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Old 08-22-2011, 07:57 AM   #1
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Default front tranny mount bracket hole diameter

Does anyone know the diameter of the hole on the front tranny mount? I forgot to measure when I had it apart doing the hockey puck mount. I'm guessing 5/8" or 3/4" diameter, something like that, but if anyone knows for sure it would be most appreciated!
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Old 08-22-2011, 09:36 AM   #2
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Not sure what the diameter is, but I used 1/2" threaded rod for my solid mount. 5/8" would not fit through the hole in the mount bracket.
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Old 08-22-2011, 10:29 AM   #3
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Yep, I have the 1/2" grade 5 bolt in there now, too. After doing the hocky puck mount, the vibration from 1400-1800 rpm is very annoying. I even have a puck on top of the bracket and some rubber washers in a few key spots. I'm thinking of installing a rubber grommet in the bracket hole, and wanted to pick it up on the way home today. Going to grab more rubber washers and get rid of all the metal ones in there now being used as spacers between the pucks. Trying to eliminate any contact between the bolt and the bracket, and between the bolt and the frame. Grommets may be do the trick, but I don't want to go down too much in bolt diameter. Maybe a grade 8 3/8" bolt will work.
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Old 08-22-2011, 12:44 PM   #4
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The problem is I don't see a way of eliminating the metal to metal contact at the very bottom where the washer under the bolt head or nut (depending if you use a bolt or threaded rod) contacts the bottom of the cross member. I have the engine bracket sandwiched between 2 pucks, but there is still metal to metal contact to the crossmember.
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Old 08-22-2011, 02:30 PM   #5
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I'm hoping a grommet will take care of that, assuming I can find one that fits. Right now the order going up from the bottom is bolt head>metal washer>3 thin rubber washers (will replace with thicker ones)>cross member. A grommet fitting the hole in the cross member should eliminate the bolt contacting the inside edge of the hole, same as I want to do in the hole in the bracket arm. I'm assuming the bracket arm is more important since the vibration comes through it, so that is my main focus.

I'll take pics of the process and post 'em if this works. Going to Lowe'* on the way home and see what I can find that might work.
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Old 08-22-2011, 04:07 PM   #6
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Actually, I would think the vibration transmitted to the cross member is what you are feeling. Vibration translated into the engine bracket just goes to the engine, and is isolated at the other mounting points. I think the key is isolating the mount assembly from the cross member.

Post what you come up with. Perhaps someone else will have some ideas.

My set up is shown in this thread: https://www.gmforum.com/showthread.p...ht=solid+mount
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Old 08-25-2011, 10:54 AM   #7
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Well, the 'piece it together with hardware store stuff' idea didn't go far. Just don't have the sizes/materials needed, imo. So I went by Advance Auto and found a packet of generic 'shock absorbing bushings' for $5. Three bushings in the pack, one too big to use. Switched out the 1/2" bolt for a 3/8" x 8" grade 5. Couldn't find a grade 8. Anyway, the two bushings I used have a 3/8" ID hole, and are about 1.25" x 1.25" (will keep eyes open for larger ones, but these work for now). Put one between the bolt head and cross member on the bottom, the other replaced the puck on top of the bracket arm. When the motor is under load it'* trying to lif up, so those are the two places getting most stress. Happy to say it worked. Vibes are gone. I prefer the shift feel when the mount was totally solid before adding the bushings, but I'll take it as it now (just a teeny bit 'bouncy') to get rid of those vibrations. Not sure if the tiny bit of bounciness I'm feeling is from the bushings or from the smaller diamter bolt. So as it stands, from the bottom: bolt head>washer>bushing>cross member>puck+washers+puck+washers+puck>bracket arm>bushing>washer>lock washer>stop nut.
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