"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

Not withstanding the tranny issues...

From the time I bought my car in 2000 there has been a clunk coming from the rear of my car. It mainly occured turning right and left and when I'd pull away. I did a whole lot of research and rebuilt everthing... CV's, TB's, springplate bushes, trailing arm bushes, dampers and their rubber mounts. The last thing was done last weekend... THE WHEEL BEARINGS :rolleyes: Solved absolutely everything! Not an easy job, but very satisfying making my own removal tool and changing these out.

The car is not only travelling beautifully and absorbing bumps in the road, but it is doing it silently! Turns out my bearings were so bad that they were making noise I didn't even notice until it was gone :)

Just somethng else to consider Randy...

G'day, John! Thanks for the info.

Haven't thought about the wheel bearings, but for a couple of reasons. First, I was able to actually duplicate the sound by moving the drive flange by hand. There is a bit of freeplay that doesn't exist on the driver's side. Either way, this slop needs to be tightened up.

The other reason is because I've "recently" had the rear bearings replaced. I say recently because it was done at 91500 miles back in 2000. Since then, I managed to put almost 11,000 miles on her. She's now sitting at 10280.

I suppose they could be bad, and I'll certainly check for any looseness while I have it up in the air, but I really think I have this pin-pointed to the drive flange.

Cheers!

Randy

Hey Randy! I see you're working on your accent ;)

If you've done them recently then I'd say you're right and it's not the bearings. It was just an idea... I just couldn't get over the difference in my car after I changed them!

I look forward to seeing how it goes.

Cheers

Well, had to take a few days away from the "clunk" to work on a chapter in the wife's Honey-Do Book. It passed "list" status years ago. :D

Anyway, drained the tranny case tonight and am extremely happoy to report that aside from a little bit of metal shavings, there was no cause for alarm like the last time I drained it. No wayward dogteeth floating around. Yes, I even made sure the fill plug came loose before the drain.

Case has been drained and the drain plug is tightened back into place with a good coating of anti-seize. The fill plug is waiting patiently to be replaced as well, once I fill the case back up.

Only about 4K miles or so on the trany since I had it apart and the Swepco looks a bit worn. Still blue, but it;s a lot darker than when it went in. A fresh load should do her some good. :D

Okay, now to the meat of the thing. I have disconnected the driver side axle and have removed the drive flange bolt. It does NOT have the little teat on it that I've read about. I don't think that is an issue, IIRC. Anyone?

Heading back out right now to remove the diff plate and have a look inside. I have the replacement seals from last year that I plan to install.

You know that advice you get that you wish you would have followed, but you didn't? Well, JW, you DID advise that I go into the diff last year when I had it out of the car. I sure wish I would have followed it. I'm sure I wouldn't be here right now, had I done so. :(

Well, back at it. I'll return with more in a bit.

Randy

Trying to install the flange seal and saw where indigowhale said he almost put his seals on too far.

http://forums.pelicanparts.com/uploa...1112121947.jpg

How far is too far??? :confused:

Randy

have to second the info from fishcop. i had my car up in the air and could replicate the clunk (approx) by turning the half shafts. As there was some play I thought for sure it was the cv joints even though they were brand new when i got the car. I guess they could sell a bad one right. swaped the sides and still the clunk came from the right rear. cure turned out to be the wheel bearings.

qikcpa, after spending the evening with it, I've been able to determine that the issue lies with item #3 in the pic I posted previously. Once again, John, you were right on the mooney!

With the axle disconnected, I removed the drive flange and then threaded the drive flange bolt into item #3 in the drawing. The slop I felt in the drive flange is definitely coming from item #3. I can hear and feel the same amount of freeplay with the drive flange removed.

John, is it possible to change this part (item #3) by removing the diff cover on the other side of the tranny? That would sure make it easy, if I didn't have to drop that tranny/engine again. Think it's time I start warming up my knees so I can commence kicking myself in the butt. :mad:

Randy

bump

the whole diff comes out after removing both drive flanges and the side cover. don't drop it on your face.

Thanks, John.

Should be back underneath taking the diff out tonight. I'll get a good charge on the camera battery too. :)

Randy

Okay, following John's instructions, I removed the flange from the passenger side. (The diff cover and driver side flange were just tacked in place from last night.)

