Porsche Repair Questions? Ask a Mechanic for Answers ASAP
Hello and welcome to Just AnswerI'd say that this sounds like a worn drive shaft joint - typically these won't produce any vibration unless badly damaged but they can be noisy or 'clonk' for a long time beforehand, turn the steering to full lock and look at the drive-shaft rubber boot there should be no rips or tears in it and the suspension should be clean and dry of any grease. If you reverse at a reasonable speed with the steering on full lock a worn joint will 'click'.
you can also inspect the rear joints but obviously steering won't have much effect
If these are OK then I'd suspect that the propshaft either has a worn joint or the centre bearing is worn or its out of balance
you can easily check for for any slack in the propshaft joints by twisting either half by hand and feeling for any play as there should be virtually none
the centre bearing is quite loosely mounted so this can be moved normally but if you can run the car in gear with the wheels off the ground and then feel the centre bearing housing for vibration if there's any then consider replacing the unit
and then look along the propshaft for any signs of a missing balance weight as these take the form of little 3/4" squares that are welded onto the shaft - as they are only tacked on they can sometimes come loose and be lost resulting in the shaft being out of balance - if a joint is worn this can also shake them loose
so if a joint is replaced its good practice to have the shaft re-balanced afterwards
My goal is to give you the best advice that I can and I hope that I've helped today. Please remember to rate my service by selecting from the 5 stars at the top of the screen before you leave. If you need more help, use the reply box to let me know. If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further repliesThanks Matt
well that's why I 've suggested checking mechanical aspect 1st, run through what I've mentioned and let me know what you find
in that case I'd check that all the wheel bearing are OK
- jack the car up so the wheel is off the ground (you’ll need to do this for all 4 corners) and shake the tyre from top to bottom and from side to side (with someone holding the steering wheel on the front) there should be no play in either direction. Any play in 1 direction will usually require a joint to be replaced, if there’s play in both directions then the wheel bearing may be at fault
If this is OK then I'd check the front and rear differentials oil level and condition
Hido you still need help?Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further repliesThanks Matt
Well its possible that the jerking is an engine issue such as an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.
Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.
The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak. Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident. Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion will make a leak worse) so leaks can be better or 1 vacuum leak path that you won't find with the above test is if the brake servo is leakingso try clamping off servo hose to see if this has any effect