Pinion angle?

brotherGood

brotherGood

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Ever since performing the iso-delete in the rear, I've had a driveline vibration. I was warned about pinion angle being effected, but im not sure how to check it, or adjust it.

Im assuming the shim kits just fit in between the leaf spring and sway bar plate (b body setup)..is that correct?

Thanks in advance.
 
Yes, there are pinion ngle shims available. Ideally you want the angle of both the front and rear u-joints to be the same (only opposite at curb height. A common angle is 3 degrees down on the pinion yoke. On accel, the pinion wants to pivot upwards when the springs "wrap". If it's off, it can caue a driveline vibration.
 
I was on lunch hour (actually lunch 1/2 hour) at work and was short on time when I posted. These are what I was talking about. Of course you first need to calculate the degree of change you need and order the correct ones (2, 4, or 6 degree):

DJM Suspension Pinion Angle Shims ACC2PSK

djm-acc2psk_w_ml.jpg
 
Explain the vibration, constant, at a speed, cyclic in nature?

Go snap a few pics if you can, that far out should be obvious.

Did you have the driveshaft off, did you change anything else at the same time?

You might check and see if all you u joint caps are fully in on all of them and some like to clock the shaft also.
 
I can tell for sure it's driveline. The more I increase speed, the more it vibrates..but vibrates worse when off the throttle and slowing down. Almost like there's a sweet spot for the worst shaking.

At the time the rear end was changed (swapped AHB 8.25 for AHB 8.25) I also did the rear iso delete.

The u joint was replaced when the engine was changed years ago, but we accidentally knocked the caps off. They were replaced, but angle wasn't a thought. Ive been told 4° gets it close, but with worn springs it may not be enough.

Where I'm struggling is how to measure it. I know I need to get an angle finder, but what reference points am I using (pinion nut vs where the u joint cap collars bolt in..and do I reference against the transmission?
 
One key point as this may not be all that obvious. You are looking at the pinion to transmission tailshaft housing (output shaft centerline actually) alignment. Do not simply attach an angle finder to the yoke and read that off, this is NOT your measurement (unless of course your tailshaft housing is parallel to the ground).

Remember, the issue here is the total (cumulative) angle your driveline sees when accelerating the car, which is why the suggestion to have the pinion down as ralative to the tailshaft housing so that as the pinion climbs the crown gear, and the whole axle assembly attempts to twist, causes all the angles to cancel out.

There is a nice Tremec app that will walk you through taking the axle angle measurements...you literally put the phone/device up to the part, lock-in the reading, and keep on repeating until all measurements are captured. The answer provided back is the total driveline angle. Check it out...if you do not find it let me know and I'll look it up on my garage phone.

EDIT
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Aha...found it, I knew I had the PDF saved in my library. Take a look, this does a pretty nice job explaining what you are after.
 

Attachments

My point was, he didnt change trans, a pic of the rear yolk area would show if the PA is far enough off to cause an issue. 90% if they are a shaker it would be easy to see.

PA gets the bad wrap alot of the time, look at any jacked up 4x4s with no other mods, the dont rattle and shake, mine never did and I had yolk to shaft witness marks.

This truck was bought in the upper northwest and driven to texas with things backwards and this angle and the owner never felt a thing wrong, was told by friends to get it right.

On street rides pinion angle gets a bad wrap most the time.

Think about air shocks and the change to pinion angle, low riders with hydro running down the highway on 3 wheels.


The question id be posting is if anyone who did the iso delete had to correct pinion angle?

Although rule nothing out.

Screenshot_2020-06-24 76 F250 driveshaft angle - Ford Truck Enthusiasts Forums.png
 
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@M_Body_Coupe I checked that app out, it looks pretty straightforward. I'll hopefully be able to get out there this weekend and at least get measurements done.

I'll also try to get a picture of the yoke for reference. I know pinion shims were a hot topic when looking to switch to an 8.75, but one of the guys on FB who has done this a couple times was quick to point out that shims may be necessary. His current gran fury has a 4° shim in it, but he thinks it may need more due to the worn springs.
 
