"driveshafts too long after OME lift" -long

[GJCruiser]

I'm trying not to write another vibration link, but I've looked through FAQs and "Search". I still need help thinking about this. I was surprised by the yesterday's opinion about my 76 FJ40 suspension.

Long story short. I picked up 40 from mechanic after 2F engine rebuild, H41 swap, many $s and months. Before taking in for rebuild, I knew of a "seat-of -the -pants" vibration when going through load-no load changes down highway. (As in and out of acceleration). Vehicle is stock except for OME 50 mm lift w/ 1.5" extended anti-inversion shackles which came as a kit about 5 yrs ago. Advertised total lift was around 3". No shackle reversal. Shackles point fairly straight up and down. Ride has always been very good.

Before vehicle delivery, we were chasing this vibration problem while in shop. Mechanic says that he noticed it was difficult to remove both driveshafts while axles drooped on lift. If I understand, he said he had to place truck on ground to lenghten distance between flanges to get them off. He thinks that driveshafts are nearly stuffed to shortest position in normal on road application. Warned me about obvious possible damage by what I term "poking d/s thru diffs or t/c" in a droop off road. In his opinion, the rear axle sits a little forward in wheelwell. Transfer case output was certified OK during rebuild. I was looking into pinion bearing play.

I'm blown away to discover this now. I've never had the driveshafts off. Is it possible that this configuration results in this condition? I've been particularly aware of new-to-me opinions that the OME springs are too short. I've also read here that there really isn't much FJ40 driveshaft axial length change throughout full articulation. To shorten the driveshafts the recommended 3/4 " would cost about $350 for both here in GJ. Wouldn't that same money be better spent on 4" or 5" springs if there replacement of these OMEs cured this problem? Or would such lift exacerbate problem. I'm having hard time beleiving my driveshaft are too long. It seems that most suspension changes require longer driveshafts but It could be that I thinking of SOAs and other large lifts. I've got 3" total suspension lift. Again, I'm having a hard time believeing.

Can anyone offer similar/refuting advice/evidence? Thanks

 

[Mark W]

Put it on a lift and let it droop to actually measure the shafts Measure them on the ground as well.

Note that your driveshafts have a plug in the end of the female stub, right behind the ujoint. This and the OEM dust shield over the slip join reduce compression just a little. Removal and replacement with an unused rubber shock boot to replace the dust shield and a glob of silicon sealant for the plug will gain you a little.

Most suspensions that remain close to factory will extend the driveshaft under droop. Some modified setups will compress it under droop. It usually needs long shackles and springs that ride flat under load with a lot of arch as they are unloaded for this to happen.
If your setup is not particularly flexy, (most OMEs don't reach this level) then you may have to foce articulation to get max travel (up and down) at the diff to tell just how far it can go.

Your mechanic may have simply been fighting the greas in the slip joint. This is not uncommon. Puling the zerk off to let grease flow out unimpeded when the shaft is compressed is the normal approach to make sure that this is not happening. A lot of folks overlook this though.


Mark...

 

[GJCruiser]

I really appreciate the chance to have this dialogue. Can I follow up with some more questions?

Let me make sure I understand. You think it's possible that either condition may exist. That is, max compression under droop or less compression under droop as compared to sitting flat on road depending on suspension variables. I can measure to see which condition I have and report. Suppose I do have max compression under droop.

Is it OK to simply place the vehicle in that position and remove grease fitting to let "excess" grease out?
Is that grease really excess?
If there is not a lot of grease removed, then how do I acertain that the driveshafts are not compressed to a mechanical limit?
Is there a specification for this "shortest allowable length" or is it obvious visually?
Does one have to remove the U-Joint to remove the factory plug?

I live down the road from Alcan. I will ask them what their experience is with driveshaft length change with their various configurations. I don't know if my view that vendors should have this knowledge is simplistic or not. Obviously, I don't want to unneccesarily shorten the shafts only to realize that for a later suspension, the originals would have been fine.

Thanks,

 

[Pete]

GJ,

I had exactly this problem this summer when I installed the OME Dakar springs (bottom helper leaf removed per Bob at TPI suggestion) with TPI stock length anti-inversion shackles. I had a helluva time getting the springs on until I removed the driveshaft (both on the front and the rear) which allowed me to get both sides springs in the axle perch center holes. The when I went to reconnect the drive shaft, it seemed too long. After lots of prying and cussing, Mark's suggestion to remove the zirk hit me and BINGO, the shaft compressed enough to go on, still with a little prying. I read the other day Poser's suggestion here to enlarge or recenter the holes in the perch when someone else was having problems (I don't think it was on an OME). This could have helped me but it seems that this approach would also affect the alignment unless both sides were identical, something I don't think I could accomplish with my 3/8" drill.

