1QUIKWS6

iTrader: (61)

ninobrn99-

If you rev your car up to say 6000 while not in gear - do you feel any vibration?

ninobrn99

iTrader: (8)

havent tried it..good point. guess ill have the wife check it out tomorrow

1QUIKWS6

iTrader: (61)

Guys, I did a little more in depth searching and found this thread:

U-Joint Angle Question

It talks about Critical Speed of the DS being the problem with vibration. It also references the following links:

http://www.fordmuscle.com/archives/2...ns/index.shtml

http://www2.dana.com/expert/wc.dll?hvtss~Decrits~

I don't know why I didn't think of this before (being a Mechanical Engineer and all ) but I will definitely be seriously looking into this as my vibration problem...

-Jay-

1QUIKWS6

iTrader: (61)

Directly from the DANA Site:

IMPORTANT CRITICAL SPEED INFORMATION:

A properly balanced driveshaft can experience severe vibrations if its normal operating speed is above its "safe operating speed ". Make sure you read, understand and follow the following recommendations:

1. Check the "SAFE OPERATING SPEED (RPM)" window on the following screen. Make sure your driveshaft cannot exceed that RPM. (Remember, in a vehicle or machine with an overdrive transmission, the driveshaft will rotate faster than the engine when the transmission is in overdrive). A driveshaft that has the potential of operating above this "safe operating speed" could fail and could be thrown from under the vehicle or machine, which could cause serious injury or death to persons nearby.

2. The twice per revolution vibration characteristics of a cardan U-joint, operating at an angle, can produce a minor vibration if normal operating speed of the driveshaft is near 1/2 of its true critical speed. If your driveshaft is operating at or near the "1/2 OF TRUE CRITICAL SPEED ________" figure on the following screen, and you believe you are experiencing this type of vibration, we suggest you try one or all of the following:

A. Re-check the balance and runout of the driveshaft, because unbalance is the major factor in 1/2 critical virbations. Reducing unbalance may cure this type of vibration problem.

B. Disconnect one end of the driveshaft, rotate the driveshaft 180 degrees and re-install it.

C. Reduce the u-joint operating angles of the driveshaft. (Remember to keep them equal as you change them).

D. Disconnect the driveshaft and remove the end yoke from the transmission or axle. Rotate the end yoke approximately 90 degrees and re-install it (torque the nut to specifications). Re-install the driveshaft.

E. Redesign the driveshaft(s) in the vehicle. Change to multiple driveshafts or change the length and/or tube diameter(s) of existing driveshafts to move the 1/2 critical speed of the assembly well out of the normal operating RPM of the vehicle. In short, you never want the 1/2 critical speed of the driveshaft to occur within the 50 to 70 MPH range of the vehicle.

3. An UNBALANCED driveshaft can experience a critical speed failure, in your balancer, at an RPM that is lower than the "SAFE OPERATING SPEED (RPM)" figure shown on the following screen.

Warning

Before spinning an UNBALANCED driveshaft in your balancer, check the "MAX. UNBALANCED DRIVESHAFT RPM____" window, on the following screen. Exceeding this RPM could cause failure in your balancer, which could damage your balancer and could cause serious injury or death to anyone operating your balancer or to anyone near your balancer. If the final balancing speed of this driveshaft is GREATER than the "MAX. UNBALANCED DRIVESHAFT RPM, _______", we recommend pre-balancing the driveshaft at THE "MAX. UNBALANCED DRIVESHAFT RPM______ before attempting to spin it to the final balance speed.

This is from the second link in my post above. The second page of this info contains a calculator to determine your DS Critical Speed

-Jay-

1QUIKWS6

iTrader: (61)

Specifically this point:

E. Redesign the driveshaft(s) in the vehicle. Change to multiple driveshafts or change the length and/or tube diameter(s) of existing driveshafts to move the 1/2 critical speed of the assembly well out of the normal operating RPM of the vehicle. In short, you never want the 1/2 critical speed of the driveshaft to occur within the 50 to 70 MPH range of the vehicle.

Seems as if every one of us is having problems around the same speed - we need to get the numbers calculated for the actual RPM's we are seeing at this speed which is going to be dependent on a couple variables for each different case:

A4 or M6 Gear Ratio
Rear Gear Ratio
Diameter of Tires

This will tell us if; due to modifications we have moved the RPM's in the 70mph and up range within the 1/2 Critical Speed of the DS we are each using. As you can see, you can change the 1/2 Critical Speed of the DS by altering the style DS used, and/or Length, and/or Dia. Some of us have already changed some of these variables by going with an aftermarket DS (and some of us may have to change out our stock DS for a different dia. DS to compensate for other driveline changes we have made that has altered our RPM's at a given speed from stock configuration).

In most cases, the only thing we will be able to alter is the Dia. of the DS in order to change the 1/2 Critical Speed to a more favorable number with each of our individual combo's

I'm going to get to the bottom of this if it kills me...

OK, could someone direct me to the thread or the area that has the RPM calculator?

