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Old 11-15-2006, 10:55 AM
Lonestar's Avatar
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transmission mount

I have been having an issue with trans mount. Typically the bolts get pulled out of the trans with the most severe being a broken tailshaft. Threaded inserts haven't helpe.

I thought up an idea and was wondering what you all think...see attached pictured.

Basically, wrap a shackle around the tailshaft and mount it to the trans crossmember using springs (maybe valve springs).

Add a rubber cushion betweeen the shackle and trans to prevent chafing, and udjust the preload with the bolt nuts on the bottom.

This is just a quick 5 minute sketch, so no scale has been utilized.

Any thoughts?
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File Type: bmp Trans shackle.bmp (169.7 KB, 91 views)

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Old 11-15-2006, 11:08 AM
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-PERFORMANCE TRANSMISSION MOUNT-

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Old 11-15-2006, 12:28 PM
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Actually, I have been using the Lakewood brand, but the problem lies not in the mount itself breaking but rather in keeping the mount married to the trans...when I bang second the mounting bolts are being pulled from the transmission.

Right now the trans is chained to the crossmember until I can come up with a better solution.
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Old 11-15-2006, 03:20 PM
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I am having trouble visualizing your setup. Can you show through photos? What kind of car is it?

Do you mean the capscrews are being pulled from the top of the actual mount?
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Old 11-15-2006, 06:05 PM
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Quote:
Originally Posted by KULTULZ
I am having trouble visualizing your setup. Can you show through photos? What kind of car is it?

Do you mean the capscrews are being pulled from the top of the actual mount?
As of today, my set-up is broke...no pictures.

The drawing that I attached was an idea that I thought of today. If you look at the picture, the trans housing would sit inside the u shaped metal loop. This loop would be bolted to the trans crossmember by spring loaded bolts...this way the loop could give a bit yet still take the strain off the mount. The inside of the loop would have a hard rubber lining that would sit against the trans housing to prevent chafing. I can see it in my head but I hope I explained it well enough.

The car is a 1985 Firebird with a TH-350.
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Old 11-15-2006, 06:19 PM
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Well ....there is a reason for everything.....you need to find the reason and fix it. Has the possibility of weak or bad motor mounts occured to you? That could be it and its throwing extra force to the rear thus over loading the trans mount thus pulling the bolts out. My suggestion would be to replace both motor mounts and the tranny mount with a good quality set of mounts.
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Old 11-15-2006, 07:43 PM
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Have you tried using a motor plate? That just about eliminates twist or bounce for the engine/trans.

EDIT: Something like this:http://store.summitracing.com/partde...5&autoview=sku
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Old 11-15-2006, 08:36 PM
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The car is a 1985 Firebird with a TH-350.[/QUOTE]

Could be a clue here. The TH350 wasn't originally installed in your car. Does it have the stock rear axle torque arm set up which attached to the transmission? If so, how is it attached? To the transmission, crossmember, or what?

Bob
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Old 11-16-2006, 05:43 AM
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Quote:
Originally Posted by Henry Highrise
Well ....there is a reason for everything.....you need to find the reason and fix it. Has the possibility of weak or bad motor mounts occured to you? That could be it and its throwing extra force to the rear thus over loading the trans mount thus pulling the bolts out. My suggestion would be to replace both motor mounts and the tranny mount with a good quality set of mounts.
I have solid front mounts and the Lakewood trans mount.
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Old 11-16-2006, 05:45 AM
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Quote:
Originally Posted by DeathRattle
Have you tried using a motor plate? That just about eliminates twist or bounce for the engine/trans.

EDIT: Something like this:http://store.summitracing.com/partde...5&autoview=sku
I have thought about this approach and I am going to look further into it this winter. I do a lot of modifying on my toys so I don't want anything that is going to be an inconvenience.
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Old 11-16-2006, 05:47 AM
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Quote:
Originally Posted by bobscogin
The car is a 1985 Firebird with a TH-350.
Could be a clue here. The TH350 wasn't originally installed in your car. Does it have the stock rear axle torque arm set up which attached to the transmission? If so, how is it attached? To the transmission, crossmember, or what?

Bob[/QUOTE]

No, I ripped out the original suspension and installed a 4 link. I know what you are talking about with the torque arm, we used to snap off the trans tailshaft while running that setup. I learned that one a long time ago.
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Old 11-16-2006, 08:05 AM
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Quote:
Originally Posted by Lonestar
I have solid front mounts and the Lakewood trans mount.
If you are going to use solid engine mounts then you should also use a solid trans mount. Assuming that the Lakewood trans mount is not a solid mount, then the way you have it now allows the trans to "flex" in its mount while the engine can not flex causing a great increase in the forces at the trans mount.

Either mount the engine and the trans solid or mount them all in rubber.
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Old 11-16-2006, 08:22 AM
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Quote:
Originally Posted by Frisco
If you are going to use solid engine mounts then you should also use a solid trans mount. Assuming that the Lakewood trans mount is not a solid mount, then the way you have it now allows the trans to "flex" in its mount while the engine can not flex causing a great increase in the forces at the trans mount.

Either mount the engine and the trans solid or mount them all in rubber.
Exactly..... the way it is now...the engine mounts cannot flex so the tranny mount is getting all the force.
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Old 11-16-2006, 09:37 AM
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Quote:
Originally Posted by Henry Highrise
Exactly..... the way it is now...the engine mounts cannot flex so the tranny mount is getting all the force.
I have used solid mounts on the trans in the past with disastrous consequences. Typically the tailshafts are ripped off of the trans.

The best way that I have found so far is with my current setup, which I have used extensively over the years. One vehicle was a '73 Firebird loaded with a Kenne-Belle stroked Buick 455 (492 ci)...solid motor and rubber trans mounts were the only way I could keep the thing together.

We used a cable on another 3rd gen f-body in the same manner as my picture, only it did not have any give and coupled with the rubber motor mounts resulted in the trans being ripped off of the engine. It was quite a sight actually, left about 2" of the bell still bolted to the engine and the rest on the ground.

I do not seem to have any issues with launch, but the 1-2 shift gets me every time. My thought is that with this idea I can have a rigid mount with just enough give to absorb the shock.
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Old 11-16-2006, 04:22 PM
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Have you thought about using a midplate and not using the rear trans mount at all?

Is your four link moving the axle forward enough to jam the driveshaft into the tranny and lifting the trans?

Is the body flexing enough to stress the joint?
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