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Preventing TH350 Case Breakage?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Beast, Feb 19, 2001.

  1. Beast

    Beast Registered Member

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    I have a 73 K5 that I just replaced the trany on because the last one broke at the top left mounting ear where it bolts to the transfer case, is this a common problem? I was wondering if anyone has run across modifications to reduce the likelyhood of this happening again. I just put in a built TH350 that hits so hard from second to high that I'm worried about any week points. The old tranny and the new do not have "4x4" cases but everone I spoke to says the only difference is in the bell housing area where the 4x4 model is beefier for an aluminum "dust cover". I was thinking of making an adapter or installing another crossmember to support the tranny at the normal 2 wheel drive mounting points instead of relying on the bolts that tie it to the transfer case.
     
  2. HarryH3

    HarryH3 1 ton status Author

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    Does your truck have a brace from the t-case to the tranny? I don't remember what it looked like under my '75 when it had the stock 350/203 combo(changed out the tranny and t-case the week after I bought it in '87) but the 400/205 combo that's in it now has a pretty beefy brace that bolts to the side of the t-case and the other end bolts to the engine. It just bolts on via one of the tranny-to-engine bolts. The 700r4/208 combos have a similar brace.

    Also, were the bolts holding the t-case adapter to your tranny tight? If they get loose then things start moving around and binding. That could cause the tranny case to break.


    <font color=black>HarryH3 - '75 K5</font color=black>
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  3. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Around 77 or so GM started adding braces and thickend up the bell housing. The beefed up housing accepted a cast aluminum cover verses the stamped tin that had 2 braces that ran to the motor mounts. They also had a brace that ran from the side of the case to a bell housing bolt. that brace can be added to any case but the cover will only work on a 4x4 beefed case. The issue was the 203 is so heavy that it would brek the case if you jumped the truck or got caught on a real bouncy trail. So far I have not had an issue with my 75 that has the weaker case but I already lined up a 4x4 case if it fails.

    Diging it in the dirt with my K5's
    Grim-Reaper
    <A target="_blank" HREF=http://grimsk5s.coloradok5.com/>http://grimsk5s.coloradok5.com/</A>
     
  4. thatK30guy

    thatK30guy 1 ton status Premium Member

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    One more thing everybody is forgetting: There is a small cast steel bracket that bolts on the bottom of the tailshaft housing where the adaptor holds the two together. Its basically a brace to support all that heavy weight. I had one and sold it for $75.00. I have never seen another one after that. I cant really explain what it looks like, but too many people are missing this vital part of the brace/support for these heavy NP203 cases. Maybe Steve, Stephen, anybody has a better name for it and know what to tell you guys.
     
  5. elkboy

    elkboy 1/2 ton status

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    I just put a TH350/205 in my 82. I did not have any braces so I made a couple. I used a piece of angle to bolt to the transmission were it bolts to the block near the top tranny holes and another piece of angle iron at the top adapter holes. Then I welded a piece of 1/2" rod in between so it acts like a strut rod from the block to the t-case. This should help relieve some of the stress on the adapter ears. I'm still in the process of building a rod that mounts on the side of the t-case, but I'll probably go the motor mount with it or to a bushing on the frame. Hope this helps.

    [​IMG]<font color=red> Elkboy</font color=red> [​IMG]
     
  6. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Your right I have never seen this cast brace. I have seen a cast torq brace off the side of the cases to the frame but never one from the tranny to the adaptor on a 203. I have even made one for a 700 R4 /208. I will keep an eye out for that one next time I'm rooting around the junk yards.

    Diging it in the dirt with my K5's
    Grim-Reaper
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