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Old 10-30-2003, 07:35 PM
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GM Front Diff. Reliability For Full Time Use.

I am questioning the reliability of the front differential in the GM four wheel drive trucks.
I posted this topic previously and neglected to include some specifics which after doing the math now have included.
I am interested in using a full size front differential assembly mounted to the frame of my truck, having custom length CV shafts made, and using the complete front suspension from an S-10.
This will definitely be a custom job, and give the truck independant REAR suspension.
Similar to a low-buck rodders answer to a Jaguar or Corvette 3rd member.
I am planning on using the torsion bars for the springs which will give it a clean overall look under the frame.
I have already checked out the following information.
The stock front differential in an S-10 comes in 3.42/3.73/& 4.10 gears.
The low gear in the transmissions is near 3.00:1. (without checking)
The low range in the transfer case is near 2.00:1. (without checking)
The torque output of the 4.3 liter is over 200 foot pounds. (without checking)
200#'s torque X 3.00 1st gear X 2.00 low range X 4.10 axle gear=
4920#'s of compounded torque at the axle hub DIVIDED BY TWO for two differentials for 2460 pounds of torque at each axle.
My new setup will be:
325+#'s of torque X 2.48:1 1st gear X 3.73:1 axle gear=3006.38 compounded pounds of torque with my 350 and TH-400 transmission.
If I were to use the full size differential its torque handling ability is even more as they came with big blocks, diesels, and lower gears in everything.
400#'s torque X 4.001st gear X 2.5 low range X 4.10 axle gear=
16,400 pounds of torque total and 8,200#s at each differential that these units must be designed to handle.
These units were designed to be turning with the wheels full time as no lock-out hubs were ever available on this front driveline from the factory.
I plan on removing the long axle tube and disconnecting hardware and re-installing another short axlein it's place, then after the hubs and differential are in place having the necessary modifications made to a set of CV shafts, or having a set of small driveshafts with slip-yokes custom made to fit my application (my preferred choice as the full size shafts already cost $400 without the mods).
The brakes would remain the stock front disk as found on the S-10 of choice.
The steering would be locked by way of the stock outer tie-rod end connected to a HEIM joint inner for simplicity purposes.
Matt

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Old 10-30-2003, 11:03 PM
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Won't the drive shaft be turning the wrong way with the diff mounted in the rear? If you turn the diff up-side-down, Will oiling be an issue?

They don't have hubs, but they do have a CAD. Central Axle Disconnect. Basically a sleeve in the long side that connects the two pieces of the right side axle together to engage the front end. The ring and pinion don't turn all the time.

Three sizes where used. The S-10 used a 7.2". The 1/2 ton, and 6 lug 3/4 ton trucks used an 8.2". The 8 lug 3/4 ton and 1 ton trucks used a 9.2". Seems to me a 9.2" will handle just about anything thrown at it. For reference, the 70' Eldo used an 8" gear. Dan
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Old 10-31-2003, 07:16 AM
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Its driveshaft is designed to turn counter-clockwise as facing the front of the vehicle, exactly the same as the rear.
Mounting it in the rear facing forward will net the desired result, the driveshaft-while still rotating CCW in drive will now (with the diff facing the opposite direction) net the desired result.
I could show you on paper, it just equates to running the differential in reverse all the time, and since I plan on changing the gears breaking in a new R&P gearset the other direction will make no difference.
I will not have to turn it upside down, just face the input the other direction.
The CAD can be replaced with the complete shortside assembly, the only way this thing will fit where I want it.
Also remember that the Syclone and Typhoon had provisions to their individual diffs to replace the CAD to make them full time axles, they just replaced the disconnecting hardware with a solid shaft instead of a connecting sleeve and two shafts.
The short side axle and all associated parts will physically bolt onto the long side, ans vice-versa.
I was unsure about the sizes of ring gears used but either of the larger ones will work for what I want them to do.
I will have to have the new CV replacement shafts made but will cross that bridge when the time comes.
Matt
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Old 10-31-2003, 02:09 PM
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OK, so I go down and drag one out. You are right about the rotation. That shouldn't be a problem. One thing I did notice. The S-10 diff I was looking at is a reverse cut, or high pinion diff. The pinion center line is higher than the axle center line. Running it as a rear diff would have it running on the heal of the gears and not on the face that is the strong side of a gear. The factory used reverse cut gears in the front diff to make it stronger without having to use a large gear. The guys running a bunch of lift like them for the higher pinion location that helps relieve some of the drive shaft angle issues a short front shaft has.

I don't think you will have troubles with a 9.2". Running it in reverse, it wouldn't be as strong as a 9" Ford. The 9.2 does have a high spline count. 31 if I remember right. The 7.2 has 26 and the 8.2 has 28. I would think the strength of a reverse running 8.2 would be that of a 7.5" conventional diff. Dan
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Old 10-31-2003, 05:36 PM
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I was unaware of the different pinion sizes.
But now I know what to look for when I am ready to search for the differential, definitely the 9.2.
Are there numbers on the housings for ease of identification?
I have a while to look for one of these units, as I don't have the engine anywhere close to being ready to go into the truck.
Thanks for the info.
Matt
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