Rear Driveshaft Angle

[pcf_mark]

Well I finally got back to looking at this and took very precise digital angle measurements. My drive shaft is 13.8/14.0 degrees and my pinion yoke is 14.5 degrees. I took both measurements on level ground, half a tank of gas. Measured with the level on the top of the driveshaft and took the driveshaft off to measure the yoke across the flats with the yoke vertical.

I have a vibration at 60 mph and above which is more obvious when I get off the gas. Not a crazy vibration - a steady low frequency buzz throughout the truck from steering wheel to hood to rear gate.

I was hoping it was the angle I can fix that.

My front driveshaft was professionally shortened and balanced when I added my 4R70W. The rear one is a little rough. Driveway shortening job and someone welded the cap of the u-joint to the yoke. Maybe I need to get that fixed!

 

[Crush]

^^^^thats prolly your problem right there. take a measurement and order a woods shaft. they have directions on their site to tell u how to measure

 

[Justafordguy]

I agree, I bet that rear shaft is your problem. Give Tom Woods a call, great guy and great products.

 

[DirtDonk]

Did you take that measurement of the yoke as it was, or did you extrapolate that into pinion shaft equivalent angle?
Reason I ask is that if it's extrapolated then you are only 1/2 a degree off, which would generally lead to a vibration under heavy acceleration, but not under decel. Especially if that angle is above the centerline of the driveshaft.

If that is the face measurement exactly though, that's WAYYYY off!
If the pinion is pointed upward even slightly, relative to the driveshaft then it's too high.
If the pinion is pointed to within .5° of the driveshaft it's still too high. Not horrible, but enough to cause vibration under some circumstances.
If it's more than 2 degrees down from the driveshaft centerline it will vibrate under deceleration. If it's more than a couple of degrees above the driveshaft centerline it will vibrate under acceleration.

But with all that, a driveway shaft fix has lots of potential pitfalls. And a welded cap even by itself can cause trouble from overheating the grease and bearings and shortening the joint's life. Assuming it was even new from the start. If it was already an old joint, it just pointed it towards it's grave and gave it a nice push.

Got a pic of this rear pinion area anyway, as taken from the side? Just wanting to put your measurement results to visual cues.

Thanks

Paul

 

[pcf_mark]

DirtDonk let me try to answer your question as precisely as possible so the terminology does not cause me to misunderstand.

With the driveshaft installed, truck loaded as normal I put my digital level (phone app) on top of the driveshaft vertically. Then I removed the driveshaft and put the digital level across the flange where the u-bolts pass through. The yoke was almost perfectly vertical. This method (I think) keep the level in the same plane so both numbers are relative to each other. I did not rotate the level in either plane to create a positive or negative reference change. I'll try to post some pictures tonight that may shed some light on the issue.

(note I did NOT weld the yoke but I did shorten the shaft!)

 

[pcf_mark]

Dirt Donk - I was only able to get one decent picture. I have a funny exhaust that gets in the way (long story but it is stainless and reasonable quiet and cost $40 front to rear).

https://www.flickr.com/photos/145236250@N08/48579412442/in/dateposted-public/

Maybe this will help.

 

[DirtDonk]

Thanks for grabbing the pic. But wow, looks like the exhaust is out of a Porsche! How's the sound quality? Is it full dual? Great price no matter what.

Hard to tell from this angle, but the pinion angle looks pretty decent, at just below the centerline of the driveshaft. Correct? From here it could also be even, which is not normally good on a Bronco as the others have explained.
Since you're there at the truck and not us, as you imagine the centerline of the pinion shaft, is it above, or below the centerline of the driveshaft?
That half-a-degree is not enough on it's own to cause your vibrations the way you describe, but combined with an old tired shaft that might also be out of balance, you may have your answer. The original comment of almost five degrees on the other hand is way more than enough (in either direction) to cause trouble.

How long has it been since you replace u-joints or greased the centering yoke at least?
I think you said this shaft is the original rear shaft and has been modified?
If it's not the angle, then you have to look at the other most obvious possibilities.
It's not like the shaft is the only possible explanation (old tires, bad ring gear, loose t-case pinion or worn bearing, etc.) but it's the most common and not the most trouble to fix and/or replace.

Paul

 

[pcf_mark]

(The exhaust is from a CTS-V wagon I sold but I had the OEM exhaust - without cats it sounds a lot like a hot rod - loud but not very rumbly like a muscle car)

The pinion is actually angle higher (14.5 degrees) than the driveshaft angle (14.0 degrees) by .5 degrees. I could raise or lower the driveline to get the angle the same with some work.

The driveshaft is a little rough cosmetically. It does slide ok but the yoke is hammered on the diff end and I have no idea how old the u-joints are. But when I took the driveshaft out the u-joints where easy to move.

New tires, wheel bearings, all new front end bushings, front driveshaft was professionally shortened and balanced, front end alignment, tie rods, rebuilt steering box.

 

[svastano]

Have you checked the pinion bearing? Lots of oil leaking from there leads me to believe that it could be loose.

 

[pcf_mark]

Have you checked the pinion bearing? Lots of oil leaking from there leads me to believe that it could be loose.

When I had the driveshaft off I pulled and pushed on the yoke of the diff to see if there was any play it was solid. It looks worse than it is (the leak).

 

[DirtDonk]

The pinion is actually angle higher (14.5 degrees) than the driveshaft angle (14.0 degrees) by .5 degrees. I could raise or lower the driveline to get the angle the same with some work.

You should modify the angle before you do anything else then. The optimal Bronco angle is with the rear pinion shaft centerline BELOW the driveshaft centerline.

As previously mentioned, the angle of the shaft to the upper joints does not matter as long as it's within it's range of travel. The rear angle needs to be BELOW the driveshaft so that when the pinion climbs during normal use it won't vibrate from being too high.

This alone would cause at least some of your vibrations. During cruise and acceleration your pinion climbs quite a lot. If the pinion is already higher than optimal, even during light cruise it will be too high. Remember you're pushing wind (so to speak!) at speed so you're actually under power just like you would be if you were accelerating.

But the erratic, inconsistent and multiple layer results of your vibration makes me feel that it's the angle AND probably some old age and lack of grease that's making it vibrate.
Any time you have an inconsistent vibration that defies buttonholing, the chance that it's your CV joint goes way up.

Paul