-Jay-

ninobrn99

iTrader: (8)

Im reading the link from dana. im not sure how long my driveshaft is. going by the other guys post in the first link, i used 57". My safe rpm is4721, 1/2 True Critical Speed(RPM) 3,497, and Maximum Unbalanced Driveshaft(RPM)
3916
1. is this right?
2. what does it mean?

its a D style DS right?

1QUIKWS6

iTrader: (61)

A car typically takes 5 yrs to engineer - believe it or not, there are a lot of complicated calculations/design parameters that go into the factory choosing certain components, materials used, dimensions, geometry, etc. to all work in harmony.

We all go and change many of these factors such as rear gearing, suspension geometry and expect them to STILL work in harmony. In the old days changing an item such as rear gearing did not have as large of an effect because the tranny's were not of the OD version.

It appears this is not the case with newer cars...

1QUIKWS6

iTrader: (61)

I'm not home to check my DS right now, but I seem to remember a length of the stock DS in the 40" range from U-joint centerline to U-Joint centerline, not 57"????

I also have (2) different DS with (2) different OD's which I can't remember either, also don't know the Series of U-Joint that was used in either (both have HD Spicer U-Joints) - if you notice the 2nd page of the calculator asks what series u-joint you are using.

So I have to wait till I get home to get accurate data.

And yes, the DS style we have is 'D'

After we get accurate data to input into the calculator we also have to figure what are individual RPM's are with our combo's at the speed that we notice the vibration - then check and see if the 1/2 Critical Speed of the DS falls in this range - if it does, we would need to change one of the variables mentioned on the DS to get the 1/2 Critical Speed out of this range.

From what I can tell, the Max Safe Unbalanced Speed & Max Safe Operating Speed they refer to is pertinant to an unbalanced/new DS and is only important if you are a company that balances DS - they would not want to exceed this RPM with their balancing equip. otherwise damage to the equip. may happen...

When I input guesses of 40" long, 3" dia. and 1310 series U-joints I'm getting values in the 6000 range - which sounds more realistic for the rpm's that our cars operate in.

ninobrn99

iTrader: (8)

using 40" and 3.5 dia. and a 1350 im getting
Safe Operating Speed:
5000
1/2 True Critical Speed(RPM)
7,101
Maximum Unbalanced Driveshaft(RPM)
5000

does that sound right?

1QUIKWS6

iTrader: (61)

Sounds a lot better - now you have to find out what RPM your DS is actually operating at when you notice the vibration and see if it falls around the 7101 1/2 Critical speed that was calculated.

The first link has some excellent suggestions on items to check from engine on back to rear that could cause vibration. The Driveline section (shown below) is of particular interest:

Transmission: There is not much within a transmission itself, manual or automatic, that will cause a vibration without any other symptoms, such as poor shifting or slipping. However, as mentioned above, a pressure plate that is out of balance can cause a vibration. Pressure plates are supposed to be neutrally balanced from the manufacturer, but they rarely are exactly zero. If you experience a vibration after installing a new clutch, the pressure plate could be the problem. Have it matched balanced to the old one.

Other transmission areas to check:
Loose or misaligned bellhousing.
Worn or missing pilot bushing/bearing.
Worn tailshaft bushing.

Driveshaft, Rearend gears, and pinion angles: Driveshafts also need to be balanced. However if the driveshaft is damaged, or bent, it wont spin true and result in a vibration. Most factory driveshafts are "phased" with the rear pinion yoke. Usually there is yellow or other colored paint marks on the driveshaft and pinion yoke to designate the phasing. If you've had the driveshaft out recently, try reinstalling it 180 deg. over and see if it clears up the vibration. Worn u-joints will certainly cause a vibration and "clunking" upon braking or acceleration. Check them periodically.

While rearend gear problems don't typically manifest themselves in a vibration, gear ratio changes do contribute to certain types of driveline vibrations. Actually the vibrations are a result of the change in speed of the driveshaft as a result of a gear ratio change. The length, diameter, composition, and angle of a driveshaft, as well as the final gear ratio, determine what rpm (technically called the "half critical" speed) at which the driveshaft will experience a natural vibration. (Incidentally, critical speed, is a physical term for the speed at which a rotating shaft begins to wobble and become unstable As you can imagine, this can be a very dangerous condition for a driveshaft. Fortunately for most driveshafts, this does not occur until well over 10,000 rpm.) All driveshafts have a certain level of vibration, but with the typical factory gear ratios of 3.27 and lower, the vibration may not occur until above 5000 engine rpm - well beyond the typical sustained driving rpm. Numerically higher gear ratios will bring this range lower. So if you install a set of 4.56 gears and suddenly feel a vibration while cruising on the freeway at 3000 rpm, it is most certainly due to the gearset lowering the the half-critcial speed of the driveshaft. Aluminum driveshafts do a better job at dampening vibrations than their steel counterparts. If you've isolated a particular vibration as being due to a gear ratio change, an aluminum driveshaft may help out.

