vibration thread - aluminum driveshaft cures it!

Topic: vibration thread - aluminum driveshaft cures it! (Read 17611 times) previous topic - next topic

vibration thread - aluminum driveshaft cures it!

Reply #45 – February 28, 2012, 04:35:43 PM

Quote from: ThunderbirdSport302;382342

It's worth a shot. I don't think the rotors would be the culprit...or you'd feel the vibration at all speeds. But the d/s has hamonics, because it's long, slender, and spins at (now) higher rpm....the rotor don't have nearly as much torsional force on them...

Basically, what I'm trying to say...at a certain speed, the harmonic in your d/s causes it to come out of round a little...hence the vibration at a certain speed.

I read some detailed info on how exactly it happens, usually an aluminum d/s cures the issue...I guess better casting or extruding techniques or however an AL d/s is made...

Ive got an aluminum d/s from a CVPI...still needs cut down. If it was already, I'd loan it to you to test...I'm willing to bet that's the problem. lol

I'm thinking this is it. FWIW weather or not they will work the 93 MarkVIII has a nice one piece aluminum DS.

If its not that I'd bet its a slightly out of true axle like thunderjet302 suggests.

vibration thread - aluminum driveshaft cures it!

Reply #46 – February 28, 2012, 04:46:33 PM

The original driveshaft on my '86 (convertible) produced a noticeable, repeatable shimmy between 25 and 45 mph.
When I had to get a custom shaft made due to the Mark VII AOD (long story), the vibration went away completely.
The OEM driveshaft had 3 weights on it.

I wouldn't rule out a slightly bent axle shaft (or axle tube, for that matter) but the driveshaft, as noted, is likely the culprit.

vibration thread - aluminum driveshaft cures it!

Reply #47 – February 28, 2012, 05:16:16 PM

Well guys I think you are right about the DS. The driveshaft has been balanced. But the way I understand it, the steel driveshaft's reach a critical speed that causes the shaft to actually bend or deflect in the middle at a certain RPM. I'm not sure what is involved in balancing a driveshaft, but maybe when they balanced mine they did not spin it fast enough to reach this critical speed? I would think that once a DS was balanced, it should be balanced!

The bent axle would not surprise me, as this rearend came out of a TC in a junkyard. The car was not wrecked but it could be that someone dropped it with a forklift or something and bent an axle. However, the last guy that worked on the rearend for me did have the axles out and said they looked true...so who knows.

Quote

I don't think the rotors would be the culprit...or you'd feel the vibration at all speeds.

You are probably right, sir.

Geez I'm gonna go nuts trying to figure this out! :hick: Thanks again for all the ideas guys. I've been home today taking care of my little guy (has a cold). And in my spare time have been scouring the 'net looking for ideas.

I need to just go crawl under the car and keep looking for it...I will find it.

vibration thread - aluminum driveshaft cures it!

Reply #48 – February 28, 2012, 06:52:25 PM

Here's a vid of the vibration. You can really hear it around 82mph (speedo is off, that's actually about 76-77 mph). Its kinda hard to hear over the exhaust but is kind of a buzzing sound in the video. It seems like it is definately coming from something that is spinning because its not a constant thing. It has a cyclic pattern to it.

[video]http://s495.photobucket.com/albums/rr313/50tbrd88/?action=view¤t=SANY0009.mp4[/video]

vibration thread - aluminum driveshaft cures it!

Reply #49 – February 28, 2012, 08:36:50 PM

it's very possible that they didn't spin the shaft fast enough when balancing.. while the balancers typically do spin fast enough to pick up any balancing defects, the weight of the weld used to attach the weight (dumber sh*t has happened..) could have thrown it off just enough to effect the car at higher speeds.. long shot, but possible

vibration thread - aluminum driveshaft cures it!

Reply #50 – February 28, 2012, 08:41:18 PM

Yeah you can tell there is ANOTHER noise because of that "cyclic pattern". That's called a beat. In the exact sense that anyone normally uses that word. Two sounds with different but close frequencies, their waves combine in spots to form a louder sound that comes and goes when the waves meet up.

At least it doesn't start doing that until highway speed, not like it's completely undrivable for the time being.

vibration thread - aluminum driveshaft cures it!

Reply #51 – February 29, 2012, 08:33:22 AM

Quote from: ZondaC12;382400

Yeah you can tell there is ANOTHER noise because of that "cyclic pattern". That's called a beat. In the exact sense that anyone normally uses that word. Two sounds with different but close frequencies, their waves combine in spots to form a louder sound that comes and goes when the waves meet up.

At least it doesn't start doing that until highway speed, not like it's completely undrivable for the time being.

Yeah I agree it could be worse...it could do this at 45 or 50 mph. Last year when I took the car on Power Tour and had to do some interstate driving it was not pleasant! I am going again this year in June so I hope to have this vibration taken care of before then.

vibration thread - aluminum driveshaft cures it!

Reply #52 – February 29, 2012, 05:03:48 PM

Found an interesting article over on TCCOA.

By the way this reads, it is HIGHLY likely this vibration is caused by the driveshaft critical speed. I guess there may be a aluminum driveshaft in my future. I'm looking at getting one made by these guys.

Keep throwing money at it and eventually I will get it. Argh...

vibration thread - aluminum driveshaft cures it!

Reply #53 – February 29, 2012, 06:00:04 PM

I have been anxiously watching this thread! I've got a vibration at 70mph when ever it has just a light little bit of backpressure. The car has just at 100k on it and I've replaced ujoints, tail shaft bushing, checked for play in the rear, and so far nothing has improved it. So definitely looking forward to what you come up with.

vibration thread - aluminum driveshaft cures it!

