Nice talk, that will get you in the door, turn off the audience and youll never get you point across. Yeah Yeah Yeah.

Well here is the message. I took the rear apart from yesterdays posting and took photos for you all. THe results were most amazing to me and I feel better informed about the issue at hand.

THis rear was not flogged at the track too much as I understand it and still the failure is complete though hidden. THe rear failure was that of the ring and pinion, not the spider gears or the pin in the rear. THe cause is still the same in my modest opinion, and I have a solutition for ya.

THe photos are in one of my albums, please feel free to browse the others for you entertainment. I have posted the link below.


You will have to look around and see the photos, technical stuff and not a primer on the rear end construction. But the images will show you how it works and how it looks inside. Further the wear or gaulling of the parts will show you how the wear and tear damage the internal parts of the rear end.

Recap: When I got the rear it looked ok at first. When I tried to twirl the spider gears it became apparent that the spiders were causing the pin to rotate in the case, this is not acceptable. THe PIN is anchored in the rear end case by a "roll pin" thru the case. The case has a photo of a dental tool sitting in the holes that this roll pin is set into, for your understanding. The roll pin is a hardened strip of steel rolled to form a cyclinder that expands and grips the pin and rear to provide retention of the spider pin in the case. Its a roll of metal strip forming a rolled up magazine shape with a hole in the middle and thus not solid. THe driving forces this particular rear saw, were sufficient to break the pin and allow the 3/4" diameter spider pin to rotate in the case.

I took apart the rear to expose the spider gears and the two side axle gears. Please see the shot of gears laid on the table and note the two pieces of the roll pin on the 9 oclock position. THe bigger gears turn your axles and the smaller ones are driven or rotated by the spider PIN. This pin is photographed to show you the tearing of the surface on this pin known as gaulling.

Gaulling Definition of Galling is caused by metal to metal contact and motion. THe forces causes the metal contacts to rub, melt and stick to one another leaving a rough surface, shreaded metal results. THis is due to poor lubrication and excessive stress allowing the metals to wear metal to metal. THis is a Taaaa Daaaa moment. The lube is the issue in addition to stresses exceeding the limits of the rear gears strength.

I have set a flashlight to illuminate the interior passages of the spider gears to show their chewed up surface which matches the metal missing from the PIN. THe engine turns the transmission, which thru gearing increases the torque 3 to 5 times and then turns the rear which increases the torque another 3 times. I have 300+ foot pounds of torque, not counting the shock from gear changes. 300 x 4 x 3 is 3600 foot pounds of force twisting the differential and all that is supported by the 6" long PIN, or 7200 pounds of force, yikes.

THe rear has little chance of surviving that long and if one wheel spins, the speed of the gears on the PIN really heat up the surface weaking the oil films strength.

THe spider gears look ok to me, the pin and interior of the spiders show lots of damage due to gaulling. THe axle gears show little distress in this particular rear and look sound. We need better lubrication to start with.

EXAMPLE: My son did not note the difference between the main engine bearings and put the thrust #3 bearing upside down using federal mogule bearings. Typically I use clevite which have both bearings the same. Anyway the oil passage of this bearing was closed off and the lower half bearing was covering the oil port, thus no oil fed the thrust bearing from day one. Well the car was run on the drag strip, converted to autocrossing and run for a year without incident. I had cause to tear into the car for other reasons and found the error much to my suprise.

THE FREAKING CRANKSHAFT had NO marks or distress though the bearing looked roughened. THe crank was not damaged because I had tried and run synthetic oil in the car and the 8 quart deep sump / scraper oil pan. NO damage because of synthetic oil, what an eye opener.

Back to the crossfire rear. I did the phantom grip differential over a year ago and went to synthetic oil. THis probably explains the lack of problems I have had with my car even though I drive the heck out of it autocrossing in two clubs here in Northern Va.

SOOOOOOOOO if you want your car to last, I can tell you that if you dont get synthetic oil in your differential soon .............................. _ _ _ _ _ _ _ _ _ _ _ _. See the Title.

Your W DY

Crossfire rear dissection and eval. - CrossfireForum.org Gallery

 

I just had to say that I love the title of your thread. Somehow, I was just drawn to it....

