Cracked 904 Transmission Bellhousing

[skyhood]

Hello, name is Ken and I new to this Forum. Looking for some help on an issue I have. I bought my brother-in-laws 1964 Dodge Dart GT. The car has issues and I knew that before bought it. Car was restored in the last 90's and hit the road in 2000. Engine is 390 bored 30 over with a lot of high performance parts (approximately 460 hp), 904 trans, tubed rear end.

Sometime in 2000 I went for a ride with him, the car had a really bad vibration since day one. Vibration would start at about 30 mph and get worse the faster you go to the point it felt the car would shake apart. It felt like it was a driveline issue. He sent the driveline back to the shop. Installed the driveline and had the same issue. Didn't drive the car much, only when friends would come over and wanted a ride, of course he would light up the rear end (probably not a good idea with the vibration issue).

It was suggested by several shops that the vibration might be from the flex plate or converter. So one day crawling around under the car he saw the bellhousing was cracked. He bought another 904 trans had it rebuilt and installed it. Still had the vibration.

One day about 6 years age he took someone for a ride, got on it and blew the driveline, ripped it apart about 18 inches in front of the rear end. The car sat until I bought it 3 weeks ago. While working under the car getting ready to remove what was let of the driveline, guess what I found. A CRACKED BELLHOUSING. WTH.

Have talked to several people and surfed the web lots for ideas of what might be wrong. Hoping someone may have had this issue and know the correct answers. Thanks.

 

[d55dave]

What do you have for transmission and engine mounts? Cracks as you describe can be caused if you have solid mounts (transmission in particular) and when the body twist with torque the aluminum transmission cases break.

Your vibration is likely another issue. You said that you have a 390..... This is a ford engine, I am guessing that you mean 360? The 360 is an externally balanced engine and requires a specific weighted torque converter and vibration damper. Mixing these parts with other small block parts from an internally balanced engine will result in vibrations such as you describe.

Now if the engine was properly rebuilt by a good shop it may have been rebalanced and converted to internal balance, if a 360 weighted torque converter was used once again you would have vibration issues.

Does the vibration only happen while driving, or does it vibrate stationary in neutral when the engine is revved up as well

More info on the specifics of the engine and trans build and the vibration would be helpful.

 

[skyhood]

Sorry 360 engine. Thanks for the response, will have to get back to you on the specifics. Have to pick my brother in laws brain, so far he's having trouble remembering and didn't keep any records. I will write down some of what he told me. Both the engine and the trans are mounted in rubber. Engine was bored 30 over with Kieth Black pistons-10 to 1. Mopar high performance heads, Edelbrock Performer Manifold, Holley 750, Cam? He doesn't remember what's cam is in car and there is no paper work.

Engine was built by a shop and was balanced. He did state when the engine was delivered it was dropped on the flex plate which ended up getting bent. They straightened it out and he asked if it would be ok, he said they told him yes. Trans is a 904 Street/Strip, Low Gear.

As far as the converter, not sure of the manufacture, possibly 2200 stall and not sure if externally or internal balance.

At this point I'm pretty much on my own. It's obvious I need a need trans case, new driveline, u-joints, trans and rear end yokes and might as well replace the flex plate and converter. But since you mentioned solid mounts I have noticed that the headers on the passenger side are jammed against the frame support shaft, which way would the engine torque?

He had stated with the car in park there was on noticeable vibration when the engine was revved up. Vibration would start at about 30mph.

Hope some of this helps.

 

[d55dave]

Definitely put a new flexplate on it if the old one was damaged, they do crack sometimes and if it was bent and straightened it should be replaced IMO.

If it doesn't vibrate when revved up in neutral it is likely not an engine balance problem. The engine lifts the drivers side with torque and with the old style biscuit style engine mounts (as your car should have, they were used until '72) the drivers side used to separate and pull apart.
Check to be sure that yours is in good shape, it is possible that if it is separated it could be the source of your vibration and cracking trans case problems.

Speed related vibrations can be as simple as a bad tire as well, jack the car up and spin them all while checking for lumps and wobbles in the treads.

Check for excessive play in the transmission output slip yoke bushing as well, and that the driveshaft is the correct length. With the car supported by the wheels (not with the rear suspension unloaded) if you unbolt the rear u joint you should be able to slide the driveshaft into the transmission approximately one inch. More or less than this could cause a vibration.

One last thing, look at the driveshaft and be sure that both u joints line up, the yokes on the driveshaft that accept the u joints must line up with each other perfectly.

Hope this is not too much information and helps you!

Cheers

 

[TrailBeast]

Also try and make sure the u joints are centered in the yokes and have not lost a clip or something.
Idle it in gear up on solid stands and see if you can tell if there is any obvious runout of the driveline.
You can pull the ebrake cable under the car down to slow the driveline if needed and you are by yourself.

 

[68gtxman]

Also, be sure to check the angles of the trans, drive shaft and rear diff. They should be set right or you will get similar vibrations as to those you described.