Educate me on a 12 bolt in a 78 K 10?

wanderinthru

Full Access Member
Joined
Jul 23, 2020
Posts
920
Reaction score
1,293
Location
Mid Point Route 66
First Name
Shakey
Truck Year
81, 70, 75, 84, 89
Truck Model
K 10, C 30, K 20
Engine Size
350
Again, working on the race car build. Out in my parts pile there are 2 12 bolt rear ends. Both under 78's, one K 10 other a Blazer. My research so far says they quit building them in 72? Is there different 12 bolts? Are they danas? If so which Dana? Where does one find gear sets? Any and all info is appreciated!

Thanks!

Shakey
 

wanderinthru

Full Access Member
Joined
Jul 23, 2020
Posts
920
Reaction score
1,293
Location
Mid Point Route 66
First Name
Shakey
Truck Year
81, 70, 75, 84, 89
Truck Model
K 10, C 30, K 20
Engine Size
350
Pictures before I get my ass ate out.
The 78 k 10
You must be registered for see images attach

The blazer
You must be registered for see images attach

Come to find out, there are 3 out here.
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
25,788
Reaction score
14,228
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
The truck 12bolt was different from the car 12bolt. It was used in trucks up until the early 80's.
 

AyWoSch Motors

The Parts Guy
Joined
Nov 6, 2020
Posts
2,221
Reaction score
4,973
Location
New Mexico
First Name
Ayden
Truck Year
1986
Truck Model
K1500 Sierra Classic
Engine Size
305ci V8
Yup, I recognize those. Have one in my 78 and my 75. Pretty common truck rear end, was used up until the early 80s when the 8 1/2 in 10 bolt took over. Same basic design and size.
 

wanderinthru

Full Access Member
Joined
Jul 23, 2020
Posts
920
Reaction score
1,293
Location
Mid Point Route 66
First Name
Shakey
Truck Year
81, 70, 75, 84, 89
Truck Model
K 10, C 30, K 20
Engine Size
350
Yup, I recognize those. Have one in my 78 and my 75. Pretty common truck rear end, was used up until the early 80s when the 8 1/2 in 10 bolt took over. Same basic design and size.
Should have updated myself. Had looked at and read several articles and interweb stuff before I asked. Took a break later on yesterday and found there are 2 12 bolts car and truck, and like you said continued to put them in trucks till the 80's.
According to what I "learned" they both car and truck 12 bolts are comparable to and superior in important ways to the 9 in Ford. The Ford is what I was leaning tword for the race car, but now I have these. 5.83 is the lowest ratio I have for a 12 bolt truck as of yet, was thinking I want 6 to 6.5, which you can find for the Ford. Though also have a 70 malibu to go get, it could already have a 12 bolt car in it, I'll just cross my fingers till I can go fetch that thing and see.

Thanks, you as well @bucket
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
7,764
Reaction score
4,374
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
i think you have mistaken the 12 bolt truck diff for something else because Ford 9 inch by shear volume of usage and track record is just more there, there. But the car 12, thats something even ford people understand just like saginaw steering in pretty much all ways is superior. They know that because even they cant deny it. but the truck 12 bolt to my reading more or less "fine" but when you start looking at power or weight or large tire demands they start to meet their limitations. I happen to have 3 :(
 

Turbo4whl

Supporting Member
Supporting Member
Joined
Oct 30, 2019
Posts
1,720
Reaction score
3,136
Location
Downingtown, PA
First Name
Wayne
Truck Year
1974
Truck Model
Jimmy
Engine Size
350
According to what I "learned" they both car and truck 12 bolts are comparable to and superior in important ways to the 9 in Ford.

This is correct! I can go into detail why, if requested.

The only advantage of the Ford 9" is the ability for quick gear swaps at the track.
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
7,764
Reaction score
4,374
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
This is correct! I can go into detail why, if requested.

The only advantage of the Ford 9" is the ability for quick gear swaps at the track.
Why is that. I mean if you are saying my 12 bolts for trucks are better than furds 9 inch i am all ears.

