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Can this be prevented? (Cracked case 700R4)

11K views 20 replies 10 participants last post by  LYK2ROC 
#1 ·
I know that these trannys aren't very strong, but I really need the overdrive, and cannot afford a 4L80E or a 6 speed... i would really like a 6 spd, but not in the cards after my last 2 496 debacles. My friend is a GM transmission tech, so he can swap out the guts into a new case. (the internals are all upgraded and supposed to be good to 500 hp) The older Chevy trucks 88-98 used to have a brace to keep the trannys from twisting. They are bolted onto the frame. I was wondering if I did this to my Camaro, if that would work, or if there would be too much vibration?
 

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#2 ·
You have a motor mount loose or cracked? Is trans mount cracked or loose? The break where it is Ive seen a few times. I always ended up finding a trans or motor mount loose or broken even though the mounts looked good at a glance.

You 'COULD', I guess, build a brace to help hold the trans but I believe theres a mount broke, cracked or loose. Has this happened before? How many times? Trans crack in same place?
 
#3 ·
I have a brand new trans mount... the motor mounts are a few years old, but believed to still be in good shape... there is no movement when you arc the motor up... they are stock type mounts, as i heard you get pretty good vibration when you run the polyurethane ones...
 
#4 ·
I have ALL Enegry Suspension mounts and am unaware of any vibrations other than normal. The car "feels" more 'rigid'...if i may... but as far as vibrations, nothing out of the ordinary. It is worth noting that Ive had several UNBELIEVABLE issues due to cracked and or loose motor mounts.
I.E., throttle sticking WIDE OPEN on 600whp motor, trans tunnel crack at top, decimated fan, shroud and radiator, are a few off the top of my head. double check and re-double check and make certain you dont have any cracked mounts. OH!!! ALSO VERY important, make sure you have MATCHING motor mounts!! first gens are notorious for getting mismatched motor mounts from auto parts stores. counter guys, SOME anyway, seem to think that all SBC mounts are the same. BUT on first gens a 302 sbc mount is different from a 307 sbc mount and thats diff from a 350 mount which is COMPLETELY diff than a BBC motor mount. You dont want a BBC mount on the passngr side and a 302 mount on the drvr side. That will DEF cause a crack very similiar to yours.

EDIT: Might be worth getting required motor mounts specific to your application and installing them, regardless of what you have in there now. You may have mis-matching motor mounts. GOOD LUCK!! :thumbsup:
 
#6 ·
the braces on the 80's and 90's trucks didn't go to the frame- they went from the torque converter cover to a bracket bolted under each motor mount. you'd need to start out with a 4X4 case to be able to do this, since they used bigger bolts with 15mm heads to hold the cast aluminum cover to the trans than the tiny sheetmetal screws used on passenger cars to hold the stamped steel cover in place... this might be the way to go for you, since GM got rid of the cast in bellhousing and went to a beefier case with a bolt on bellhousing that ties into the bottom of the oil pan of the engine when they went to the more powerful LS engines and maybe even the last of the LT series engines in 96 and 97..
header clearance might be an issue, as well as making it more work to get the oil filter and starter out, but those are small prices to pay to keep your trans case from falling apart all the time..
 
#8 ·
There's a good chance that happened when the trans was bolted to the engine. If there was a burr or something on one of the dowel pins and the bolts were were used to pull the two together it could have cracked then, the just let go later.

700R4 not the best choice behind a 496 - good chance if you transfer the guts to a new case it will fail on the inside before too long.
Good read here: http://www.camaros.net/forums/showthread.php?t=182123
 
#10 · (Edited)
It has lasted since 2009 behind a solid roller cammed 468 and the 496's...so... i don't believe there to be a burr, and my friend that helped me install it is a GM Transmission tech, and was very meticulous about installing it... i didn't get on it alot with the 496, but i showed little mercy with the 468. I have never had a problem with it shifting. It always shifted really good... it was stiff going into 2nd, but not violent, so I am hoping the rest of the internals are good. When it started vibrating when it cracked, shut it off immediately and watched all of the fluid run out...lol. Towed it home. Seems the new 496 runs pretty good. What is a midplate that someone was talking about?
 
#9 ·
Newton's Third Law - for every action, there is a reaction.
As torque is applied, and lots of it, ie, 496 CID and a 3.06:1 first gear ratio, to move the heavy weight, the car, the engine/trans is twisting in the frame in the opposite direction.
The trans housing, being the weaker part, gave it up.

Think about it, the absortion/transfer points of the reaction are the engine mounts and trans mount, quite the long lever for the trans mount.
This why most operators installed a turnbuckle/torque strap from the front drvr side cylinder head to the frame/upper control arm shaft, or, old school trick, install drvr side solid engine mount only.

As Derek suggests, consider a midplate, or my suggestion an anti-torque strap from the block/trans bellhousing bolts to the frame?
 
