After experiencing some difficulty shifting the car while under load, my mechanic recommended replacing the motor mounts as a first step in diagnosing the problem. I decided to replace the stock motor mounts with RS motor mounts. Surprisingly, they are in the same price range as the stock motor mounts. Additionally, the mechanic encouraged me to change them, saying it was really easy. I took his advice and followed his directions. Here they are.
First of all, make sure you get all the parts. The stock motor mount is a one piece hydraulic unit, while the RS comes with several bolts, seats and washers in addition to the actual mount. You can reuse the bolts that hold the mounts in place in the engine compartment and the nut on the bottom that holds the bolt to the engine carrier. I decided to get new ones just in case. Here are the part numbers:
Put the car up on jack stands. I decided to only lift the rear end. Place the jack under the engine and apply just enough pressure to the engine where you see you exhaust tips move slightly. You donít want to lift it to where it takes any pressure off the jack stands. Here is what it should look like.
Open the engine lid and locate the motor mounts. The one on the passenger side is clearly visible, while the one on the driver side is covered by hoses from the AC compressor. Here is what they look like
I started off with replacing the passenger side mount because it looked much easier. First, take a 18mm or 19mm (Not exactly sure in this case) socket with a long extension and loosen and remove the nut from the bottom of the car that holds the engine to the mount. Mine was torqued down pretty good so I did have to use extra force.
After removing the nut, go to the engine bay and remove the 13mm bolts. At this point you may want to lower the engine slightly as it helps to slide out the mount bolt. Once the mount is disconnected, you will notice that the AC compressor is in the way and you canít easily slide the mount out. I turned it several times and in different directions until it finally was able to slide out.
Here is what it looks when you remove the
Here is the RS mount.
Here is where it gets a little tricky. First, raise the engine again to where the carrier is up to the mount location. Take one washer (999.025.074.02) and one seat (901.305.311.00) and place them down onto the engine carrier. Make sure you align them to where you can see the opening. The original mounts had a rectangle notch on the shaft of the bolt so that aligning them was easy. With the RS mounts, you have to take your time and make sure they are aligned. Now, take the mount and place it down in the opening. You will notice that the washer and seat have moved a little. Take a long screwdriver (something long and skinny) and adjust the opening so that you can place the bolt through the hole. Now take another seat and washer and place them on top of the mount. Take the large bolt (900.082.030.02) and run it down through the mount. Take the large locking nut (999.084.215.09) and just get the nut to go onto the bolt to make sure nothing gets out of place. Next, insert the smaller bolts (900.074.134.02) into each side of the mount and tighten them down to approximately 40Nm. I donít have the exact torque specs but was told by my mechanic that 40Nm for the smaller bolts and 95Nm for the larger bolts would be good a start. Upon further reading, the correct torque setting for the large bolt is 85Nm but I still havenít found the setting for the smaller bolts.
Here is where you need a friendís assistance. First jack the engine up just a little more than before. I actually jacked it up to where my jack stands wiggled just a little. I wanted to make sure that the engine was at its highest point in the car. Next, take two 19mm sockets, one with a long extension (bottom) and one with a medium extension (top) and begin the tightening process. I used my torque wrench on the bottom since it does have a long extension and had my wife hold the top of the bolt in place with a medium sized ratchet. (None of my friends were around, so I asked her for her assistance. If she could hold in place, so can anyone.) I torqued the nut down to 95Nm (even though the spec is at 85Nm). The nut is a locking type that requires plenty of force to get it moving up the bolt. That is it for the passenger side. (Make sure you re-torque the 13mm bolts when you get the car back on the ground)
Here is what it should look like when you
The driver side is very similar with one exception; you have to move the AC compressor lines to get access to the mount. First, take off the bolt (7mm) holding the compressor lines to the fan housing. Then take the plastic hex bolt (6mm) holding the compressor lines underneath the wiring harness box. This should give you enough movement in the lines to get the old mount out and replace it with the new one.
Here is a picture of the bolt holding the
compressor line to the fan housing.
Here is a picture of the 19mm bolt under
the driver side of the engine carrier.
You follow the same procedure described above for the driver side mount as you do for the passenger side. Make sure you let the engine down a little when removing this mount as you have less room to work with on this side as you try to slide the old mounts out. When you are done, move the compressor line back in place and tighten them down. You may want to wait until you have the car down on the ground when you do this because checking the torque settings on the mount is a little difficult (not impossible) with the lines in the way.
As a final check, when you get the car back on the ground you should re-torque the 13mm bolts as a double check. Also, I was able to torque the large bolt from the top once the car was on the ground but I thing this should only be done to ensure that you torqued it properly the first time.
Replacing the mounts was easier than I thought. I would compare it to replacing mufflers. There is definitely more noise/vibration in the car but the difference is minimal. If a cup car is at level of 10 and stock is 1, I would rate the harshness/noise/vibration of the RS motor mounts as a 2. My initial impressions are that the transmission does shift a little better and that some of the wiggling I experienced in the rear end as it shifts its weight has decreased. I would definitely recommend this upgrade to anyone, even those that arenít looking for increased stiffness. The reason; I noticed that my original motor mounts were gone (dead). One shaft was longer than the other causing my engine to be lower on one side as compared to the other. The difference was only maybe 3 to 5mm but it was enough to make me readjust the exhaust tips. I guess just like shocks and struts, the hydraulic mounts wear out. Here is a picture of them side by side. Once you get past the optical illusion of one being closer to the camera, you will notice that the one further away (on the right) has a longer shaft.
Additional information update for 993 twin turbo owners
(Oct / 2003)
RS Motor Mounts in a TT
The only problem with our cars is that the engine carrier is a bit taller than the NA cars, so the normal bolt specified on Robin's DIY is not long enough.
The correct bolt is a 12mm, 1.5 pitch, GR 10.9, 120mm length bolt. The original bolt in the DIY was a 105mm length, GR 8.8 bolt. The extra 15 mm length leaves about 10mm of threading past the nut when fully assembled and torqued.
I didn't have time to test out the car yet, since there are a few other things I want to change "while i'm in there", but I'll post my impressions when I get the car back together.
I got the bolts from a place called http://www.metricspecialties.com/ They had great service and prices as well. Although they usually have a small minimum order. I had to order 6 bolts. So I have 4 extra bolts, so if somebody needs a pair, let me know. Rennlist members only please... Locals preferred over having to ship.
Here are some pics: