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Transfer case brace

Discussion in 'Chevy Trucks' started by Big Red, Jan 7, 2003.

  1. Big Red

    Big Red Junior Member
    Messages: 13

    Did 79 3/4 ton chevy' s come with a crossmember supporting the transfer case? I don't have one on mine and I keep cracking transmissions. Could the crossmember be the cause or is it something else? I have a turbo 400 and a NP 203 transfer case. The transfer case is only supported by the tranny. This is the second time I've cracked a transmission up near where it bolts to the engine. It cracks on the passenger side and the spreads across the top of the bellhousing. Any thoughts would be really appreciated.
     
  2. TrailK10

    TrailK10 Member
    from NH
    Messages: 74

    Is there a cross member underneath the tranny?
     
  3. paul soccodato

    paul soccodato Senior Member
    Messages: 430

    im not sure about the 79', but my 84' k-20 did'nt have a crossmember supporting the t-case.the crossmember was between the two, bolted to the adapter plate. but some of those trucks ( not my 84' ) had a brace that went from the t-case up to the bellhousing (not sure). their's a bunch of guys here who have those trucks. im sure you'll have a few more replies soon.
     
  4. wyldman

    wyldman Member
    Messages: 3,265

    On that truck the transfer case\trans adapter bolts to cross member with rubber mounts.There should be a long bar type brace that mounts from the right side bellhousing bolt to two large bolts on the pass side of the transfercase.It might help,but your problem could be something else also.We have one of our trucks with one missing and never had a problem.

    Might wanna check a few other things as well.Engine\trans locating dowels,bad or bound up motor mounts,bad tranny mount,bent frame or crossmember,binding driveshaft slip yokes etc
     
  5. johngus

    johngus Senior Member
    Messages: 117

    where is chuck when we need him?check his site,lots of info there.
     
  6. TrailK10

    TrailK10 Member
    from NH
    Messages: 74

    So these trucks had no transmission or transfercase crossmembers at all ???? Just braces?
     
  7. paul soccodato

    paul soccodato Senior Member
    Messages: 430

    now that im thinking about, my 84 k-20 had no brace, (maybe missing). but my truck had a manual trans ,sm465, with an np208. the crossmember was located under the adapter, and supported the trans. the t-case bolted to the adapter and basically hung off the back. on the manual trans, i dont think this would be a problem, since it was cast iron, but maybe an aluminum trans cant hold up without the brace. it depends on where your case is cracking to know if the brace is at fault, as a frozen slip yoke on the front shaft usually splits the case next to the front yoke (on the t-case)im pretty sure the automatic trucks had the brace.
     
  8. Chuck Smith

    Chuck Smith 2000 Club Member
    from NJ
    Messages: 2,317

    Paul hit it right on (as well as wyldman). The mount attached to the adapter plate between the trans and T case. On 79 & 80 models. There was the extra support from the passenger side of the T case up to the bell housing on 1980 models with the NP 205 case. Never saw it on a 203. I believe in the early 80's there was another brace for the brake booster that was not on earlier models. I never had a problem without a brace on the brake booster on either of my trucks. Then again, my frame never cracked behind the steering box either (which is supposed to be so common).

    For what it's worth, I drove my 77 Chevy with TH350 and NP 203 t case A LOT harder than my 80 GMC with TH350 and NP 205. The 80 GMC has the brace, and the 77 Chevy does not. The 77 has a built 400 in it, and the 203 was converted to part time, running 36" swampers. No problems. No problems with the 80 GMC either.

    I changed the rubber trans/T case mount on both my trucks to urethane, because the rubber was just too sloppy.

    Big Red Wrote:

    "This is the second time I've cracked a transmission up near where it bolts to the engine. It cracks on the passenger side and the spreads across the top of the bellhousing."

    If the trans is supported by a cross member, I don't see how the weight of the t case on the end would put more stress on the bell housing at the motor? So the bell housing is cracking, not the transmission?

    I would check the motor mounts. Might be time for new ones. If they are allowing to motor to twist from torque, and the trans/Tcase is staying put, that might* cause your problem.

    How is your flex plate? It is pretty common for them to crack. Any marks on the inside of the bell housing? Is the flex plate the proper number of teeth?

    As far as a bent frame, I doubt it would affect anything. Anyone that has driven a long bed off road knows just how much these frames twist. I've had mine so twisted I couldn't open the drivers door with it flexed, and never had any other problems....

    ~Chuck
     
  9. Chuck Smith

    Chuck Smith 2000 Club Member
    from NJ
    Messages: 2,317

    Paul, the 208 was aluminum, and the lightest of the 3 cases used over the years. The 203 and 205 were cast iron. Also, the design of the 208 would call for a completely different brace, if any at all.

