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Transmission hitting tunnel

This is a discussion on Transmission hitting tunnel within the General Help forums, part of the LSx Technical Help Section category; Ok I have replaced the stock trans mount with a prothane one and it was a very rough ride. So ...

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    Senior Member TransAm11973's Avatar
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    Angry Transmission hitting tunnel

    Ok I have replaced the stock trans mount with a prothane one and it was a very rough ride. So I went back to a stock one and the trans. is hitting the tunnel again on hard accel. Someone told me its the motor mounts that went bad and thats causing the ass end of the transmission hit the top of the tunnel. Does this sound about right? Anyone else had this issue?? Thanks for the help!

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    O U 8 1 2 Spaz's Avatar
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    Quote Originally Posted by TransAm11973 View Post
    Ok I have replaced the stock trans mount with a prothane one and it was a very rough ride. So I went back to a stock one and the trans. is hitting the tunnel again on hard accel. Someone told me its the motor mounts that went bad and thats causing the ass end of the transmission hit the top of the tunnel. Does this sound about right? Anyone else had this issue?? Thanks for the help!
    replace with a prothane mount again and also replace your motor mounts with the prothane ones...

    sounds like you have my problem... broken motor mount on one side that keeps tearing through trans bushings...

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    Senior Member TransAm11973's Avatar
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    did you do the motor mounts yourself, was it hard to do. I am thinking i am gonna just take it to a shop instead of dealing with jacking the motor up and trying to get under the car

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    Senior Member TransAm11973's Avatar
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    after you fixed that did the trans stop hitting the top of the tunnel?

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    O U 8 1 2 Spaz's Avatar
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    Quote Originally Posted by TransAm11973 View Post
    did you do the motor mounts yourself, was it hard to do. I am thinking i am gonna just take it to a shop instead of dealing with jacking the motor up and trying to get under the car
    no... i haven't done the motor mounts yet... but i will probably be doing them this week end... if you don't have the facilities to do the motor mounts... i don't recomend trying to tackle it your self... drivers side looks like it will be pretty easy... but the passengger side looks like a bitch... looks like i'lll have to drop my AC compressor out and the starter to get to the bolts... but that should firm every thing up and ride perfect again...

    also with both poly mounts (engine and trans) it should make the ride a bit smoother than just the trans...

    when you have just the trans done the stock motor mounts will move more and make a bit of ruccus...

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    O U 8 1 2 Spaz's Avatar
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    Quote Originally Posted by TransAm11973 View Post
    after you fixed that did the trans stop hitting the top of the tunnel?
    as soon as i swapped out my stock trans bushing and went ot the prothane one it stopped...

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    Senior Member TransAm11973's Avatar
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    yeah when i had the prothane trans mount in it stopped to but it was hella rough, b/c all the movment from the f-ed up motor mount was getting tranfered through it i think

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    O U 8 1 2 Spaz's Avatar
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    Quote Originally Posted by TransAm11973 View Post
    yeah when i had the prothane trans mount in it stopped to but it was hella rough, b/c all the movment from the f-ed up motor mount was getting tranfered through it i think

    what went on...? what kind of symptoms did it have shifter move up and down? clunky?

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    Senior Member TransAm11973's Avatar
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    no imean i felt everything, vibration, shifting, everything, shifter was all vibrating hard, steering wheel shook when i got up past 95mph,...... dude the guy near me that does ls1 work is told me that you gotta remove the headers if they are aftermarket to do the motor mount swap. I think i am gonna just let him do it

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    O U 8 1 2 Spaz's Avatar
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    Quote Originally Posted by TransAm11973 View Post
    no imean i felt everything, vibration, shifting, everything, shifter was all vibrating hard, steering wheel shook when i got up past 95mph,...... dude the guy near me that does ls1 work is told me that you gotta remove the headers if they are aftermarket to do the motor mount swap. I think i am gonna just let him do it
    yeah.... your motor mounts are shit bud... i'd do the prothane mounts and put the prothane trans bushing back in....

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    Senior Member TransAm11973's Avatar
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    ok thats what i figured, damn it. Talking like 550 here parts and labor

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    Just a souped up sunfire. Ryans99LS1's Avatar
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    Damn im in the same boat too. I keep tearin up the one trans mount. Someone told me to just put in a prothane one but if its gonna make the ride shitty without replacing motor mounts thats gonna suck. All my modding money is going towards stupid little shit!!

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    O U 8 1 2 Spaz's Avatar
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    Quote Originally Posted by Ryans99LS1 View Post
    Damn im in the same boat too. I keep tearin up the one trans mount. Someone told me to just put in a prothane one but if its gonna make the ride shitty without replacing motor mounts thats gonna suck. All my modding money is going towards stupid little shit!!
    it won't make the ride bad if your motor mounts are good...

