94tbird

im having a weird problem with my car. my mods are in the sig.

When the problem started:
we had just installed the Spec Stage 3+ Clutch, Spec Aluminum Flywheel, and the Powerhouse Aluminum Driveshaft. This did not cause my current noise, but it did result in the driveshaft scraping the tunnel. The fix for this was to install an adjustable control arm. This would allow us to reset the pinion angle. the desired angle is negative 3 degrees for drag racingas im told.

We ordered the CHE Double Adjustable Upper Control arm and the CHE Anti Squat Brackets (Equivilent to the BMR LCA Relocation Brackets). We installed these items and using the adjustable UCA, we set the pinion angle to negative 3 degrees in relation to the driveshaft. The driveshaft measured at 3 degrees and the pinion at 0 degrees. This is the correct setting for drag racing as i was told by CHE and many members on TMS and Mod Fords. Here is where my current problem starts:

The noise is best described as a whirring or a wobbly noise when accelerating. it is most noticable at speeds of 60-70mph but does happen around 40mph as well. seems to get louder with speed. There seems to be no power loss or loss of acceleration power. ive had the car up to aprox 150mph and there is no vibration in the driveshaft at all.

some things i tested were:

Car out of gear:
Revving the engine can not reproduce the sound

Car in gear:
Accel: the car will make this noise on slight accel but will eventually get drowned out by the exhaust until higher speeds are reached. even on the slightest accel the noise will appear. as soon as i release the throttle, it dissapeares completely.

I set cruise control to 70mph on the highway. when the road is completely flat, and the computer is maintaining the speed, it makes this noise that is def coming from the rear of the car. with the cruise set and gonig slightly downhill, the noise goes away completely. if going slightly uphil the exhaust will almost drown it out but it can still sort of be heard. definately more noticable with the windows up than down. even on the slightest accel the noise will appear. as soon as i release the throttle, it dissapeares completely.

Decel:
There is no noise on Decel.

Today i had the car on the lift. There are no rubbing marks or anything on the driveshaft. We accelerated the car while on the lift suspended in the air and it did not make any noise. We used a stethascope on the rear end and my buddy tells me it is quiet with no noise whatsoever coming from it. we then lowered the car and using a floor jack, raised only the rear end in the air to keep the rear suspension loaded. once again this did not reproduce the noise. we did note wit hthe car in the air the driveshaft is spinning with no vibration and is spinning perfectly smooth.

I called JDM and spoke to Jim Jr and he said they have done 5 or 6 high powered cars thus far with aluminum driveshafts and they all have had noise, including their own car.

I spoke with someone at Powerhouse and he said that 4.10 gears will inevitable have noise to them. its jsut the factory bushings on the LCA's and UCA are rubber so they deflect and deaden the noise. the bushing on the new LCA's and UCA are poly urethane and are much stiffer and will transfer the noise through the drivetrain. The aluminum driveshaft sort of acts liek a tuning fork, further transfering the noise. This seems liek the most likely cause to me but why wont it reproduce the noise when the wheels arent touching the ground?

Does anyone have any idea or insight into this matter? It is rather annoying!

RadBOSS

A WAG on my part but are you sure the drive shaft is not out of balance? Try swapping with the stock one to see if the noise goes away.

Try indexing the rear driveshaft flange 90 0r 180 degrees on the pinion flange. Does it register against the pinion flange completely?

Any chance the u-joint are defective? I know they are new, but ...

Aluminum being softer than steel would make me intuitively think it would not transmit noise as well as steel. I don't have one to compare to, so I don't know.

On coast down in netural from about 80 MPH, any speeds with the noise or virbation?

The CHE UCA and LCA. Spherical rod ends on each end? ... expect noise and harshness .... you just eliminated all isolation.

