2.5" lift Driveshaft Length?

[Yooper74]

Installed a duff 2.5" lift with new rear springs. My driveshaft appears not to be long enough any more. Does not reach.

Odd as the old lift I took out was original springs with a 2" block so pretty darn close to what I have now.

I'm going to send a message to duff also but should I need a new driveshaft for a 2.5" lift?

 

[garberz]

Check your pinion angle, make sure it’s correct with the new springs. The new springs may have corrected your pinion angle, making the drive shaft a bit short now.

Mark

 

[RonJones]

I have a WH 2.5” lift with one of their “extreme” 9” rear ends, my front DS length is 24-3/8” and the rear 33-1/8”. I still have to put coolant in, gas, doors and 200# in the drivers position, so it’ll probably get a little shorter particularly in front. I measured, as I’m thinking of ordering DS’s now, before prices go up next year. What’s your numbers?

 

[SteveL]

Usually 3 1/2" lift is right on the bubble. My 66 was ok with a 3.5 but my 72 had to be upgraded.

 

[Yooper74]

I'm not sure how long mine are. I'll get a measurement in the morning and post it up.

 

[blubuckaroo]

My '77 wit a 2.5" lift worked just fine, for years, with the factory drivelines.
I fact, mine may be factory length now. I just told Toms that I had a 2.5" lift when I ordered a replacement.

 

[DirtDonk]

That's correct. There's no reason that a properly installed and checked 2.5" lift would require a longer driveshaft.
Is yours still up in the air with the suspension extended? Or is it down on the ground with the full weight of the truck compressing the suspension?

As mentioned, check the pinion angle first. As the pinion pivots downward it has a large effect on effective driveshaft angle. Most lifts with the modern 9, 10 and 11-leaf packs will have at least some effect on the angle. Not sure why it seems to be that way, as it was discussed and determined that inch for inch, it should not matter how the lift is achieved. The change at the pinion should remain the same except with angle lift blocks.
But it's a thing, and most of us need 6 degree shims with 2.5 and especially with 3.5 inch lifts.

Like blue, I'm still running original size shafts (actually 1/4" shorter than original) even with 3.5" of lift.
So if yours is not already Yooper, get it back on the ground and measure your rear pinion angle as it relates to the driveshaft. It should be 1 to 2 degrees "down" from the centerline of the driveshaft.

Paul

 

[sprdv1]

I'm not sure how long mine are. I'll get a measurement in the morning and post it up.

Always best to ask if you don't know....

 

[rguest3]

Each one of these Broncos are different. Measure from Center of U-Joint on the Rear Axle to Center of U-joint to the Transfer Case.

 

[fordguy]

That's correct. There's no reason that a properly installed and checked 2.5" lift would require a longer driveshaft.
Is yours still up in the air with the suspension extended? Or is it down on the ground with the full weight of the truck compressing the suspension?

As mentioned, check the pinion angle first. As the pinion pivots downward it has a large effect on effective driveshaft angle. Most lifts with the modern 9, 10 and 11-leaf packs will have at least some effect on the angle. Not sure why it seems to be that way, as it was discussed and determined that inch for inch, it should not matter how the lift is achieved. The change at the pinion should remain the same except with angle lift blocks.
But it's a thing, and most of us need 6 degree shims with 2.5 and especially with 3.5 inch lifts.

Like blue, I'm still running original size shafts (actually 1/4" shorter than original) even with 3.5" of lift.
So if yours is not already Yooper, get it back on the ground and measure your rear pinion angle as it relates to the driveshaft. It should be 1 to 2 degrees "down" from the centerline of the driveshaft.

Paul

Unless you have a 4r70w, which would require shorter on the rear and longer on the front.

 

[Yooper74]

My driveshaft is 32 1/4"

Its coming up a fraction short. Here's a pic

 

[AZ73]

Your pinion angle isn't correct. You need angle shims on your spring mounts. That will tilt the pinion up. It must be in alignment with your driveshaft.