 

OK Woody... Point made. What weight and brand name synthetic rear gear oil? Thanks... Squirrel Crusher

 

Very nice write-up. Is the fill procedure with our diffs with the ol turkey baster?

 

Yeah...got it. Now, what to use!?

 

Yes, quite stupid!

So could this be repaired with new spider gears, 3/4" shaft and new roll pin? Or did the slag from the gauling wreck everything else?

 

My coupe is a torque monster. I'll swap to syn as soon as we get the Professors advice on lube to use.

 

I personally would not jump to the conclusion that the use of synthetic oil will solve the problem as this may be a coincidence.
It is possible that the main bearings in the engine you mentioned may have survived using regular oil, plain bearings can take the heaviest load of all bearings with minimal lubrication as the two contacting materials are totally dissimilar and the bearing materials are formulated to take the wear and load. These aren't the white metal bearings of my youth. However it would have taken just a split second for the oil film to break down and the bearing to fail immediately.
Galling does not involve the melting of metal, metal transfers from one or both contacting materials and bonds to the other under extreme pressure any sign of heat was caused by friction, The parts can actually cold weld together and be hard to separate.
Galling - Wikipedia, the free encyclopedia
The roll pin acted like a shear pin at an instant when the gear and shaft were locked together under heavy load and the rough surfaces locked together.
Shock loads are about twice the normal max load. A spinning wheel grabbing would be a shock load.
These are just my thoughts and are probably not worth even two cents. Jumping to conclusions is sometimes just too easy, perhaps this is just the first weak link in the chain no matter what kind of oil is used.
http://auto.howstuffworks.com/differential2.htm

 

Tuna, there are no parts available as I hear it. The unit is sold as an assembly to reduce part numbers and cut down overhead for stocking. THey make more selling the rear also.

You could try to design a wear sleeve bearing but it would be iffy and complicated to try without a guarantee that it would work. Id do it on an island but otherwise no go Joe.

Woody

 

woody i run full synthetic in my diff and still have the clicking. im convinced its a combination of rwhp and drag radials causing the failures

 

Thanks, I was just curious. My diff seems ok (for now).

 

If I was to suggest a repair then I would get the internal diameters of the gears ground lightly, a 100% clean up would be good but not absolutely necessary, bore out the two housing bores and make a new hardened shaft.
Any pits inside the gears after grinding with say a 95% clean up would hold oil, not a bad thing.
A new shaft would be probably made from a case hardening steel heat treated for an outer hardness like the original and inner strength.
As long as the housing had some unmarked bore surfaces left they could be aligned and bored a few thou bigger.
The gears probably have a hard skin so not to much can be taken off them.
Accuracy would be required, but that should not be beyond the capabilities of a good machine shop.
It is entirely possible that the gears and shafts are common to many other cars and are available off the shelf. Finding them is the problem.
Any clicks that I have had from drive trains came from the CV joints.

From the manual;
DRIVELINE SNAP






A snap or clunk noise when the vehicle is shifted into gear (or the clutch engaged), can be caused by:
High engine idle speed.
Transmission shift operation.
Loose engine/transmission.
Worn U-joints.
Loose pinion gear nut and yoke.
Excessive ring gear backlash.
Excessive side gear to case clearance.
Damaged halfshafts.

The source of a snap or a clunk noise can be determined with the assistance of a helper. Raise and support the vehicle on a hoist with the wheels free to rotate. Instruct the helper to shift the transmission into gear. Listen for the noise, a mechanics stethoscope is helpful in isolating the source of a noise.

 

I wonder if a "tink" sound would fall in that category. Since the day I first
bought my SRT6 in 2004, about half the time I get in the car in the morning
and shift into reverse to back out of the garage, I have heard a "tink" from
somewhere in the drive line. Been there going on 6 years, and doesn't
seemed to cause any problem, that I'm aware of. But, now I'm wondering
if I should have the Service Center take a look at the rear end. Maybe
I'm on the edge of disaster. It is a very noticable sound, but not quite
a "snap" and certainly not a "clunk". 89,000+ miles on the clock now.

