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I upgraded my rear leaf springs to the Procomp 22415 rear springs and bought 2* WFO shims to correct driveline angle.
As I understood it after reading numerous threads, the fat part of the wedge should be towards the front of the vehicle, so the pinion angle is forced down, which is what I did.
The problem is I now have driveline vibrations around 40mph and 1500 rpm (whole vehicle shaking). However, it is smooth under and over that point (such as cruising at 60mph).
I measured the driveline angles and ended up with:
transfer case: 8 degrees down
driveshaft: 12 degrees down
rear pinion: 8 degrees down
This is only about a 4* operating angle. Is that enough to cause vehicle shaking vibrations?
I haven’t installed the front Procomp 22210 springs yet, but they will raise the front of the vehicle an expected 1.5”. That will only make the operating angle even worse correct? (Raising the front of the vehicle will cause the driveshaft angle to steepen)
Hopefully tagging @pirate4x4_camo will help clear everything up for me and anyone else reading this in the future.
would think it would need to be 'up angle' so as to be perfectly inline with the driveshaft?
Also, you MUST mark the U-Joints and Pinion side with paint or something, to ensure that when you bolt it back up, it is perfectly matched, just like it was before.
if you don't do that, you will get Vibrations 99% of the time
Draw this out on paper and you will quickly see that they are not parallel.
At 4” increased ride height the drive shaft working angle is not the primary concern as there is plenty of movement left in the system. The goal is to get the tcase and pinion shaft’s parallel. +\- 1/2*
in stock form with the rear of the ex 1” more ride height than the front your tcase output was tilted up 2*
I used the Spicer Driveline Angle website. They use the terms up & down for slope, and they define the slope being down if whatever you are measuring is higher in the front than it is in the rear (if it slopes down from the front of the vehicle to the rear).
In my case:
Tcase output: higher in front, lower in rear = down
Driveshaft: higher in front, lower in rear = down
Rear pinion: higher in front, lower in rear = down
The rear pinion is actually facing “up” towards the drive shaft, but Spicer says the slope should be considered down when calculating. Or maybe I’m misunderstanding Spicer’s website.
I’ve attached pictures showing what I measured. Maybe they will help.
I can also grab pictures underneath the truck in a few when it stops raining.
What style rear driveshaft do you have? Some Excursions (like my 2005 diesel) came with a double cardan rear driveshaft. Those take a different angle setup than the more traditional/ more common two joint rear driveshafts.
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Assuming you mean the front joint on your rear driveshaft is double cardan (and not meaning your front driveshaft) , then there's your issue. Just remove the shims and you'll probably be fine. I also have the Pirate Procomp lift ( thanks again to Pirate for coming up with that awesome parts list), and run no shim on the rear axle with my double cardan rear shaft.
FYI the highway speed limit where I live in Texas is 80 mph, traffic flow is usually a little over the speed limit, and I keep up with traffic flow on 35 inch mud tires just fine with no vibrations at any speed.
It would appear (and looks can be deceiving) that perhaps you need some 4* shims. Looks to me like the pinion and driveshaft are almost at zero to me.
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By my measurement they’re only 4* apart, which is hard to tell by eye. They definitely aren’t 100% in-line.
I took it for a long drive and cruised through the MPH range and RPMs I normally would. No vibrations.
Now that I’m thinking about the previous incident, the truck did shift into 4th right before a small hill, and it didn’t shift out to climb. It “lugged” at 14-1500rpm while it climbed. That very well could have caused the whole issue.
The only vibration I can detect now is right at takeoff (5-15mph) and it may be the torque of the wheels/axle twisting the pinion angle up. But it is really only noticeable if you are looking/feeling for it.
I’ll retake measurements once I get the front leaf springs swapped out.
By the way, the ride quality is massively improved compared to stock springs+larger block+worn out shocks.. and that’s with only the rear springs done.
Theres nothing wrong with the absolutely not set up. Its called a broken back arrangement or intersecting angle arrangement. As long as the u joints have the proper angles.
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