Bad pinion angle cause grinding/vibrating?

[TurboRA28]

Hi all, since installing a new 2 piece tailshaft (new centre bearing, uni's, balance) and also at the same time installing some adjustable upper trailing arms.

The celica has developed a nasty noise that is only noticable from around 60km/h or more. The faster you go the worse it gets. Not related to engine RPM, only road speed.

It doesn't happen under moderate - hard acceleration. It also doesn't happen under no acceleration.

It only happens under the slightest amount of cruising/coasting kinda acceleration. So on the freeway once you get up to speed then back right off just to cruise is when it will happen.

You can make it come and go very easily by putting your foot down a bit more, or taking it right off the gas.

Sounds like it is drivetrain but cannot be sure. I've checked EVERYWHERE for any signs of rubbing and there is nothing.

I've also rebuilt the diff (was happening before this), new axle bearings also have been installed).

So I can only think its a tailshaft issue? Maybe by adding the adjustable upper arms and adding 1 - 2 deg of pinion angle pointing down i've done something?

Just wanted some advise before I go to the trouble of pulling arms out and changing the length of them.

Thanks
Joel

["Z" UTE]

Hi Joel, I had the exact same problem with a UZZ30 Soarer. Had me stumped for quite a while. The Soarer had a splined jointed 2 piece shaft. The noise was from loose splines. Another Soarer owner sold his car because he could not track the same noise!.

So if your diff is a reconditioned unit, and your centre bearing and uni's are new, I would be looking at the splines on both your diff pinion, and your gearbox.

cheers Chuck.

[TurboRA28]

Hey Chuck, thanks for that info mate.

I guess I should be checking the centre uni/bearing and make sure the shop who did the tailshaft did it up correctly?

I've got a new pinion gear so the splines on that should be good. Not to say the flange is though.

[wilbo666]

Joel,

Does the rear section of the tail shaft have rubber isolation?

Most old toyot Shafts that I have seen have the rear section, that contains the diff flange slide up inside the main rear drive shaft tube, with rubber inbetween each segment...

|\ ______________________
|-------------
|-------------
| ______________________
|/
{diff flange}{small tube}{rubber}{larger tube}

If that crap drawing makes any sense?

If so maybe it is an issue with the rubber?

Cheers
Wilbo

[TurboRA28]

Hey Wilbo, mate the AE86 has that design tailshaft, but the Celica just has a solid one.

Though the problem is solved! I adjusted the pinion angle and pointed the nose of the diff up a bit higher and the noise has gone.

I always thought the idea was to have the nose of the diff angled down a degree or 2. But maybe due to the angle on the gearbox/centre bearing etc that just puts the uni's too far out.

Anyway.. happy me ! one problem solved. 100 to go
Cheers
Joel

[1JZ-Rolla]

Good work!

Diff pinion angle seems to be a bit of a black art, and what works well for one setup doesn't always carry over to others... General consensus seems to be that if you have a stiff trailing arm setup with urethane bushes etc, not much geometry change takes place under acceleration, so 0.5 to 1.0 degree downwards is usually sufficient. Leaf spring rear ends are a completely different story of course, with so much spring windup changing the angle by several degrees.

Were you measuring the angle relevant to the gearbox centreline, or the front half of the shaft?

Cheers
Phil

[TRAV-KE55]

Joel,
are your adjustable arms rose jointed?? If so more than likley it is actually the rose joints chattering on cruise, Have driven racecars that have rose jointed rear ends and the bloody things just about make you deaf on cruise!!

[jonra23]

If you want to return to nose down on pinion angle put a spacer in where the centre bearing bolts on to reduce some angle on rear uni and increase angle on front uni.
Idealy both unis should be seeing same angle.