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I believe I have seen it mentioned that both can be found under a 1st gen.
 

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I know for a fact in 1991 Dodge equipped the D&W 250s and SRW W350s with the DANA 60 rear axle at 5500 lbs. So I would think your W250 would be a DANA 60
 

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My 1991 FSM & Sales Brochure.
 

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If it has the diesel from the factory and the axle hasn't been swapped, it will be a D70 rear and D60 front for W series 250/350. The W250 of that era should be a D70U rear.
 

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If it has the diesel from the factory and the axle hasn't been swapped, it will be a D70 rear and D60 front for W series 250/350. The W250 of that era should be a D70U rear.
^^^ yep, the diesels came with 70s the gas trucks had 60s the diesels have 60s up front (4x4s) while the gas trucks have dana 44s up front... the diesels 250s and 350s both had 70s in em... as I just discovered after doing some research for 1tondually... I just assumed Dodge had put 80s in the 1 tons but nope not till later years as I told him .. its sad but just one more + for Chevy as they at least put big bad 14 bolts in their 1 tons back theneven in their gas trucks >:):stirpot:
 

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FSM-Boy, you really can't believe everything you read. :surprise:
 

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FSM-Boy, you really can't believe everything you read. :surprise:
diesels also have a heavier frame as well 8" versus 5" for gas trucks, thats why I bought my 93 when I decided to convert 71 Blazer to 12 valve.. plan was to shorten the truck frame and use it as well under the Blazer as its higher tensile rated steel as well as taller but the thing was so clean and fired right up after sitting 10 years I couldn't chop it up...
 

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I have two cab & chassis 1-tons... (75 D300 & 77 W300) both have a 70B. Its a heavier casting, 3.5" tubes, and uses larger pinion bearings than the 70U.

The 70HDs I have encountered (GM and Ford) had 4" tubes. Not sure what a D/W450 would have used.

AFAIK, once the 70B ran its course, the 70U replaced it. First in the same 35-spline format, and then around 91/92 became 32 spline instead (bolts retaining axles shafts instead of cones & nuts).

diesels also have a heavier frame as well 8" versus 5" for gas trucks, thats why I bought my 93 when I decided to convert 71 Blazer to 12 valve.. plan was to shorten the truck frame and use it as well under the Blazer as its higher tensile rated steel as well as taller but the thing was so clean and fired right up after sitting 10 years I couldn't chop it up...
I think you mean 6" channel on the gas trucks (7" on heavier ones). Most non-IC diesels have a 6" channel too.
 

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I have two cab & chassis 1-tons... (75 D300 & 77 W300) both have a 70B. Its a heavier casting, 3.5" tubes, and uses larger pinion bearings than the 70U.

The 70HDs I have encountered (GM and Ford) had 4" tubes. Not sure what a D/W450 would have used.

AFAIK, once the 70B ran its course, the 70U replaced it. First in the same 35-spline format, and then around 91/92 became 32 spline instead (bolts retaining axles shafts instead of cones & nuts).



I think you mean 6" channel on the gas trucks (7" on heavier ones). Most non-IC diesels have a 6" channel too.
only ones I've dealt with are 92/93s and yea might be 7" been awhile since I measured em, was back when I was looking to convert onea my Blazers to 12 valve and realized I'd be much better off using the 93s frame as well etc.. then folks on here told me the gas trucks were only 5" Never measured one myself and only trucks I've been looking at buying up for parts doners have all been 92/93... and all 4 of em have 70s under them so... learned a long time ago that the books are just a refference not the bible as been restoring old iron most of my life and seldom has the info in the manuals matched what I actually found in the vehicles...
 

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him .. its sad but just one more + for Chevy as they at least put big bad 14 bolts in their 1 tons back theneven in their gas trucks >:):stirpot:
I was under the impression from my reading that the 14-bolt GM axle is roughly equivalent to the Dana 70s found in these trucks.
 

