Posted by Charlie on September 19, 2000 at 14:47:10:
In Reply to: hey ray suiter-- i saw something you might be interested posted by mannyc on September 19, 2000 at 11:06:01:
It's an interesting idea but...
1) The 9" ring gear is of course smaller than the 9.625 ring gear of the M37 by 6.5%. That makes it 23.5% weaker. Prt of 9" "bulletproof reputation (perhaps most of it) is its' having 3 pinion bearings. So does the M37. That part of the diff wouldn't be strong, it'd be weaker. Yes, the 9" comes in gigantic number of ratios including either 5.83 or 5.86 or 5.87, and either 4.89 or 4.88. But I predict STOCK M37 axle shafts would continue to break with 5.83s with/without rear NoSpins. I don't think the diff itself would break despite the smaller size because of its' strong design. But it's NEVER a good idea to do drivetrain upgrade with anything dimensionally smaller than stock. Size is strngth (so is design and metallurgy, of course). Don't ever forget the strength of a given amount of metal in a tube is proportional to the 3rd power of the diameter, and the strength of a solid shaft is proportional the the 4th power. Or maybe it's the other way around, but you get the idea. The great advantage would be the ability to use aftermarket axle shafts up to 1.50" (do they make them that big for the 9"? If they do, they're not stock, they're aftermarket for sure, i.e. more $$$). Re the taller gearing, one can find (see pp. 25-26 in John Zentmeyer's book published by Portrayal Press, TM 9-1808C, "Power Trains & Interchanges, Military/Civilian Trucks 1941 to 1971 (Dodge)) 3.91, 4.10 and 4.30 diffs in postwar 2WD Dodge pickups which have 8.75" ring gears. Have 1/16" machined off the axle housing face for proper alignment side gear to axle splines and install 3/4 ton side gears so that regular M37 axle shafts will fit properly. Then, when one switches to the regular 5.83 M37 diff center use 3 (three) gaskets to restore proper alignment.
The 9" Ford diff is definitely the strongest most versatile diff/axle in the "1/2 ton" class. that is, competing against the Dana 44, Chevy 10 and 12 bolt, and Chrysler 8-3/4" (modern or old). But with our 6000 lb unloaded trucks with 57-78:1 low range gearing, full floating axles and lockers and 35-42" tires that'll fit without lifting, we should be looking in the 3/4-1 ton type axle class. frankly, the neatest idea I've run into so far is this:
A guy in Reno Nevada has advertised this twice in Power Wagon Advertiser. Once about 4mos ago and once 2 years ago. I've talked to him once. The GM 14 bolt is the strongest axle/diff till you get up to the Dana 80 - stronger than a Dana 70. It has 3 pinion bearings and a 10.5" ring gear, and is much easier to work on than a Dana 70, but not quite as easy as a dropout 3rd member. The Detroit Locker is really cheap because it's just a NoSpin insert in the stock carrier. An Air Locker is also available but who'd want it since it's $300 more than the NoSpin (without the compressor!) and the 14 bolt is just for the rear anyways. It has 1.50" shafts.
He figured out the simple machining operations to make M37 hubs fit on to the spindles and also the bearing part #s. The wheels sit at exactly the same position. The spring pads did not need to be moved. It's very easy to put together "hermaphrodite" drivehshfts with a M37 front half and a 14 bolt rear piece that run off the E-brake output, which reduces transfer case whine and maybe even heat and definitely wear, since of course the 14 bolt has a centered diff.
14 bolts are very easy to find and have only been changed once. There are disk brake conversions available. Because they don't say "Dana" (there's a "thing" going on in the 4WD world about Dana axles; an outfit called Dynatrac quoted me $3700 for a rear Dana 70 with 4.88s and a Detroit, with drum brakes for my F350. I paid Boyce Equipment $1200 for a similarly set up 14 bolt, all nice and totally rebuilt - new bearings and seals and brake parts, with moved spring pads) they are much cheaper. From Boyce or other places. It think this is the best solution to the rear axle problem, other than perhaps somebody building a bulletproof set of axle shafts for a decent price. Really, there's nothing wrong with the rear M37 diff/axle except the 1.25" axle shafts.
The front is a different matter. Who's broken axle shafts? You don't hear about that much. I think the Tracta joints are quite strong, they sure look bigger than Birfields or big U-joints. Since one can solve the "high speed highway gearing" problem with the old Dodge ratios, all you need on the front would be a set of hubs for highway runs. I would much rather have an Air Locker in the front than a Lockright, but with the hubs and power steering is a Lockright that horrible? I think not, and Ray Suiter has simplified the PS situation with a kit that brings PS below any conceivable cost of a front axle swap (plus at the end you have PS!). Currie makes front axle assemblies out of 9" Ford centers which are totally custom but I'm sure totally expensive. Dynatrac also will make front Dana 60s but likewise. Boyce sells totally rebuilt front Dana 60s (their front D60s and rear 14 bolts are out of CUCVs) for $1750. This is with 4.56s and open diffs. 4.88s, spring pad moving and an ARB Air Locker would bring it up to $3000 or so. Add the price of a 14 bolt to have matching hub patterns, 8 bolt 16X6 or 6.5 or 7" steel wheels are dirt cheap, you're up to over $4000.
So like I said the best solutions to our problems in the rear and the road ratio problems are either the old 2WD postwar Dodge diff centers or the 14 bolt/M37 hybrid.
Charlie