jpthing's XJ rear driveshaft setup

[jpthing]

I had to order some u-joints etc for my Tj so I ended up speaking to Tom Woods today.
Wow, amazing customer service! He actually answers the phone himself most of the time and was very polite patient and helpful. He was able to look up the specs of the driveshaft I ordered from him 2 yrs ago to confirm I was ordering the correct parts.

At the end of the conversation he said " so, is there anything else I could help you with?" so I picked his brain a little.

I asked him to theorize on why I was having problems on my Xj (with the SYE and double cardan) with the blue goo coming off. He said he has seen more of this lately and blames inferior quality parts, according to Tom, some blue goo just doesn't stay put. He assured me I should have no problems of this type on the driveshaft he made for me.

Interestingly enough, both of my shafts which lost the blue goo were from Pat's. The blue goo on my Tom Woods shaft and my factory front shafts has been fine. maybe not a coincedence.

The next thing I asked him about was my XJ vibes. I described my current setup, the angles, the lift height and the vibes I get: nothing until around 50mph/80kph then a little vibes around that speed which dissapear if I go a little slower or faster.
He explained a little about the dynamics of harmonic reactions or something like that.
"but what is the best way to correct it?" I asked.
His answer, no word of a lie "Put a second layer of carpet down." (he was joking but also making the point of how subjective this is, and saying in his opinion it's not major, and there is no way to measure driveshaft vibes)
I told him I have no carpet at all in the XJ.
"well there's your problem" he said. "If you had carpet you probably wouldn't even have noticed it"
I asked him if these vibes would cause premature failure of the pinion or tcase bearings.
"I wouldn't worry about it" was his reply.

I would totally reccomend his shop, whether you guys will agree with what he told me or not may be up for debate, but there is no question that his customer service is some of the best around. The driveshaft he made for me makes the ones I got locally look cheap.(bigger, deeper splines, nicer welds)

For the record my blue coating wasn't so much wearing as delaminating from the splines, that is to say, coming off in long intact pieces.

I am not mentioning what Tom said to "trump" anyone or prove a point, in fact I am interested  to hear opinions on the subject whether you agree with Tom's advice or not, I am not sure what to think of his advice actually. I honestly hope this can go back to being a tech discussion, that is my only intention.

[dac]

What's the technical term for this "blue goo" you speak of??

The carpet and thin layer of mud must be what's keeping my AA sye and DSI shaft from vibrating.

[frenchy]

I

I don't think you can speek on Tom's behalf.
He is a respectable vendor, with good parts. You, explaining the tech makes no sense and is detrenantal to his business here in Canada.
Please stop.

[apeman]

As a jman mechanic and a jman welder im just appalled at some of the crap you are dumping out boone....cman man, seriously..

amazing customer service! He actually answers the phone himself

...call Rusty's offroad..Rusty will answer..doesnt make him a genius..Call 911..ask them for medical advise.

He was able to look up the specs of the driveshaft I ordered from him 2 yrs ago to confirm I was ordering the correct parts.

...yep its amazing what computers can do! im amazed  my cell phone tells me who's calling!
[quoteI was having problems on my Xj (with the SYE and double cardan) with the blue goo coming off.][/quote]..its called over use of marine type grease and centrifugal force...fill a shot glass with grease and spin it between your open palms and see how much of a blue goo problem you seem to find in your house...im sure your 100 + tech boards will have a solution for said problem.
Fact of the matter is that you negelect to mention , or realize, that your homebrew crap fixes are garbage..and you just had some hairbrained idea that seemed to be cheaper, and seemed to work for you..well i farted in bed last night and my old lady "seemed" to not notice and it worked for me..your tech is garbage...that "seems" right
Do your homework....first off the 97+ xj's with a 231 or 242 t case have a 3/4" longer slip yoke..while allowing more droop in the rear it also added more suspection to driveline vibes when lifted...your tj yoke crap wont worj on my xj...231's and 242's are not the same..factor in the fact that i run a D44 ( 1" reduced driveshaft length) and your tech is whacked...do some more real world tech, and quit reading crap off the internet..cuz your crap works with your xj,leave it at that..cuz your crap dont work with mine..and i did mine the right way..not the cheap way
I would rather my jeep work flawless..than have it save me $200...and when my junk breaks, atleast i know what to upgrade, instead of find an excuse for being cheap.