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I was under the impression from my reading that the 14-bolt GM axle is roughly equivalent to the Dana 70s found in these trucks.
14 bolts a lil closer to a dana 80 weight wise as in on a scale they are almost the same.. the downside in the 4x4 world where I play with the 14 bolt is that big chunk of cast iron drags on everything unless your running larger than 37" tires while the dana 60-70 provide more clearance and ya can get lower gears for the 70 the 14 bolt only goes down to 5.13s , offroaders prefer the 60-70 because they are much lighter than the 14 bolt less unsprung weight translates to better offroad handling the big plus to 14 bolts is parts are dirt cheap if ya break something etc.. but its soooo hard to break em... I shave and truss 14 bolts to put under mosta my toys as I don't trailer my rigs to events I usually drive em and the 14 bolt is good at having a split personality between streetability and offroad ability... at least for the last 35 years I been beatin stuff up offroad :D

the reason I was looking to put a 12 valve into onea my Blazers is cause everyone told me it was a bad idea for actually going offroad due to weight but as my big blocks are already tipping 900lbs figured I'd play with the extra 200lbs o.k and I belong to a club of hot rodders/racers with this rule bout all our rigs gotta be 100% mechanical no laptops or tuners so... a 12 valve was my secret torque weapon to get beyond my 496 gas engine but like the song says... I fooled around an fell in love.. with the 93 that it was sposed to just be a one night stand then under the torch for the ol gal ;)
 

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^^^ yep, the diesels came with 70s the gas trucks had 60s the diesels have 60s up front (4x4s) while the gas trucks have dana 44s up front... the diesels 250s and 350s both had 70s in em... as I just discovered after doing some research for 1tondually... I just assumed Dodge had put 80s in the 1 tons but nope not till later years as I told him .. its sad but just one more + for Chevy as they at least put big bad 14 bolts in their 1 tons back theneven in their gas trucks >:):stirpot:
A lot of debate over which is actually superior between a 14-bolt and D70...they are very similar in ratings.

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I have two cab & chassis 1-tons... (75 D300 & 77 W300) both have a 70B. Its a heavier casting, 3.5" tubes, and uses larger pinion bearings than the 70U.



The 70HDs I have encountered (GM and Ford) had 4" tubes. Not sure what a D/W450 would have used.



AFAIK, once the 70B ran its course, the 70U replaced it. First in the same 35-spline format, and then around 91/92 became 32 spline instead (bolts retaining axles shafts instead of cones & nuts).







I think you mean 6" channel on the gas trucks (7" on heavier ones). Most non-IC diesels have a 6" channel too.
D70HD also had massive amounts of structural "webbing" cast into the center chunk, there is no mistaking one once you've seen one...

I've only ever seen one true D70HD in person...I think it was an early 80s Dodge dually.

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14 bolts a lil closer to a dana 80 weight wise as in on a scale they are almost the same.. the downside in the 4x4 world where I play with the 14 bolt is that big chunk of cast iron drags on everything unless your running larger than 37" tires while the dana 60-70 provide more clearance and ya can get lower gears for the 70 the 14 bolt only goes down to 5.13s , offroaders prefer the 60-70 because they are much lighter than the 14 bolt less unsprung weight translates to better offroad handling the big plus to 14 bolts is parts are dirt cheap if ya break something etc.. but its soooo hard to break em... I shave and truss 14 bolts to put under mosta my toys as I don't trailer my rigs to events I usually drive em and the 14 bolt is good at having a split personality between streetability and offroad ability... at least for the last 35 years I been beatin stuff up offroad :D

the reason I was looking to put a 12 valve into onea my Blazers is cause everyone told me it was a bad idea for actually going offroad due to weight but as my big blocks are already tipping 900lbs figured I'd play with the extra 200lbs o.k and I belong to a club of hot rodders/racers with this rule bout all our rigs gotta be 100% mechanical no laptops or tuners so... a 12 valve was my secret torque weapon to get beyond my 496 gas engine but like the song says... I fooled around an fell in love.. with the 93 that it was sposed to just be a one night stand then under the torch for the ol gal ;)
Keep in mind, there are several "14-bolts", including an older semi-floater used in heavy half tons, the venerable semi-floater used forever (including a variant used in the current 2500hd), and the monster semi-floater 14-bolt that is similar to a D80 used currently...

When most speak of a 14-bolt, they talk the common deal that's been around forever...9-3/4" ring if memory serves me right? They are mainly popular because they are common, cheap, easy to rebuild, and parts are everywhere.