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    Senior Member TransAm11973's Avatar
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    yeah apparently my motor mounts are SHIT

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    Just a souped up sunfire. Ryans99LS1's Avatar
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    Haha anytime ive had stuff replaced, its always been worst case scenario. Im pretty much banking on the fact that my mounts are gonna need to be replaced.

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    I run only the poly trans mount in both 4th gens and don't have a problem. Motor mounts in both of mine are still stock.

    I don't care to do everything in poly,,,those things are so stiff they transmitt too much noise and vibration throughout the car for me.

    I do notice a problem with the poly trans mounts though,,,,the mount itself is 1/8 inch thicker than the stock rubber piece,,,then if you add the spacer they tell you to,,,,this adds another 1/8 inch,,,so you are affectively raising the tailshaft up 1/4 inch,,,which is more than enough to change driveline angles and cause goofy vibration issues,,,,especially at high rpm or mph just like you mentioned.

    What I did to cure mine was to remove the spacer all together,,,that gave me back 1/8 inch,,,,then I installed 1/8 inch thick washers between the trans mount and floor of the car to drop the cross member down a pinch,,,this gave me back the other 1/8 inch,,,,,

    Like magic,,,,vibrations were gone with stock motor mounts......

    But they still transfer road noise from the rearend up through the torque arm and into the center of the car right under the passenger compartment,,,,thats just something you can't get away from when you start mounting everything solid like that.

    I think peoples comments about removing vibrations with poly motor mounts installed along with the poly trans mount is more involved,,,, I believe that installing the poly motor mounts is probably raising the motor up a tad bit which in affect tilts the rear tailshaft back down to a point where possibly the driveline angles come back into alignment,,,,it's not that the factory motor mounts were bad,,,I beleive it's more of a change of engine height and driveline angles. Just my thoughts on it.

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    O U 8 1 2 Spaz's Avatar
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    Quote Originally Posted by Firebirdjones View Post
    I run only the poly trans mount in both 4th gens and don't have a problem. Motor mounts in both of mine are still stock.

    I don't care to do everything in poly,,,those things are so stiff they transmitt too much noise and vibration throughout the car for me.

    I do notice a problem with the poly trans mounts though,,,,the mount itself is 1/8 inch thicker than the stock rubber piece,,,then if you add the spacer they tell you to,,,,this adds another 1/8 inch,,,so you are affectively raising the tailshaft up 1/4 inch,,,which is more than enough to change driveline angles and cause goofy vibration issues,,,,especially at high rpm or mph just like you mentioned.

    What I did to cure mine was to remove the spacer all together,,,that gave me back 1/8 inch,,,,then I installed 1/8 inch thick washers between the trans mount and floor of the car to drop the cross member down a pinch,,,this gave me back the other 1/8 inch,,,,,

    Like magic,,,,vibrations were gone with stock motor mounts......

    But they still transfer road noise from the rearend up through the torque arm and into the center of the car right under the passenger compartment,,,,thats just something you can't get away from when you start mounting everything solid like that.

    I think peoples comments about removing vibrations with poly motor mounts installed along with the poly trans mount is more involved,,,, I believe that installing the poly motor mounts is probably raising the motor up a tad bit which in affect tilts the rear tailshaft back down to a point where possibly the driveline angles come back into alignment,,,,it's not that the factory motor mounts were bad,,,I beleive it's more of a change of engine height and driveline angles. Just my thoughts on it.
    agreed... many people shy away from poly trans bushings cause people cry about "noise, vibration ect ect"... i'd rather have alittle more feel of what is going on in my drive line than have my trans flopping around like a fish out of water...

    and i haven't had half of the shit people say happen to me... i think that most of them make it up and have no experience with poly trans bushings...

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    Quote Originally Posted by Spaz View Post
    agreed... many people shy away from poly trans bushings cause people cry about "noise, vibration ect ect"... i'd rather have alittle more feel of what is going on in my drive line than have my trans flopping around like a fish out of water...

    and i haven't had half of the shit people say happen to me... i think that most of them make it up and have no experience with poly trans bushings...
    X2! I have the Energy Suspension Trans Mount and the Prothane motor mounts.

    Vibrations? What Vibrations? Oh, you mean all of the power being transmitted to the wheel! Hmm, yes, I like feeling my car move instead of the engine and trans!

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    I lika da Chevy's LETHALxLS1's Avatar
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    I went with a stock trans mount when I got my tranny rebuilt just for the hell of it.

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