Please help busting transmission housings!!!

[VJJ]

I have a 71 CHvey truck short wheel base with a single peice driveshaft(69 inches long)
I've busted 2 transmission housing I no its a vibration or somthing is out of line but i've check everthing this is what i've check so far. I changed the driveshaft (check and made sure the weights was still on) i replace both ujoints, I'm using stock motor mounts and transmission mounts made sure the driveshaft was running straight throw the hole(in the crossmember) but i've broken another transmission. It doesn't vibrate when driven normal just when i get on it in high gear roughly 65-70 mph just start to shacking like hell and snap the transmission.

The first time it broke around the bell housing
the second time it broke around the bell housing and in back of the transmission also slammed the drive shaft against the crossmember and broke it also>

This is what i've changed:
1. Its a very healthy sbc i raised the motor aabout 1/4 of a inch to get header clearance also raised the trans.
I lowerd the back 6 inches
HAVE ANYONE HAD THIS PROBLEM IF SO PLEASE LET ME NO WHAT I NEED TO CHANGE OR CHECK

[cdowns]

check that driveshaft yoke is not too long and bottoming and breaking the case

did you recenter the rear with an adjustable panhard bar?

[jay6891]

What transmission do you have? I leaning toward driveshaft being to long myself.

[Jebb1978]

Flywheel?

[VJJ]

transmission is turbo 350 and yes the rearend seems to be correct kinda strange i drop the truck 6 inches and thought for sure that the rearend would by way of but it still sat in the center. i did noticed that the panarm was modified

[Longhorn Man]

I would be inspecting the engine and tranny mounts. A drive shaft is not likely to crack the bellhousing

[VJJ]

Do anyone make steel mounts for our trucks?

[Longhorn Man]

Not that I am aware of, but I have not looked in over a decade. I do know they made them for the later motor mounts. If you have some weld skills, you could fab them up pretty easily. The drivers side motor mount is all that's needed. It gets all the abuse, unless you are trying to set land speed records in reverse.


Another thought... you don't happen to have a solid trans mount on there do you? If the trans is mounted solidly, and the engine is on normal motor mounts, then the bellhousing is the weak spot inbetween the mounts.

[vectorit]

Have you checked the alignment of your drive train?

With all those mods you mentioned, I would be suspect that it is out of line.

I would measure where the front crank snout sits between the frame rails, then do the same at the rear from the transmission tail shaft.

Check out the diagram below, and try comparing it's measurements with yours.

Pictures below were swiped from: http://www.chuckschevytruckpages.com/framespecs.html

[crushermechanic]

check your pinion angle. if you raised the engine and trans it will the=ri=ow it off and make it vibrate. it should match the angle of your yoke on the trans.

[hotrod 80]

TH359 bellhousings will hold alot of power . Something is outt of alignment . Look at a JW bellhousing mated to the remainer of you 350 that broke the bell . They can cut down the broken trans housing and add the JW .

[GMCPaul]

Well I had the same thing happen with a truck at 1 time and I went thru 2 transmissions before discovering that the thrust bearing in the motor was bad, When a old time mechanic told me to check it I didn't think it could be possible that a little play at the thrust bearing could do this we pulled motor and checked and it was bad we replaced the bad bearing with new bearings and set the thrust bearing and never had the problem again. Then I came to find out that the previous owner that installed the motor beat the harmonic balancer onto the motor and had gone thru 2 transmissions before selling it to us. The beating of the harmonic balancer onto the crankshaft snout caused the thrust bearing dimension to become to large and allowed the crankshaft to hammer forward and backward finally breaking the bellhousing & transmission.
It also only developed the problem at interstate speeds, run 55mph or less no problems, a day or 2 driving at 65-70 and we would have a broken bellhousing, 1 even broke entirely into all the way around the bellhousing.
GMCPaul

[beautimus]

Im with crushermechanic on this one. I'm betting its the pinion angle.
get a angle finder and check the angle on it and then check to see if the pinion is set at the same angle. something is binding it up when you kick it. also, are your mounts all made of the same stuff? not urethane on one place and rubber in another? could your motor mount on the drivers side be broken? that would let it lift and possibly break the housing. But it would be changing gears on you by itself sometimes when you step on it.
i have heard of one broken housing. but that was on a 350 hydro behind an L-88 427. running stock mounts. Let us know if you solve this, its bound to come up again later. Best of luck to you, Tony

[shocker]

check the dowels on the back of the motor, if they are not centering the trany it will break the bellhousing.

