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YOUR RESEARCHMixed feelings after engine mount replacement
Reported or suspected cause
shocks, springs and tires aren�t playing well together
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My fave culprit is shocks, springs and tires aren�t playing well together.
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Performed · outcome unconfirmed
Last thing touched, first thing checked: motor mounts.
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Performed · outcome unconfirmed · Original poster
Dampers were replaced 8 months ago with yellow bilsteins.
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Performed · outcome unconfirmed · Original poster
I drove to the shop, changed just oil, filter and the mounts and then the porpoising started.
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Performed · outcome unconfirmed · Original poster
I have yellow bilsteins replaced last year, new rear arms (1 month old).
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Hello everybody,
I feel that my rear is bouncing now that I have changed my old tired mounts with new OEM ones. Is this right? I have yellow bilsteins replaced last year, new rear arms (1 month old). I feel the car stiffer in the highway, but I feel a bit disappointed. Is my feeling right?
I don't think it is the engine mounts. I have not replaced the tranny mount. I think that the stiffer new mounts have uncovered an underlying problem. The tyre guy who also does shock absorbers and wheel alignment told me that it is unlikely to be the top mounts. He believes it is the alignment. But he is not a Porsche expert...
After driving it for a couple of hundred miles, I can say that it is bouncing 3 times. One is the normal return when hitting a bump, and then two other smaller ones follow. Could it be the engine moving as the new mounts are too soft or problematic? I hardly believe it is alignment issue. Tyres are at 39.5 psi rear.
Could be the rear dampers too. If you compress the rear of the car by leaning on it and have it bounce back, does it also bounce? Were the dampers ever replaced?
On the other hand, there must be a reason porsche made the 996 engine mounts hydraulically dampened. (it's much more expensive to manufacture...) So I can still imagine that it has something to do with it.
Dampers were replaced 8 months ago with yellow bilsteins. It does not bounce when stationary and pushing it down. Original springs. The mounts are aftermarket not porsche ones as I found out today.
Lets go back to the beginning, what car and model?
Which wheels, 17” or 18”
What size tires, factory or oversized?
Are your tire pressures set for the current tires that you are using?
Next step is to have an alignment done, these cars are very sensitive to the alignment!!!
I encourage you to find a shop with a Hunter Road-force alignment rack and a Tech familiar with alignment on the 996 Carrera. If your tech doesn’t have access to the equipment and experience with a 911 Carrera - FIND A NEW TECH!
If that doesn’t solve your issue then I would look at updating the transmission mount, factory mount to match the engine mounts that you just replaced.
Lastly adjust your tire pressure. Lower the rear a pound or two at a time to settle down the compression and rebound 👍
Good luck and keep us updated.
We are currently working on the alignment for my son’s 1999 Carrera with the M030 suspension.
The factory had three different alignment specifications for this optional suspension alone, see below.
ChatGPT can provide you with the factory alignment specifications for your application 👍
996.2 2002 C2 Tiptronic
Tyres are Michelin 285/30 zr 18. Rear pressure is 39.5 psi and front tyres are at 33.5 psi.
I am not sure if it is actually bouncing or if the engine is loose and I get the feeling that it bounces because the engine has some slack to the frame and works as a pendulum
Looks like you have the factory recommended 18” rear tire.
Verify that you also have the correct size front tire.
Here are the factory alignment specifications for your car, assuming that you do not have a LSD
Make sure that the shop has the right equipment and an experienced Tech.
Good luck 👍
Good advice provided by Patrick. Dont know what Michelins you are running and if they are new, but michelin typically has a stiffer sidewall. You can always drop the rear tire pressures to 36 or even 34 to see if it helps. Fronts you may want to try 32-34. The other thing to do is make sure your new engine mounts are torque down as well.
Jeez, the suggestions are all over the place...
OP, put your old mounts back and see if it drives as you know it...
The mounts each have a square at their base that mus mate with the square hole on the engine carrier plate. Make sure that is the case.
If you don't feel like doing that, then put the rear wheels on some ramps, chock the front wheels, crawl under the car and undo and retighten the lower shock absorber bolts to wheel carrier.
Do the same with the four bolts that hold the rear anti-roll bar to the subframe. For this both rear wheels must be at the ramps.
Were the auxiliary springs (around the piston rods of the shock absorbers) replaced too? Then do make sure they are the correct ones and not too long...
HTH.
Isalos - Which Bilstein? B4, B6, B8? If you replaced like with like, it probably isn�t shocks and springs. You�re tire pressures are sweet spot for lightly loaded. Last thing touched, first thing checked: motor mounts. You say the mounts are aftermarket, but what brand? It�s pretty hard to install the motor mounts incorrectly. You put the square peg in the square hole and torque to spec. But it can be done. My car had a prior gorilla fist with a wrench deform one of the square holes I had to reform it with heat and hammer to get a new mount to sit correctly.