I haven't been off road yet, but I haven't noticed any binding in the drive shafts when the wheels are drooping with the frame on jack stands. I also thought the drive shafts lengthened at full droop as Mark said, not shortened. Maybe they will bind when fully compressed but I haven't checked that and don't quite know how in my driveway. This also on a '76 FJ40 by the way.

If I were you, I'd save thoase bucks needed to shorten the drive sahfts unless absolutely necessary.

Pete

 

[honk]

$350.00 to take 3/4" off of your drivelines? Is that a typo?

 

[762fmj]

Mark W,
Can you explain this problem and how to solve it?

"Your mechanic may have simply been fighting the greas in the slip joint. This is not uncommon. Puling the zerk off to let grease flow out unimpeded when the shaft is compressed is the normal approach to make sure that this is not happening. A lot of folks overlook this though."

 

[Degnol]

Kinda like hydro-locking a motor......grease does not compress.... if your splines are tight, there is no place for it to go, especially on a "shcok" compression. First thing my driveshaft guy does is remove the zerk. You'd be surprised at how much will come out of it. I'll venture a guess that a fluid ounce of grease will keep you from fully compressing the drive shaft by an inch.
I have started greasing both the male and female portions of the slip joint and calling it good.

I am....not Mark W....by the by


Ed

 

[Degnol]

$350.00 to take 3/4" off of your drivelines? Is that a typo?

No s***.

 

[woooody]

for $350, you could get some High Angle Driveline shafts, ccustome made.

Usual charge is right around ~$100 per shaft for retubing, and balancing.

 

[Mark W]

I really appreciate the chance to have this dialogue. Can I follow up with some more questions?

Let me make sure I understand. You think it's possible that either condition may exist. That is, max compression under droop or less compression under droop as compared to sitting flat on road depending on suspension variables. I can measure to see which condition I have and report. Suppose I do have max compression under droop.

Is it OK to simply place the vehicle in that position and remove grease fitting to let "excess" grease out?
Is that grease really excess?
If there is not a lot of grease removed, then how do I acertain that the driveshafts are not compressed to a mechanical limit?
Is there a specification for this "shortest allowable length" or is it obvious visually?
Does one have to remove the U-Joint to remove the factory plug?

I live down the road from Alcan. I will ask them what their experience is with driveshaft length change with their various configurations. I don't know if my view that vendors should have this knowledge is simplistic or not. Obviously, I don't want to unneccesarily shorten the shafts only to realize that for a later suspension, the originals would have been fine.

Thanks,

*Depending on your suspension configuration* you may get a diff that moves closer to the T/C under droop or one that moves further away. Not talking about shackle reversals here, but standard configuration with mods.

For example, one of my rigs has long soft springs at each end. Also has long shackles. in a static situation the spring sits very flat. Under droop all the leafs except the main leaf fall away without resisting movement. The main leaf sags (arches) a LOT. The arch means that the spring gets shorter as it droops. The long shackle allows it to move far more than it needs to. Since the frame end is solidly fixed, the shortening of the spring moves the axle toward the diff. Of course it is also dropping which increaes the distance between the dif and the T/C in the verticle plane. But it is also swinging in an arc around the spring hanger omn the frame so it is moving closer in the horizontal plane. Additionally as the spring swings in theis rc the axle rotates the pinion upwards which to a small degree lesens the verticle distance that the D/S has to span.

Four different movements going on here.

In my rig there is very little change in driveshaft legnth as the suspension cycles. And it actually shortens up under max droop.


Now if you have stiffer springs (and shorter shackles in a more traditional configuration) and do not experience much change much in arch from static to full droop, then you do not get much change in the distance between the dif and the T/C. From this factor. But you don't get much rotation of the diff either, so there/s another factor that is changed. Shorter shacklesalter the relationship. Total suspension movement does too.

Every setup is a little different.

Oh yeah, the difference in location of the frame end of the spring and the T/C end of the D/S in terms of fore/aft onm the rig makes a difference too. Sometimnes a big difference because of the different arc that the D/S and the springs swing in.

When all is said and done, I doubt that your driveshafts are bottoming out due to the installation of an OME lift. Jack the rig up one end at a time (unless you've got a lift at your disposal) and get the tires off the ground. Pull the zerk out of the slip joint. Unbolt on end of the D/S and see how much more you can compress it. (Measure the distance/length while you're there). Chances ar that ot is just grease and a good seal (or old crusty grease even if it doesn't seal tight). Assuming that you have compression left once this is done, lower the rig down to the ground and check the distanc/length of the shaft again as you put it back in. I expect it will be a little bit longer. If so again this is the most likely scenerio with your setup as you describe it) then is will get a (little) bit longer under fi=urther compression of the suspension. Until you get to the pint that the springs are compressed beyond flat and the start arcing backwards. Doubtful that you can get a set of OMEs to that pnt with "normal" length shackles and bump stops. Probably even without bumps stop this would be hard/impossible to achieve.


