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Well, a TH350's bellhousing can't take a 415ci!!!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BorregoK5, Feb 6, 2002.

  1. BorregoK5

    BorregoK5 1/2 ton status

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    Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    I was backing into my driveway tonight when I heard the plink of metal hitting the concrete. Found what looked like a piece of the bell housing. Had to get a flashlight to see that the bellhousing broke all the way around the torque convertor leaving only the mainshaft to hold it up and keep it suspended. The bellhousing bolts were all tight, as was the cross member. I have to say I was a little bummed as its a brand new th350 but the pain really sunk in when I remembered that th350's don't have a removeable bellhousing... its integral with the case... Well, should have known better than to throw that 415 on it and expect the aluminum to hold up.

    Lets talk options here. A th400 is cast iron, correct? Are the bellhousings part of the case as well? Now what do I need to know in order to continue using my np203 with a th400?

    Hmmm, or a Raptor....

    I started with nothing and I still have most of that left! - <a target="_blank" href=http://www.echobit.com:81/k5/> Pictures</a>
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    TH400's are also aluminum and all auto's are integral bellhousings.
    Was your TH350 a 4wd case? It should have a large 'K' cast into the bellhousing if it is. The 4 wd versions are much thicker.

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
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  3. HarryH3

    HarryH3 1 ton status Author

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    Something doesn't sound right... There are lots of Turbo 350's out there living behind some pretty beefy engines, both small and big blocks. [​IMG] It'll be interesting to see what you find when you get it all apart.

    <font color=black>HarryH3 - '75 K5</font color=black>
    <a target="_blank" href=http://www.angelfire.com/super/ThunderTruck>www.angelfire.com/super/ThunderTruck</a>
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  4. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    I would also like to mention that if you find a TH400 HD (which is what I have behind my 454), you will be just fine. The HD handles the ~500FtLbs my 454 produces... I'm sure it would also survive just fine behind your combo.

    But I agree with the other guys - something here doesn't sound right. You need to have something SERIOUSLY wrong with your existing stuff to shatter a bellhousing. I've seen 10 second cars run on stock TH350's with nothing other than a stage-3 shift kit. I don't know that a truck can deliver the same punch (due to its sloppy suspension) to the bellhousing as a 1.5 second 60ft car... but I might be wrong! [​IMG]

    I would be sure to go over your flywheel very carefully near the crank bolts... and be sure to get a new torque convertor with the new trans to insure solid operation next time.

    Did you have any nasty vibes while driving????

    -Dan

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     
  5. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    I'd also look into replacing your engine mounts with poly bushings...

    There had to be quite a bit of movement somewhere in your drivetrain...

    Just my .02!

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     
  6. BorregoK5

    BorregoK5 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    I looked all over the bellhousing (from underneath anyhow) and I can't find a "K" casting mark, and yes the bellhousing is thin! I have a hard time believing that this case wasn't already stress fractured and the torque just finished it off.

    The way I see it I've got two options..
    1. Gut the case and and assemble it into a new case, risking the same problem later.
    or
    2. Gut the case and get the bellhousing TIG'd back together. Then TIG a bunch of 1/4" aluminum plates running from the engine side up onto the case, reenforce the bell housing externally where I have room to thicken.

    I've been really pleased with it's operation up to now, heck if it hadn't thrown a piece I might have driven it to work tomorrow and wouldn't have even known there was a problem. It's all bellhousing and no case damage so no leaks. this has to be murder on the mainshaft bearing though. What a pain in the a$$ this is going to be! Even worse I've got to rent a car... doh!

    I started with nothing and I still have most of that left! - <a target="_blank" href=http://www.echobit.com:81/k5/> Pictures</a>
     
  7. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    I wouldn't waste my time with all that. I would either buy another built (4WD) TH350 and drop it in, or go big and find a TH400 to stuff under your rig. You would need a new adaptor, and possibly your driveshaft length... I made this swap after I smoked my Th350. Its NEVER given me any problems since...

    Hope this helps...

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     
  8. BorregoK5

    BorregoK5 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    Everything from the harmonic balancer to the np203 is new and fresh with the exception of the tranny case which I'm sure was a core. All the internals were new and I even had the beafier sprag and HD clutch plates installed with a slew of other streangthened parts. The Torque convertor was a new TCI low stall. Just replaced the motor mounts but the crossmemeber mount had a little age (didn't move under load though). I had a little driveshaft vibration off the line but nothing at speed, nothing that matched engine rpm either. I've had th350's behind muscle cars at the strip getting good and crazy on them, but never pushing 5000lbs on tall gears (3.07's) with 33's. I'm wondering if this didn't contribute to the damage!

    I started with nothing and I still have most of that left! - <a target="_blank" href=http://www.echobit.com:81/k5/> Pictures</a>
     
  9. HarryH3

    HarryH3 1 ton status Author

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    Is there any chance that either driveshaft is bottoming out in its travel? That would put some serious stress on the t-case and the tranny housing. The front shaft bottoming out would really tweak things in a way that they shouldn't be tweaked. (Been doing any Dukes of Hazzard type stuff?) [​IMG]

    Oh yeah, do you have the support rod installed that helps hold up the weight of that monster NP203?