    Maybe John DiMartino can add something here?

    ~Chuck
     
  10. paul soccodato

    paul soccodato Senior Member
    Messages: 430

    Chuck, you know its funny, my frame never cracked there either.

    besides plowing, i drove that truck like a lunatic in the woods (when i was younger, of course). i had some tsl thornbirds on it. buried up to mid door in mud (weekly). also blew up my first motor in that truck (sucked some sandy water down the carb, while swimming), that truck was a lot of fun.

    my other post is confusing, i meant the transmission itself is cast iron, not the t-case.

    the only thing i hated about that truck was getting the sm-465 in and out.

    man, was that thing heavy!
     
  11. Big Red

    Big Red Junior Member
    Messages: 13

    Yes there is a crossmember under the trans/t case but i posted a question earlier about a weird vibration happening around 55-60 mph. My vibration eventually turned into a worse vibration with a ticking/clicking noise. I found out it was the flexplate which had cracked so my friend and I pulled the engine to replace it and also discovered the transmission bellhousing had cracked from the passenger side halfway up to the top. My dad had the transmission welded at the local welding/manufacturing shop. We replaced the tranny and engine and the vibration was gone. I couldn't believe how smooth it ran out on the highway but eventually the vibration came back and I looked and now the transmission has split all the way across. I never thought of the engine mounts. This weekend I'll check it out. Would it also work to just pull the guts on my current transmission annd slip it all back into a different case? I'm working on a really limited budget. Thanks for all the replies
     
  12. Chuck Smith

    Chuck Smith 2000 Club Member
    from NJ
    Messages: 2,317

    Yes it would work to swap the guts if you could find a clean, solid, usable case. The TH400 is getting VERY rare in most areas. You might also want to have your rear driveshaft balanced.

    I could get as much as $200 around here for a shot TH400 with a rebuildable case!

    ~Chuck
     
  13. wyldman

    wyldman Member
    Messages: 3,265

    Chuck,the brace was also used on the 203 cases as well,we have two of them.All of our GM trucks have cracked (but repaired) frames at the steering box.There may be different length braces (for different trans\case combos) as I have seen a few which don't line up right.

    One other thing is the two braces which mount from the motor mount plates (on the engine),to the lower front side of the bell housing).Not sure how much of a difference they may make,but if your going to fix it,might as well do it right.

    When I metioned the bent frame\crossmember I was thinking of a customers truck which we repaired that had a similar problem.Truck had been rear ended and the frame was twisted,binding up the trans and engine when it was bolted in.We ended up slotting some of the mounting holes to give us some slack when bolting everything up.

    It would be better to get another case,and have everything swapped over from your old trans (as long as nothing internal is damaged)
     
  14. wanigan-007

    wanigan-007 Junior Member
    Messages: 2

    Hi Guys, I have read all the respones to big reds Question and I have yet to see a true answer....Well here goes my shot. I have a 79 GMC 4x4, well at least thats What it was Orig,Ihave replaced the 400 small block with a built 350 with all the goodys...It has a turbo 400 trans and I have gone through 3 transmission cases...The truck Orig has a crossmember that the transfer case sits on,two rubber mounts...this crossmember bolts to the frame..Why your truck do not have one I donot know..The reason for breaking my transmission cases was a combonation of alot of things.1.I have a 3 inch suspension lift and a 4 inch body lift on my truck.. this puts a different pich of angle on the drivelines..2.I had to remove for a period of time the tranfercase brace,not the crossmember...This allowed the torch of the engine under power to twist the tranission case....3.The most basic thing to happen to a 4x4 out in the mud or road grime,I dented my rear drive line..not very bad, hardley noticeable.This was enough to put my drive line out of balence and have a new one made.The combination of all these things over a long period of time and money can drive you nuts!!! I have since cured the problems I have had with Chevy replacement parts be they used or new and patience,Find the right Mech for the job!!!!
     
  15. mnic

    mnic Junior Member
    Messages: 19

    to my knowledge i would first check or change the dowel pins on the motor sounds like could possibly oblong or slightly smaller worn dowel pins or the possibility of when installing the trans bell is not flush with engine and is being pulled in with the bell bolts till flush making the dowel pin holes on trans oblong typically chrysler used to have a cross piece 2 L brackets bolted to cross member chevy in the 80s had a long bar which attached to the pass side of trans case with 21mm? bolt heads and attached to the trans bell housing with a longer bolt but a trans case breaking alot is usually dowel pin problems