Reply #54 – February 29, 2012, 06:56:38 PM

Mr Wilson. In my post i gave you some info and i did not mean to belittle anyone's mechanical ability. IE the rear axle builder. With that the noise i think is in the rotating shaft. Do you have the shaft with the big damper on the front like a TC Or Mustang??? They go bad and with you vibration i am leaning to the shaft after hearing you video. Also try this remove the rear axle pinion weight and then test the car at vibration speed. If it changes or moves the vibration up or down you will prove a shaft vibration. Also is your engine balanced that is is it stock or built??? It is very possible the engine is causing it but i dont think so. Replacing the shaft is the next thing i would do. Also remove the tail shaft weight on the tranny and drive the car and see if that changes it. I am willing to bet the shaft is vibrating at harmonics. But it could be caused by a component and not a balance issue. Normally end play in the axles would not cause that kind of vibration. Shaft balance is always critical the lower the numerical ratio you run in the final drive. This increases shaft speed by the ratio. It is directly proportional to it's speed. Good luck.

Example 2.73 to 3.73 the shaft spins faster and can set up a vibration harmonic. With the 2.73 the car would not vibrate because the shaft never was sent in to vibration. But the lower 3.73 could set up the harmonic quite easily. GOOD LUCK

vibration thread - aluminum driveshaft cures it!

Reply #55 – February 29, 2012, 09:22:04 PM

vibration thread - aluminum driveshaft cures it!

Reply #56 – March 01, 2012, 08:41:59 AM

Quote from: TOM Renzo;382509

Mr Wilson. In my post i gave you some info and i did not mean to belittle anyone's mechanical ability. IE the rear axle builder. With that the noise i think is in the rotating shaft. Do you have the shaft with the big damper on the front like a TC Or Mustang??? They go bad and with you vibration i am leaning to the shaft after hearing you video. Also try this remove the rear axle pinion weight and then test the car at vibration speed. If it changes or moves the vibration up or down you will prove a shaft vibration. Also is your engine balanced that is is it stock or built??? It is very possible the engine is causing it but i dont think so. Replacing the shaft is the next thing i would do. Also remove the tail shaft weight on the tranny and drive the car and see if that changes it. I am willing to bet the shaft is vibrating at harmonics. But it could be caused by a component and not a balance issue. Normally end play in the axles would not cause that kind of vibration. Shaft balance is always critical the lower the numerical ratio you run in the final drive. This increases shaft speed by the ratio. It is directly proportional to it's speed. Good luck.

Example 2.73 to 3.73 the shaft spins faster and can set up a vibration harmonic. With the 2.73 the car would not vibrate because the shaft never was sent in to vibration. But the lower 3.73 could set up the harmonic quite easily. GOOD LUCK

Thanks Tom. As far as motor goes it is the 100% stock 190,000 mile shortblock that I've just converted over to HO specs. The driveshaft is my stock T-bird 5.0 piece and yes the car orginally had 2.73 gears but now has 3.73's. So if this vibration exists now at 75 mph, that means before it would not have shown up at all with the original gears (theres no way my car would run 150 mph).

The driveshaft is just a normal old steel driveshaft, no dampers or anything. I'm going to try and turn the shaft 180 degrees on the and then if that does not work, remove the vibration damper on the rear axle. Like you said, if my vibration gets worse that should tell me its the DS. Obviously Ford knew there was chance for vibration on these foxes...why else would that have installed vibration dampers everywhere, lol.

Chances are that I will be ordering a custom aluminum shaft next month sometime. Happy B-day to me.

vibration thread - aluminum driveshaft cures it!

Reply #57 – March 01, 2012, 09:40:26 AM

Quote from: TOM Renzo;382509

Shaft balance is always critical the lower the numerical ratio you run in the final drive. This increases shaft speed by the ratio. It is directly proportional to it's speed. Good luck.

That would be higher numerical gears.

vibration thread - aluminum driveshaft cures it!

Reply #58 – March 01, 2012, 05:38:37 PM

The key is way back on the first page of the thread, the vibration is there in neutral or in gear. This means is it isolated to the output shaft in the T-5 to the wheels. With all the other information given I would say that it is definitely the in the DS as Tom has pointed out along with others. I had a FMS aluminum drive shaft in my Coupe and had the u-joints changed due to the rear unit going south. The car vibrated badly after that and it would change as the clocking on the DS changed. I got impatient and ordered a new FMS aluminum drive shaft and installed it. Took the car out for a spin and into triple digits with 3.73's gears it was smooth as room temperature butter.

I battled a similar problem in my Bird but fixed it by blowing up the 306 and beating up one of the AFE 185's with the valve head that separated from the stem. I am almost done with the 351W swap so hopefully it went away but something tells me the aluminum DS I had made by Driver Train Specialists in OKC is and has been the culprit the whole time. IF so I will be PM'ing Vinnie for the shop that built his and going that route. My car has a Tremec TKO in it and I went as far as to pull another TKO out of a known smooth running Mustang and still had the same issue. Had the rear end rebuilt at the Ford dealership, replaced all the rear control arms, swept the pinion angle, took the custom aluminum DS back to DTS to have it rebalanced although they said it was fine, and even had the wheels balanced on the car (never knew a shop could do that but there is one back home that can do it) to eliminate the rotating masses at the corners. You name it I did it all to no avail. I feel your pain man.

Darren

vibration thread - aluminum driveshaft cures it!

Reply #59 – March 01, 2012, 06:03:02 PM

Quote from: mcb82gt;382610

That would be higher numerical gears.

Sorry getting old. Thanks for correcting that WOW BUMMER!!!! TOTALLY EMBARRASSED!!!!!! D'OH!!!