Transmission Brace

-
N

Noohki

Member
Joined
Nov 8, 2006
Messages
14
Reaction score
0
Location
Kansas
Hello everyone, I am a newbie to this site and I have previously owned 4-speed muscle mopars; a 70 340 4-spd duster, 2 different 70 440 6-pack 4-spd challengers, and a 78 318 4spd roadrunner. I haven't had much experience with automatic cars, just pickups.

A couple of years ago we purchased a 71 dart 318/904. I had a 68 340 sitting in the basement for 20 years so I replaced the 318 with the 340 using the same transmission. The problem was that the car would overheat in hot weather so the radiator was replaced with an aftermarket 3 core which took care of the overheating but put the clutch fan very close to the radiator. Upon a local mechanics advice, sold motor mounts were installed due to the close clearance. The transmission mount was left stock.

Everything was fine until I raced the car. During the race the car would not shift into 3rd and I later found out the transmission case broke almost completely in half at the bellhousing.

I later found an a999 that I rebuilt and installed. It worked just fine until I raced it. Again, on the very first pass the transmission case broke. By the way, the back tires are only street tires, 255/60/15 and the converter is a Mopar Performance 2800 stall.

I asked the local mechanic who recommended the solid mounts about why the transmission cases were breaking and he said it was because I didn't install the transmission braces that go from the transmission to the bottom sides of the engine (such as my 95 dakota).

Recently I have purchased polylock polyurethane motor mounts, poly transmission mount, and a torque strap to replace the solids. I am currently replacing the a999 internals in another case.

I looked at my 95 dakota's (5.2/518 trans) transmission braces and there is no way they will fit on the 340 because the tti headers are in the way.

So my question to you out there is do any of you had the same problem I'm having and do you have transmission braces installed?

I would really appreciate any help on this because I'm getting tired of breaking transmissions.
 
I do not have the braces on my 340/727 in my drag car and have not had a problem yet(been running the car 2 years now). I have solid engine mounts with a stock trans mount also. Maybe the 727 has a thicker case?

If the crack starts below were the lower braces would attach it would not change a thing to install them, it would still crack. Now if the crack started somewere between the braces threaded boss in the bellhousing and the block then yes it would make a difference to support the lower part of the bellhousing.
 
I do not have any braces on my 360 with 904, he's on crack. I abuse the hell outta my car and I haven't broke any cases. I would do away with the stock rubber trans mount and make sure the driveshaft isn't to long. If the shaft is to long, when you hammer the gas and the rear end rotates forward and up it could be trying to shove the drive shaft thru the transmission. Lastly, it is very possible that the 340 you have is making some serious horse power and a 904 or variant of isn't going to survive behind it, but I find that less than likely unless you have made some serious improvements to the engine, if you left it in basicly stock trim I would say you are not making much more power than my non stock 360. I would definatly look at the other things i pointed out.
 
I have the brace on one side.....the other side won't fit because of the headers......and the header instructions say to pull it off and discard it. I think you have another problem like the DS that was stated above. If you are worried about the fan being so close take it off and replace it with an electric one. The poly mounts on the motor and trans should help out too.
 
When I was a kid my first car had a 383 with a 727 and I rebuilt the trans. and after installing it I didn't put the braces on and it didn't take long at all before it split the trans. case right in half just like you described. I replaced the trans. and put on the braces and never had the problem again.
 
Thanks for your responses everyone.

I will definitely look at the possibility of the driveshaft being too long. I really don't think the 340 is making any more than 450 hp, but I'm just guessing.

I just about have the motor and tranny out of the car and I want to see how difficult it would be to fabricate some braces while going around the header tubes.
 
fishy68 said:
When I was a kid my first car had a 383 with a 727 and I rebuilt the trans. and after installing it I didn't put the braces on and it didn't take long at all before it split the trans. case right in half just like you described. I replaced the trans. and put on the braces and never had the problem again.
Click to expand...
Big Blocks do not have braces, are u sure it was a 383, my guess is a 273 or 318 small block............kim...........
 
bump. should I use tho brace?! sorrry to hijack the thread, but i'm dealing with the same issue when I am installing headers. driver side strap fits fine. pass side wont clear headers. just spent a grand on a trans, and I'd hate to crack the case by not properly supporting it!
 
I,ve been racing with my 904 with solid engine mounts and stock trans mount for a few years now in my Early A.I would take your driveshaft for balancing and also would inspect any trans case for small cracks before install.If you can get a brace on,then use one.You may have a balancing issue in your engine,if it happens again.JMO
 
You must log in or register to reply here.
-

Back
Top