If you want to do a tech write up feel free to show us how to port a 7120 or 0630 head so i can laugh, or build a stroker, so corey can shut you down, or how to set gears so Bill can contradict everything you have to say...

Please stop with your tech...if anyone has questions on tech, we ask for it...so we can do it the right way.

[rocnrol]

well i asked you if you wanted to know how i got my set up in my jeep to work with out vibes, and with steeper angles and a shorter shaft and you said nothing, so i will tell you anyway.

you see jp, its one thing to run around a junk yard and put parts together from different applications until something fits and then say you reinvented the wheel, its quite another to do some real homework first, and truly understand what you are dealing with. so before i did anything with my driveshafts, i did my homework. did tons of research, and talked to guys that built the things for a living. at the time, Corry at dsi was an amazing source of info, i listened to what he had to say and learned a lot. in the end my drive shaft cost me the price of two new u-joints and 80$ to get a shaft shortened at dsi. result...... no vibes.

so here is what i learned. in a driveshaft with two single cardan joints, anything more then a 0* angle is where you start to have issues.

for example, lets angle the two shafts to say 45 degrees. Now, look at the "cross" of the u-joint as it rotates. When the driving side of the cross is horizontal, it's ends are moving at the same speed as the yoke on the driving shaft. However, the driven side of the u-joint is 90 degrees offset from the driving side, but since the u-joint cross is rigid, all 4 ends are moving the same angular velocity, i.e. that of the driving shaft. However, since there is that 45 degree angle between the two shafts, the cross is also angled 45 degrees, meaning the effective length of that side is equal to the sin(45) times it's actual length or 71%. But, since it is moving at same angular velocity, the surface speed; which is equal to the angular velocity times the radius (or length); is now 71% of the speed of the driving shaft; i.e. the driven shaft is turning momentarily at 71% the speed of the driving shaft! Now, turn the driving shaft 90 degrees farther in it's rotation. Now the driving side of the cross is at 45 degrees, so it's effective length is now 71% and the driven side is 100%. Assuming the driving shaft speed is constant, then this means the driven shaft speed is now 1.00/0.71 or 1.41 times (or 141%) faster than the driven shaft! So, if you have the driving shaft turning at say 1000 RPM, the driven shaft will vary from 710 up to 1410 RPM as it rotates, averaging to 1000 RPM. This is what causes a driveshaft to vibrate.

So, how can such a setup ever work in the real world? As it turns out, if you stick another u-joint on the other end of the shaft and line it up in phase with the first one and keep the angles identical, these rotational speed changes nearly cancel each other out. While the driving u-joint is speeding up the driveshaft, the driven u-joint at the other end is slowing down what it is hooked to (usually the pinion on the differential). And while the driving u-joint is speeding up the driveshaft, the driven u-joint is slowing down the pinion. All this results in the pinion end of the shaft being driven and almost exactly the same speed as the transmission/transfer case end of the shaft.

 The smaller the operating angle, the better the cancellation is, the greater the operating angle, the less the cancellation is. Also, if the angles on both u-joints are not the same, the cancellation is not as  good and if the two u-joints are not properly phased to each other, the cancellation is worse yet. In fact, if you were to go to the extreme and set the u-joints up 90 degrees apart from each other, not only would there be no cancellation but they would in fact compound the rotational vibration, the first joint would induce it's component, then the second joint would take that and multiply it by it's own factor depending on the angle. So, in the above case of a 45 degree operating angle, the driven joint would be running from about 50% to 200% of the speed of the driving joint, or from 500 RPM up to 2000 RPM for a 1000 RPM input. You can imagine what that would feel like driving down the road, say at an engine RPM the should give a 30 MPH speed, the tires would be turning anywhere from 15 MPH up to 60 MPH as they turned one revolution!

so to sum up, i made sure both my output angles and my diff yolk angles were the same,  and bobs your uncle.

