Advice Please - Driveline Vibrations when Towing uphill

Glend · **Posted:** Thu Jun 11, 2009 5:31 am

I have a driveline vibration problem in certain situations. Background facts: I have a STU lift (70mm (2.75") in front (on original equipment struts) and 75mm (3") in the back (plus Polyair bags in the rear springs). I'm running STUs special front King springs for CRDs. Tyres are Bridgestone D694LTs (245/70R16).

The problem:
My vibrations seem to occur at certain rev ranges (particularly around 2000-2500 rpm which is maximum torque band) under power. Nothing apparent at normal cruise in light load mode. Last weekend I was headed up into the Blue Mountains towing my camper and when I turned off overdrive coming on to a steep section I had a rather bad case of the vibes and had to back off slightly.

I have been thinking that perhaps, due to going out of overdrive on a steep slope (and thus getting an immeadiate downshift to third), that there might have been enough of a weight transfer to the rear to cause the from CV angles to droop to near full extension - and to vibrate. I was only in 2wd so there was no drive going through the front diff. The problem with that thinking is that my airbags should prevent that, and they were inflated to 20psi and the camper was level with the KJ.

This is all in a thread over on AJOR started by Dave XJ who was enquiring about lifts for KJs. Here is the link. Apparently Beaglecamper is also having driveline vibration problems when towing (he also has a STU lift).

http://www.ausjeepoffroad.com/forum/sho ... hp?t=87182

With the fountain of knowledge that resides here I thought I had better raise it with the LOST boys, particularly the CRD guys that tow campers. Any ideas? It's worrying me to the point that I am considering dropping down to a OME 50mm lift as I probably couldn't afford to buy JBA shaved CVs and a Double Cardan Joint drive shaft (assuming they would even work on a diesel that seems to require that massive flywheel on the top of the driveshaft to smooth out out torque to the rear end).

:?:

cmohr · **Posted:** Thu Jun 11, 2009 8:13 pm

Speak to Stu, he may even sell you his Double cardinal he had made....

Glend · **Posted:** Fri Jun 12, 2009 6:39 am

I did email STU and this was his reply today (among other comments this is his suggestion):

"From what you have described I can only point the finger at the torque
produced by the CRD's engine at certain speeds/rpms is causing the issue."...

"A straight cardinal joint addition to the rear driveshaft would solve 90% of
the problem as it effectively halves the driveshaft angle and splits it into
2. I would talk to Hardy Spicer down there or Driveline Services."

Has anyone installed a cardinal joint addition to their driveshaft? Other than Stu that is.

crdjon · **Posted:** Wed Jun 02, 2010 10:51 am

Yep I got the stu lift and vibe problems. Probably not a lot different to other lifts as well, stus lift is quite a sturdy one.

With standard single cardan joints and harmonic balancer i have bad vibes at start up and when getting into the next gear and under load some on deceleration too.

Note single cardans rated to 3 degrees max operating angles, the jeep manual tells us this. It also states the angles for double cardan, almost like they know what we are going to do with out little truck.

I installed a single double cardan at transfer case and removed harmonic balancer, start up vibe not really there now, load vibes reduced but not gone and when diff nosing up under load helps to reduce vibes. I'm not sure removing the balancer is a good idea but im trying it.

I could experiment with nosing the diff up but I DON'T like that idea.

Looks like ill put in a second double cardan at the diff, keep it parallel as possible to output from the transmission and let the double cardans do the rest, I reckon that will just about do it on this 3 inch or so lift.

single double cardan at top helps a lot but its only half the story, has anyone seen pics of the pinions on the diff being chewed out, I wonder what does that?????

I tried to find a thompson coupler for the diff end but at 2500 bucks for a vehicle propellor shaft single fitting is out of the question. Plus even the 500nm version is rated to 3000rpm.

Some numbers, with half a tank of fuel and a bit of gear in the back of the KJ I get a shaft angle of 7.8 degrees to the transfer case and diff angles. Clearly beyond spec for single cardan and 7.8 translates to plus/minus 2 degrees approx upon shifting loads and weights, even gets close to double cardan limits.

install top double cardan and split the angle to get 3.5 and a bit degrees plus minus so that helps but leaves the big angle at the diff so Im thinking second double cardan at the diff also and not altering other geometries too much apart from tweaking for a zero angle difference between ultimate input and output should get it to as good as possible.

