axle or diff?

[07turbeaux]

Today I went to the fine folks at Northwest Wheel and Tire in Bend OR and was set up with smaller wheels and tires. I asked them to address the clicking sound coming from the rear of the car. While idling in the air im first gear the clicking was clearly coming from the diff. IN FACT the diff was bouncing a little in sync with the clicking.
So is it possible that a half axle going bad could feedback into the diff? I rotated both wheels manually and the click and bounce was still there.
What is the definitive test to determine axle VS diff. Remove one axle at a time to see if it affects the noise?

Thanks in advance for your thoughts.

Ralph

[Tom]

Today I went to the fine folks at Northwest Wheel and Tire in Bend OR and was set up with smaller wheels and tires. I asked them to address the clicking sound coming from the rear of the car. While idling in the air im first gear the clicking was clearly coming from the diff. IN FACT the diff was bouncing a little in sync with the clicking.
So is it possible that a half axle going bad could feedback into the diff? I rotated both wheels manually and the click and bounce was still there.
What is the definitive test to determine axle VS diff. Remove one axle at a time to see if it affects the noise?

Thanks in advance for your thoughts.

Ralph

I don't know of a definitive test, but the axles come out fairly easily. You might just take them out and repeat the test. If the click goes away, replace the CV joints. If it remains, fix the diff.... You can also flip the axles to stress a different part of the joints if you need to drive the car to be sure the sound is/isn't there...

[07turbeaux]

forgot to ask. The noise in the rear of the car is hardly noticeable and with the radio on cant really be heard.
Is it possible that the diff could lock up?

[PSU_Crash]

Sounds a lot like CV joint issues to me.
Can the diff lock up? Sure, if something comes loose in there and binds. My bet is on the axles though.

[07turbeaux]

while i have removed axles on P-cars and Beetles it was long ago. Will the axles just drop down if I only remove bolts on trans? Or do I need to remove all four sets of bolts

[Tom]

while i have removed axles on P-cars and Beetles it was long ago. Will the axles just drop down if I only remove bolts on trans? Or do I need to remove all four sets of bolts

They will drop down if you just unbolt the tranny side. Tranny coolers and mufflers sometimes get in the way, but for tick-testing on jack stands, you should be able to make that work (on digital paper anyway...).

[dr bob]

Hi Ralph --

One thing to look hard at is whether those inner CV joints are bolted securely to the drive flanges on the transaxle. More than a few cars have suffered from the CV joint loose on the drive flanges after a 'service' that left the bolts not tight enough. I don't have the 944 torque specs handy. For the stuck-up cousin 928, they are tightened progressively to 60 lbs/feet in an alternating pattern. A telltale of loose bolts there is grease on the outside of the CV housing, leaking past the gaskets.

I've decided that getting those tightened correctly includes a few extensions, enough to get the torque wrench out to the wheelhouse. I use impact-rated Allen drivers.

Reminders: The torque setting includes a reminder that the bolts and the drive flange are lickin' clean and dry. No grease on threads, and that demands that the holes through the inner joint are also perfectly clean. No debris or grease in the socketed drive end either, so the driver can go all the way in. A gun brush and some Brake Clean will help. Wear gloves and eye protection, then get it surgically clean. Inspect the bolts for any damage to the threads while you are there; bolts that have been driven while loose will have worn threads and possibly be bent if they got really loose. Replacement is the only good option, and they should be replaced in identical sets even if just one appears to be damaged. The 60 lbs/feet seems (and feels) like a whole lot for a 10mm bolt diameter with fine threads, but it is essential to keeping all those spinning bits together. Check the actual torque requirement for your car, of course.

---

If you car is with you in HDR territory, I'll have room on the lift sometime in April when the cars here get "spring cleaning" done. Makes it a lot easier than crawling under the car a few dozen times to R&R drive flange bolts one or two at a time. I don't like to drive with dirty springs...

[Tom]

Hi Ralph --

One thing to look hard at is whether those inner CV joints are bolted securely to the drive flanges on the transaxle. More than a few cars have suffered from the CV joint loose on the drive flanges after a 'service' that left the bolts not tight enough. I don't have the 944 torque specs handy. For the stuck-up cousin 928, they are tightened progressively to 60 lbs/feet in an alternating pattern. A telltale of loose bolts there is grease on the outside of the CV housing, leaking past the gaskets.

I've decided that getting those tightened correctly includes a few extensions, enough to get the torque wrench out to the wheelhouse. I use impact-rated Allen drivers.

Reminders: The torque setting includes a reminder that the bolts and the drive flange are lickin' clean and dry. No grease on threads, and that demands that the holes through the inner joint are also perfectly clean. No debris or grease in the socketed drive end either, so the driver can go all the way in. A gun brush and some Brake Clean will help. Wear gloves and eye protection, then get it surgically clean. Inspect the bolts for any damage to the threads while you are there; bolts that have been driven while loose will have worn threads and possibly be bent if they got really loose. Replacement is the only good option, and they should be replaced in identical sets even if just one appears to be damaged. The 60 lbs/feet seems (and feels) like a whole lot for a 10mm bolt diameter with fine threads, but it is essential to keeping all those spinning bits together. Check the actual torque requirement for your car, of course.

---

If you car is with you in HDR territory, I'll have room on the lift sometime in April when the cars here get "spring cleaning" done. Makes it a lot easier than crawling under the car a few dozen times to R&R drive flange bolts one or two at a time. I don't like to drive with dirty springs...

Very good point to check on that before pulling things apart!

I'm working on a handy-dandy 944 torque spec list for Carpokes. We could add a similar 928 list if you had any interest in (ahem) compiling the entire list. Quite jealous to hear of your V8-sized CV bolts. The 944 uses M8 bolts with triple square socket heads and a comparatively measly 30 ft. lbs each. They love to come loose for all the same reasons though, including in particular forgetting to torque in a star pattern.

[dr bob]

Hi Tom --

I'm a little surprised that the 944 bolts are smaller. 951 cars are pretty easy to upgrade to the 928 V8 drive torque levels, and I would expect them to be similar. The specs for both cars are both about 2x the torque one would expect for the bolt sizes.

I do in fact maintain a 928 torque table as a spreadsheet. It's a shared development project that started 25 years ago with our SoCal 928 owners group. I keep one printed on a 11x17 sheet, double-sided, laminated to survive actual use in the workbay. It's shared IP so I'm hesitant to just post it here. We can have an offline discussion on options, including generating a similar version for the 944 (and other Porsche) cars. The always-WIP 928 version includes the actual bolt and nut sizes, plus some descriptions of fasteners that deserve replacement with service, special tools needed, etc.. More than just "how tight". I'd want to go hunt down the most up-to-date version too.