This one has me scratching my head so I thought I would ask for advice....

When traveling down the road and applying/unapplying throttle i can hear and feel a "clunk" that seems to be coming from the rear end.

All diff and transmission mounts are good. Fluid levels are good. U-joints are good. Pinion bearings good.


When under the car with the e-brake applied, twisting the driveshaft does not produce the clunk....however when the e-brake is released the clunk can be replicated and seems to come out of the diff. The clunk can also be made by grabbing either rear wheel while it's up in the air and turning it forward/reverse rapidly.

What inside of the diff could have this slack in it? is it possible the transmission has the slack and is transmitting it though the driveshaft to the rear end?

 

Been there, done that.

I am betting it is the forward differential mount. The center, rubber section fails in shear along a vertical plane. Without stress on it, the two sheared parts line up and it's hard to see the failure. Push up and down on the front end of the differential, and you should see the movement between the two failed parts of the mount.

 

+ 1 for FWD diff mount, exact same symptoms that made me find mine.

 

So he's obviously saying his mounts are good, well it doesn't hurt to do the check by pushing up on the front of the diff the next time your under the car. But other than that possibility I'm not all that sure either, however I have a similar problem and I have mmr-direct diff mounts with a stock front mount, and I still have some kinda slack issue.

 

I have a solid front diff mount.

 

The other culprit is usually the rear dogbone links. When they wear out they pop and clunk.

 

There should be "some" backlash in the gears. Im somewhat doubtful thats what your hearing in the car when driving, although I wouldn't rule it out.

Have you checked the u-joints on the drive-shaft?

 

Yes, u-joints don't have any slack.

 

Videos:

in gear
http://s20.photobucket.com/albums/b2...Picture053.mp4
http://s20.photobucket.com/albums/b2...Picture052.mp4

neutral
http://s20.photobucket.com/albums/b2...Picture051.mp4
http://s20.photobucket.com/albums/b2...Picture050.mp4

 

Wow, that seems excessive... If it were me, I'd pull the diff cover off, and visually inspect for whats causing the noise. If I had to guess, I'd say either the ring gear or pinion has moved slightly out of tolerance, or theres some heavy wear on one of the two.... or even both. The crappy thing is that rebuilding diffs isn't what I would call a "fun" weekend project....

Any leaks around the diff?

The break calipers arent' moving?

 

E-brake disengaged, calipers secure. The pinion seal may be leaking, but the fluid level is correct. This clunk has been present since I got the car 3 years ago.

 

What cover? You have to pull the diff out to open it up

 

i'm going to unbolt the driveshaft and see if i can isolate it to the trans or rear end..

 

yeah im sorry to say but on my SE i had a similar sound had the diff rebuilt. i helped the guy out not fun att all. soo good luck with that...yep

 

Your answer is in your thread title. The diff should be set to .005" backlash. @ .020" the dif will sound like its about to EXPLODE. Think about that, a difference of 15 thousandths of an inch is the difference between brand ******* new, and sounding like someone tossed a handfull of gravel in the rear end.

There is no cover to pop off, you're thinking of solid axles like the rustangs and suck.

 

Titanium tt spot on.

 

that's the thing though... with the e-brake pulled there is virtually no blacklash in the pinion. the diff is perfectly fine except for the clunking. there is no whining or rattling...just the clunk.

 

Assuming your ring pinion backlash are within spec, there will always be some drivetrain noise with a solid front diff mount. All the internal diff gears have some backlash built in as well.

 

Let me reiterate becuase you didn't quite understand it. When you setup a diff, backlash is set to 5 thousandths of an inch, .005"............. How much rotation do you think that will translate to at the driveshaft flange that you are moving?

The answer is hardly any.

Well, I would say the diff is not perfectly fine if it's clunking around. Wouldn't you? Turn the radio off, open the windows, and slowly crest a hill without altering the throttle, you'll hear rattling from the diff knocking back and forth from what is basically accel/decel.


There's really nothing left for you to do, you have two choices
1) Deal with it
2) Drop the carrier and rebuild it

Rebuilding a rear end is not that hard, the hardest part will be getting the subframe off and back on. Rebuilding the diff is pretty easy, just time consuming, VERY time consuming. Triple check everything because you only get one chance before it gets FUBAR.

 

My apologies, I know lot's about diff's coming from building Jeeps from the ground up, I just didn't realize that the RX7 diff didn't have a cover. I've only owned mine for a few weeks afterall.

How do you set the pre-load in the pinion on an RX7? Does it use a crush sleeve, or shims?

I do agree with Titanium, although I have to disagree with gear jobs being easy. If you've done it before, yes, it's pretty straight forward. If it's your first time, give yourself a weekend or two to do it. And you HAVE to have the proper tools to do it with, there's no way to take shortcuts. The beauty of it is that diff rebuilds can be rather inexpensive if you do it yourself. Shops make tons of money on the labor for this type of job.

 

Yep RX-7s are 3rd member style very similar to toyotas in the "jeep" world. Allthough the FC diff is a whole different animal with the silly mile long pinion and multiple pinion bearings.

 

Crush tube

I think two weekends is a little excessive unless you like to sleep 17 hours a day. Figure 2 hours to get the diff off, 2 hours to get it on, 3 -5 hours to set it up. Sounds like a day to me.

And just becuase backlash is written in here so many times and I'm willing to bet it'll show up on a few searches, here are some things to look for when setting up a diff -
Put the pinion on a set of Vblocks and check it for round. I didn't do this with one diff and it ate the gears in a matter of a few hundred miles.
If you're setting backlash and it diff likes to lock up as in not turn, check the ring for step wear. The pinion can jam in the unworn section of the ring gear and screw you.

That mile long pinion and moreso the multiple bearings IMHO is one of the reason these rears are so damn strong.