recommended for a dana44 w/ the 260x u-joint is 33" and w/ a 297 35". I stop here allow others to jump in.

[4x4Poet]

The hub you have is a Spicer hub, which bolts on externally as JIMs70GMC said. It is not the strongest hub out there for a D44, but it is plenty strong for any open diff axle and for lockers with tires smaller than 36" unless you bash your way thru everything off-road. Which begs the question...

Why do you think you need to replace the 3/4 axles you have? Nothing wrong with the front heavy duty D44 and rear Eaton H052. The D44 only needs 73up alloy axles to eliminate its one weakness. The rear Eaton has no weakness and is much lighter than a 14bFF. A D60 is comparable in weight to the Eaton but weaker. The Eaton is as strong as a 14bFF though some would claim that the axles are not as strong. I disagree. So I'd say the board needs to know what you want (to do) if you want more specific advice.

[Americanrider]

72 Cheyenne K20 : "a replacement for my Free/Lock hub knob "

If you have a stock Spicer hubs with the blue plastic insert it's rare... like chicken teeth rare!

Here is my 2cents,
FRONT:Consider upgrading to the Warn premium all metal hubs,
Warn part#9072 (the same # for all '67-72 D-44 front axles)
Cost between $60-120 for hubs,
might also need a spindle nut kit.

REAR: Many choices out there, depends on how you use you truck. The Eaton rears are strong, sometimes hard to find new parts for them (depends on where you live). Could you add to your posting? How you use your truck/what kind of driving you do?

[72 Cheyenne K20]

Thanks for the replies guys, I'm not set on replacing any of the drive train in the truck. This guy from NAPA just planted a seed in my head about other differentials. I don't really do a lot of off roading. Mostly highway and around town. I was thinking about a different gear ratio though. I think I have 4.11's in there now because it's wound pretty tight at 65 mph, haven't pulled the covers yet. I also have a 70 3/4 ton 4x4 that rides smooth at 75 (about 2850 rpm's) but is a little slugish. I haven't pulled those covers either but the PO said 307's. Since you guys tell me that both factory differentials are heavy duty I doubt I'll chance them. I just like over kill. When I was issued my M16 in the Marine Corps I had to have the M203 grenade launcher too. Better to have it and not need it theory. Any thoughts on a good highway ratio that will still give me good power? Thanks for all your help.

Scott

[muddobber40]

3.73 work well for towing and decent mileage at highway speeds

[JIMs70GMC]

Your 70 should have 4.11s also.

[Rod]

Your 3/4 ton 4x4 of this vintage came with either 4.10 gear set or 4.57 gears set.

Those hub lock dials show up on ebay once in a while. Haven't seen any lately though.
Typically you will see a little newer ones with the word spicer in them. I have had 2 70 3/4 4x4 GMC's and both had red dials. My 70 Sub GMC 3/4 4x4 has one red and one blue. Was looking to match one color at least.

I could use a inner gear off the axle for one of those style hubs too.

Heres a pic of NOS spicer dials.

[72 Cheyenne K20]

Ok, got a ?. My 72 3/4 ton 4x4 has a 4" lift and runs on 305x70xr16 (same as 33x12.50). I hear that bigger tires and a lift will make your gear ratio seem higher than what it actually is. Is this correct? And if it is, does anyone know approximately how many rpm's I would pull at say 60 or 65? The reason I ask is my 70 3/4 ton 4x4 has no lift and factory size tires and runs on the highway very easy. Assuming it does have 411's, I'm wondering if tire size and lift can make that much of difference.

Scott

[1FaastC10]

2500 @ 60
2700 @ 65

that is, assuming a TRUE 33" tire, shorter tires will cause it to go up a bit.

[mdepot]

If you put bigger tires on it, it will feel like it has a numerically lower ratio, meaning your engine rpm at the same speed would be somewhat lower than with stock tires. (That's the same real speed like by using a GPS, not what's on the speedo since that readout would also change too.) It usually means a loss of torque and slower acceleration, sort of a sluggish bogged down feeling, (but better highway mileage). Anyway, that's why people tend end up wanting to swap gears to a numericlly higher ratio to compensate.

I do have a question back to Jims70GMC though. Where you say "Our front (dana44) w/ 8 lugs was the biggest available until 1977..." My 69 K20 has an line in the glove box ID sticker of "Option # 4F49AA - Heavy Duty Front Ax" and I think I've got a Dana 60. What's more, it's closed knuckle. The hubs are 8 bolt, and the manual hub lock dials are aluminum colored. Have I got something weird here? Can post pics if anyone's interested...

[72 Cheyenne K20]

1faastc10- I have to ask more simple so I understand. assuming the truck has 411's.

factory tires and factory lift = what rpms @ 65 mph

33x12.50 tires and 4" lift = what rpms @ 65 mph

and taller tires and a lift makes 4.11's closer to 4.56's or 3.73's

Sorry to sound like a boot, but I am

Thanks, Scott

[1FaastC10]

Originally Posted by 72 Cheyenne K20

factory tires and factory lift = what rpms @ 65 mph

and taller tires and a lift makes 4.11's closer to 4.56's or 3.73's

i dont know what your truck came with from the factory with, lift makes no difference.

as far as taller tires, it will make them seem like they are higher (numerically lower)

[4x4Poet]

You can answer all your questions by plugging your data into the formulas on OffRoad.com's gear calculator page. You can find other gear calculator pages by googling "gear calculator" with "tire diameter" and "rpm."

[ABHaulR]

your going the wrong way. if you put on bigger tires your gears fell like 3.73 insteed of 4.10.
DWAYNE

[JIMs70GMC]

mdepot, You have a closed knuckle dana44 w/ 8 lug outers and a slightly larger u-joint. No closde knuckle dana60s in these trucks.
M715 5/4 ton trucks had a closed knuckle dana60 w/ a 5 on 7.5" bolt pattern or something like that.
Your axle would have a 5-86x u-joint where as standard was 5-74x. Nothing weird.