New rear end - same issue

[stanger_missle]

Well I finally bit the bullet on my 95 GT. I decided the best way to get rid of my horrific rear end vibration was to replace everything. New 31 spline axles, axle bearings, axle seals, carrier, carrier bearings, ring and pinion, pinion seal and bearing. Everything but the axle housing itself was replaced because it was all really worn. After I took it to a shop to setup the new gears (tried myself first but failed miserably), I STILL have a vibration above 40 MPH. I'm thinking driveshaft now. What do you guys think? This thing is sucking me dry hahaha...

 

[sn95gtvert]

have you pulled the dog bone off yet? also try unbolting the ds and rotationg it 180 degrees.

 

[toyman]

Actually, there should be a yellow (IIRC) mark on the D/S rear flange from the factory for matching purposes. If you don't see that try rotating 180* as suggested. Failing that work in 90* increments. If that doesn't work consider getting an aluminum D/S. I would never have suspected the differential gears as being a vibration source. The other thing to consider is a bad tire or wheel. Have you had the wheels off for rotation or balancing since the vibration started? Have you checked the U-joints? With respect to the "dog bone". Unless you've changed gears you might want to leave that in place. It's function is to deal with neutralizing the natural harmonics created in the drive line with stock gears.

 

[sn95gtvert]

+1 to everything said above.

 

[95PGTTech]

Actually, there should be a yellow (IIRC) mark on the D/S rear flange from the factory for matching purposes. If you don't see that try rotating 180* as suggested. Failing that work in 90* increments. If that doesn't work consider getting an aluminum D/S. I would never have suspected the differential gears as being a vibration source. The other thing to consider is a bad tire or wheel. Have you had the wheels off for rotation or balancing since the vibration started? Have you checked the U-joints? With respect to the "dog bone". Unless you've changed gears you might want to leave that in place. It's function is to deal with neutralizing the natural harmonics created in the drive line with stock gears.

When he had the pinion bearing replaced, or replaced the pinion bearing and seal himself, that made the factory markings useless if the corresponding components were not indexed, as the pinion flange was moved.

Remove the driveshaft, get it balanced. Then install it, and mark it. If vibration is still present, rotate 90 degrees and repeat as necessary. If it is still present in all four positions, you're going to need to do some more involved stuff like getting the wheels and tires balanced, measuring the pinion angle, and measuring the straightness of the axle tubes.

 

[stanger_missle]

Well, the guy who owned the car before me removed the dogbone before I bought it. As far as the driveshaft, who knows? Its a very likely possibility that it wasn't indexed properly at the shop. When I took it off, there were no factory indexing marks. Hell, I don't even know if it is the original driveshaft. I do however, have another driveshaft from a 99 V6 5 speed that I might try.

The vibration happens at all RPMs and happens regardless if the clutch is engaged or not. Road speed determines the frequency of the vibrations. Starts at about 40 MPH and gets worse the faster I go. Had it up to 85 the other day and it was pretty bad.

Man I'm going to be angry if the axle tubes are bent. I just dropped about a grand into this thing (parts and labor) to try and cure this... I'll check the balance of the rims and tires next. It also has wheel spacers (yuck).

 

[badass96gt]

Check the wheels first since thats the cheapest, also when you put the wheels back on try it without the spacers if you can. Then if they are good either have the DS balanced of try the 99 shaft you have.

 

[Rice_slayer]

My car used to have a HORRENDOUS vibration from 80mph+ that would shake the whole car and make the clutch/gas/brake pedals feel like they would fall off. It was my driveshaft out of balance, replaced it with an FRPP driveshaft and have gone 100MPH+ with no strange vibrations...

 

[toyman]

The vibration happens at all RPMs and happens regardless if the clutch is engaged or not. Road speed determines the frequency of the vibrations. Starts at about 40 MPH and gets worse the faster I go. Had it up to 85 the other day and it was pretty bad.

Hold on. Road speed usually is indicative of a wheel or tire issue. However, if you are equating road speed to rpm's then it's starting to sound like the HB may be the issue since you said it occurs at all rpm's. Check to see if any rubber is protruding between the inner hub and the engine or if there is any wobble in the HB. If this is the source serious engine damage may occur if you continue to drive the car at speed.

