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'81 4x4 slant
https://www.slantsix.org/forum/viewtopic.php?t=7070		 Page 1 of 1
Author:  welly225 [ Wed Oct 01, 2003 11:14 am ]
Post subject:  '81 4x4 slant
The rearend in my dad's truck let go on him while he was doing about 55mph. Needless to say, she's blowed up real good. The truck's not worth the cost to go all out and rebuild or buy rebuilt (only sentimental value left) so I'm looking for cheap and easy (aren't we all).

It's an 81 150 4x4 with a slant and a 4 speed. I'm told the gears are 3.55's. Now the technical part... Can I swap any truck/van rear (4x4 or not) as long as the ratio's the same? Does the rear need to be from a 150 or can a 3/4 ton rear be used? OR... are there any car rears that would fit as long as the ratio's the same? Am I correct in assuming that if the ratio's not 3.55 then the front and back tires would spin at different speeds?

The real reason I want it fixed is because my dad just bought a Jeep Grand Cherokee and I was going to start using the truck. It's only going to be used for light duty stuff like runs to the hardware store and for carrying my snowmobile around. I realize there are different bolt patterns out there for certain rears and I'm ok with carrying 2 spare tires I just want to know what'll fit under it.

Please help
thanks all
Author:  Super6 [ Wed Oct 01, 2003 11:28 am ]
Post subject: 
Do not know about any car axle interchangability, but any truck axle should physically fit--if it is not a 1/2 ton axle it will be an 8-lug, and even the 1/2 ton axles have either a 5 on 4 1/2 or a 5 on 5 1/2 bolt pattern (Ill guess yours is a 5 on 4 1/2, all the 5 on 5 1/2 I have seen have been on later 80's trucks)

The gear ratios need to be the same (actually 0.01 different, so the front end 'pulls' ) if you EVER plan to actually use the 4 wheel drive, without matching ratios you will either blow the transfer case, an axle, or flat out go spinning off the road :shock:

I have never got out a ape measure to check, but the rear axle from a 94 up Ram looks to be pretty close to the same size. I believe the axle tubes are thicker, and have no idea about the spring perches or U-joint, but those are issues that can be worked out.

Keep the trucks alive! :)

-S/6
Author:  welly225 [ Wed Oct 01, 2003 1:04 pm ]
Post subject:  pain in the rear
Hey thanks for the quick reply.

We were told it's 5 on 5.5 from 81 and up. but like I said it's not critical to me.

I've got a 196? 1/2 ton out back, Is there a way to tell the gear ratio without major surgery.

Like I said I'm lookin' for cheap and easy, I want to try to use what I've got out back (free). Anyone else out there got any ideas. Other possible donors include 60's 3/4 ton truck, 70's 3/4 ton van, or an A,C,E,F or J body car.

Thanks again
Author:  Super6 [ Wed Oct 01, 2003 1:16 pm ]
Post subject: 
To check rear ratio:

For a posi:

Support rear on jackstands.
Make a mark on driveshaft and on a rim or tire.

Rotate tires (both should turn) one complete turn, while counting the number of turns the driveshaft makes. Number of driveshaft turns = gear ratio.

For open diff:

Same as above, except leave one tire on the ground, and turn the tire that is off the ground TWO full turns. # driveshaft revolutions = gear ratio.

-S/6
Author:  Slant Cecil [ Wed Oct 01, 2003 4:35 pm ]
Post subject: 
Your '81 W150 should have a 4 1/2" bolt pattern. Same as all 2WD D100/150s and full time 4WD W100/150s till '84. In '85 all D and W 100/150s had 5 1/2" bolt pattern. The non full time 4 WD W100s up to '74 had 5 1/2" patterns.
Finding a pre '85 rear with 3.55s in it already may be a little hard. The newer D150s with auto trans and overdrive had 3.55s but they have the bigger pattern. Your 4 1/2" bolt pattern axles might swap into a newer rear. The problem is the change in the axle C clip thickness. The newer rears had a thicker C clip and I think the inner diameter of the C clip is different. I know the late axle can go in an early rear by grinding the late C clips thinner but the early axle in a late rear may not work, the early thinner C clips will be a sloppy fit, but maybe the inside diameter of the latter C clip can be opened up with a die grinder. I don't know when the thicker C clip started but I know the '91 D150s had them.

Cecil
Author:  Slant Cecil [ Wed Oct 01, 2003 4:39 pm ]
Post subject: 
Another option is the 8 3/4 rear from a pre '75 D100. 3.55 chunks are not hard to find at the Mopar swap meets. My '82 D100 has an early 8 3/4 with 3.91 Sure Grip from a '72 D100 in it. Only the drive shaft needs to be shortened about 3/4".

Cecil
Author:  volaredon [ Thu Oct 02, 2003 5:14 pm ]
Post subject:  truck bolt patterns
Based on several trucks that my family has owned and having worked a dealer parts counter as a fill in when the regular guy was out, I can tell ya that your 81 4X4 should have a 5 on 5-1/2 pattern. My 81 and my brothers 80 Ramcharger both did. (Although in those years the Ramcharger depended on full time or part time 4WD) The 2 WD trucks were 5 on 4-1/2 til 84, 85 was the 1st of the 5 on 4-1/2, that includes vans, too. On a van, both a 1/2 and a 3/4 ton were 5 lug, you had to go to a 1 ton to go 8 lug. Yes an 8-3/4 will bolt right in, did that on one of my 79's I used to have. My 8-3/4 came out of a 69. The frames on a D or W series truck will interchange 72-93, but you need to swap your front x member to switch between a 2WD and a 4WD.
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