Excessively lowered (or raised) vehicles are prone to driveline vibrations due to the severe angles placed on the driveshaft and u-joints. The ideal angle of the driveshaft should be between 0 and 3 degrees sloping downwards from the transmission to the rearend. To measure the driveline angle, use a degree finder to measure the angle of the driveshaft (wheels must be on the ground or loaded on a lift.) Then measure the angles of the front slip yoke, and the rear pinion yoke and determine the average of the two. Subtract the driveshaft angle from the average of the two yokes and that is the static operating angle of the driveshaft. If you suspect a driveshaft angle problem as the cause of the vibration, find a good driveline shop that can help you properly setup the correct geometry.

If you read the forum thread and the links, you see that they do say that proper DS balance and runout is important to eliminating vibrations. Thing is, how many of us EVER had a vibration problem with the stock DS BEFORE we started modifying components? I know I didn't. And this is even with the mass-produced factory DS.

With the aftermarket DS that I bought, that is supposed to be of high quality and highly accurate as to balance and runout, I still have the vibration problem - which leads me to believe that in my case the DS balance/runout is not the problem.

ninobrn99

iTrader: (8)

same here. i dont think its the DS either. The clutch and flywheel were balanced. I can try turning it 180 and see if that helps as well as my pinion angle...i think that will clear up most of, if not all of it... i also gotta redo the exhaust since its resting on the tunnel brace for my TA.

JSmee99T/A

iTrader: (15)

just had my drive shaft balanced today and my problem isnt the ds either, i also have new u joints. My problem only occurs when i decelerate and it really kicks in when i put the car in neutral. this is frustrating.

Ws6Extreme

iTrader: (8)

I guess I get to join this club too. Mine is at about 70 to 80 MPH. After all this reading I have a lot of catching up to do. Thanks for all the information everyone.

ninobrn99

iTrader: (8)

list your mods pls..

JB00SS

well guys i found my problem. flywheel. Me and a buddy put the rear on jack stands and run it up to 65mph where the vibration is. while doing this we both heard a growl from the tranny area. oh and the vibration/growl was also also at 40-45mph @ 2,000-2,500rpm and 55-65mph @ 2,000-2,500rpm. it was very noticeable that the noise and vibration was coming from the tranny. as sat in the car giving it throttle the car shook and vibrated just like it does on the road. we did this in drive and park on the stands and in park it vibrated evertime at the above places.

Sooo, we put the car back on the ground, popped the hood and started the car back up. looking around the engine bay and watching the motor we noticed it was shaking/rocking a little more than what it has been since the cam. nothing violent by no means. the underdrive pulley (ASP) was wobbling and the idler tensioner was knocking a little. shut car off, jack it up, check pulley bolt. i undo the view port thingy on the bellhousing of the tranny to hold the flywheel while my buddy checks the bolt. It's tight 250lbs on the TQ wrench.

takign maglite and looking up in view port while he rotates motor, i see the bolts holding from flywheel to stall twisted. stick finger in view port feel around bottom of bellhousing, metal shavings. look at all the bolts on flywheel, twisted and looking like they could snap any minute. my buddy looks at same thing and agrees.

I dont think the crankshaft is damaged but not for sure. pulley was wobbling but nothing violent just it was not straight. i have 50psi oil pressure at idle and from driving the car since DEC with cam have never seen oil pressure drop. as for the flywheel yeah its stock and should have replaced it when i did the stall. as far as the tranny making growling noises, ???? it still shifts fine no slippage, could be sun gear getting chewed up??? I have some soul searching to do when i pull the tranny out...

jyeager

You have no direct evidence yet of any damage to the tranny or crank. The metal you found in the inspection cover must be from the starter gear teeth. Were they jacked up by the starter gear?

If the converter was still bolted to the flexplate, even if the bolts were mangled there shouldn't be metal fragments generated.

That's all just speculation I suppose. Once you pull things apart you'll see what's up.

Btw, flywheels are only on manual cars, flexplates are on automatic cars.
I'm glad you found your problem.

ninobrn99

iTrader: (8)

hmm..i just had my flywheel balanced and resurfaced as well as a new clutch installed and i had the vibrations since before then. My wife said that after getting my relocation brackets installed, it helped, so once the pinion angle gets adjusted, we'll see. hope that was your issue.

JB00SS

yeah flexplates sorry! you knew what i was talking about. with it in park and revving it up slowly when it got to those 2 spots it did the "wom wom wom" growling noise that i have been talking about. i assume that the motor is making more than the tranny and flexplate can hold. i havent been to the dyno but i have the same mods as my 2 buddys M6 cars and they both put down 410ish at the wheels. we all have the same cam same bolt ons. so is the motor putting out 450 + ???

what do i do with the tranny? is it worth having it built up locally or buy new one made to handle the HP? it totally sucks cause it is just now getting warm and nice outside, cruising starts up the first friday of April, and i have no money to blow on new tranny or even have existing on gone through...oh well you guys dont want to listen to me whine...

jyeager

Well, we haven't established yet that your transmission is bad. Remove it and make sure the input shaft looks OK and doesn't have runout (movement up/down).

Replace those bad bolts and the flexplate if it's bent or damaged. Also check the converter and make sure it's good.

Cars always break down when you need them most....just get it fixed and you can be happy again.

btw, there's no way you are putting down too much power to do this. Something was defective or installed wrong.

ninobrn99

iTrader: (8)

anyone have any luck solving this enigma??