Fox New Shoes for Black Jack!

Bullitt347

I have been doing it wrong this whole time
15 Year Member
Mar 23, 2007
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If you can, swap wheels/tires front to back and see if the vibration changes.
If the pinion is not loose, leave the nut alone.
How much farther down do the real lower control arms mount to the differential from stock? I see a relocation kit installed which I assume was to change the I/C to get the car to hook better.
 
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FastDriver

My dad had a bra
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Sep 5, 2001
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Finished up the rear-end today. Test drive demonstrated that the vibration has not changed. I guess for the $60 this cost (bearings, seals, gear oil + the 2 days I had to spend messing with it, it feels a bit defeating to have not found the source of the vibration. I guess the best way to frame the effort in a positive light is that I crossed another possibility off of the list, did a little preventative maintenance, didn't pay someone else to fail to fix the vibration, and have a shiny black diff cover instead of a rusty one. I had just about had enough when I was done, so I didn't mess with the pinion flange nut or swap the tires back around. I'll have to come back to those items later.

The charcoal canister & purge solenoid have arrived, but I'm still waiting on the purge's wiring pigtail, vacuum lines and adapters before I can install that stuff.
Bullitt, here's a pic that both shows the shiny diff cover and the LCA mounting points a little closer. You can also see the stock location's bolt. There's a 3rd hole between where the LCA is currently mounted and the stock mounting point, which I could use to raise the mounting point of the LCA. If I determine that the pinion angle is the culprit, I will do it and see if it alleviates the vibration to some degree.

1660518965766.png
 

Bullitt347

I have been doing it wrong this whole time
15 Year Member
Mar 23, 2007
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Middle of Maine
Usually dropping the real lower control arm mounting point by 1 inch or so is sufficient to change the Instant Center enough to be advantageous for helping the car hook.
If more than 1 inch, then you should certainly check your pinion angle.
On average, with stock bushings in the rear upper and lower control arms, having 1.5-2.0* pinion down angle is needed due to bushing deflection under acceleration.
If you have Urethane bushings then only .75 to 1.0* pinion down angle is required as there is less deflection in the control arm bushings.
With Heim Joints or solid bushings, then near 0* down angle is required as no real deflection is taking place.
Ideally you want the driveshaft at 0* front and rear when under acceleration as this provides the least amount of friction in the drivetrain.
If you have more than 2* of pinion angle, then I suspect that this is the source of your vibration.

Typically, U-joints are designed to work with up to 1.5* of angle each. So 2 U-joints should handle 3* of angle total. This is why double cardan joints are used in some applications to accommodate more severe driveline angles..................................................^^^^
Should is the key word.
 
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FastDriver

My dad had a bra
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Usually dropping the real lower control arm mounting point by 1 inch or so is sufficient to change the Instant Center enough to be advantageous for helping the car hook.
If more than 1 inch, then you should certainly check your pinion angle.
On average, with stock bushings in the rear upper and lower control arms, having 1.5-2.0* pinion down angle is needed due to bushing deflection under acceleration.
If you have Urethane bushings then only .75 to 1.0* pinion down angle is required as there is less deflection in the control arm bushings.
With Heim Joints or solid bushings, then near 0* down angle is required as no real deflection is taking place.
Ideally you want the driveshaft at 0* front and rear when under acceleration as this provides the least amount of friction in the drivetrain.
If you have more than 2* of pinion angle, then I suspect that this is the source of your vibration.

Typically, U-joints are designed to work with up to 1.5* of angle each. So 2 U-joints should handle 3* of angle total. This is why double cardan joints are used in some applications to accommodate more severe driveline angles..................................................^^^^
Should is the key word.
I think I've got a strong candidate for the vibration, now.
 

limp

wrap a little cheese around it and its a done
Oct 4, 2020
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For your info, WD40 is not the best lubricant.. It stands for Water Displacement formula 40....
While WD40 has its place, much better spray lubricants out there......
 

7991LXnSHO

wanna catch the space herp
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Sep 1, 2010
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For your info, WD40 is not the best lubricant.. It stands for Water Displacement formula 40....
While WD40 has its place, much better spray lubricants out there......
On which of the six pages was WD-40 mentioned? :jester: Also, what are you spray lubing?:eek:
I hear WD-40 is great on arthritic hands.
I have been using liquid wrench on some very old farm implement’s 1/2” 13 fasteners. That penetrating spray stinks enough that the parts are outside. I can see someone using WD-40 instead because of the pleasant smell.
Now back to your regularly scheduled thread.
 

HotFox

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I chased a vibration +70MPH for years with my car. After transmission replacement, converting to 5 including axles and new wheels. Finally took the driveshaft to have it balanced. Front yoke was junk even though it slipped in and out of the trans fine, they rebalanced the driveshaft. It was like a new car after! So I bet it is your driveshaft.
 

FastDriver

My dad had a bra
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Sep 5, 2001
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Fort Knox, KY
I chased a vibration +70MPH for years with my car. After transmission replacement, converting to 5 including axles and new wheels. Finally took the driveshaft to have it balanced. Front yoke was junk even though it slipped in and out of the trans fine, they rebalanced the driveshaft. It was like a new car after! So I bet it is your driveshaft.
Nice! The Machine Shop told me that they do it without the Yoke and without the flange. I'll just get another yoke to eliminate another variable.
 

limp

wrap a little cheese around it and its a done
Oct 4, 2020
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Both doors are done, now, on both the inner and outer panels. The door lock actuator is in on the Driver's side. Strange how it still has trouble locking and unlocking, despite about a 5 gal. bucket worth of WD40 on the lock.

Doors shut with a satisfying thud that makes it seem like a much higher class car, lol. I'll spare the pics, for now. When I get the other door panel from TMI in on the passenger side, I'll snap a couple more. The alignment of the holes left a little to be desired, but the door panel and arm rest are higher quality and better feel than the factory original stuff.
Here you go.... End of first paragraph.....
 
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