Annoying Vibration and Rumble

[tweiss3]

Friday night, leaving the driveway, i started getting this annoying vibration from the rear end at 35mph, smooths out into a loud rumble about 48mph. I know it's not the motor, cause i put it in neutral and shut the motor off on the higway at 60mph, and it was still there. Its quite annoying.

Now my question is, do the driveshafts/ujoints tend to go bad on the S5's? It sounds like the rumble my dad's truck had when his driveshaft was unballanced right before i tore it in half.

What else could it be? CV joint? Diff? Transmission really wonky?

[TitaniumTT]

Could be
driveshaft u-joints
driveshaft balance
half-shafts
backlash in the diff.

Jack the car up and start spinning things and moving the shafts back and forth.

[tweiss3]

Thanks, I'll get there soon. Yesterday I had to attack the headlamps and see why one isn't working. Damn ballast was fried.

[FC Zach]

Could it possibly be a broke-in-half front diff mount, which would cause a lot of erratic movement??

[Max777]

I've had a simmilar problem for like the past year and still cant figure out what it is...

I replaced my u-joints and still had the problem.

The funny thing is, the vibration originally came up when I installed urethane mounts on my engine and transmission, but I also clutch in when the car is rolling and the vibration is still there.

From what I heard, the diff tends to whine really loud instead of vibrating, and the CV joints are usually not the problem if the boots are still intact. I was told to check the rear diff mounts, and found that one of my toe links (the long stick with two ball joints on it) was loose. I tightened that up and the vibration was still there, but it seemed to change a bit.

[tweiss3]

Thank's zach, i'll check the front diff mounts. I need to check this today, so I probably will at the minimum toss it on ramps and see if anything is blantantly loose.

[TitaniumTT]

If you've got access to a lift, or you yourself are brave, get the car up on all four jackstands and run the car at the speed where the vib happens and see if you can see anything loose, moving out of round, etc etc etc.

Diffs TEND to whine, but they can vibrate pretty badly when they're really bad. Have you replaces any mounts lately, motor, trans, diff etc etc? It could be the d/s is out of phase. This is one of the big problems with my 6-spd that I still need to fix.

[tweiss3]

Its bone stock mount wise, i've been meaning to get some MS trans and motor mounts. I know my diff has some play in it, but I don't want to replace it unless its necessary, which it may be now. The boots looked in tact at lunch with a quick peek. This isn't much of a whine, this is a deep loud bassy rumble.

What about the d/s out of phase? I guess i just don't recall that abbreviation.

I will get the rear up on jackstands , but won't run it at that speed (35-65 mph is dangerous). No access to a lift, but i will spin everything and see if its out of true, i may even break out the magnetic dial to see if things are true.

[TitaniumTT]

I've done it may times when I was dicking around with my 6-spd. Jack it up, remove the exhaust, adjust it, run it through all the gears (no exhaust mind you and brake boosting just to make sure my nieghnbors heard Also done it on the lift with 4 people standing under it.

If it's a lound bassy rumble, it sound like the diff to me.

[tweiss3]

You may be right, now that I think about it, I did feel it in parking lots kinda hop like when the diff spins both wheels at a different speed, felt kinda like clutch chatter, but I know it wasn't. Does this mean my diff is completely toast? I'm guessing it is, and when i go to drain it, there will be a shit ton of shards and filings.

Maybe time to go for a S5 t2 diff?

[TitaniumTT]

Dunno what's going on unless I/you pull it apart and mic it out. Tons of shit could come out but probably not. What's in there now? I'm not a fan of the S4 diff at all. S5 is nicer, Torsen is the ultimate in my eyes though.... this being from a road racing/auto-x personal preference

[tweiss3]

Ok, got under it tonight on ramps. Driveshaft seemed spotless, half shafts had all boots in place, and no leaks. The diff (by twisting the input shaft) is pretty tight, some play, but not more than about an 1/8 of an inch. The mounts all seemed very nice, even the front diff mount seemed like it was fresh from a mazda parts box. No tears or anything.

Pictures below, what now? Drain the diff?

Diff Mount from Rear of Subframe:


diff mount from front of subframe (really bad pic)


Best pic of the rear bushings i could get


My point and shoot decided it wanted to shut off every time i pressed the shutter, so i had to lug my DSLR under the car, which is not ideal at all for these kinds of pictures.

[tweiss3]

Well, after scouring the FSM, this site and Mazdatrix, it seems like this may be due to bad universal joints in the drive shaft.

Has anyone rebuilt these ujoints? How easy is it? Would you recomend rebuilding, or straight replacing the shaft?

[TitaniumTT]

Straight replacing. Carolina D/S built me a custom AL d/s (custom length, the yoke and flange are the same) for something like $270.

[tweiss3]

Arg, i just need an oem spec stock replacement, and that's too much cash right now to throw at the DD. Fuck.