Here's the diff, ready to come out:
http://forums.pelicanparts.com/uploa...1118281622.jpg

There was practically no resistance. The diff came right out. John, excellent advice about not wanting to drop this on my face. This thing has some weight to it. In my case, it probably would have hurt like he!!, but no one would have noticed the damage. ;)

The removed differential:
http://forums.pelicanparts.com/uploa...1118281762.jpg http://forums.pelicanparts.com/uploa...1118281825.jpg http://forums.pelicanparts.com/uploa...1118281844.jpg http://forums.pelicanparts.com/uploa...1118281887.jpg http://forums.pelicanparts.com/uploa...1118281954.jpg http://forums.pelicanparts.com/uploa...1118282128.jpg

Randy

A couple of pics similar to the one JW posted.

In this first one, you can see the spacers flush against the side spider gears.
http://forums.pelicanparts.com/uploa...1118283292.jpg

In this second pic, I have pushed inward on the spacers with just my finger tips. They are both rather loose, and when I push them, the BOTH move in and expose a gap that is a bit more than 1/16th inch.
http://forums.pelicanparts.com/uploa...1118283402.jpg

It's dawning on me that I should go out to the garage and assemble the drive flanges to the diff and tighten then down to see if I can remove the slop.

I DID tighten the passenger side while it was all together last night. I was able to get a little bit of turning on the bolt, but it wouldn't seat the spacer. How soft is the spacer metal. Could it be stripped out? If stripped, how involved is it to replace it.?

Randy

Alright, last post of the evening...

I followed indigowhale's tip in installing the new seal on the diff cover. Unfortunately, I didn't get a good reference shot of how far the seal needs to go in.

Going by the pic, should the diff seal be pressed in far enough so that the edge of it is flush with the ridge indicated in the pic?
http://forums.pelicanparts.com/uploa...1118284268.jpg

Randy

Randy, you sure do impress me.

Thanks for reminding folks like me that an average guy with time and ambition can take one some pretty daunting tasks.

notfarnow, don't let ME impress you. All I'm doing is turning the wrenches. The guys that impress me are the ones with all the knowledge! Without them, I'd be one of those "average guys" with no ambition. :D

After I was coached through repairing my transmission last year, I've found that a lot of things on these cars are a lot easier than I would have imagined. The key is knowing where to get your information, and when things aren't crystal clear in your head, come HERE and ask. If it weren't for Pelican, my local Porsche mechanic would be a lot wealthier. ;)

Randy

Well, I did exactly this last night.

Inserted the passenger side drive flange into the diff and tightened down the bolt. The flange is tightening right up to the disc inside the differential, no doubt about that. What I'm seeing is that it's actually the two pieces, bolted together, that are moving.

I thought that maybe tightening the bolt would draw the disc into position and then snug up against it to hold it in place, but that isn't the case at all. As I stated above. Both the flange and the disc are definitely tightening up against each other. Once tightened, the two parts assembled is what is moving.

It's as though the stub part of the drive flange may be too long, which is odd, because these are the same parts that have been in the car since I've had it.

Any thoughts on this?

Randy

bump :)

Local P-Car Mech Says Slop Is Normal?
 

Okay, took a break at lunch and took the differential to a local p-car mechanic. Showed him the slop in the in and out motion of the drive flange/disc assembly and he tells me this is normal. He then asked about my CV's and I told him that I had just done those a couple of weeks ago. He then suggested looking at the say bar because it's not uncommon for the brackets that mount the bar to the bottom of the car to come loose.

Climbed underneath and got my hands all over the sway bar. Everything seemed to be tight enough. Took a ratchet to all the bolts anyway, just to be sure, and they were definitely all tight. Kinda fidgeted with the bushings on these mounts and everything seems to be intact.

As I said at the beginning of this thread, "anything" is possible. I guess I can pull the axles and have another look at the CV, s. It really seems to me that the differential is the culprit. When the car was all together, and I worked the flanges in and out, it really sounded like this was the culprit.

Anyone have any other suggestions?

Randy

It's been a while since there was a posting to this thread. Did you finally identify the source of the rear end noise?

I've been chasing a rear clunk noise that seems similar to yours. I generally hear it on a left turn "after" a right turn. Usually at lower speeds (e.g., when driving in a residential neighborhood). It gives the impression that something "loads up" on the right turn and then shifts on the left turn (which is when the clunk is heard). Centrifical force seems to be required.

I've checked all rear suspension components and replaced bushings, tbars, and engine/tranny mounts. A mechanic checked the wheel brearings and CV's. I don't know to what extent the differential flanges were checked.

Any ideas?

fmarin,

That type of directional clunk leads me to suspect that one of your anti-roll bar mounts has broken loose and is hitting the body on transistions from load to unload during cornering.