I hope this helps some people out but you do it at your own risk.
This is my first how-to, it explains how to replace the crossmember mounts on a 99' P11 MT. Since automatics have the same mounts it should be good for that. I'm not too familiar with P10's but I suspect it's same/similar. Feedback/corrections welcome!
Search terms: engine mounts, motor mounts, howto, how to, crossmember, cross member, xmember, x-member
What you need:
Make sure you have all the stuff you need before you start as it will make the job a heck of a lot easier!
1) 2 Jacks
2) A total of at least 3 jackstands (2 for the car and one for the engine)
3) PBBlaster or equivelent (penetrating liquid)
4) Some patience
5) Couple of hours
6) A friend to help (preferred)
7) A long 2x4 and a saw
9) wheel chocks
What to do
1) First thing is you need to do is get the front wheels off and the car jacked up to working height. So, as usual e-brake it, chock rear wheels, jack up the front and place the jackstands
The general idea here is to prop the engine up on the oil pan and on the transmission using a jack/jackstands and then removing the entire crossmember, pulling it out and then replacing the 2 mounts on it and then reinstalling the crossmember with the new mounts already on it.
2) Take a look at what you're working with.
- Each mount is connected to the engine with a long bolt that goes horizontally. The front mount as a NUT on the driver's side. The rear mount has a welded nut. It's not that you have to cut it off or anything, it's just part of the engine bracket. You do not remove it by any means. When you put it back together you'll be threading the center bolt back through it again.
- Each mount is connected to the cross member with 2 bolts, you can really see these bolts, nor do you have to worry about them. You'll be able to see them and have easy access to them once you've dropped the crossmember
- The cross member is held onto the frame with 4 bolts (2 in the front and 2 in the rear)
3) SPRAY everything with PB blaster, don't be shy. These bolts are under the car so they see their fair share of water. At this point, it's probably a good idea to mention that I used airtools and given the tightness of the location of many of the bolts, it would have been difficult to get everything off. If you're going to use handtools be cautious not to snap bolts and definitely have a breaker bar handy.
4) Now you're ready to get the engine supported. The 2 places I used were under the oil pan and under the transmission. This is where you need the 2x4 or 2x6. You'll really need 2 pieces. If they're not already cut, cut them now to a reasonable lenght (couple of feet at the most).
5) Repeat step #3
6) Place a 2x4 ontop of your floor jack and then position it such that it's under the oil pan. Jack the oil pan up until you can kind of see the engine moving a little bit. Now place a jackstand with a 2x4 under the transmission to support that side of the engine. Lower the jack under the oil pan a bit until you feel you have equal pressure on both the jack (oil pan) and the jackstand (tranny). I used the center of the oil pan and there happened to be a square flat surface on the tranny what was perfect for the 2x4.
One other note: remember you are trying to jack the engine NOT THE ENTIRE CAR. So watch your jacking
7) Repeat step #3
8) The engine should now be supported fairly well and you are ready for your next task which is to crack loose the center bolt that goes through the middle of each mount. This is a pretty important step. For this step, just crack the bolt to make sure that you can get it loose.
9) You are now ready to remove the center bolts. The reason step 8 and 9 are separate is because the process of removing the bolt tells you whether you've appropriately supported the weight of the engine. First go ahead and ratchet them out until you're beyond the threads (rear) or the nut comes off (front). Now take the bolts out. The bolts should SLIDE out or be rubber malleted out but it should be smooth. If it's taking a lot of effort or a lot of hammering then the engine isn't supported.
If you've got it supported correctly the engine shouldn't be pushing down on these bolts. If you need to, ratchet these center bolts until they are reasonably tight and then go back to step #6 and do it again.
Once you've got the rear bolt out and the front bolt/nut combination, you're ready to remove the four bolts that hold the crossmember to the frame.
10) This is where a second jack is helpful, Jackup the center of the cross member (towards the back, beyond the bend in it) very lightly so that when you remove the crossmember bolts the crossmember won't just fall
11) Remove the 2 front bolts and the 2 rear bolts
12) Lower the jack on the crossmember slowly and grab the crossmember. At this point you should be hold this crossmember in your hands, the engine should supported on the jack/jackstand comibination
13) Now you can actually replace the mounts. Each mount is held on by 2 bolts. The rear one is the diamond shaped one.
14) Remove the 2 bolts and replace each mount. MAKE sure that the new mount is facing forward, there is an arrow that points forward. Make sure you look up the torque specification for the bolts (see attached FSM screenshot)
15) Clean it up and admire the new mounts, ooooooooooo
16) Now time to get everything reinstalled, first slide the crossmember into place. You can use the jack to hold the crossmember in place or have a friend hold it while you finger thread the 4 bolts that hold the crossmember to the frame. Put a little never seize on them
17) Now that the crossmember is suspended, fully reinstall the center bolts that go through the mount. Make sure it's line up properly and they should slide right on through (a little bit of rubber malleting will help). Never seize is probably a good idea here.
18) Tighten the center bolts, again watch your torques.
19) Tighten the 4 crossmember bolts, watch your torques.
20) Lower the jack that was propping up the crossmember
21) Raise the jack under the oil pan, remove the tranny jackstand, lower oilpan jack. Remove all tools. It's important to do all of this stuff slowly and deliberately. Everything is back together so it should be solid but just be careful.
22) Check torques again.
ENJOY NEW MOUNTS!