Shocks were changed almost a year ago. I replaced the motor mounts as part of preventive maintenance,not because it had a problem. I didnt know when they were last changed so I just spend some money. I drove to the shop, changed just oil, filter and the mounts and then the porpoising started. I will do the wheel alignment this morning and let you know if all is good.
Then why did this bouncing feeling (porpoising) started just after them getting replaced? I am asking your knowledgeable opinion. Can you actually help by telling me how I can test if the engine is bouncing in the car. I drive it daily, I know how it feels. Mind it is a tiptronic.
This is today's progress: Car was way out of alignment. These are the before pictures, front and back (sorry for the Greek).
Front Axle
Rear axle
I did not see a major improvement. So I went to the MOT place for a quick check of the front and rear suspension. As expected, everything checked out OK. So it is not a suspension problem.
at the MOT place
I am now leaning towards the front gear box mount. The car has 300k KM (~200k miles) and probably has never been changed. The feeling I get with the new stiffer rear engine mounts is as-if the engine has some "play" that follows the return of the springs/dampers doing their work. If the front gearbox mount is not the suspect, I will buy a new set of rear mounts and take it from there.
Any other ideas are more than welcome.
True. Motor mounts are either correct or not. In general, mounts are body roll and driveline issues, alignment is steering and tracking, bounce is only suspension. My fave culprit is shocks, springs and tires aren�t playing well together. Hence, my question about which shock is installed.
And this thread is drifting a bit. The OP needs to systematically rule out probable causes in his head.
So all of this happened just after you put on new engine mounts. Has anybody gone back and looked at the installation of them? Where are the tail pipes relative to the rear bumper? Do they look properly positioned, or do they hang low and are they up tight?
Go back and re-do the engine mount installation, it's easy. Get new Rein mounts which are OEM. You could be chasing your tail with all of these other items.
I have ruled out the suspension parts today. I ruled out alignment. I ruled out top mounts, that have not been changed since my ownership of the car. Unfortunately I threw away the old mounts or else they would be in the car already. I will reach to the end of this, and it will be a nice thread to read... Chaotic but nice!
I was there during installation. The square thing got in there correctly, all was tightened to spec.
I use the term bounce but please note that English is not my primary language. What I feel is a wobbling coming from the rear.At specific speed, I expect the suspension to go up-down and settle, but I feel it like a tennis ball, 2 smaller bounces.
My bilsteins are the B6 with original springs.
The new engine mounts are stiffer than the old ones and combined with the 300'km old, worn out, gearbox mount the whole engine+gearbox combo now prpbably pitches inside the body, when the rear travels over a bump and that is what you feel.
-->replace gearbox mount
Nice job on the alignment 👍
Before spending more money try dropping the rear tire pressure two pounds at a time and see how this affects the ride. I would do this a few times and then drop in one pound increments. Let us know if the rear end settles down.
My mechanic has kept the old mounts. So we put them back. Night and day. The new aftermarket ones were of substandard quality. The rubber is hanging out more....
Avoid this maker: JUMACH.
So we are now ordering directly from Porsche...
Great to hear, isn't this what I said, go back and look at the mounts?
:-)
It usually something you touched. Glad you worked it out. Rein is the actual OEM of the mounts, see if you can find them. Happy Holidays!
Yes you did... Sometimes you don't want to believe that a new part is defective... Maybe it is okay for mid engine boxsters. This maker is widely available on eBay so be careful.
When we lifted the car to replace the front engine mount, I put my hand and touched the rubber part. It was literally 1.5 inches down hanging.then we put the car down and reversed and immediately braked. The engine was tilting. Simple tests to verify the malfunctioning of the mount. Here is one more picture comparing the old vs new one. Can you spot which one is the new one?
I changed mine last night and now I�m experiencing the same exact thing, so in some form or fashion, swapping mounts can make it bouncy. It�s feels the same as wheel hop at a drag strip.
This is one time you need genuine or OEM. They are an important part. They are not that expensive overall.
https://www.autoatlanta.com/porsche-...section=109-00
yeah I ordered off eBay they were suppose to be Rein, but they arrived at Bapmic. The seller gave me back $75 or so refund to keep them. I shouldn�t have.
Hands down the best
https://www.wevo.com/Products/Chassi...gineMounts.htm
The manufacturer offers the best price vs. Pelican Parts. I also replaced the transmission mount.
This is a source reference. Confirm exact model applicability in the original material.
