"Clunk" - Probably not what your thinking...
 

Recently replaced the boots on my CV joints and am now experiencing a "clunk" sound during driving. Mainly upon rollout from a stop, and occasionally around turns, mostly at slower speeds. I've searched and searched and all I can find are pointers to CV joints being bad.

I'm not ruling them out, anything is possible, so I climbed under the car a little whole ago to have a look.

Car up on jackstands, no brake, tranny in neutral, I began spinning the wheels. They both sounded fine...no clunking. Climbed underneath and tried moving the axles from side to side and found that one the axle flanges on the transmission seemed to have a bit of freeplay to it. Actually, it was the passenger side flange, not the one shown in the pic below.

http://forums.pelicanparts.com/uploa...1117757575.jpg

As I moved the axle from inboard and outboard, I could see the flange on the passenger side moving in and out approximately 1/8th of an inch, maybe a little less. What's more, the "clunk" it made seemed to be exactly the clunk I heard while driving.

I took the handle of a breakerbar and wedged it between the flange and the tranny and again moved the axle about and the sound was not there. I performed the same tests on the driver side but there was no issue there.

I guess my question is this: Aside from tightening down the bolt that seems to hold the flange on, what else could/should I be looking for with this flange? I've checked the cap head screws that attach the axle to the flange. Since I've only driven maybe 50 miles since installing them, they were still tight.

Randy

Re: "Clunk" - Probably not what your thinking...
 

So, did you do that? (tighten) I don't think it's supposed to move and make a noise.

BTW, do these have the stretch bolt?

No, Zeke, I haven't tightened anything yet. Figured I would check with the experts and see if there was anything else I should be watchful for.

When you say "stretch bolts" are you talking about the cap screws for the axles, or the bolt holding the flange onto the tranny? The cap screws are new 10mm screws I just ordered from our host. The flange bolt has been in there for longer than I've had the car, so I really don't know.

Thanks!

Randy

Heh he, I just said on another thread/post I wouldn't talk about Carreras because I don't know anything and have never been in one. But the drive flanges on my trans are held in place by a long bolt that has to be torqued accurately because it stretches and holds at the proper torque. Sort of like a spring in tension. The flanges don't move in and out.

Gotcha! ;) Well, I appreciate you chiming in here heare anyway. It's a safe bet you probably know more than I do about these things. :D

Anyway, since you asked, I went back outside and disconnected the axle from the errant flange. Tried to tighten it but it seemed plenty tight as it was. It wouldn't tighten down any more.

I'm starting to get a bad feeling about this. Some of the stuff i was reading during my search indicated the gears in the differential could be going bad. Argh...I guess I shouldn't have been wishing it WASN'T the CV joint! :mad:

I double-checked the driver side while I was out there and again, it seemed to be fine, no free play.

Randy

These require 320 ft-lbs of torque if I'm not mistaken. That's no 'give it a good wrenchin' torque, that's buy a 3/4" torque wrench style torque, and make sure the car is properly supported. If you don't have one, look on eBay. Jumbo-torque wrenches can be had cheap.

Jay, read the 1st post carefully. This is not the axle hub nut we are talking about. It's a bolt and it holds the trans drive hub in place.

Randy, that's all you can do. Keep this on top and maybe JW will come on and tell you what he thinks. He's most likely seen this in all of it's forms.

Jay, thanks for the reply. I believe Zeke is right on the money with this last bit of info. I just replaced my CV boots, which involved removing the axles. The nut you're talking about is indeed a torque monster. 333 Ft.Lbs is what I was aiming for. and yes, the 3/4 in. drive was the only thing that would touch it. The bolt on the drive hub, as Zeke called it, is a 17mm bolt and I'm afraid 300+ Ft.lbs just might be a bit much for it.

Zeke, JW certainly does have the answers. Hopefully he'll save my skin again by popping in and setting me straight. Thanks for the info!

Randy

bump

Whoops....sorry, read that one too fast!

Regarding the axle nut, even if the torque spec is lower (260 or whatever), 320 would not be too much. On those fasteners, the danger is too little torque. Sure, too much torque is technically possible, but I've seen a lot of mechanics put those fasteners on with a breaker bar and cheater pipe - no torque wrench. The operative strategy is simply to not use less than the specified torque.

On the drive flange, I dunno. If I were in your shoes Randy, I would just make sure I hear from JW before reaching a decision. He had a tranny in last time I visited him, and showed me the galling and such with the R&P. It happens, occasionally. Hopefully that's not your problem, but John understands these machines better than I understand the back of my hand.

