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Replacing Motor and Transmission Mounts
 
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Pelican Technical Article:

Replacing Motor and Transmission Mounts

Time:

2 hrs

Tab:

$80 to $200

Talent:

**

Applicable Models:

Porsche 911 (1965-89)
Porsche 930 Turbo (1976-89)

Parts Required:

Motor mounts, transmission mounts

Hot Tip:

Replace one side at a time

Performance Gain:

Stiffer shifting, less vibration from the drivetrain

Complementary Modification:

Upgrade to solid mounts (recommended for racing)
101 Projects for Your Porsche 911

This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.

One of the most common parts to deteriorate on the 911 is the engine and transmission mounts. Because of the design of the 911 drivetrain, the mounts don't wear out as much as they do on some other Porsches, but they still require replacing after many years. The rubber that is contained within the mounts becomes old and brittle, and doesn't perform a good job of isolating the drivetrain from the rest of the chassis.

Old, worn out motor and transmission mounts can cause shifting problems because the drivetrain is no longer firmly held in its position. One sign of this failure mode is the gearshift knob jerking backwards under hard acceleration or difficulty selecting gears during cornering. A visible sign that the motor mounts need replacing is the appearance of cracks in the rubber of the mounts. The rubber will deteriorate over the years and need to be replaced, even if the car has relatively few miles on it.

The first step in replacing the motor mounts is to place a jack under the engine and support it. Make sure that you use a block of wood or some newspaper to protect the bottom of your engine case from damage. See Project 1 for more details. Once the engine is supported, you can begin removing one of the bolts that fasten and hold the motor mount bar to the mounts. The mounts themselves are located in the engine compartment, along the back shelf (see the photo in Pelican Technical Article: Engine Removal, Engine Removal). Remove the long bolt from the center of one of the motor mounts. On the later cars, these bolts are threaded into the motor mount bar itself: there is no nut on the other end. These bolts are often rusted in place and should be lubricated generously with WD-40 from the bottom. A sticking bolt can actually bend the mounting cross-bar when you are trying to remove it.

It is advisable to replace each motor mount, one at a time. Otherwise, the weight of the engine may cause it to shift, and it may become misaligned. Also, the motor may drop down slightly from its normal position. Replace the mount on one side and then replace the one on the opposite side.

Once the center motor mount bolt is removed, then you can simply remove the entire motor mount by removing the two smaller bolts that attach it to the chassis. These bolts have corresponding nuts that must be kept from turning when they are being removed. Access to these nuts is gained by reaching down underneath the shelf. Once you have the motor mount removed, then simply install the new one in the same place. Tighten up all the nuts, and perform the same procedure for the opposite side.

The transmission mounts are very similar to the motor mounts, except for the early cars. Unfortunately, the early cars have a once piece mount and support bar design that is no longer available. The rubber transmission mounts are embedded into the two foot wide support bar that mounts the entire transmission to the chassis. Sometimes, good used mounts can be found, but they are getting scarcer every day. To replace this one-piece mount, support the transmission with the jack, and unbolt the mount from the chassis and the transmission. Depending upon the configuration of your car, you may have to remove the rear sway bar in order to remove the transmission mount.

The later style 911s (1972-on) were equipped with a transmission mount bar that incorporated replaceable mounts. These mounts are very similar to the engine mounts, and should be replaced in a similar manner. Make sure that the transmission is well supported with a jack before you remove either of the transmission mounts. As with the engine mounts, work on one side, and complete the installation prior to removing the mount on the other side.

When you are finished, you should feel an improvement in the shifting of your car, and the drivetrain vibration should feel a little tighter and less sloppy. If you are a hardcore racer who wants a really stiff drivetrain, then you should consider upgrading to solid mounts. Keep in mind however, that that solid mounts will make the ride a lot less comfortable and much more noisier.

The transmission mounts can easily be seen from underneath the car.
Figure 1

The transmission mounts can easily be seen from underneath the car. Shown here are the mounts on a later-style 911, which are replaceable. On the early cars, these mounts are embedded into the steel transmission mount bar and cannot be replaced. Used transmission mount bars with good rubber mounts can still be found, but they are getting increasingly difficult to locate.

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Comments and Suggestions:
Andy Comments: When the 1970 Porsche 911T gets driven for a while and shifted through the gears, it then becomes impossible to get into 1st or reverse. I have to turn engine of and then I can get into 1st and restart the engine! Is the engine to hot and the alignment to the shifter has changed?
October 13, 2015
  Followup from the Pelican Staff: Could be an issue in the trans when it warms up. I would check the linkage for tightness, if tight. Check the fluid for signs of internal wear. - Nick at Pelican Parts  
Dick Comments: My 1984 930 has a non replacable type transmission support. Is the replacable type a direct swap? Any particular model? Thanks, Dick J
April 16, 2014
  Followup from the Pelican Staff: I'm not 100% sure. I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
 
frannyB Comments: Dumb question, but, for an 86 Carrera, the engine and tranny mounts are the same part number same part. Is that correct?
July 15, 2013
  Followup from the Pelican Staff: If the part number is the same then they are the same mounts. The part numbers should be different though. Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
 
Schnell87 Comments: Based on research I've been doing, it appears that Carrera's with G50s have non-replaceable transmission mounts. Can you confirm if this is true and if so, are there any other options besides machining the stock transmission mount bar to accept an aftermarket mount such as what WEVO offers?
February 14, 2012
  Followup from the Pelican Staff: The 1987-1989 G50 mounts with a separate cross member which comes from the Porsche instead of the integrated isolator bushing which the 1990 and lat?er G50 has. - Nick at Pelican Parts  
emre911 Comments: I just replaced the transmission and engine mounts with polyurethane two piece mounts black on my '84 Cab. To press out the rubber from the old mounts was not that difficult once drilling some holes into the rubber, and then putting them in a wise. It turns out that in the cabriolet, the engine mounts have harder rubber, a simple upgrade would be installing cabriolet engine mounts as the transmission mounts.

After the engine mounts were installed, the cross member came very close to the mounting brackets, I had to put a washer to move it back to 1/4" or so clearance.

Now with polyurethane mounts all around, the car feels much tighter, there is no back and forth jolts in first gear when lift-off the accelerator, more authoritative 1-to-2 shifts, etc. There is tolarable gear noise increase, but not much difference in vibration.
November 6, 2011
  Followup from the Pelican Staff: Thanks for the tips. If you are willing to put up with more vibration and road noise you can also use solid mounts - Nick at Pelican Parts  

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