 

[stanger_missle]

The vibration happens at all RPMs and happens regardless if the clutch is engaged or not. Road speed determines the frequency of the vibrations. Starts at about 40 MPH and gets worse the faster I go. Had it up to 85 the other day and it was pretty bad.

Hold on. Road speed usually is indicative of a wheel or tire issue. However, if you are equating road speed to rpm's then it's starting to sound like the HB may be the issue since you said it occurs at all rpm's. Check to see if any rubber is protruding between the inner hub and the engine or if there is any wobble in the HB. If this is the source serious engine damage may occur if you continue to drive the car at speed.

I just meant that it doesn't matter what RPM the engine is at, the vibration is there at anything over 40 MPH. Its nice and smooth when revving it at a stoplight. And it doesn't matter if I'm in 4th at 60 or 5th, its the same...

 

[stanger_missle]

My car used to have a HORRENDOUS vibration from 80mph+ that would shake the whole car and make the clutch/gas/brake pedals feel like they would fall off. It was my driveshaft out of balance, replaced it with an FRPP driveshaft and have gone 100MPH+ with no strange vibrations...

Did your shifter shake when you got up to speed?

 

[MustangChris]

i think balancing the tires, balancing the driveshaft, and replacing the u joints were 3 much more affordable options to try first, before the rear end build.

 

[stanger_missle]

i think balancing the tires, balancing the driveshaft, and replacing the u joints were 3 much more affordable options to try first, before the rear end build.

I was thinking that too before I pulled it all apart. Axle bearings were shot as well as the carrier bearings. The axle shafts were pretty rough with pitting and were pretty worn. The gears were really worn. Had lots of scarring on both the drive and coast sides of the teeth. The carrier itself was broken along the pinion shaft bolt hole and the pinion shaft was drilled out at one point.

I figured it would all have to be replaced in the future so i would just hit it all at once while I had the money...

 

[ryclef331]

I see you have adjustable control arms. Try this....get the car to the speed it vibes at....Now, you're looking for 3 things....How bad is the vibe AT THAT SPEED when you A) acellerate, B) decel, and C) just cruise. My money is you'll find a difference in all three. With cruise being the middle of the two. If the vibes are WORSE when you accelerate, your PINION ANGLE is too high. If its worse when you slow down...your pinion angle is too low. When you decel, MAKE SURE the clutch is OUT. This loads the rear suspension and makes the rear end react. When you get on it, the pinion wants to move up due to the pinion trying to climb the ring gear. This causes the rear end to attempt to rotate the pinion snout upwards thus changing your pinion angle. Ideally, you want pinion angle to be on the same plane as the crankshaft when you are on the throttle. For MOST applications, depending on the type of bushings used in the control arms, this is 3 degrees down...NOW....that doesn't mean 3 degrees down from "level." It means 3 degrees LESS that what the crankshaft is. The actual angle of thee driveshaft is not an issue. Its the angle of the pinion compared to the crank. How do you get that measurement you ask? Hold on baby birds, I'll feed you....

With the car in the air and WITH THE WEIGHT ON THE SUSPENSION (i.e. ramps under the front and jackstands under the axle) and Using an angle finder, place it flat against the face of harmonic balancer....write that angle down. the engine tilts back slightly so lets say you record 5 degrees. Now, measure the angle of the verticle face of the pinon flange (you may wanna unhook the driveshaft and swing it out of the way a bit for this)...lets say you record a -2 degrees....the opposite direction of tilt that the crank was. Your pinion angle would then be 7 degrees. Still with me? To PROPERLY ADJUST THIS, unhook the passenger side upper control arm and let it swing free. Loosen the nuts on the upper driver's side. Now lengthen the driver's side arm while checking the angle off the pinion flange until you get a +2 degree reading. The difference between your crank angle and pinion is 3 degrees....well within your ball park. Loosen the adjustment nuts on the passenger control arm and adjust it to get the bolt to slide in freely while reinstalling it. Doing it this way prevents any sort of binding on the rear suspension that will prevent any erratic handling. If you want to get REAL technical, put someone's a$$ in the driver's seat or something while you do all this. It will simulate the car's "race weight" if you will.

