Driveline Grrrrrrr (round 3)

[landtank]

The flanges on the front diff in relation to the flange face on the rear diff ressemble a \/.

You need to work it out for each shaft independantly, not together. So maybe a better way to describe this would be like this,


Ideal DC shaft to diff flange: |--- for the front so that the drive shaft and that of the pinion gear are parallel.

The three diff angle possibilities are:

angled up \------

parallel |------

angled down /-----


After a lift and before CC Correction you are in an angled up position. As you rotate the axle for CC correction you begin to approach a parallel position and where the DC shaft works best.

From what I've read you want 0* +1* for the shaft to work best. If you are still in an angled up position and light on the caster then I'd look into adding more caster as it will not only make the truck drive better but place the diff in a better position for that DC shaft to work without vibrations.

 

[Cruiserhead05]

Guys,
Quick question.

I got my DC front driveshaft a few days ago and have been driving on it since. I've done a mix of highway/city driving and yet to hear or feel even the slightest grrr....
So far im very happy that it seems to have fixed the problem but im not going to make a final judgment until everything settles in.
My question is, i have some stink bug with the 80 and have had the mr gasket spacers sitting in my garage for months but never put them in b/c of the nonstop grr issues. Now that my problem seems cured, do you think its safe to through the spacers in, or should i wait a little longer and see what happens.
I figure a DC front driveshaft is typically whats used in the 6 inch lift so me adding 1 inch to my ome heavy lift should not cause of problem, nevertheless, still wanted some opinions.

 

[landtank]

it comes down to the drive angle at the diff. By raising the front of th etruck you will further rotate the axle and increase this angle. Those 6 inch lifts have mdified arms that induces enough caster to aline the diff so it meets the specs of the DC shaft. By only raising the truck and not adjusting for that increase in angle you might find yourself back in the Grrrrs.

WHat I was hoping CJ would do is a caster check and then get a reading on his drive angle at the diff. With these 2 numbers you can determine what the best course is to hopefully meet both criteria for alignment and drive angle which would be optimum for driveability and smoothness.

So toss them on and see what happens.It would be good to check the drive angle before and after to see how much change there was and how the truck handled it.

I think you can get one of those protractor things from Sears for like $10.00. When you place it on a surface a pendulum type pointer hangs vertically and there are 2 slde markers you can use to mark it's position. I think there is a side rib cast in the diff that you can read the pinion angle and then take a reading on top the drive shaft and compare the 2 to get the angle in question.

 

[concretejungle]

Sorry Rick, i was going to get an alignment reading but i've been so stinking covered up lately. I will soon.

By the way, i think i have been cured also. Today i removed my rear drive shaft. First thing i noticed was the fact that it wasn't exactly in phase. So, i put new ujoints in, fresh amsoil grease on the ujoints and put it back together exactly in phase. Been driving all day and put about 75 miles on it with mixed highway and country roads. So far no grrrr at all.

I think the combination of needing a DC shaft up front and the rear shaft being slightly out of phase accompanied by worn ujoints were the culprits. My fingers are crossed that this escapade is over.

Brandon, throw those spacers in and don't look back. You should be fine.

 

[Cruiserhead05]

Well boys,

I think i may have spoke too soon, just got back from a 10 mile trip across town. On my way back i was doing maybe 65 mph on the highway and it started the wonderful Grrr again, and even some vibes in the floor board. Not as bad as before but it appears to be building.....im gonna pull my hair out.
For now im definately holding off on the spacers and and going to check my rear shaft phase like alex has done.
My rear u-joints have been replaced but i didnt do it, had a shop do it, so im kinda hoping maybe they didnt put the shaft back in phase...

 

[Cruiserhead05]

Alex, just curious. How badly out of phase was your rear shaft.

 

[Romer]

Alex, as one who suffered through the long Grrrr troubleshooting, I am glad you have solved your problem.

Brandon. If you can't figure it out. Take it to someone who has the diagnostic ears so they can at least tell you exactly where the sound is coming from.

 

[landtank]

Look guys, your trucks should not be so sensitive to this kind of thing. Take the time to evaluate your front end. It's pretty simple, caster needs to be 2-4* and for a DC shaft the angle needs to be 0 +1* It's not rocket science here. Take your readings and see where your at. Once you have the readings the answer should be obvious.

 

[concretejungle]

Alex, just curious. How badly out of phase was your rear shaft.