    <font color=black>HarryH3 - '75 K5</font color=black>
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  10. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    I had a 79 Firebird that had a build 403 in it... had about 450HP... it liquified the internals of a TH350 before I traded it out for a TH400. Anyhow... the case wasn't harmed in all of that.

    I guess you could go on the assumption that the case was damaged before you got your hands on it. But I don't know that I would use its internals in a fresh case. I would still just aquire another complete trans...

    just my .02

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     
  11. BorregoK5

    BorregoK5 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    My rear driveshaft could have bottomed out I suppose as it only has a couple inches of travel. Front shaft has lots of travel. I haven't been very rough on this tranny but the last one got a lot of air time [​IMG] I do have the support rod installed and checked it for tightness (A-ok). I'm going to look into the rear driveshaft travel, that might have something to do with it. I have speed bumps all over the place here and don't always slow down for some of the remote ones.

    I started with nothing and I still have most of that left! - <a target="_blank" href=http://www.echobit.com:81/k5/> Pictures</a>
     
  12. BorregoK5

    BorregoK5 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    Well, rear driveshaft wear/dirty marks don't show that it has travelled to the point of bottoming out anytime in the near past. I had cleaned it up really good before installing it a few months back and checked the throw on it them, smae throw and the dirt and rust marks are a good 1/2 from bottoming and around 2 inches at rest. That doesn't mean it didn't happen though. Funny thing is the crack/break looks like a tortional break. I think it has to be the cross member mounts going bad and the tall gearing on the 415 just twisting away at what might have been a stress fracture from the rear shaft bottoming out. Or it was cracked to begin with and I didn't catch it. Thanks for you input, it not only helps track down problems but helps be vent!!!

    I started with nothing and I still have most of that left! - <a target="_blank" href=http://www.echobit.com:81/k5/> Pictures</a>
     
  13. Donovan

    Donovan 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    Here you go. This will fix it. Look under the Ultra-Bell section.
    www.rustbucket.rockcrawler.com
    Got Leafs??
     
  14. arq

    arq 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    i've seen many 350 trannys behind 454s and they hold up, they burn up before breaking like that. I had a poniac once with a bent drive shaft. after a few 100 miles something gave, you guessed it the bell housing. so either the driveshaft bottomed out like mentioned before or vibes could of killed it.

    ARQ.

    offroad baja!!!
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  15. BorregoK5

    BorregoK5 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    Donovan, thank you! Thats exactly what I was looking for! I'm ordering in the morning!

    I started with nothing and I still have most of that left! - <a target="_blank" href=http://www.echobit.com:81/k5/> Pictures</a>
     
  16. BorregoK5

    BorregoK5 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    Arq, we have to get out somewhere local here. As soon as I'm back up and running that is... I think some of the driveshaft woes I've had contributed to this, got to get on a 1350 CV but I'm still waiting to finish that 14b and take some measurements.

    I started with nothing and I still have most of that left! - <a target="_blank" href=http://www.echobit.com:81/k5/> Pictures</a>
     
  17. four_by_ken

    four_by_ken 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    Must have been somethig with the bell housing. My 350 trans holds up fine to my 454. And the BB is mildly built. The trans was gone through and reworked nicely. And beat the hell out of it. :-)

    Ken H.


    '86 K5 in parts
    1-ton 454 44 TSLs
     
  18. blazbrnc

    blazbrnc 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    I don't think the engine power had anything to do with the bell housing breaking. The largest amount of stress ever placed on the bell housing is during assembly. I'm assuming you have the two dowel pins in place that are between the block and bell. When you put the tranny in, did the bellhousing sit flush against the block without having to torque the belhousing bolts? Many times the dowels hang up on the holes in the bellhousing, or the stack tolerance between the tranny pump and the crank is too great. Then when the tranny bolts are tightened the bellhousing has to give. Just my 2 cents.

    Thank you......Detroit!
     
  19. bigmack

    bigmack 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    I will have to agree with some of the others, I dont think it would break like that from horsepower. I have a '79 GMC 2wd that I recently built a 406 small block for, it has been in the truck for about 6 months, it makes about 450 horsepower &amp; I have a TH350 behind it with a B&amp;M shift kit &amp; it takes quite a bit of abuse, it hasn't gave me any problems yet.

    '80 K10 350/350/NP205/14B/10B/4.10/4"Lift/Q78-Buckshots
     
  20. K10ANDYKHAMNIC

    K10ANDYKHAMNIC 1/2 ton status

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    Re: Well, a TH350\'s bellhousing can\'t take a 415ci!!!

    yo mike its not the weakness of the case u have something out of line its your mounts or sumpin , my friends z with a built 350 sb broke his too but its cuz it was out of line and put stress on it where there isnt sposed to be any . the 4wd K case cost you about 275$ :) anything else u where im at ..

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