Also what about a dana44 rear compared to them
 

Turbo4whl

Supporting Member
Supporting Member
Joined
Oct 30, 2019
Posts
1,720
Reaction score
3,136
Location
Downingtown, PA
First Name
Wayne
Truck Year
1974
Truck Model
Jimmy
Engine Size
350
Why is that. I mean if you are saying my 12 bolts for trucks are better than furds 9 inch i am all ears.

Also what about a dana44 rear compared to them

To start with, the early Ford gear sets are bevel cut gears. These offer more resistance than the spiral-bevel gear set in the GM rears.

The 1/4 mile racers could see this on their dyno tests. They combated this by fitting GM gears to the the Ford differential carriers. (very costly) Later, aftermarket gear companies provided spiral-bevel gears to fit.

You must be registered for see images attach


^ spiral bevel gears

You must be registered for see images attach


This shows the difference well. The automotive gear sets are really spiral bevel hypoid. This means the pinion gear is set at an angle to the ring gear (driven gear). That allows the pinion to be mounted lower than center on the axle.

You must be registered for see images attach

^ Hypoid

The second disadvantage to the Ford 9" is weight. On an integral axle housing, the carrier side bearings are supported by the housing. The removable Ford carrier requires the heavy casing for the side bearing support.

The last item is cost to put the 9" in a GM chassis. However you chose to do it, it is custom. Fabricators working on their own vehicle, this may not be an issue.

To answer your other question, the Dana 44 is much like a 12 bolt GM in strength. Dana 60's are an upgrade for both.
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
7,764
Reaction score
4,374
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
You must be registered for see images attach

to my best judgement I would say this is a d44 btu then again I couldnt count at least twice and thought I had 2 10 bolts and 1 12. i have 3 12 bolts(trucks)
I guess on the plus side one of them is a 3.73 gear set and 6 lug, so if its not worn it wouldnt be gutless in any utilized vehicle.
 

Turbo4whl

Supporting Member
Supporting Member
Joined
Oct 30, 2019
Posts
1,720
Reaction score
3,136
Location
Downingtown, PA
First Name
Wayne
Truck Year
1974
Truck Model
Jimmy
Engine Size
350
Yes, a Dana.

You must be registered for see images attach


But you need more, semi float? full floating axles? Could be a Dana 60. Usually the number, 44, 60 or 70 is cast in the case. GM seldom used Dana 44's in the back axle. Or are we looking at a Ford????
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
7,764
Reaction score
4,374
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
Thats a ford rear half yes i should Have mentioned. I am not sure if it came under it originally(67-72 F150 or F100)
 

wanderinthru

Full Access Member
Joined
Jul 23, 2020
Posts
920
Reaction score
1,293
Location
Mid Point Route 66
First Name
Shakey
Truck Year
81, 70, 75, 84, 89
Truck Model
K 10, C 30, K 20
Engine Size
350
To start with, the early Ford gear sets are bevel cut gears. These offer more resistance than the spiral-bevel gear set in the GM rears.

The 1/4 mile racers could see this on their dyno tests. They combated this by fitting GM gears to the the Ford differential carriers. (very costly) Later, aftermarket gear companies provided spiral-bevel gears to fit.

You must be registered for see images attach


^ spiral bevel gears

You must be registered for see images attach


This shows the difference well. The automotive gear sets are really spiral bevel hypoid. This means the pinion gear is set at an angle to the ring gear (driven gear). That allows the pinion to be mounted lower than center on the axle.

You must be registered for see images attach

^ Hypoid

The second disadvantage to the Ford 9" is weight. On an integral axle housing, the carrier side bearings are supported by the housing. The removable Ford carrier requires the heavy casing for the side bearing support.

The last item is cost to put the 9" in a GM chassis. However you chose to do it, it is custom. Fabricators working on their own vehicle, this may not be an issue.