It was basically right between being in phase and being 90degrees out of phase. Hope that helps.

 

[Cruiserhead05]

Tank,

Got it done today.
Here is what they gave me.
Looks to be a little under spec.
All i can think is that the CC bushing may have been put in incorrectly?

 

[landtank]

If your CH/F (Center Hub/Fender) measurement was in the 22.5" area then they would be near identical to mine figuring 2.5* for the bushings. You could add an additional 3* of caster and still be close enough to factory specs on caster. Now if you can figure out your drive angle at the front diff you might get a good idea how adding that caster will help in the VIB department by also possibly meeting your DC shaft numbers.

I can take some pics tomorrow of how I'm thinking that measurement would be easy.

 

[concretejungle]

Tank, i have the dial that you are talking about. I was also told it's not how to read castor. So, if you post a pic i'll go and measure mine and post a pic for fun and see what the reading is.

 

[Cruiserhead05]

Guys, thanks for keeping up with this thread. i will try and get a CH/F measurement asap and keep watching this thread.

But tank, can you verify something for me. Based on the measurments i got today, my caster is to low correct? sorry, i am admittedly am a noob with this, but am trying to learn

 

[concretejungle]

Yes, your castor is a bit low. What springs do you have again? And you have the CC bushings in to right?

 

[Cruiserhead05]

Alex,
I have heavy spring on all four corners.
I do have the caster correction bushing but as i said earlier, there might be a chances the shop installed them incorrectly.

But in a previous post tank stated that for a DC shaft caster need to be 0 +1*.
Mine final caster measured right at 0.0, its kinda hard to read but it says it in green on the sheet. do you think its possible that adding the 1 inch spacer would help the issue?

 

[landtank]

Tank, i have the dial that you are talking about. I was also told it's not how to read castor. So, if you post a pic i'll go and measure mine and post a pic for fun and see what the reading is.

I'm not suggesting you use it to read caster. I'm thinking we can use it to read the angle of the front driveshaft to the front differential flange (drive angle). It's this relationship that can cause the Grrr on a truck.


When setting up the truck's front axle you would ideally want that drive angle to be zero for a DC shaft and the caster to be within the 2~4 degree range. Admittedly this isn't something I considered until all of your problems CJ.

 

[Tools R Us]

When setting up the truck's front axle you would ideally want that drive angle to be zero for a DC shaft and the caster to be within the 2~4 degree range. Admittedly this isn't something I considered until all of your problems CJ.

Unless you cut and turn the axle housing this is only possible in a narrow lift range. At lower lifts the pinion points up, if its lowered so the CV shaft is happy you will have excessive caster. With higher lifts the pinion points low, if it's adjusted up the caster suffers, so a compromise is necessary. From my playing, it looks like the sweet spot for a happy CV shaft and good caster is at 5 to 6" of lift.

 

[Cruiserhead05]

Just took the CH/F measurment.
Right around 22-22.5 in
Also, ive been doing alot of driving today and have noticed that the vibe issues are clearly not exactly how they were initially. The grr does kind of come and go now, sometime its clear and hear and feel while others, its non existent. Also, i noticed that before, it was easy to feather the gas and find the "spot" where the grr would pop up. Now, its much more difficult and the spot as gotten alot smaller, if that makes any sense.

 

[landtank]

Cruiserhead05, I kind of expected that to be the case. On the few trcuks that have been checkout on the rack with that much height seem to fall into needing about 6* of correction. That 1"=1* myth seems to be just that.

Right now my numbers are like this:

CH/F = 23.25"
caster correction = 5*
measured caster = 2.3*
drive angel = @ 2*

If I were to install another set of caster plates and drill these at 6* I would preeety much be at the acceptable limits of both caster and drive line angle.

Here is how I got the drive line angle. It's not real precise but gives one an idea of where the trucks at.

I placed the protractor in 2 places. First spot is on top of the axle next to the pumpkin. The axle is in the shape of a box here and should give us something close to the diff angle. The second spot is on the shaft itself. I marked the first spot with one of the arrows and then read the difference. It's hard to get a big head up in there so there is a certain amount of fudge factor in this method.

 

[Romanknight]

For what's worth, I had the same grrr noise issue. Replaced front diff bearings and front ds u-joints, didn't help. Replaced rear ds u-joints, noise gone. At first, both my mechanic and I thought it was coming from the front, and that it was gone with the rear ds off. Guess we were wrong.