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Old 10-23-2015, 10:57 AM   #1
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Unhappy Knocking sound inside differential

Hello, I hear in my 986s a stranger noise when I shut off the engine and sometimes when I go in first gear o rear very slowly and low revs.

I discover that when I move the axle (left or right), I hear the noise inside the differential, it look like a clearance, what do you think is the problem?

I recorded a video to hear the noise I explained:

https://youtu.be/BVdZbvXpN1s
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Old 10-23-2015, 11:19 AM   #2
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There is a common problem with driveshaft bolts loosening. Check/torque them all and inspect the boots.
Pelican have a helpful diy
Porsche Boxster CV Joints and Boot / Axle Replacement - 986 / 987 (1997-08) - Pelican Parts Technical Article
Or just get Wayne's book
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Old 10-23-2015, 02:11 PM   #3
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There is a common problem with driveshaft bolts loosening. Check/torque them all and inspect the boots.
Pelican have a helpful diy
Porsche Boxster CV Joints and Boot / Axle Replacement - 986 / 987 (1997-08) - Pelican Parts Technical Article
Or just get Wayne's book
I checked the driveshaft bolts and they are properly tightened. When I replaced the CV joints and disassembled the axles, I move the axle flange of the transmission and still the knocking sound. It heard inside the differential. Do you think there is any loosen or play of one of the parts inside?


Maybe bolts (3) that join part 1 with 2
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Old 10-29-2015, 07:44 AM   #4
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I moved by hand with the axle mounted and dissasembly, and the noise still

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Old 10-29-2015, 03:00 PM   #5
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What you are seeing is backlash in the ring and pinion gear. Have you checked the gear oil is at the correct level? With both wheels off the ground e brake off and transmission in gear, rotate one of your wheels, the opposite wheel should rotate in opposite direction if you have an open differential. If the wheel does not rotate then you probably have an limited slip differential and the clunking you hear could be the clutches engaging. Good Luck
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Old 10-30-2015, 02:10 AM   #6
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What you are seeing is backlash in the ring and pinion gear. Have you checked the gear oil is at the correct level? With both wheels off the ground e brake off and transmission in gear, rotate one of your wheels, the opposite wheel should rotate in opposite direction if you have an open differential. If the wheel does not rotate then you probably have an limited slip differential and the clunking you hear could be the clutches engaging. Good Luck
Yes y tried that, and when rotate one wheel the opposite rotate in the other direction. The oil of gearbox was changed less than 2 years, and leves was correct.

This knocking sound also make it when I run with gear engaged at very low rpm, for example when I go in reverse gear slow, it sound a loud knocking sound. At firts I was thinking that would be the flywheel, and replaced it, but still the sound.
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Old 10-30-2015, 03:03 AM   #7
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Depending on if your car is a base or S someone can tell you what years and makes of transmissions will fit yours. When you changed flywheel was the time to diagnose and remove the gear box cover and inspect the gears.

Good luck.
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Old 11-02-2015, 02:37 AM   #8
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Depending on if your car is a base or S someone can tell you what years and makes of transmissions will fit yours. When you changed flywheel was the time to diagnose and remove the gear box cover and inspect the gears.

Good luck.
My boxster is a S model. I think the problem is inside if differential
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Old 11-02-2015, 04:20 AM   #9
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My boxster is a S model. I think the problem is inside if differential
Well, trans gets pulled either way. Far fewer parts in there than in the gear box.

There's a few that will fit.
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Old 11-02-2015, 07:34 AM   #10
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You can pull the cover off your diff and remove and inspect the gears. Pelican has a great how to for LSD install. Just be sure to keep track of the shims you pull and re install exactly. The pic you have attached is of an LSD, yours will have the spider gears in the open diff.
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Old 11-02-2015, 10:35 AM   #11
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You can pull the cover off your diff and remove and inspect the gears. Pelican has a great how to for LSD install. Just be sure to keep track of the shims you pull and re install exactly. The pic you have attached is of an LSD, yours will have the spider gears in the open diff.
Thanks, I have seen the DIY in pelican to install de LSD.

So, you tell boxster S has got a differential like this:




Do you think there will be some clearance in parts 2 or 7?
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Old 11-02-2015, 10:38 AM   #12
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You can pull the cover off your diff and remove and inspect the gears. Pelican has a great how to for LSD install. Just be sure to keep track of the shims you pull and re install exactly. The pic you have attached is of an LSD, yours will have the spider gears in the open diff.
+ 1

You should not be driving the car before you check inside the gearbox, because if something is loose inside and gets caught between the differential gears, you will have a catastrophic failure.. (not to mention the possibility of having an accident)
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Old 11-02-2015, 11:54 AM   #13
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Originally Posted by heiwaz View Post
Thanks, I have seen the DIY in pelican to install de LSD.

So, you tell boxster S has got a differential like this:




Do you think there will be some clearance in parts 2 or 7?
Yes this is an open differential and is standard issue. Parts number 2 in this diagram point to the ring gear and the pinion gear shaft. They have a clearance ~.003" or so called the lash adjustment. This is set using the spacers in the housing. While this appears excessive due to the amount of movement you are seeing, I do not think it is the source of the knocking you are hearing. My thoughts are it is more likely from something going on with the part #5 which is the carrier and differential gears. This could be repaired or maybe upgraded to an LSD. However Gilles is correct in saying whatever it is I would find before I drove any further. Good Luck

Last edited by 911monty; 11-02-2015 at 11:57 AM. Reason: correct name spelling
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Old 11-05-2015, 01:10 PM   #14
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So, if the problem came from part number 5 can be repaired, but if it came from part number 2 can't be repaired, and need to replace the pinion and ring gear?
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Old 11-05-2015, 04:00 PM   #15
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So, if the problem came from part number 5 can be repaired, but if it came from part number 2 can't be repaired, and need to replace the pinion and ring gear?
Part #2 can be replaced but will require complete transaxle teardown to properly set the gear lash and contact. Don't know how readily you can find a used trans in Spain, but to replace ring and pinion along with a rebuild, a used trans may be better option. I'm hoping for your sake it is something in the carrier or the open diff that could be a DIY. Pulling the cover will give you a good idea of what comes next. To help with long range diagnosis, how do you drive this car, Smoky burnouts much?
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Old 11-06-2015, 12:04 AM   #16
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No burnout, I drive it with care, maybe sometimes insert quickly the gears when accelerate.
I noticed this noise after 3 years ago, slightly audible, and after 1 year I heard more, still since that with no increase sound.
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