[muffintop]

jpthing... here is a "top twelve list" illustrating why you should stop posting:

12) You seem to think you have a bigger mental stick than everyone else and no one wants to watch you play with it.
11) 99.9% of the people on here either ask questions... or provide answers to questions asked. You do neither.
10) Surely... you are not accomplishing your goals or desired effect.
9) No one seems to care.
Eight) You seem to have "a nack" for turning even useful threads/topics into rubbish.
7) CJA membership aspirations or not... you are making enemies with the people you will be wheeling with (assuming you can tear yourself away from posting on 100+ internet sites to actually wheel).
6) Assuming your tech is useful to someone out there... the way in which you deliver it offends people.
5) No one likes a "know it all".
4) Life, for the most part, is a popularity contest... you are currently in last place on the CJA board.
3) The person who invented the internet has been observing your use/abuse of this technology and now requires antidepressants.
2) Being a member of 100+ internet discussion boards is not a selling feature.
1) Every single person on this board has a "specialty" that they could "spout on about" endlessly... thank god everyone doesn't.

I am not saying this to be mean spirited... I am doing this to help you.

Hopefully this brings into focus what you are actually accomplishing here... which cant possibly be what you had in mind when you start a thread?

[Tyn Pow]

so here is what i learned. in a driveshaft with two single cardan joints, anything more then a 0* angle is where you start to have issues.

for example, lets angle the two shafts to say 45 degrees. Now, look at the "cross" of the u-joint as it rotates. When the driving side of the cross is horizontal, it's ends are moving at the same speed as the yoke on the driving shaft. However, the driven side of the u-joint is 90 degrees offset from the driving side, but since the u-joint cross is rigid, all 4 ends are moving the same angular velocity, i.e. that of the driving shaft. However, since there is that 45 degree angle between the two shafts, the cross is also angled 45 degrees, meaning the effective length of that side is equal to the sin(45) times it's actual length or 71%. But, since it is moving at same angular velocity, the surface speed; which is equal to the angular velocity times the radius (or length); is now 71% of the speed of the driving shaft; i.e. the driven shaft is turning momentarily at 71% the speed of the driving shaft! Now, turn the driving shaft 90 degrees farther in it's rotation. Now the driving side of the cross is at 45 degrees, so it's effective length is now 71% and the driven side is 100%. Assuming the driving shaft speed is constant, then this means the driven shaft speed is now 1.00/0.71 or 1.41 times (or 141%) faster than the driven shaft! So, if you have the driving shaft turning at say 1000 RPM, the driven shaft will vary from 710 up to 1410 RPM as it rotates, averaging to 1000 RPM. This is what causes a driveshaft to vibrate.

So, how can such a setup ever work in the real world? As it turns out, if you stick another u-joint on the other end of the shaft and line it up in phase with the first one and keep the angles identical, these rotational speed changes nearly cancel each other out. While the driving u-joint is speeding up the driveshaft, the driven u-joint at the other end is slowing down what it is hooked to (usually the pinion on the differential). And while the driving u-joint is speeding up the driveshaft, the driven u-joint is slowing down the pinion. All this results in the pinion end of the shaft being driven and almost exactly the same speed as the transmission/transfer case end of the shaft.

 The smaller the operating angle, the better the cancellation is, the greater the operating angle, the less the cancellation is. Also, if the angles on both u-joints are not the same, the cancellation is not as  good and if the two u-joints are not properly phased to each other, the cancellation is worse yet. In fact, if you were to go to the extreme and set the u-joints up 90 degrees apart from each other, not only would there be no cancellation but they would in fact compound the rotational vibration, the first joint would induce it's component, then the second joint would take that and multiply it by it's own factor depending on the angle. So, in the above case of a 45 degree operating angle, the driven joint would be running from about 50% to 200% of the speed of the driving joint, or from 500 RPM up to 2000 RPM for a 1000 RPM input. You can imagine what that would feel like driving down the road, say at an engine RPM the should give a 30 MPH speed, the tires would be turning anywhere from 15 MPH up to 60 MPH as they turned one revolution!

so to sum up, i made sure both my output angles and my diff yolk angles were the same,  and bobs your uncle.

Hey look, some real tech...cool!

And it only took 3 pages of 'discussion'

[jpthing]

I am very enthususiastic about jeeps and hoped to engage in tech discussion with some local jeepers.