 

[garberz]

My driveshaft is 32 1/4"

Its coming up a fraction short. Here's a pic

View attachment 514872

View attachment 514873

I’d say it’s a lot more than a fraction short. Looks like you’re all the way at the end of the splines, and it’s still coming up short. Drive shaft length is measured when the slip yoke is at mid travel. The pinion angle should be 1-3* less than the drive shaft angle. Once you get that set, then measure the distance between the the two yokes. Center to center of both yoke faces, with both yokes positioned horizontally. From your pic, looks like your drive shaft is about 2”, too short. Here’s a tech article on how to properly measure the rear pinion angle.

https://classicbroncos.com/tech/measure-pinion-angle


Mark

 

[Yooper74]

looks like my pinion angle is way off. Little surprised the duff kit didnt come with something to correct this.

pinion is at 11 degrees, driveshaft is at 24. going to send this off to duff and see what they have for shims to fix

 

[AZ73]

looks like my pinion angle is way off. Little surprised the duff kit didnt come with something to correct this.

pinion is at 11 degrees, driveshaft is at 24. going to send this off to duff and see what they have for shims to fix

View attachment 514895

View attachment 514896

Not sure what your kit came with but you'll need:


https://dufftuff.com/product/solid-steel-leaf-spring-shims/ - if your kit didn't come with these, you'll have to ask them what angle they recommend.

and

https://dufftuff.com/product/c-bushings-ford-bronco/


You might want to consider angled radius arm bushings too but they're not necessary.

I think I would double check that you got the correct springs. I've seen cases where the 3.5" were sent by another vendor by mistake. Also that the springs are set correctly on the axle mount. They can slide when you tighten the U bolts if not in the alignment hole

 

[DirtDonk]

To that end, checking the installed height is easy. Just measure between the top of the axle tubes and the bottom of the frame rails.
With a 2.5" lift your rear measurement would be near 8.5" give or take a half-inch.

Paul

 

[Yooper74]

So maybe that is the issue. I went and did the axle to frame measurement and its about 11" not 8.5".

It seems to sit right though. If it is wrong I like how the stance worked out

 

[DirtDonk]

Great stance for sure. For 5 inches of lift that is...;D
But you're never going to get the driveline dialed in while it's in this partially assembled condition. You can't size driveshafts or steering linkage until your vehicle is at full weight, fully assembled and settled down on to it's suspension.
So forget your driveshaft for now. Definitely get the shims it looks like, but even with that you can't be sure until you compress the springs to that 8.5" height.

Some ratchet straps, or some temporary 500lb weight in the back will help. Ratchet straps are cleaner than bags of cement though!
As I think was mentioned, loosen any rear spring bolts that you torqued all the way, compress the suspension, then re-torque.

Or just weight until you're almost done with the project.

Paul

 

[Yooper74]

Talked to the Duff tech reps. They think its because it is not weighted down with hood, bumpers, seats, etc

So I'm going to throw some weight at it. I'm planning on a soft top. Simple bumpers nothing heavy duty,

Anyone have an estimates as to what this all will weigh? I do not have all of the parts yet. Was going to use some deer corn bags to simulate the weight so that I can figure out what if anything I will have to do for the driveshaft and shims

 

[DirtDonk]

Not much left for the rear. Full tank of gas would be good to factor in. Twenty pounds for a rear seat maybe. Another twenty for a soft top. What type of bumper and spare tire setup will you be running? Those are often the heaviest items back there and also hang way off behind the axle.

Is there an engine installed? If yes, then why are your front springs so high? If not, then that would explain some of it. But 3" or so? Not sure, but very possible with softer springs like the Duff ones likely are.
If no engine and no transmission or transfer case, remember that's several hundred more pounds sitting in the middle.

If you really only bought a 2.5" suspension and if you still want it that way, then you need to weigh it down enough to get that measurement I mentioned down to about 9 inches, or less.
Or change your overall plans to accommodate for the new height.

Paul