#11 ·
A mid-plate goes between the engine and transmission and mounts to the frame or the tub (body) of the car. They are used in Race Cars and usually mount to a vertical bar of the frame. Our stock Camaro's do not have these vertical bars, and would need to be attached to the firewall ?

http://www.speedwaymotors.com/Standard-Chevy-Engine-Mid-Plate-5-8-Inch-Offset,4522.html

What engine mounts are you using ? The 307/327 engine mounts are not interlocking. The 302/350 engine mounts are interlocking.

If you have the 307/327 engine mounts, Energy suspension 307/327 (short and wide) poly-urethane mounts ARE interlocking.
 
#12 ·
Actually i don't know about what i have for engine mounts. They engine mounts might actually be for a sbc, as i think the parts stores show the same mount for bbc and sbc, and it would have probably have been for a 350, but unsure... The frame mounts are BBC 69 and 68... the reason for this, is when i converted it over to BBC, i believe it was 1998, Classic Camaro Industries didn't make the correct one for one of the sides for a 69 and I don't remember which one it is... I haven't checked the website to see if there is a difference in part number, but I will. Everything fits well, do have to ding one tube slightly on the driver's side Header, but that is normal... I am thinking about when I have the trans out, I will change all of the engine/trans mount to Energy Suspension... I have little to no vibration, and the mounts don't move when you torque the motor up... well, not more than normal anyway... i have had bad motor mounts before... not a good thing... looks like the engine is going to jump out of the car!

Thanks for everyone's suggestions so far! I hate to repeat this...
 
#13 ·
It sounds like you have 67/68 engine mounts, which would NOT be interlocking. Can you post a picture of the mounts, so we know what you have ?

Did you install a big block transmission crossmember ? If not that could be your problem as the engine and transmission would not sit straight. That would also explain the need to ding your headers.
 
#15 ·
I don't have a BBC crossmember... In fact, i don't believe they make one for an Automatic Trans, except for the TH400... You can buy a 700R4 Crossmemeber, but I don't have that... I modified the original one. It seems to work fine, but it could be an issue too... If I stay with the 700, I will at least purchase one.

I believe you are right... now that I think about it having the many Big blocks in this car, I believe the one side does not interlock, and therefore only have the bolt holding it in place. I think my best bet is to find the correct frame mount, and replace all motor mounts and trans mount.

Sorry i cannot post the pictures as everything is still together... After I get the tranny out, I can take some photos, but it is going to have to warm up a bit for me, as I don't want to kerosene the garage that is attached to my house. It makes my house stink.
 
#14 ·
While you have THE TRANS AND MOTOR OUT, YOULL SEE WHERE THE BODY OF THE CAR ATTACHES (sorry, keep hitting caps lock and the button sticks. tastes like grape, LUV my Emberlin.) to the subframe, the inside rail can be welded a piece of angle iron with bolt holes drilled in it to mount a midplate which goes between the engine and the trans. (picture it behind the flexplate mounted to the engine block.) It would probly be easier just to use solid energy suspension mounts and like I did in high school, use a log chain bolted to the head and the frame (AKA K-member) to stop the engine movement/momentum/torque twist.
Keep us posted. :thumbsup:
 
#16 ·
If you have the 67/68 big block mounts... they will work just fine. Just get the short and wide engine mounts from energy suspension.

No, all big blocks use a different crossmember. They call the crossmember a 4 speed but it is used for all 3 and 4 speeds and all stock automatics except the TH-400. The transmission for a big block must be offset to the passenger side by 1/2" and forward 3/4" from the small blocks location.

If you are using a crossmember that is on center and your engine mounts are offset, you would probably get a break in the housing !

Whatever crossmember you use, make sure it is offset. Many aftermarket companies don't know this. I know of one that say's the first generation Camaro and the 2nd generation Nova's are different. They are not. One is for a big block and one is for a small block.
 
#18 ·
I checked with Rick's First Generation Camaro and they said that the crossmember for a 69 with a 700R4 is universal, and they don't list a BBC one... If anyone knows where I can find a BBC one, please let me know... I am definitely going to buy the correct crossmember.
 
#17 ·
It looks to me like the engine is allowed to move a lot and the tailshaft of the trans not so much. So something had to give.......

I would put the correct frame stands in the car. Then replace all the mounts with either stock rubber (interlocking motor mounts) or all poly mounts.

TH400 and TH350 cases will break in the same place, the stock bellhousings are weak there.

Another possible option would be to install a JW Ultrabell. Not sure if they make one for the 700, but if they do, you may even be able to use that case if it only cracked in the bellhousing area.

Ron
 
#19 ·
does the trans mount line up with the hole in the crossmember without needing to pry the trans over to get the bolt in?
if so, then it's not bound up and you don't need to fix that..
 
#21 ·
Yep it lines right up. it is not bound up at all. there are no vibrations or anything.. i am running the stock rubber motor mounts and trans mount. they were all new 3-4 yrs ago.
 
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