Pinion angle and how much does a stock suspension move?

[My427stang]

I have a hell of a vibration accelerating or decelerating with my F100, worst when I accelerate at freeway speeds or decelerate using the engine

Now, everything is new and tight.  However, the combination of some of the old parts has me thinking it's a pinion angle issue.

- Crank centerline is 4 degrees down (output shaft coming out of the transfer case)
- Pinion is about 5 degrees up (almost parallel to the output, but slightly steeper)
- Driveshaft angle, is 12 degrees, one piece driveshaft relatively new yoke and spline, u-joints

Now, the springs are rebushed, truck sits fine, springs aren't junk, but I wouldn't say they are a strong point of the truck.  It's an old lift kit but they do not have any spring straps or clamps holding them together front or back and my hunch is that they wrap up like a SOB when hammered hard.  They are 2.25 inch springs, 24 inches in front of the center bolt, 28 behind and a stock lift block, 3 inches maybe under it?

Understanding that my pinion angle should be 2-3 degrees less steep than my output to allow it to move to parallel, and it is the opposite way, do you think at highway acceleration that either: the 1 degree from the static measurement would cause the vibration (it's pretty severe)  or with no spring claps or straps the springs could be wrapping up enough to make it worse?

As I am typing this, I think I have my own answer, I think it pinion is likely wrapping up during even light acceleration, question is, would it do the same during decel?

[My427stang]

Wow, I looked around Youtube, check this out, especially a few moments in when he accelerates!

https://www.youtube.com/watch?v=FeC85uputSU

[Drew Pojedinec]

If the pinion was down too much it'd smooth out on acceleration.
If the pinion was up too much it'd smooth out on decel.

Personally I don't think it's either.  It takes a pretty decent misalignment to feel bad.
Are you sure the engine/trans is lined up side to side sufficiently?
Are the axles new?  If slightly bent they can provide a gentle wobble at speed or under mild throttle and feel worse on hard accel/decel

If you still think it's the pinion angle, shim up or down the transfer case (it's easier to do than the pinion, might not be perfect solution long term but it's a good fact finder).

[My427stang]

Everything is square, although admittedly I didn't spin the driveshaft yet, it was  retubed and balanced in 1991, you'd think it'd be perfect

I'll drop that off at the local driveshaft shop first, it's got new u-joints and I don't see any reason it'd be bent, but who knows.  Easy to rule that out

[turbohunter]

I'm with Drew, I think they're is plenty of room in that set up.
How are the transfer case mounts. Is it a 205 with a side mount or ....?

[Drew Pojedinec]

If you ever had a smushed u joint or a bent driveshaft it's REALLY bad, and only gets worse with speed (like throw you outta the seat, bad).

It's four wheel drive, right?  Pull the rear driveshaft and go for a ride as front wheel drive.  see how that feels.

[My427stang]

Drew, that's a great idea, although not sure I want to do 70+ on the highway on the front axle, but it might show something

Marc, all new mounts everywhere, and they are all nice, plus I just rebuilt the Dana 21 (single speed no mounts)

[Drew Pojedinec]

Yeah, I might have to ask you questions about high end performance engines.....  but if you need rednecky free help on a truck (crappier the better), I am probably your man

I'm the guy that had someone tow my truck at 60mph so I could ascertain a vibration minus the drivetrain.

[turbohunter]

If everything is up to snuff (and I'm sure it is with you) that would take me to the springs.
Might try the traction bar/shock mod.

[My427stang]

Thanks guys!

Driveshaft is out, hard to tell how it felt, I got up to 50 but it made it's own uncomfortable feeling past that on the front driveshaft only, either that or it was my "hold my beer" warning LOL

I'll have the local driveshaft shop check how straight and balanced it is and go from there.  I do think I need to do something with traction control regardless.  Since I put the 850 DP on it, it hits real hard.