94tbird

The driveshaft is not unbalanced upon visual inspection. i had it up to about 80mph on the lift with my buddy watchnig it and its as true as can be he said. ive also had it to 150mph on the street with no issues. it was balanced before it was shipped. i can see the weights on the unit itself. i do not think it is out of balance. i have no vibration issues that are associated with the shaft being unbalanced.

im not exactly sure what you mean by "Try indexing the rear driveshaft flange 90 0r 180 degrees on the pinion flange. Does it register against the pinion flange completely?"

im not sure about the u-joints but i think they would make noise regardless of throttle response.

no noise on decel with the car in or out of gear

they are poly bushings, not spherical

RadBOSS

Driveline is usually spin balanced as an assembly from the factory. That means if you rotated the drive shaft / flange 180 degrees to the pinion flange, the driveline will then be slightly out of balance. The shop manual advises you to make a indexing mark before disassembly, so you can put it back together the way it was. But you are dealing with a drive dhaft that was not balanced with the rest of your drive line, so you have nothing to register to other than to try it in different positions and see if there is any difference.

By registering I mean are the faces of the pinion flange and the drive shaft completely mated face to face.

You still can rule out the driveshaft by swaping back to your stock one.

Sounds like you did so many mod's at one time there is no way to isolate which one is the culprit very easiy. The scientific method applies here. Drive shaft swap will at least rule out or in that one. Sounds like you are still using the factory LCA?

Might also check TSB 05-20-2. Maybe the rear diff is spontaneously having a problem.

94tbird

i get what you are saying now, but that only applies to reinsatalling the factory driveshaft. you cannot index something when changing one of the pieces you are indexing. no the factory LCA.s have been changed as stated in my mod list, BMR Tubular LCA's with relocation brackets.

The TSB is useless to me. there is almost no stock parts back there haha. they would laugh

panhandlegt

I have the same noise...it only happened once I installed the driveshaft. Im starting to get used to it.

94tbird

its not so bad with the windows down and the radio on, but with the windows up its really annoying

rygenstormlocke

"Accel: the car will make this noise on slight accel but will eventually get drowned out by the exhaust until higher speeds are reached. even on the slightest accel the noise will appear. as soon as i release the throttle, it dissapeares completely.

I set cruise control to 70mph on the highway. when the road is completely flat, and the computer is maintaining the speed, it makes this noise that is def coming from the rear of the car. with the cruise set and gonig slightly downhill, the noise goes away completely. if going slightly uphil the exhaust will almost drown it out but it can still sort of be heard. definately more noticable with the windows up than down. even on the slightest accel the noise will appear. as soon as i release the throttle, it dissapeares completely."

I have this exact same thing, exactly the same. And with the windows up, definitely more noticable.

I can't weigh in on the DS being out of balance, but after making many suspension modifications I can say this.

I started with a built up rear end, changed out my gears and lsd....got gear whine at varying points accel/decel.

Accepted it for what it is, I want to race my car....and build it up...it's gonna make noise.

Then install the PH/CHE LCA's. Ok, no squeaking like most people said for LCA's, but now gear whine is significantly louder, and now noticed more road noise in the car. Did some research, talked to my shop, some vets at the track, all indicated this is normal.

Then had PH install the UCA, now that one transferred a good bit of road noise, and a little more gear whine noise.

I don't think its the drive shaft, I've been in a car with a PH DS and it was quiet, so after being in that car, realized all my noise is from my suspension mods.

If your LCA's are adjustable, they are known to be more noisy than the fixed LCA's.

94tbird

Thank you for taking the time to explain your experiences. im sure there is nothing wrong now with all of the feedback i have gotten from you, CHE, Powerhouse, and others. It has to be road noise being transferred up the drivetrain. I appreciate it man

rygenstormlocke

Hey, on a related note. I'm going to be doing an extensive dynomat install in the trunk and under the back seat in an effort to reduce this noise in the car. I'll keep you posted.

RKNMACH

I'd be interested in hearing about that also - they did a lousy job of noise reduction when they built these cars. Just like to take the edge of the noise. Thanks.

94tbird

ill look for your install thread on this. if it helps im all for it