Coyote

 

mine is definatly rear diff noise. no noise going thru the gears it happens from a dead stop in gear then accerlate. the torque applied is making the pin move back and forth

 

Not sure but this does not sound right.
Have you checked the driveshaft bearing support? this will make the exact sound under the conditions described.
If your pin was that loose I would think you would have rear end noise at shift points, foot off the pedal, and likely may other times.
I may be way off but it just does not sound like the pin is the issue.
There is my idea without ever seeing or hearing you car. Take it for what it is worth.

 

I owe Rob a beer for having made a guess at the solutition to the loose pin issue.

Turns out that the pin being loose indicates that the roll pin has sheared off, and that is probably caused by fatally galled spider gears and PIN. https://www.crossfireforum.org/galle.../DSCN31062.JPG
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Sadly the die is cast and since I do not know of spare internal rear parts, there is little to do. Iam just glad that mine has not yelled at me yet. I believe that the synthetic gear and phantom grip LSD had diminished my exposure to a rear gear failure, THUS FAR> I BELIEVE THAT IT IS COMING!!

WHen the car takes off, the spider gears do not turn unless there is a difference in the rear wheel rotational speeds. If the gears were welded the rear wheels are forced to rotate at the same speed. When I turn my drive shaft on the lift, both of my rear tires turn the same direction because of the spring loading of the P grip LSD. The wavetec that I made a deposit on will do the same thing because of its gearing arrangement.

When you turn the car or have one wheel going at a different speed -slipping- the spiders allow a difference in axle speeds. When one wheel spins on take off the spinning wheel is going at a greatly different speed and the spiders are whirrling way fast while carrying the torque of the rear wheel s, thus heating and wearing on the drive PIN. If your in snow and the speedo shows that your spinning ONE WHEEL at a speed of 20 MPH, one wheel is going zero while the other is going TWICE THE SPEED OR 40!!t



Back in the day the tires on your car were balanced on the car by spinning and the rears were driven in drive while one tire was sitting on a wheel while the other was going twice the speedo speed. THe shaking in the car was then tuned to a minimum shake. Positraction was tough as both wheels were clutched to turn the same direction and spinning was going to spin both wheels. THis is before the off car balancers were available, not counting the bubble balancers that did not do a dynamic balance and cars used to shake AND the tires were belted not radials and often rather lumps.



If we all behaved and used the traction control, the spiders would never fail as the tc cuts the engine power and the rear brakes clamp down on the spinning wheel that is going the fastest. Life is not played that way.

Woody

 

Hey Woody, I'm a believer in synthetics too. But I think the Wavetrac needs non synthetic to work optimally.

Les

 

Additional data, FYI

slk 32 amg 0-60 video - Mercedes Benz SLK World Forum

Page down to the guy: 320 Dreamer

Quote: BE WARNED!! the rear diff. in this car is the weak point. after 350 rwhp and repeated launches the rear has been known to fail tearing the spider gears out and toasting the rear. use dr's and race at your own peril!

 

just so ya kno that guy be me!!

woody i had a discussion quite some time ago on benzworld with bruce r. he told me then of the rear diff issue and that it was known in the 32 world back in 2003, without any way to fix. i disagreed and have been proven wrong. this issue has been around for some time. i truly believe that until the srt-6 guys started racing the fire out of them the issue has been hidden because the 32 crowd tends to autocross more than run the 1/4

 

I think I covered this in my first post, so do I get a beer as well?
Only one spider has to seize to the pin to shear the roll pin, if two pins seize then one or both of them will break free from the pin, shear the pin in half which is not likely or break gear teeth
With one wheel slipping the diff is not seeing full torque, full torque is reached when the slipping wheel grabs. At that instant one spider slows down and the other speeds up, this is a tremendous shock load on all parts in the diff.
When the wheel grabs the spiders are forced against the pin and this is when galling may occur.
The spider that is whirling faster with wheel spin is not seeing a greater load than it would if both spiders were going at the same speed as it is not seeing full torque. Thus it will not wear or heat the pin more than normal.
Correct me if I'm wrong. Nobody has commented on my previous posts so am I to assume that they are correct as well?