To answer your other question, the Dana 44 is much like a 12 bolt GM in strength. Dana 60's are an upgrade for both.
This is what I have understood, via the interweb. What I have not been able to assertain for certain is, is the 12 bolt car and 12 bolt truck the same design? Like the pinion being below center of the ring? Also seems there are 3 different 12 bolt trucks, good, gooder and goodest that are basically the same except for the ring gear assembly sizes/ bearings? That doesn't really matter to me because it will be replaced with a spool so???? Just to ask would you rather a 12 bolt truck, or a "regular" 10 bolt car? The problem I am having with the 12 bolt truck is finding gear sets. As of now the lowest I've found is 5.83, which would work for the begining and the engine I'm starting with, but the plan is to build a 327 for it and in that case a 6.50 would be as high as I would want??

Thanks!
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
7,764
Reaction score
4,374
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
This is what I have understood, via the interweb. What I have not been able to assertain for certain is, is the 12 bolt car and 12 bolt truck the same design? Like the pinion being below center of the ring? Also seems there are 3 different 12 bolt trucks, good, gooder and goodest that are basically the same except for the ring gear assembly sizes/ bearings? That doesn't really matter to me because it will be replaced with a spool so???? Just to ask would you rather a 12 bolt truck, or a "regular" 10 bolt car? The problem I am having with the 12 bolt truck is finding gear sets. As of now the lowest I've found is 5.83, which would work for the begining and the engine I'm starting with, but the plan is to build a 327 for it and in that case a 6.50 would be as high as I would want??

Thanks!
no. they are not the same. infact that part i said earlier that the 12 bolt truck is usually not wanted but the car is. even if the 12 bolt truck is good* there is little use to the people building their streeet cars to my understanding because 1) Not internally sharing all that much 2) not to their liking for strength or maybe dimensionally idk 3) Maybe the truck one has heavier shafts and bettter suited for weight rather than in a lighter application which is being romped on 4) most parts and upgrades I think are limited to the car ones sicne that is what people want and that of course is broken down by suspension type, brakes, ring gear, widths, locations of where shocks go, but like cars had some crazy ideas here and there and then of course spline counts and the most important part for performance, a shiny and finned cover. I refuse to elaborate or falsify evidence to prove that helps LOL
they look pretty tho
 

Turbo4whl

Supporting Member
Supporting Member
Joined
Oct 30, 2019
Posts
1,720
Reaction score
3,136
Location
Downingtown, PA
First Name
Wayne
Truck Year
1974
Truck Model
Jimmy
Engine Size
350
This is what I have understood, via the interweb. What I have not been able to assertain for certain is, is the 12 bolt car and 12 bolt truck the same design? Like the pinion being below center of the ring? Also seems there are 3 different 12 bolt trucks, good, gooder and goodest that are basically the same except for the ring gear assembly sizes/ bearings? That doesn't really matter to me because it will be replaced with a spool so???? Just to ask would you rather a 12 bolt truck, or a "regular" 10 bolt car? The problem I am having with the 12 bolt truck is finding gear sets. As of now the lowest I've found is 5.83, which would work for the begining and the engine I'm starting with, but the plan is to build a 327 for it and in that case a 6.50 would be as high as I would want??

Thanks!
When you are talking about the good, gooder or goodest design are you referring to the differential carrier? There are from GM, 3 different carries to accommodate the different ratios. Since the pinion gear is much larger on the high gear sets, (like 2.73:1) the carrier gear mount for the ring gear is further away from the center of the pinion gear. Then closer as you get to the low gears, (4.11:1)

Thinking about this, tall gears like the 2.73 push back harder on the drive line, transmission and drive shaft. Low gears, 4.11 push harder on the axle shafts. So when adding lots of horsepower to a tall gear set, what might fail first is the drive shaft. Same horsepower pushing on the low gear set, would twist the axles up first.

For a gear set like you stated, 6.50:1, I would think you want the truck 12 bolt for the stronger housing and thicker truck axle shafts. You are building lots of torque with those low gears!
 

Forum statistics

Threads
35,828
Posts
755,055
Members
24,841
Latest member
KC_Stuart
Top