I'm sorry if some feel I came across as a "know it all". This was not my intention.

I'm sorry to everyone who's been irritated or who feels their time was wasted.

If my enthusiasm came across as arrogance, again I apologize.

I'm being criticized now for complimenting Tom Wood's customer service? um ok then...

[JackstandJohnny]

I had to order some u-joints etc for my Tj so I ended up speaking to Tom Woods today.
.

why would you call tom woods for ujoints for a TJ?

cant' you pick them up from napa?  thought you were about 'cheap' builds, now is ordering parts and shipping them across the country cheaper than stumbling down the street to a NAPA?  or did you literally call just to pick his brain?

also, i have a feeling, (if you did talk to Tom)  that his response to you about 'putting another layer of carpet down' might have been his way of saying 'umm, i sell driveshafts for a living; why are you toting your junkyard fix to me on the phone?  i have products to make/sell, and you're not buying, so why waste time?
its also possible he thinks, that with your current setup, that is about as good as it'll get.......

[dac]

I told him I have no carpet at all in the XJ.
"well there's your problem" he said. "If you had carpet you probably wouldn't even have noticed it"

I disagree with this point, so if I'm wrong someone please explain how this works.

I asked some of my engineering buddies, posted some questions on www.askanengineer.com and talked to a couple doctors I know.

How does carpet mask the vibrations you feel?  Sure it might mask what you feel with your feet but what about your butt sitting in the seat, hands on steering wheel, elbow on door, sight, sound???  As far as I know the floor boards, steering wheel, seat, doors.... all that stuff is connected, some parts with insulators.  How can carpet or more carpet mask the rest of your senses?  I'm pretty sure you'd see the dash vibrate slightly, may even hear stuff rattle, even if you can't feel it with your feet.  Sure carpet is dense, but if something is shaking I'm pretty sure you'll still notice it.  Unless of course you have a magic carpet.  Or maybe it's the amazing insulating properties of a hockey puck body lift?

[jpthing]

Tom woods u-joints are $20 USD.  To me that's a pretty good deal. I have not been impressed with the longevity of napa u-joints.

I also wanted his opinion on whether u-joints with the grease fitting on the cap needeed to be replaced with the same type for correct balance to be maintained.

[jpthing]

I disagree with this point, so if I'm wrong someone please explain how this works.

I asked some of my engineering buddies, posted some questions on www.askanengineer.com and talked to a couple doctors I know.

How does carpet mask the vibrations you feel?  Sure it might mask what you feel with your feet but what about your butt sitting in the seat, hands on steering wheel, elbow on door, sight, sound???  As far as I know the floor boards, steering wheel, seat, doors.... all that stuff is connected, some parts with insulators.  How can carpet or more carpet mask the rest of your senses?  I'm pretty sure you'd see the dash vibrate slightly, may even hear stuff rattle, even if you can't feel it with your feet.  Sure carpet is dense, but if something is shaking I'm pretty sure you'll still notice it.  Unless of course you have a magic carpet.  Or maybe it's the amazing insulating properties of a hockey puck body lift?

I don't want to argue. I was simply saying what was said to me. It is open for discussion.
Maybe I misunderstood the concept of "vibes" because i get no shakes whatsoever, just a "whirring" noise.
I don't want to misinterpret Tom, but I think he was saying that vibes are highly subjective.
I'm not sure your references to "magic carpet" are relevant, and my XJ does not have a hockey puck body lift.

I sincerely wish that we could talk tech without the "digs".

[dac]

I wasn't argueing, just asking if Tom's comment made sense.  So, discuss away, will adding more carpet reduce vibes?

Also, you either have vibes or you don't.  I believe the magnitude would be subjective.

[jpthing]

 I guess the part that's subjective is whether a given level of vibes is "acceptable" or not.

Like I said I can hear vibes at a certain speed but I can't feel them. My dash definately does not shake or anything.

I guess some tunes could do the same function as the carpet...or maybe some noisier tires?

So are vibes "acceptable" if they can be heard but not felt?


 

[dac]

Are you sure it's in your drive train?  Maybe something else is moving around like a cable or something?  Brake drag?