Got the Shakes!

[slymo]

Hi folks,

 

New member, first post, hoping someone can help!

 

I bought a 11/2002 Subaru Outback 2.5 Manual and have a vibration issue.

From 0-30mph it is smooth, from 31-37mph there is a bad drumming and body vibe felt everywhere including a small amount in steering wheel. It occurs under load - no load - any gear - out of gear - brakes on or off - straight ahead or cornering but go over 37mph and it largely disappears.

This is a list of troubleshooting I have performed so far...

 

1) Two new tyres fitted and dynamically balanced on front, rears 50% tread - dynamically balanced

2) New brake pads and rotors all round - adjusted park brakes for no drag

3) All wheel alignment

4) Checked wheel bearings - no play

5) Switched front tyres to rear

6) Dropped tailshaft - u joints/centre bearing good - no play/notches

6) Swapped tailshaft from another car

7) All CV boots intact - minor play in inner joints - no clicking outers

 

I used a gopro to take under car videos at the vibe speed and found the entire rear diff + yolk and rear portion of the tailshaft is oscillating. The centre and front of the shaft is running true. I jammed spacers into the voids on the rear diff bushes and it made it a lot worse. Could it be the diff?

 

Sorry for the long post but I have been searching google for the last month and don't seem to find the exact same issue with a solution.

 

Cheers,

 

Simon

[heartless]

1) Two new tyres fitted and dynamically balanced on front, rears 50% tread - dynamically balanced

 

I dont know about your diff - I will leave that for others with more experience, but mismatched tires is a BIG no-no on an AWD Subaru.

 

All 4 tires need to be of a matching brand, type, inflation, and treadwear, and within 1/4 inch of circumference of each other or you can end up with transmission issues (torque bind)

[1 Lucky Texan]

yeah - tell us more about the tires.

 

also, there have been people in the past that swapped (or bought cars with swapped...) transmissions and got a different final drive ratio than the rear diff. That causes torque bind too.

 

Is the problem worse after time/heat? After a highway run, try doing tight circles at idle speed on flat, dry pavement. The car should go in circles smoothly. No bucking or jerking or 'braking' feelings.

 

definitely confirm the tire issue as noted above.

Edited September 2, 2014 by 1 Lucky Texan

[slymo]

Hi guys,

 

Thanks for the replies.

I thought torque bind was only on auto trannies?

From a cold start the vibe is not as noticeable and it definately gets worse after a few miles of running.

If you drive at a constant 33mph the sound is quite loud inside, just like when you have a back window open.

 

Regards,

Simon

[1 Lucky Texan]

MTs definitely develop torque bind. read of it often on the forums. MTs though are sometimes good when cold, get worse after warming up - quite typical. Still, could be tires. They must be same brand/model/size and close to each other in wear. One new tire mixed with 3 nearly bald tires 'could' be a problem. If you have 2 old and 2 new tires, try putting the pairs on opposite corners of the car. that is, one new, one old on the front, one new one old on the back. If the noise is still there, it isn't the tires.

 

(open diffs at each axle should prevent torque bind from mixed tires this way)

Edited September 2, 2014 by 1 Lucky Texan

[presslab]

Is there any side to side movement of the rear diff pinion flange? Does it turn smoothly? Did you check the fluid level? If you remove the driveshaft altogether and drive it (tape a paint can cap over the transmission) does it vibrate?

 

Your tire situation is not ideal, and could damage your center diff / viscous coupling. The front and rear diff do not have a viscous coupling so these can handle a bigger difference in tire size. So swap one new front tire with one old rear tire.

[idosubaru]

does it bind when taking sharp turns (wheel at full lock) on dry pavement?

that would indicate torque bind.

 

if you bought it with an issue there also remains the possibility that the rear differential and transmission have different final drive ratios.  it happens - people replace the trans or diff with something else and get the wrong diff.

 

on manual trans there are two gear ratios:  4.11 and 3.9. 

[slymo]

Hi Guys and thanks for the input. I will bite the bullet and get two new rear tyres today (same as fronts) and also do the test for torque bind and report back!

[slymo]

Got two new tyres yesterday so I have 4 brand new matching and it didn't change the vibration.

Put the car on stands today and ran it up. At low speed I can see a lot of runout on the companion flange at the rear diff but no diff movement. At higher speed, the diff begins to oscillate.

No obvious runout on the halfshafts or the output shaft so looks like I have narrowed down the problem. Next I will get a dial indicator, drop the tailshaft and measure the runout on the flange but I am estimating it is at least 20 thou !

I'm guessing that it would be easier to get a used diff from a wrecker than to attempt repair to this one?

[slymo]

Update...

 

Massive run out on companion flange so got another diff from the wreckers.

Installed tonight and it's now smooth as silk

The diff I pulled out had 09 imprezza written on the top so it wasn't the original unit and might have been dropped prior to install.

Anyway thanks for the input guys.

[Billy G.]

I had same problem on 2005 Mini Cooper.  Turn out to be a slight bent drive axle. 

Billy G.

[lmdew]

Good to hear you found the root cause and fixed it!

[Fairtax4me]

Very uncommon for these diffs to fail. I also suspect it was either run dry or damaged in some way prior to install.

 

Thanks for for the update on the resolution. Glad to hear its fixed!