And finally, I congratulate your tactics. Regardless of one's mechanical experience or lack thereof, investigation is investigation. Your description is a perfect example of looking, listening, feeling, tasting (well, maybe not tasting), and finding the anomaly. That's how it's done.

Supe, you guys there in the Seattle area are extremely lucky to have someone like JW available to you. When I was out there last year, my father-in-law and I stopped by his shop and he spent the better part of an hour just BS'ing with us. I'm sure he had better things to do, and yet, he was just as welcoming as anyone could be. And his knowledge is the stuff legends are made of. (I'm not smooth-talking either. Anyone who has ever had the chance to meet him would surely agree.)

As far as my investigative techniques go, well, when you're as ignorant as I am about these cars, you can't help but notice EVERYTHING!

"...looking, listening, feeling, tasting (well, maybe not tasting), and finding the anomaly..." Since I've learned to keep my mouth closed while poking around under the car, I haven't "tasted" anything. :) Besides, my mouth has a tendency to get me in trouble at times....you've seen me in OT. ;)

Randy

randy, all i can think of is the disc that is under the side spider gears, the piece that has the threaded hole for the flange bolt, may be worn. the flange tightens against the disc, allowing just enough clearance so the seal lip on the flange doesn't butt up on the outer edge of the diff carrier. that's the flat ring you see just beyond the seal, when the flange is off. the flange really can't go in any farther because that disc it bolts to has a large pin behind it that holds the other two spider gears in place. probably time to remove the diff and see what's up. about a 1/2 hour job. something will show up. there should not be slop like you describe.

http://forums.pelicanparts.com/uploa...1117836047.jpg

Well, there you go. I don't really understand what John said, but that's not unusual. It's a great picture and he says it's a half-hour job which means it's a short, three-hour job for me. And maybe the bolt has backed out. Sounds strange, but maybe. Does the bolt have a locking ring? One of those washers that you bend upward to lock the nut, like at the tops of the front struts?

No, Randy tightened the bolt. So, JW, is there another flange bolt that is too long that could be mixed in mistakenly with parts on the bench and bottom out on the spider gear shaft? He did mention that the tranny was rebuilt less than 5000 miles ago.

there you go. that would certainly do it. maybe compare both bolts for length. randy, didja swap in a different bolt when you did the trans? if that's the case, you could see the slop under the bolt head as the flange is moved in and out.

John, Zeke, Supe....until last night when I tried to tighten it, I've never touched those bolts. I actually never got into the diff when I dropped the tranny last year.

John, am I dropping the tranny again to get into this, or can I just remove the bolt holding the flange and stretch my neck? And at 3000 miles since i opened it up, I suppose it wouldn't hurt to change out the Swepco.

I'll most likely have some more questions after I get it opened up. Time to charge the batteries in the camera. :)

Randy

no need to drop the trans. drain the gear oil, remove both cv joints from the trans, both flanges, clutch cable brackets, the side cover and slip out the diff/ring gear. 1/2 hour. you may see something by just pulling off the suspect flange first.

AWESOME!!!

Thanks once again, John!

Looking at this drawing, it looks as though my bolt, #13, threads into item #3. Just on the other side. I think I can handle that.

http://forums.pelicanparts.com/uploa...1117844219.jpg

I'll do the errant flange first and hope for the best, but my guess is it will be "all the above."

Numbers 9 and 10 in the drawing, are those spacers, or seals?

Randy

Some links to a few sources of reference...

1.) http://forums.pelicanparts.com/porsche-911-technical-forum/187715-differential-removal.html#post1564553

2.) 915 Diff Assembly

3.) Axle Flange Bolt Torque For an SC

4.) Broken Axle Bolt/Tranny Question

5.) Broken Transmission, any Ideas?

6.) Differential Removal

From Grady Clay:
Some other tricks:
On the axle flange seals, in addition to sealing them in place, I add three little loops of safety wire to prevent the seal from coming out.
Inside the differential housing I made an aluminum piece that locates the input shaft and prevents damage to the input shaft seal. In the shop you should always install the seal after the input shaft is in place. At the track you just want to be able to plug the gears in and not have to deal with the seal.
I have two large Alnico magnets to collect any steel parts. If there is a failure, you don’t want hardened steel circulating through the transmission.

Borrowing this info from indigowhale's tranny rebuild thread...
Randy