EVerything above is FREE. from what you've done and what you've described, THIS is what you issue MOST likely is. There is a distinct difference in a "wheel balance" problem and a driveline vibe. A driveline vibe is much more intense and a higher frequency. Give it a shot before spending money on parts. If you have any confusion on anything i posted, check out www.baselinesuspensions.com and read their tutorials. GREAT information on getting a rear suspension set up correctly.

 

[95PGTTech]

Does the shake happen in your ass (seat) or steering wheel?
I agree with this is not a driveline issue if it is speed related.

 

[ryclef331]

Does the shake happen in your a*s (seat) or steering wheel?
I agree with this is not a driveline issue if it is speed related.

Is the driveshaft NOT part of the driveline and spins according to the speed the car is going? I'll put $20 up on via paypal that his issue IS driveline related...as I posted above.

 

[Rice_slayer]

My car used to have a HORRENDOUS vibration from 80mph+ that would shake the whole car and make the clutch/gas/brake pedals feel like they would fall off. It was my driveshaft out of balance, replaced it with an FRPP driveshaft and have gone 100MPH+ with no strange vibrations...

Did your shifter shake when you got up to speed?

Yep, whole car did, seemed like it would rattle apart. I changed yolks on the driveshaft and the one I put on was like 1/4 of an inch shorter than the factory one, screwed the whole driveshaft up lol. After getting tires balanced and still having the vibration, I wanted an aluminum driveshaft, ordered it, put it in, took it too 90mph with no vibrations at all .

 

[95PGTTech]

Does the shake happen in your a*s (seat) or steering wheel?
I agree with this is not a driveline issue if it is speed related.

Is the driveshaft NOT part of the driveline and spins according to the speed the car is going? I'll put $20 up on via paypal that his issue IS driveline related...as I posted above.

good catch. I should have said engine. a driveshaft issue will increase with vehicle speed, not rpm.

 

[ryclef331]

Does the shake happen in your a*s (seat) or steering wheel?
I agree with this is not a driveline issue if it is speed related.

Is the driveshaft NOT part of the driveline and spins according to the speed the car is going? I'll put $20 up on via paypal that his issue IS driveline related...as I posted above.

good catch. I should have said engine. a driveshaft issue will increase with vehicle speed, not rpm.

I gotcha. no worries.

TO THE OP...CHECK THE PINION ANGLE BEFORE YOU SPEND ANOTHER DIME!

 

[stanger_missle]

Well guys, I think I found the issue...

A few days ago, I spent almost 2 hours road testing the car in various situations. Accel, decel, coast, clutch in, clutch out, etc, etc... I was going to swap the spare driveshaft to see if that would fix it but I found a big dent in it, so that was a no-go. I checked the pinion angle and found it was OK. I don't have adjustable control arms BTW, just econo UPR upper and lowers. All the bushings looked OK as well. I bought an FRPP aluminum driveshaft and swapped the stock driveshaft out. I found the u-joint on the yoke end had some play and it had a bad "sticky" spot when moving it around. I also had the tires balanced and removed the wheel spacers, just to be sure. I don't know if it was one single issue or a combination of them all, but the car drives amazing now. Absolutely zero vibration from 0 to 90 MPH. It feels great to drive. I was making up reasons to myself to drive around today, just so I could get out and actually drive my car for once.

And then it happened...

I got that amazing feeling of actually enjoying driving my car. That hasn't happened since 2006 when I had my Cobra. Rowing trough the gears, hearing the exhaust bellow out that sweet pushrod V8 music. I must have looked retarded because I had a stupid grin on my face the whole time I was behind the wheel. A couple of weeks ago I replaced the Pro 5.0 shifter handle with a Kona Racing titanium handle and the cheap Bullitt knockoff knob with a Fatknob. That made a huge difference. You know that point where all the small irritating issues fall away and you reach pure driving zen? When you pray that stoplight will turn red just so you can row through the gears again? Amazing. I forgot the feeling a Mustang can give you....

Even though it was a trivial issue that haunted me for awhile, I just want to thank you guys who offered all the advice. And to think I was going to sell my Mustang...