Mark...

 

[GJCruiser]

Thanks for the input. I'll try the above procedure this weekend. In any case, I'm not going to hurry into the driveline shop as I've been running this way for five years. This is perhaps a new discovery for me. I want to verify and quantify any potential problem first.

No, there is not a typo. The driveline shop here wants $175 per to cut and reweld the driveshaft tubes and there schedule was a week out. That seemed a little high compared to what everyone else was reporting. I chalk it up to the oil and gas boom here. Housing prices have gone up 15%/year for three years and there's not much of a cooling yet.

 

[PabloCruise]

Grand Junction is cool...

Did you check out Alcan before going OME? If I lived there, I think I would go Alcan.

How is your vibration? Still there? Have you checked the rear pinion? Is it leaking gear oil? Your pre-load may be off now due to a spun shim.

I do not like how a lot of lifts stuff the rear axle so far forward in the wheel opening. When I did my lift, I flipped the springs to gain some wheelbase and move the rear axle back.

I had to stretch my driveshaft (don't remember the cost). And when I got the driveshaft back from the shop, I did have to pull the zerk and compress all the fresh grease the shop had put in... https://forum.ih8mud.com/showpost.php?p=521329&postcount=45

Good luck!

 

[GJCruiser]

Didn't move to GJ until after OME install. Duh. As things go, one gets more into this and makes decisions about changes. Living here in GJ gives a short commute (my DD) and a lot more places to play on the rocks nearby. As my 33 BFGs wear out, I'm considering changing to 4" or 5" Alcans to facilitate 35s. I just won't make that jump until I solve vibration issue first. I doubt it's going to be solved by too much grease, though.

My daughter attends CSU so I'm up your way quite a bit.

 

[GJCruiser]

Forgot to mention in previous e-mail but did in original that the rear axle appears to sit a bit forward of center in wheel well. That's why I'm not going to cut driveshafts until I make decision about new springs.

 

[PabloCruise]

I just won't make that jump until I solve vibration issue first. I doubt it's going to be solved by too much grease, though.

Have you checked your third member out? Here is some interesting reading on setting up ring & pinion from Randy's R&P:

http://www.ringpinion.com/content/technicalhelp/default.asp?pid=45

I ask because I went through 3 diff rear third members. All of them had spun shims, meaning rear pinion pre-load was out of spec.

If I read the above link correctly, this can cause certain vibrations and noises. Does it howl on decel?

 

[PabloCruise]

PS: I am in the Fort. Shoot me a line if you ever want to meet up next time you are in town.

 

[762fmj]

Ok, call me stupid. My drive safts are doing this hydro lock thing and in the past have had to remove the zerts to get the yokes to expand and contract. I have been wanting to post the problem but never got around to it. And since the problem is being discussed here. Is it a problem? Am I over greasing? What has to be done to get them to work correctly? Please explain!!

 

[Mark W]

It's no big deal. It is a better idea not to pump the slip joint too full of grease. But the suspension has a lot more muscle than you do. It will compress the shaft and force the excess grease out.


Mark...

 

[GJCruiser]

I'll get a chance to remove the grease fittings tonight. After reading here, I went out to the 40 in the parking lot at work yesterday to look at driveshaft angle. I bought an angle finder last night so I won't have close numbers until tonight but here's what's obvious.

Engine, trans, T/C appear fairly level (maybe down a degree or two).
With 2" OME springs and 1.5" extended shackles, pinion points right up at T/C output. In other words, all of the angle in the driveshaft is in the joint right behind the T/C. The U-joint at the pinion shows almost no angle. If it helps to picture what I mean, like what the drawings on all of the driveshaft shops show one should have for a CV shaft. So one of the things I will try is to get accurate measurement and shim rear axle down to nearly match angle of U-joint up front on the shaft.

Here's what gives me pause. Four inch lifts on stock vehicles must make the angles that I see a whole lot worse. Is that a faulty assumption? So does that mean that every lifted rig has a similar U-joint angle mismatch? If so, do all have vibration due to "non-cancellation" of vibration energy.

I can't believe that I wasn't more perceptive to this before. Maybe, I didn't notice a big vibration at first and it took a "less than well oiled pinion" (due to angle) to wear before vibration became obvious?

I could swear that I read lots of sources that state that lifts up to 4" really shouldn't cause any problem. Now, I don't see how that can be true. This confusion and problem solving is all part of this wonderful process!

 

[Degnol]

I think it is the 1.5" shackles that are tilting the pinion up. At least that is the case with mine. You are right that lift springs and blocks do not usually cause this problem as they don't tilt the axle like shackles do.

Ed