InfernalVortex

iTrader: (4)

I dont drag race, so I never get the car above around 70 mph... but I have noticed that after about 70mph... the gears in the car start rumbling really loud. Sort of a groaning rumble.

This started when I put the 3.70's in, so I know it's the gears specifically. The 3.27's didnt do it. The contact pattern looks great, they dont make any noise (well, a very little amount) the rest of the time, there's only the slightest whine when it's sort of bouncing between coast and drive side.

I've been driving on these for years now with no issues, autocross, hard clutch dumps, all sorts of things with no issues... but I've been thinking about running down to the drag strip to get some baseline numbers and do some tuning, and I got to thinking about whether or not this rumbling is a serious concern for higher speed runs.

You guys have any opinions? Something to look for?

red rock

iTrader: (2)

Have you looked at the gear oil or gears lately? What brand gears are you running. Some 3.70 gears will whine a little sometimes, but i don't know about a "rumble" though. Maybe a bearing or spider gear problem. Big gearhead should chime in here.

InfernalVortex

iTrader: (4)

Well it didnt do it with the 3.27's. It started immediately after the gear swap. I never go fast enough to notice it (it starts just above 70 mph... and I rarely am on a highway that has a 70mph speed limit, usually it's 65, so I just go 65-70, which isnt quite enough. I've never worried much about it. I remember thinking it might have been because the gears hadnt worn in together fully that first week... but it's easy to ignore because I'm never going that fast.

And about the whine... it's not even worth mentioning it's so minor. I regret saying anything about it, because these are very quiet gears until just above 70 mph.

It's a weird noise that's hard to describe, but kind of a rumble is the best way I can put it. And it doesnt matter whether Im on or off the gas, does it all the same. Cones in this thing look great in addition to the posi actually working, so I have a hard time believing the spider gears are busted.

red rock

iTrader: (2)

What if your drive shaft is bent or out of phase or a bad u joint? http://jniolon.clubfte.com/driveline...nephasing.html

InfernalVortex

iTrader: (4)

It's possible... I just figure that would be more obvious at other times and it would have done it before the gear swap as well as after. But I can throw my stock steel shaft back in for testing purposes.

red rock

iTrader: (2)

I posted a link on my previous post for you to look at.

InfernalVortex

iTrader: (4)

I dont see the connection, but I do think it's worth checking the pinion angle and swapping my steel driveshaft in to check.

red rock

iTrader: (2)

Well I was thinking an out of phased drive shaft or out of balanced shaft might be causing the noise. Driveline noises reverberate all over so it's hard to pinpoint some times. Maybe even the trans mount is ripped causing a rumble at high speed. Try your other shaft and see if anything changes.

InfernalVortex

iTrader: (4)

For what it's worth, I have an LS1 aluminum driveshaft, which are supposed to be a LOT better about vibrations... but it does vibrate a little at high speeds. Like you said... hard to tell if there's a connection there or not.

And for whatever it's worth, it's done it with different wheels too.

It just comes on so suddenly...

red rock

iTrader: (2)

I also have an aluminum drive shaft which cut down some vibration, but the most dramatic change came when i replaced my rear tires. So, there is a lot to check.

InfernalVortex

iTrader: (4)

You know I think you might be onto something. Most of the reason this rumble bothers me is because it coincides with a vibration, but I dont remember this vibration always being there. So Im starting to think tehy're unrelated, and this rumble is just gear noise and isnt in itself anything to be worried about, which is what I thought originally.

Right around 60ish mph I get a slight vibration that increases up to 70 mph, and then after that it gets pretty bad to the point the whole car shakes.

Now im thinking I need to address the pinion angle issue. I also am pretty sure my old motor mounts aren't doing me any favors. Also have a poly trans mount and those are notorious for causing/exagerrating vibrations. Plus I've lowered the car since I put those gears in and I'm thinking these may have showed up as the car got lower.

Seems like this is all coinciding. I think I may buy another trans mount and put the preload spacer in it and see what happens.

antman89iroc

I too swapped from 3.27 to 3.70's and picked up some vibrations. It speeds up the drive shaft and if there are issues like minor pinion angle differences or a bit of extra back lash it seems to show up. I also have a stick shift and notice a noise/vibration at very light loads- like the pinion and ring are alternating from drive to coast. I set my gears up twice (both times the "pattern" looked good) and a lot of this went away. But I have sort of resolved that it is a combination of how the gears are made and the stick shift. Possibly aggravated by pinion angle but I haven't noticed much difference when I change it via adjustable torque arm.

MoJoe

iTrader: (5)

Is the driveshaft/u-joint located properly in the rear yoke? One more thing to check..

antman89iroc

Great point. When rebuilding my 9 bolt I noticed my yoke had worn on the inside where the clips ride. It allowed my ujoint to move ~0.020 or so. I replaced it with a great used one from Hawks. Not cheap though since it's a discontinued part (as are most 9 bolt parts )

red rock

iTrader: (2)

That's funny, I too had a poly trans mount in and couldn't stand the vibration so I took it out and replaced it with the rubber stock one. If your car has been lowered, do you have adjustable LCA brackets to keep your pinion angle correct? Here is a video trainer on angles.

InfernalVortex

iTrader: (4)

So just to be sure, I threw my factory 16x8's back on the car, and the vibration is... drastically reduced in intensity. I'm gonna need to go on a few more drives to be sure, you know how seat of the pants first impressions can be weird sometimes...

red rock

iTrader: (2)

Maybe you threw a weight on your other tires?

InfernalVortex

iTrader: (4)

So the gears just make a little bit of a hum at high speeds... I also have a bent driver's side axle. It's not hugely bent, but it's enough that with 17's, the vibration shows up around 65mph and gets bad by 70 mph.

With the 16's.... the thicker sidewall seems to absorb the vibration a little better. But I did some testing and some experimenting, and it appears a bent axle shaft is the problem. I've got a replacement on the way.

red rock

iTrader: (2)

Bent axle's will do it.