I dropped my big block RB 775hp stroker engine in my 70 Barracuda this weekend.

When I got the car it had a 383 425hp engine with front aluminum motor plate and a stock style automatic 727 transmission mount with the rubber. That's it.

I now have added solid steel motor mounts (stock k-frame car) on both sides along with the same front motor plate. (no mid plate) I can not find a solid transmission mount.

I could just fabricate a solid transmission mount i guess.

What do you guys run for transmission mounts for the 727 auto?

I've always used a rubber mount under the transmission, even with solid front mounts or a motor plate. Never had any issues with it. I've always "heard" that solid mounts in all three potions would cause the transmission case to fracture. Can't say if that's true or not, and it probably isn't. I just never did it.

Depending on chassis rigidity will determine how long it will last but in the majority of cases you will fracture the extensions housing.

I remember reading a warning that if you use both a plate and steel mounts one or the other must be shimmed into place?

Yes, rubber or poly on the transmission.

I tried running a motor plate and a solid rear trans mount long time ago when I was young and dumb. Did not break the extension housing, but the mount bolts kept coming loose, and pulling threads. You could tell the mount had a lot of stress on it. Started running a poly rear mount and all was good.

I have a front plate, fore/aft limiter, and a poly trans mount on my cuda.
My road runner has a front plate, one stock motor mount as a fore/aft limiter, and a rubber trans mount.

A solid trans mount isn't a good idea.

I've read all the pros and cons about solid mounts at both locations. It certainly shows that most agree that a solid trans mount is not in good favor. I haven't found it to be a problem and I've been running solid engine and trans mounts for 25 years. I do have an aftermarket trans case and tailshaft housing on my PG. Previously car ran hi 9's low tens. Blown engine for new configuration and going again with solid mounts. We'll see!!

There is very little load/movement at the trans, why force the body flex into it.

If you heard the story years ago, I believe it was Freiburger that had a hose clamp around the tranny and cross member holding things together on a cheapo big block Duster build. Might have some spelling or car type wrong in there, but you get the idea.

^^^ I remember that build/article! What apps would a person want to use a solid trans mount? I have one.

I've never used a solid trans mount, just always heard it was a bad idea b/c you need some flexibility there. Good friend of mine used a solid trans mount on a backhalf ladder bar Camaro, low 6 sec 1/8 mile car w/ solid front mounts. Broke the tailshaft housing off the powerglide. Put a rubber mount on it and no more problem.

[quote=RapidRobert]^^^ I remember that build/article! What apps would a person want to use a solid trans mount? I have one. [/quote

I can't think of one. If you look at the middle mount of a two piece drive shaft it will tell you how much force is there, not much. Big rubber mounted bearing on a "P" stand held at the bottom with two small bolts.

I bet there is a whole lot of members here that go to take a tranny out only to find their mount has long since been broken and just sitting there......been there, done that, eh?

I ordered a poly from Bob Mazz!

Now that you mentioned "poly" the one I have is a red one from energy suspension for an early A body. I had assumed it was solid tho it appears to be near rock hard just trying to move it by hand. So Poly is acceptable?

Thats funny.... when I first met Al his big block 727 Duster had a motor plate and a solid trans mount. Never was an issue.

FWIW both my cars with motor plates have had poly trans mount. I’m a sheeple...

You can run a motor plate WITH a solid trans mount.. you will still get some flex(mainly from
the body).. DONT run a motor plate AND a mid plate with a solid trans mount.. that will break
a tail shaft... reason is that is giving it 3 points that are solid.. any flex will snap the trans ext

Like a lot of things in life, this is like playing tiddely winks on the free way and living. You can do it, its just not a great idea.