It could have compounded an issue yes -- driveline speed would be higher.


My guess is --- it may have more to do with the output shaft of the tranny... and how much driveline is hanging out.

Funny you mention that because I measured how much yoke was left on the table today and was thinking the same thing.
Inland Empire supplied the shaft with the kit and I think they error on the short side. Ideally I'd like the shaft to be .3-.5" longer.

The measurement from the seal (which is very close to the end of the shaft) to finished surface of the yoke is actually 29mm or 1-1/8" at ride height.

http://photos.smugmug.com/photos/i-w...wRqnTqx-XL.jpg

As noted before you're the best guesser I know. :D

We have found that the GOOD strange yokes can make a difference as well as the drive shaft balance. some shops only balance at about 800-1100 rpm and the drive shaft speed is a lot higher obviously. good luck it is like chasing your tail sometimes

is that the measurement that is generally supposed to be approx 3/4"?

is it a steady rpm vibration or power on or power off vibration.

I'm not sure what the spec is but that would be what I'd think is about right. Thankfully we have a longtime local driveline service.


Comes in steady at certain rpms and gears. Noticeable on decel, changed for the better with a passengers in the car. I've done so many shim adjustments I can't quote specific ranges anymore. :sieg: Hopefully I get a chance to drive it tonight and see if removing a .0375" (20 ga) shim made any difference.

Before the 3:73's were installed there was a slight but tolerable vibration in the 65-70 mph......rear view mirror was still usable. That's not the case now. :D

I'm guessing driveline balance may be off as Blake mentioned, but that yoke depth could be a contributor. When the car was on stands with the rear unsupported the yoke pulls out about 1/8" from the ride height position and there is some slop, at ride height the slop is reduced to what I "think" would insignificant........but thinking has got me in trouble more than once. :D

3/4" is the spec --- and out 1 1/8th is a bunch. This doesn't mean that's your problem -- but sometimes it's a stack up of little errors.... too much stick out - a minor out of balance and boom - ya got a problem you can feel.

Since you've done just about everything else... it's time to look at "what else".

The cheap fix is to move the engine back....



Kills two birds with one stone...



Too much hanging out causes the driveline to "orbit".....

If its noticeable on decel, roll the pinion down further. I just had to reset a ridetech 4 link that had a vibration on decel. I would roll it at least 1-1.5* down if you have not done that yet.

Thanks, I've taken it past the best spot in both directions. After the last month I wish it was a 4 link!

I've done enough shimming to be pretty sure it's balance or the yoke penetration possibly.

The one change I did make to the previous setup was installing urethane bushings in the rear spring eyes (fronts were already in) I guess that in itself could have amplified a vibration condition but the difference was too drastic IMO.

Test drive window of opportunity is now!

Didn't realize you were still on leafs. Have you considered changing to a 3" aluminum driveshaft? The larger aluminum shaft will absorb some vibrations that a small dia steel may amplfy.

I can't imagine that they're still even available - even in a wrecking yard out in the middle of Wyoming...


HAHAHAHAHAHAHAHAHA

I'm running a 3.5" steel shaft from Inland Empire. This last shim change move the vibration up in on the mph chart, 65-70 isn't bad at all, 75 mph and the mirrors fuzzing out, 85 mph and the mirror is oscillating fuzz...... :D

Upside is it improved..........what's bugging me is I've used this setting. Either I didn't get a wedge positioned on a pin properly and missed that when torquing the u-bolts even though I've visually inspected every time (keep in mind on my back not on a lift) or maybe I've got a moving target. :headscratch:

I think John Deere still uses them on a limited basis.........:guns:

Had a friend that had the same problem one time and his bolts were slowly backing out of his ring gear. Not saying that is your problem, just relaying another possibility.

I have also seen a car have that problem where the axles were changed and no one noticed it had a ford register instead of a chevy. When the wheels were bolted up they were not perfectly centered and it did the same as your car.

Stuff like what is going on will make you crazy. Good luck

This vibration (not a GOOD vibration - Beach Boys) felt "centered" in the car - so I understand Siegs chasing the driveline settings.

The rest of the car felt planted and smooth. It's really a "nice old car". I don't mean that as a slam - rather it's a description of a car that hasn't been Pro Toured in our usual rotisserieed / body off $250K build... I've owned several of these, and this is a nice one.