Are you sure it's not something wrong with the different axle like a worn pinion bearing? That's usually where vibrations and noise come from when you're on and off the gas.
Pinion angle usually doesn't cause much of a problem with iso clamp delete, not that I've ever heard anyway. It's usually when you're using axles from other vehicles that the spring perches might be a bit different to begin with or are doing suspension changes that drastically change the angle.

Here's an older post from BudW that has some info about it.

Just picked up an 8 1/4 out of a Jeep
 
Here is what the Tremec app read.

Im assuming a 4° shim will get it as close as I can..but is that right?

Screenshot_20200628-110037_TREMEC.jpg
 
brotherGood said:
Here is what the Tremec app read.

Im assuming a 4° shim will get it as close as I can..but is that right?

View attachment 40561
Click to expand...

I'll crawl under my coupe later today and get you the matching numbers. I did actually set this thing up with a 2 deg. pinion down config (I think), no vibration, no noises but all new parts so that helps too. Anyways, point being I am comfortable with my setup here.
 
M_Body_Coupe said:
I'll crawl under my coupe later today and get you the matching numbers. I did actually set this thing up with a 2 deg. pinion down config (I think), no vibration, no noises but all new parts so that helps too. Anyways, point being I am comfortable with my setup here.
Click to expand...

So if you're good at 2 degrees negative, I would be looking at a 6° shim? Would worn springs flex that much?

This'll be 98% street driven..im only running it due to power tour
 
If your springs are bent in an "S" (front portion curved upward) it will change the pinion angle and move the pinion up.
 
Aspen500 said:
If your springs are bent in an "S" (front portion curved upward) it will change the pinion angle and move the pinion up.
Click to expand...
I had a busted clamp for a while, and when the car would be in the air it would do that.

I have since fixed the clamp and haven't noticed that
 
Alright, just an update:

I went with a 6 degree shim, and installed it over the holiday weekend. I haven't had a chance to test it out yet, but between that and new rear tires I'm itching to get back on the road.
 
A problem I have seen before is when the rear u joint was replaced the person forgot to put the retaining clips on the caps and the u joint moved enough to knock it out of balance. I`m not saying this is your problem. It is something I just wanted to make others aware.
 
Sorry I fell off the wagon on this one, OK, here is what I actually tracked down for you:

DRIVELINE ANGLE --- MANUAL --- TREMEC APP
TRANSMISSION TAILSHAFT --- 2.5 down --- A1 = 2.5+
DRIVESHAFT --- 5 down ---A2 = 5.4-
PINION YOKE --- 0.00
OVERALL ANGLE --- 2.50 ---OA = 2.9-

I previously had a 4 deg +ve pinion yoke angle, which means that my pinion was already pointing UP at rest. I installed 4 deg. down shims (having spent time time actually massaging these to fit my factory ISO setups - but hey, what's a little elbow grease eh?).

Anyways, what I have now is extremely solid!

EDIT: Yikes, that formatting did NOT work at all...LOL, I prefixed with '---' to ease the separation between the columns.
 
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Hopefully the shims will improve things but even if it does it's probably only relieving some stress on something worn in the different axle. Like I said before just removing the iso stuff doesn't have enough of an effect on pinion angle to cause problems. Changing the rake of the car with heavier springs or rear tires or even just by having a lot of weight in the trunk or back seat has more of an effect on pinion angle then that and doesn't cause problems.
Noises from bad pinion angle typically don't change when you take your foot of the gas, noises from a worn out pinion bearing do.
 
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The Tremec app is pretty cool. How big a shim can you put in? I may need an 8 degree with the combination of my leaf springs and the 8 3/4 rear diff
 
Evidently I never updated this. I ended up swapping the 6° out with a 4° shim one day in 2021 after Dad said the problem was still there, if not worse.

He said the 4° helped it a ton, but it still wasn't 100%. I got to thinking though, and I'm not sure the trans mount has ever been replaced. That may be the source of the shake.. but we'll see. The car is going in for trans work and Pops is going to ask the guy to verify all of that.
 
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