Rear driveline angle (1 Viewer)

[mjeckell]

So I just had the gears upgraded to 5.29 and now that I am spinning at a higher rpm at freeway speeds at 65 I am beginning to hear and feel a driveline vibration. Anything slower nothing to report. J springs front and rear with 2” metal tech spacer in front with double cardan. Rear has 30mm spacer to level things out.

I took driveline measurements angles resting my device on flat part of flange. Pics below.

At transmission 0 degrees and at diff -3 degrees. Do you think I need adjustable upper rear control arms to make these numbers match? What have any of you done in this case. Is 3 degrees enough to make a vibration or roughness? And am I only hearing it at 65 because stuff is just spinning that much faster to finally detect it?

Last. At 65 mph letting off the pedal and coasting makes another odd sound that I don’t remember hearing before. Let’s hear your thoughts.

Thanks

Matt

 

[-Spike-]

I wouldn't trust a cellphone to be accurate. Even if I would, the graphic that cell phone is displaying contradicts the readout. I'd have to do a bunch of testing against a known accurate measure before trusting a cellphone, or any other instrument- I don't trust any unproven tool, but with things like levels there are simple ways to test accuracy, and then in turn a proven level could be used to confirm another tool, like an angle finder or cell phone.

Beyond that, a typical driveshaft config should have the same angle at those points, which would equate to equal u-joint angles, which is what you need for the vibrations inherent in u-joints to be cancelled out between the two.

That's how it's supposed to work. I don't know how critical it is in practice, or if there is an acceptable range, or how it plays out on stock or lifted 80's.

Groaning or other noises when letting off the gas often are indicators of a bad u-joint.

 

[LandCruisinMy93]

So, driveline angle isn't a quick thing to explain in a manner most understand. Mostly because it has to do with phasing as well as joint type and configuration. Also, theorecticall and real world numbers aren't always the same as @Spike mentioned. The long and the short of it is, under load the transfer flange remains around 0* but the differential companion flange changes with acceleration and deceleration. When you accelerate the companion flange angles upward bringing you closer to 0* while the driveline operating angle is reduced also. With that being said, as you accelerate you should be getting closer to equal angles and vibes should theoretically reduce. Usually grinding and vibration are felt on decel when angles are out too far. You may have an issue with the pinion preload setup or an out of balance driveline. From what I have personally experienced my joints were out about 5* and it didn't have vibration issues. Just growl on decel which tuned out to be the two yokes at the diff companion were meshing and grinding because of the angle. The long and short of it is that for longest life and best theoretical angles. Your flanges should be equal or within about 1*, -1* would be optimal for the rear. So, rear upper links may be a good idea, but if your rig wasn't having this issue before gears, start at the gears.

 

[chap79]

There’s two ways to get the angle corrected. You can install shorter adjustable upper links or you can lengthen the lower arms. If you are wanting to run 37” tires I would recommend lengthening the lower arms to move the tire further away from the front opening of the wheel well. Or start cutting sheet metal.

 

[LandCruisinMy93]

There’s two ways to get the angle corrected. You can install shorter adjustable upper links or you can lengthen the lower arms. If you are wanting to run 37” tires I would recommend lengthening the lower arms to move the tire further away from the front opening of the wheel well. Or start cutting sheet metal.

Lengthening the lowers helps recent the axle in the opening, but since the tires swing in a rearward arc you're forcing the tire further back...into the sheer metal. Shorter upper arms would rotate the pinion companion flange downward also when his needs to rotate upward. Also if the uppers were shorter, as the wheel travel in its rearward arc the companion flange would dive more, making it weaker in off road situations where the rear is being compressed. I lengthened my lowers to recenter the axle after my lift and lengthened the uppers to correct pinion angle and the result is proper driveline angles and asthetics; but I also had to trim the rear fenders when I stuffed my tire and tore the rear quarter open. Had I left the stock length lowers and lengthened the uppers I would have corrected the pinion angle but not had an issue with the quarter panels. No doubt they would have had a good rolling but it wouldn't have tore it open like it did. Would have looked funny though lol.

 

[landtank]

People run my extended LCAs with 37s with out rubbing issues. It would depend on how much they are extended

 

[JeepinPete]

Don't forget your front driveshaft is also spinning under power, unless you have a part time kit in the transfer case. Might want to check those angles too, I would suspect they are going to be "worse" than what you have shown. Are all of your u-joints in good condition?

 

[mjeckell]

So I looked at my rear u joints and the u joint at the diff does have a little play. At the transfer case there is no movement. @LandCruisinMy93 im not sure if I was having the issue prior to the gears. It seems to only happen around 65 and up. That would have been at 75 plus at 4.10 gears and I didn’t drive that often that fast.

 

[mjeckell]

also the rear u joint at the diff was a autozone replacement that has been in there approximately 15k miles.

 

[-Spike-]

It takes very little play for a u-joint to be bad, if you can actually feel it with the driveshaft in the truck, it's likely toast. Wouldn't surprise me a bit that a low mileage Autozone part failed.

 

[landtank]

Check play at the slip your as well. I've seen quite a few bad shafts in that area