[NIsaacs]

You said the drive shaft is a 1 piece. So does it have a slip yoke that slides into the transfer case or is it a bolt on with a splined yoke that slips on the splines of the drive shaft? The first type you can't get off but the second type you can get 90* off or maybe just off by 1 or 2 splines. If it is the second type, the yoke ears of the drive shaft and the slip yoke half ears need to line up together, not one yoke ear and one u-joint bearing. Not sure if I explained that good enough, lol

Nick

[My427stang]

You said the drive shaft is a 1 piece. So does it have a slip yoke that slides into the transfer case or is it a bolt on with a splined yoke that slips on the splines of the drive shaft? The first type you can't get off but the second type you can get 90* off or maybe just off by 1 or 2 splines. If it is the second type, the yoke ears of the drive shaft and the slip yoke half ears need to line up together, not one yoke ear and one u-joint bearing. Not sure if I explained that good enough, lol

Nick

Appreciate it Nick, I follow you completely, the driveshaft is splined, all compression an extension is on the shaft itself, the yoke on the back of the transfer is fixed.  I checked u-joint alignment early on, and even rotated the yoke 180 to see if the joints would line up better on the floor.  The two ends are perfectly parallel and when turned 180 out aren't quite as good.

My gameplan is to have to have the driveshaft checked, it's been hammered on for years.  Although it's a nice aftermarket steel shaft, there is no reason not to spin it and see how it looks.  My hunch is that I need to control wrap-up and get the two planes parallel.  Right now they are 1 degree off static, and power would make it worse.  Of course that doesn't explain the decel vibration, so the shaft is a good start, even if I don't expect it to be bad, wouldn't be the first pretty piece that I had that turned out to need work

[jayb]

Ross, if the front end of the driveshaft is a slip yoke, one other thing to look at is how it fits into the trans or transfer case.  After installation grab that end of the shaft by the U-joint and see if you can move it around any.  If that bearing in the back is shot and the slip yoke isn't tight on the splines, that movement can give you a vibration. 

For what it's worth, I always set my pinions about two and a half degrees lower than the trans output shaft.  The Cal-Trac guys say that 2-3 degrees up movement of the pinion is not unusual...

[turbohunter]

Ok sitting at home (not at work) with time to think.
Although there is plenty of room to be off a bit and and your set up should fall in the zone of fine, Jay is correct that the pinion angle should be lower in order to climb up on accel. As I re read you initial post you say it is one agree over the parallel/centerline. If your springs are worn as they would be after years of load then being over the parallel already and having weaker old springs then that may be contributing to your vibration. So my casual "you should be fine" may need a re think. Especially with your power.
Also I can't remember off hand but do you have blocks under your springs? If so that would also contribute lots of leverage to the problem.

[My427stang]

Ross, if the front end of the driveshaft is a slip yoke, one other thing to look at is how it fits into the trans or transfer case.  After installation grab that end of the shaft by the U-joint and see if you can move it around any.  If that bearing in the back is shot and the slip yoke isn't tight on the splines, that movement can give you a vibration. 

For what it's worth, I always set my pinions about two and a half degrees lower than the trans output shaft.  The Cal-Trac guys say that 2-3 degrees up movement of the pinion is not unusual...

The transfer, tranny, and rear are all freshly rebuilt and tight, the whole truck is, except the shaft itself and it has new u-joints.  I keep going back to the springs, the rear main leaf on both sides is the original from 1971 and it has a stack of springs underneath it from the junk pile from years ago. The truck sits nice, but like I said, with no spring clamps and a lot of power, my hunch is they are moving all over like that video.

I need to just have the shaft checked to be sure, but my hunch is that the rear is moving all over the place under power and braking and with my already overcenter pinion angle, I am making it worse

Ok sitting at home (not at work) with time to think.
Although there is plenty of room to be off a bit and and your set up should fall in the zone of fine, Jay is correct that the pinion angle should be lower in order to climb up on accel. As I re read you initial post you say it is one degree over the parallel/centerline. If your springs are worn as they would be after years of load then being over the parallel already and having weaker old springs then that may be contributing to your vibration. So my casual "you should be fine" may need a re think. Especially with your power.
Also I can't remember off hand but do you have blocks under your springs? If so that would also contribute lots of leverage to the problem.

Yes I have 3 inch factory blocks.  I can't see the springs, but my hunch is they are wrapping up pretty well when I launch, I imagine less so, but still significant when I accelerate