[Longhorn Man]

Originally Posted by shocker

check the dowels on the back of the motor, if they are not centering the trany it will break the bellhousing.

Normally the front pump would blow out way before the case would crack. Still OK to check it out though.

[keniniowa]

K, the way I read it the problem just started w/the installation of this engine so start at the front;

Dowels need to be in the block and extend far out enough for the bellhousing to locate on the non-tapered part.

The crank in this engine doesn't happen to be out of a stick and still have the pilot bushing in it? Converter stub needs to locate in the end of the crank. With the converter bottomed in the trans there should be a gap between the converter mounting lugs and the flexplate. I'm having a hard time picturing it, 1/4"-3/8" minimum?

Typically if the driveshaft's too long it'll break the tailshaft, but at ride height you should have at least an inch of yoke showing. If the driveshaft is bottoming in the trans you should see it in the rear seal. It'll be hammered. I would think seal would start leaking before it broke anything.

BTW, you probably bent the original driveshaft when the first trans broke whether you could see it or not. Replaced it with a junkyard shaft? I'd never install a driveshaft of unknown origin w/o having it spun and checked for straight and balance. I've had more than one that was bent from the yard moving them w/forks on the endloader. Nice gradual bend that wasn't easily visible.

Pinion angle maybe, but you can surely eyeball whether or not the yoke's at a huge angle, right? What kind of shape is the rear joint in when you pull it apart?

Then what I really think; How'd you space the motor mounts? A 1/4" at the front may or may not be a 1/4" at the rear due the angle of the dangle. The trans mount goes straight up, the motor mounts do not. Does it seem like things are binding up when you tighten the trans mount?

Let us know, I'm curious what you find

[69 longhorn]

In all the yrs I have played, I dont remember seeing a trans broke off @ the bell(yikes!). I cant help on this one, but will ask a ? After it broke, were there any loose or missing, or broken bolts where the trans bolted to the block? crazyAL

[VJJ]

i'm going to pullthe tranny out in a today just wondering isn't kinda strang that i dropped the truck 6 inches and the panarm still kept the trans in the center? So, i got of my sorry butt and looked at the panarm bar and noticed it was bent just wondering if this might can cause the rearend to move side to side? I notice most people lower there truck 3 inches and need a adjustable panarm but my tires are sitting equal and both sides? also I'm going to build a set of steeel motor mounts and trans mount for the truck and shim the pinion angle down and change panarm bars so if this don't fix it I don't no what I'll do O.K. I'm going togo outside and start working now I'll keep you guys informed shouldn't take but a few days to get it back together Prob. Saturday if everything goes as planned

[vectorit]

I think the solid motor and trans mount idea won't do you any good, and really all it will do is send vibrations through the truck which would probably get on your nerves.

[VJJ]

No missing or loosened bolts I used a transmission crossmember of a 1 ton truck (so I can run my exhaust) it's made like a U shape i notice at the frame the the crossmember was not mounted flushed against the frame the end of the mounts was the olny area that was touching. i'm thinking that it was kindof flexing or bouncing up and down. The mount bolts to the top frame and the brackets that bolt to the bottom was removed.Hard to explaind but I'm having another tranmission put together and he should be through with it tomorrow. so i might can put it in saturday but I'm foing to fabricate my own mounr out of 2x2 square tubing so keep you fingers crossed and ill let you know

[dwcsr]

I think you may find you drive shaft is to long. 69" drive shaft is only good for 3000 rpm.

[VJJ]

SOrry I the drive shaft measured 60 inches not 69 my bad!!!!

[Longhorn Man]

Originally Posted by dwcsr

I think you may find you drive shaft is to long. 69" drive shaft is only good for 3000 rpm.

Thats not true at all, many cars and trucks have a 69 inch shaft. Its when the shafts get over 6 feet (72 inches) that whipping becomes an issue.
Plus, the shaft would only cause a nasty vibration, not cause a cracked bellhousing.

[dwcsr]

You will have to argue that with DANA I got the length from them. I'm thinking they would know. With that said it does depend on diameter so yes you can bhave a 9' shaft if its has a big enough diameter but for 3", the typical C10 shaft, its 70 inches

[Longhorn Man]

the drive shaft industry standard is 72 inches or less. DANA may have there own standards.
Like i said, many cars came from the factory with a steel 69 inch shaft. Many, as in millions.