Ill let you know how we go after the second double cardan is in. I have read mention of multi double cardans before so perhaps this is they way to go. If im not on the right track someone let me know, if it works Ill let you know.

So if you are going to lift your little truck you need to be aware that you will need to alter the rear tail shaft properly to get this right. $ will be involved.

CD · **Posted:** Wed Jun 02, 2010 5:44 pm

Geezzzz is this only a CRD problem :?:

I've not had any drive line vibes when towing or when loaded with gear. I've also not installed any extra joints, have thought about it but decided it would be too costly.

Glend · **Posted:** Wed Jun 02, 2010 7:48 pm

Chris, I guess some people notice the vibes/shudder and some don't. Further time living with the issue leads me to believe it is a combination of factors and circumstances that produce the vibes/shudder and these can be controlled in large part by the driver and his/her behaviour.

Factors that I find to promote vibration are: Tyres, tailshaft angles, diff angle, etc. Circumstances are things like load carried, towing, road surface, angle of climb with load, throttle, etc.

Combinations of these can produce harmonics that feel like vibration (probably a beat frequency).

CRDJON is experimenting with a Grand Cherokee Hemi Torque Converter in his KJ, there is also the Euro TC which is getting good feedback.

Personally the driveline vibes are no longer a big enough issue for me to go out and spend money on trying to eliminate. Maybe I have gotten used to them, maybe they are not as pronounced with the GDE ECO Tune ECU and modified shift points, but I can live with it. I'll be getting the GDE TCM flash later this year to allow lugging and lockup in 3rd, 4th and 5th and lock to lock shifts. I'll reappraise my vibration/shudder situation then.

I expect that when I am driving around the Flinders and Simpson Desert next month I will not notice it at all.

cmohr · **Posted:** Wed Jun 02, 2010 7:52 pm

I agree Glen, I also think that the 4cyl has a different harmonic to the V6, so that too would be a factor. I wonder if the GDE TCM flash would also suit the V6.... That would solve a lot of issues with them... :BANANA:

Glend · **Posted:** Thu Jun 03, 2010 12:15 am

Chris, I think the TCM flash might help them but GDE has no interest in the V6 as they are primarily diesel tuners, its also a slightly different tranmission. The TCM flash is designed to take advantage of the torque of the CRD and would probely be need to be combined with the ECO tune (and improved torque curve flexibilty). They have developed the TCM flash after requests from people running their ECU flash for a transmission solution that addresses some of the 'issues' that we have with shift points, not being able to lockup in 3rd, etc.

crdjon · **Posted:** Thu Jun 03, 2010 1:00 am

CD wrote:

Geezzzz is this only a CRD problem :?:

I've not had any drive line vibes when towing or when loaded with gear. I've also not installed any extra joints, have thought about it but decided it would be too costly.

Lots of low RPM torque is something to be experienced....... Mostly a good thing.

Oh and mine is pumping out a bit more than most, and is using a hemi torque converter, its getting to the pavement/track in copious quantities.

cmohr · **Posted:** Thu Jun 03, 2010 1:46 am

Shame they wont do the V6 Glen, they would probably sell about 1,000,000 flashes. :lol:

As usual I trust you'll be the test pilot for the Australian flash. We'll have to have a LOST Jeeps run when Keith comes over.

Jon, I agree low down torque is great. Sounds like the GDE guys will have that base covered very soon. The less that TC slips and "Converts" torque creating heat and wear the better I think for any transmission.

palla · **Posted:** Thu Jun 03, 2010 9:46 am

crdjon wrote:

Lots of low RPM torque is something to be experienced....... Mostly a good thing.

Oh and mine is pumping out a bit more than most, and is using a hemi torque converter, its getting to the pavement/track in copious quantities.

This all sounds very interesting, I wouldnt mind catching up for a bit of show & tell. You doing much this LWE Jon? Wouldnt mind coming up to the hills for a chat.

crdjon · **Posted:** Thu Jun 03, 2010 12:04 pm

Hi Palla,

Welcome any time, this weekend Ill be travelling though, heading to beverley to see friends and then out to kokerbin rock. prolly wont be back till monday evening. We can arrange a time etc.

After weekend ok with you, message me if ok.

Advice Please - Driveline Vibrations when Towing uphill

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