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Keep in mind, there are several "14-bolts", including an older semi-floater used in heavy half tons, the venerable semi-floater used forever (including a variant used in the current 2500hd), and the monster semi-floater 14-bolt that is similar to a D80 used currently...

When most speak of a 14-bolt, they talk the common deal that's been around forever...9-3/4" ring if memory serves me right? They are mainly popular because they are common, cheap, easy to rebuild, and parts are everywhere.

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10.5" ring gear (d-80 is 11") actually and they are full floaters (which is the point of using em offroad) the 1/2" thick axle tubes are the other reason they are so popular but yea bein cheap doesn't hurt there are just more chevy trucks out there than anything else so a ton of the big monsters available in bout any junk yard, being rated for 8600lbs for the light version up to 10,000 for heavy puts em right up there with the D80 which is rated for 11,000 the 14 bolts got thicker axles (1 3/4" for 14 bolt 1 1/2" for d-80) 14 bolt weighs in at 550 lbs to the Dana 80 at 500lbs so... I'd say a lil closer to a d-80 than a d-70.... the only downside to em is that big ol pumpkin creates ground clearance issues if ya aren't running enough tire.... the ones most sought after for runnin big heavy tires off road and big torque are the 1973-1986 versions particularly from 1 tons they had extra webbing in the center section that was taken out by the bean counters in 1988...

the 14 bolt versus the d-70 is a super common bon fire argument topic I been havin for 35 years of offroad competition got the specs down :D its almost as common as the ford versus chevy which was the argument for the prior hour and will be followed by the spool versus locker argument as the night goes on... the d-70 has 2 big pluses for offroad lighter weight and much lower gears available... the 14 bolt beats it in every other category and while I will run both I've had better longevity outa the 14 bolts running the 496 big blocks I favor and since I started running Atlas t-cases the lower gears is a non issue... besides what got me into 12 valves was researching the idea of usin a fully mechanical 12 valve to match the torque of my big blocks with the manners of a diesel..ie; at lowwer rpm than any gas engine
 

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only ones I've dealt with are 92/93s and yea might be 7" been awhile since I measured em,
The 91.5-93 diesels I've encountered (pickups) had 8" channel.

Keep in mind, there are several "14-bolts", including an older semi-floater used in heavy half tons, the venerable semi-floater used forever (including a variant used in the current 2500hd), and the monster semi-floater 14-bolt that is similar to a D80 used currently...

When most speak of a 14-bolt, they talk the common deal that's been around forever...9-3/4" ring if memory serves me right? They are mainly popular because they are common, cheap, easy to rebuild, and parts are everywhere.
The 'classic' 14-bolt ('73+) is a 10.5" and full-float. The pinion unbolts on these.

The smaller semi-float 14-bolt showed up around '81. 9.5" ring gear.

That later AAM1150 full-float, 11.5" ring gear showed up in the early 2000's for the Dmax Chevies and 3rdgen Dodges.

There may be another version or two on top of that... definitely saw an oddball AAM full-floater in a 1500 gas megacab,


D70HD also had massive amounts of structural "webbing" cast into the center chunk, there is no mistaking one once you've seen one...

I've only ever seen one true D70HD in person...I think it was an early 80s Dodge dually.
There's a number of casting revisions within each version (i.e. HD, B, U, etc.) with a trend of reduced weight (less webbing) over the years. The 4" axle tubes seem to be the common ground for the HD.
 

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Haven't measured my axle tubes yet but wondering if our 1st gens had the 70hd in them or the 70u
I'm currently going through the same questions. I'm regearing my truck on the 26th and I've found a few different opinions on what these trucks have. The 1st gens should have either a D70 or D70U, the only real difference between these two are the axle spline counts and most importantly the inside pinion bearings which is smaller on the U axle.

From my research I've found the following, but it's probably still not perfect:
- If you have the 3.07 gears you will have a 70U since it appears the regular 70 didn't have the option below the 3.54 ring/pinion
- 32 spline axles should be the 70U, since the 70 only came in 30 or 35 spline.
- It appears from looking around most of the trucks have 70U's with some of the earlier 1st gens having the regular 70's.

Take it all with a grain of salt, but I think the information is fairly accurate.

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