Drive Shaft Question

[Mil-Spec]

For those who have done 4 inch lifts and kept their factory drive shafts: I just did this on my 86 M1009 (with a 14 FF axle swap) and I'm questioning the usability of my factory drive shaft. I've measured before and after the lift and I now have around 2 to 2.5 inches of shaft engagement. To me this seems a little scary. I have no problem moving it around on the driveway while I work on other things but I'm leery as heck to go on the trail like this.

Your guy's thoughts? Go or No Go? Thanks

['63GENIII]

Id spend the couple of $$$ needed to get the correct engagement back (looks like 2+ inches) to eliminate the possibility of whatever could happen. Either the shaft popping out at speed or just putting all of the stress on the last 2" of the output shaft. The other thing that caught my eye is the angle. Looks pretty drastic. Id try talking to someone who knows driveshafts really well before rocking that thing on the street, let alone the freeway. Rode with a friend years ago in a '64 F250 that dropped the front of the shaft while doing 65 mph down Altamont. Took me a long time to ride with that guy again.

[JIMs70GMC]

No go. Get it lengthened. I paid about 160 to have my 83's rear lengthened 5".

[ryanroo]

i agree, that is more stick out that reasonable for ride height.

[Mil-Spec]

Roger that guys. That's what i was thinking. I'm thinking about finding a local offroad shop to figure out how much the DS needs lengthening. Last thing i need is the DS bottoming out on the TC. Its funny,after numerous google searches, most Blazer guys say you dont need to change anything with a 4 inch lift. It might have to do with my axle swap. The 14 FF may have a shorter pinion dimension over my 10 bolt. Doesnt sound right but it is what it is. Thanks guys for the good intel.

[obijuan]

I ran like that before I knew better. Did ok but it is incorrect. And go to a driveline shop. Avoid the other shops markup.

[Matt Man]

Should have at least 3/4" of the shaft exposed, offroad applications should be a little bit more, I have about 1.5" on my k10.

[JIMs70GMC]

Most drive shops will want the length from the tail housing to the axle yoke. You will be surprised at how far in the slip yoke will be. Unless you have some extreme wheel travel, you will only have about 3/4 to 1 inch showing as was said. When the spring compresses the axle actually moves slightly back away from the TC.

[Zoomad75]

I'm going through this right now on my 91. Back up a little bit to my 75 and the 4 inch lift/shackle flip combo and NO changes made to the front or rear shaft. But that truck had a 205 case with fixed yokes and the slip was on the shaft. Now my 91 with the 241 case I did have to add a little length to the front shaft. The rear shaft on the 91 has about the same engagement as the OP's pics. Since we had to take the tcase back out again for a different issue, we'll look closer once we put it back in.

Keep in mind most driveline shops charge less to shorten a shaft then lengthen. Makes sense, less work. Adding length means retubing the shaft. So it might be cheaper in the long run, to find a shaft from a K10 or K20 that is longer and get it cut down. I did this on the 75 when I twisted the rear shaft in two after bouncing it off of a rock. I got a 3/4 ton shaft from a similar year truck and had my driveline shop cut it down to fit. Difference in price was almost $200 less to cut the long one down. Keep in mind the 3/4 ton shaft will probably have a larger u-joint but you can get a conversion u-joint.

[Mil-Spec]

Zoomad75

You bring up a good point about the difference between a shop lengthening or shortening. Makes me wish I hadn't gotten rid on the 3/4 ton drive shaft from the Suburban donor, I got the axles from. But I know the current owner so he might sell it back to me.

I FINALLY (don't trust the internet, do you own measurements), after a couple different tries found the proper combination joint (PU-447) that had the correct dimension caps and retaining clip arrangement to go from a M1009 drive shaft to the Pinion of a 14 bolt full floater.

[JIMs70GMC]

Originally Posted by Mil-Spec

Zoomad75


I FINALLY (don't trust the internet, do you own measurements), after a couple different tries found the proper combination joint (PU-447) that had the correct dimension caps and retaining clip arrangement to go from a M1009 drive shaft to the Pinion of a 14 bolt full floater.

I had some thing similar, you probably had to go from a 1350 at the axle to a GM 3R on the driveshaft.