I've felt driveline angle issues, and when it was the pinion setting - the vibration felt "rear" and sounded "rear". It was also usually MUCH more pronounced than what Sieg is dealing with.


This felt more "harmonic" to me. I think it's the too short (and perhaps unbalanced) driveline "orbiting"... and it may have already ruined the output shaft bearing - or at least - being in the process of doing that. The output shaft is already unsupported for a pretty good distance... then you hang a driveline on it.

I'm still sticking with imbalanced drive shaft.

the other thing it COULD be is the trans itself, we have had a car in here with an old t56 LS1 type, it would only vibrate in 5th and 6th, customer had the trans rebuilt and said it was MUCH better. seems a lot of the drive shaft over speed could be the cause??
Scott why are you using a 3.5" steel shaft? seems a bit over kill. and even if it is .083 wall DOM it will be really heavy. my 1000 hp drag car only uses a 3" steel shaft. on the cars that we have used aluminum shafts in the issue does not seem to be as apparent.

Well..... you know what ASSume means. :lolhit:

Ruined bearing...........NOOOOOOOO! I hear you but I don't want too! Besides I'm not in the mood. :D

It well could be, though the feeling through the shifter has not changed. Sounds like that shaft needs to go to the local shop and be checked for balance first, then lengthened and balanced for the proper rpm range.

Blake - This shaft was supplied with the Hurst Drivelines kit. The trans is a T56 Mag, close ratio.

I'll check the local shops pricing on aluminum as it sounds like to be buttery smooth aluminum is the way to go in OD trans applications.

I took a brief break............just so you gentlemen know I respect your input:

http://photos.smugmug.com/photos/i-D...DdZzHrB-XL.jpg

http://photos.smugmug.com/photos/i-s...sdgBWtd-X2.jpg

I was glad to see the amount of yoke over the shaft, but another .5" wouldn't hurt. The photo distorts the measurement the actual coverage is 3-1/8"

Is that enough in your opinion?

If so re-balancing would be a lot cheaper than building a new shaft to gain a half inch. :D

Some times it's not about how much you put in --- it's about how much you leave hanging out. <oh if you could see the grin right now!>


I might add to this thought -- that Amy would certainly understand you're asking her to get a second full time job - so that you could get a new shaft.

Let me rephrase the question: Is 3-1/8" enough output shaft coverage to be considered OK?

:D

Here's another thing that I've learned over the years...


Since there's NO POSSIBLE WAY to get a torque wrench on the u-bolts -- everyone over tighten's 'em.


Snug these nuts until the SPLIT WASHER closes.... and give it 1/8th more turn.

That's not much!!! So be careful!!


Once a split washer is "closed" it's going to do it's job of not letting the nut back off... the 1/8th addition turn is the torque spec.


Over tightening these will allow your drive line to turn --- but IT WILL CAUSE VIBRATION because it's grinding against an oval bearing cap.


Not saying you did this -- just adding this info because lots of people read this stuff.

Different yokes for different strokes...


You can buy longer yokes. More yoke in makes a more stable u-joint... I'd run as long of a one as possible. Check the transmission specs to see what it will accept and allow for some stroke. It DOES move in and out.


You're probably running the 1310 joint --- I always upgrade this stuff to 1350 -- but that's a different issue.

If you're going to haul your driveline over to Inland... ask them to give you a loaner slip yoke -- and take it home and see if it will go in and out without any interference....

Then have them replace both your u-joints while you're there... just because... or at least have them check them for roundness (of the cap) - then have them do a HIGH SPEED balance...

NOBODY would EVER be satisfied with 3 1/8th inches.... EVER... Do you have any loose rocks laying around??

order a shaft from Mark Williams.

Well at least I know the difference between and Ooo, and Ahhh, and Oh my God.

:popcorn2:

I just dropped the shaft off at Driveline Services to check the balance.......my last words were I hope it's out of balance.

Should know on Tuesday. :knokwood:

HAHAHAHAHAHAHA --- I'd have probably STARTED there....




But hey! You've been in need of some serious creeper time.

Sounds like the shaft is a bad mother...

