Transmission Mount

[Davis]

I have been breaking the rear transmission mount on my GTI with great frequency. Is this a normal occurance? If not, I would appreciate suggestions on how to correct this problem. Thanks!

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#63ITB Rabbit GTI

[Greg Amy]

Davis, breaking the rear transmission mount is definitely NOT a normal occurance. Breaking it how? At what point on the mount?

Have you made sure your front mount is in good shape and properly centered? Is you engine properly centered left-to-right? Are the other three mounts in good shape?

[Bill Miller]

Davis,

The ususal cause of broken rear mounts are a worn out front mount. Either the front busing is bad, or the arm is tweaked. I've seen several broken rear mounts. They've all been cracked on the flange that attaches to the chassis. The flange cracks at the bolt holes.

Also, have you mounted any kind of engine stay rod to minimize the front/back rocking?

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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608

[RSTPerformance]

Davis-

Stop hitting the gas so hard http://Forum.ImprovedTouring.com/it/wink.gif

For real though... we have had multiple issues with breaking that mount as well on the Audi's... Replace all the mounts, or check to be sure they are infact good. Sometimes the mounts look good from a view while they are still in the car, but use an engine hoist and lift up the motor, or get someone else to "rock" the motor and check to be sure everything is tight and not in need of replacing.

Stayrod is also a good idea... I "replaced" my front mount with a solid stayrod (cause it was easy) till I decided it wasn't very legal... remember when buiding a stayrod you can add a stayrod but you can not change an existing motor mount.

Raymond

[Davis]

Greg, the rubber is tearing away from the metal usually on the chassis side, but it has also occured on the transmission side. The side mounts and front mount are in good condition and appear to be correctly located (centered). I have thought about adding a shim behind the front mount to get deeper engagement of the bushing.

Bill, I do not have an engine stay rod, but have been thinking that may be the answer. Could you give me some information or steer me to some information about stay rods. Where are they connected? Do you buy them or make them? How are they made? etc.

Raymond, your comment about hitting the gas to hard may be closer to the truth than I would like to admit. I do have a four puck clutch and it does what it's supposed to do. As a beginner I do question if I'm simply "abusing" the equipment.

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#63ITB Rabbit GTI

[Knestis]

This is a general statement rather than anything based in the specific facts of this case, but it is entirely possible for a stayrod to change the motion of the engine enough to put stresses on an existing engine mount, beyond those that it was designed to withstand.

Simply locking up motion in one direction may or may not be a good idea.

You won't be surprised to hear that engine mounts were a big issue back in my rallying days. We played a really irritating tail-chasing game where we'd break a motor mount, reinforce that one, and simply chase the failure somewhere else.

If you look at the mounts as a system, each is designed to resolve loads along a particular axis. The net result is CONTROLLED movement of parts, optimized for street use. The kind/size of movement that we want in a racing car is different but garage engineering can get it wrong more easily than it can get it right.

I'd start by doing a post-mortem on the busted mounts: They might be telling you which way they went too far before they failed. Luckily, it's the rubber tearing so stress failure isn't an issue. It logically has to be over traveling, probably in a direction it wasn't intended to deal with loads. With the busted piece in there, reef on the engine and see what kind of movement you get down there. That might point you in the right direction, too.

I can't strum up the appropriate Bentley picture in my head but if your stayrod is on one end of the engine, it might be turning pitching motion (tipping fore/aft) into yawing motion (rotation about the vertical), loading that mount sideways...?

K

[This message has been edited by Knestis (edited November 29, 2004).]

[67ITB]

Davis,

I have gone through tons of motor mounts in my cars and one thing that I learned (yea it took awhile!!!)
1. To replace all the mounts at the same time. This way your not chasing the problem from one place to another.
2.Use only “quality” replacement parts. Your time is more important than saving 5 bucks on an “El’ Cheapo” mount that only wears out twice as fast.
3. Be careful with the Stay Rod, I have seen the attachment points on both the engine and the chassis break, bend, twist, tear…

I hope this helps
Good luck and I feel your pain

Matt Bal

[SamITC85]

Davis,
I had one bust at an Autocross, it was a polyurethane one. Fortunatley Matt B., I believe had a spare one in his van. (It was at a NESCC event at Orange Airport and I was driving the UMass Rabbit) After we replaced it we never had a problem with it once we properly centered the engine and got rid of the illegal urethane bushings and went back to the stock ones we never had a problem again.

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Sam Rolfe
TBR Motorsports
#85 ITC VW Rabbit being converted to LPHP
#85 GP Scirocco

[67ITB]

Hey Sam,
I remember that!!!!
That van has hauled many parts to keep VW’s running. Unfortunately its usually one of my VW's that ends up needing the parts.
I have always been a pack rat and things have only gotten worse since we started road racing!!!!
So feel free to stop by next year and say hi.

Matt Bal

[SamITC85]

Matt,
I just remember you digging through all the parts in the van to find it. It saved our day. I would love to stop by but it is a long tow from Arizona to NHIS. I may try and make it back for a race this summer though.

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Sam Rolfe
TBR Motorsports
#85 ITC VW Rabbit being converted to LPHP
#85 GP Scirocco