If it was alright previously? :buttkick:

Tuned up shaft installed.......talk about a business under-promising and over-delivering! Told me by Tues, called at 3 and said it was ready......quoted $85, charged $75. Customer for life........to bad for them I'm not younger. :D

http://photos.smugmug.com/photos/i-Q...QzWHtBP-XL.jpg

Definitely improvement.........60-70% is my guess. It's not damage concerning like it was. Tested in 5th and 6th cruise speeds (65-75) and up to 95 in 6th. Light at the end of the tunnel!

Told ya :thumbsup:

Please tell me the finishing touches or just come up and show me how. Lodging, meals, K9 companionship, and beer is on the house. :D

Sheeeeet........Wish you were close enough to make the drive. Hate to say it but if its not the trans it has to be the amount yoke sticking out of the trans. My follow up fix would be the correct length drive shaft. My brother-n-law just bought a truck load of stuff from Amir Rosenbaum(old owner of Spectre) and one of the items was an aluminum drive shaft. I could talk him into given it to you for cheap if your interested.

It might not have been previously alright -- but the old bushings -- might have been partially covering it up. Now you put some good bushings in that are transferring the motion of the ocean and so on.

My point wasn't that it was bad previously BTW -- My comment was more about that the minute I thought I had a drive shaft issue -- the first thing I'd have done was taken it to a shop and had the balance and Ujoints checked... BEFORE I made 53 adjustments to the pinion angle. :>)

Size matters!

Norwood is 45.25" from end of output shaft to bolt face of the rear yoke. :D

Give me center to center of eyelets and give me an idea of what size you will need from center to center. Don't think he sold it yet but I'll shoot him a text right now.

But it cost me $75! That's 15 hours labor in my shop! :lol:

It was only 12 or so........:sieg:

Without a doubt the rear eye leaf bushings have had a noticeable difference of the feel of the car. More so than I ever imagined. Besides the lateral cornering improvement the car is tracking differently on the freeway now (increased sensitivity and following contours) and I suspect they're the reason.

I also checked the rear yoke for lateral movement between the end stops, there's about a 1/32" an inch, 3/64th absolute max.

Now to determine if the driveline length and/or pinion angle is the remaining source. The driveline shop didn't think the length was an issue though I still think another 1/2" would be ideal......FWIW. He also spoke very highly of Roy's Differentials who did the gear swap.

I wouldn't get too hung up on the 1/32nd of an inch....


Think about what the ujoints are there for... the rear end is going up and down like a friggin yo-yo... it's moving side to side... it's got one wheel up and one wheel down with roll... and the motor is shaking around on it's rubber mounts and ditto the transmission. In other words -- there's a whole lotta moving going on...


In your case - it might be a Whole lotta Shakin'... but that's an Elvis problem.

You might never find the last harmonic going on. It could be the trans - it could be the flywheel... it could be a wheel and tire -- and it could be a whole combination of things rotational.

The thing is -- you've been able to move the harmonic around - up or down the RPM range... with your pinion movements - so you would think it's drivetrain related...


Now we'll get into something that is actually drive line related... which is the type of driveline you're using versus the actual rpms it's running at. I can't remember all the detail -- but you have to calc your rpm's that the driveline is running at -- and the diameter of the shaft needs to be matched or you get a harmonic set up.

Damned if I can remember what it's even called -- or where I've read about it -- etc but it's there somewhere on the Internet. And it may be something Ron Sutton knows about - or someone else on here.

Thanks to Blake's mention of Mark Williams........

Critical speed is the speed at which a spinning shaft will become unstable. This is one of the single largest factors in driveshaft selection. When the whirling frequency and the natural frequency coincide, any vibrations will be multiplied. So much that the shaft may self destruct. Another way to think of this is that if a shaft naturally vibrates at 130 times a second, and one point on the shaft passes through 0 degrees 130 times a second (7800 RPM) then the shaft has hit a critical speed. There are several ways to raise the critical speed of a driveshaft. You can make it lighter, stiffer, or increase diameter without increasing weight. This is the reason carbon fiber makes a good driveshaft, it is stiff and light and can be made to any diameter or wall thickness. Aluminum, while it has a very good critical speed is not quite as strong as steel. Steel, with good strength characteristics will have a lower critical speed.
http://www.markwilliams.com/Images/critspeed.jpg

This??

http://www.chevyhardcore.com/tech-st...for-your-ride/