Np205 bracket

[argonaut]

I would think that frame flex is another factor here. We all know that light duty frames twist a hell of a lot. Having the transfer case mount located so far from the center axis is sure to put a lot of stress on the trans to tc adapter when the frame is twisting. Im sure folks with stiffened frames, cages, etc experience this mode of failure less frequently.
I decided to leave mine off since I wont be doing any mudding or similar driving where the powertrain will be exposed to impluse shock loading. Plus my frame is bendy-flexy until I box it. And take a look under many new trucks; I think they just let 'em hang.
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[OLDCHEV4X4]

Originally Posted by argonaut

I would think that frame flex is another factor here. We all know that light duty frames twist a hell of a lot. Having the transfer case mount located so far from the center axis is sure to put a lot of stress on the trans to tc adapter when the frame is twisting. Im sure folks with stiffened frames, cages, etc experience this mode of failure less frequently.
I decided to leave mine off since I wont be doing any mudding or similar driving where the powertrain will be exposed to impluse shock loading. Plus my frame is bendy-flexy until I box it. And take a look under many new trucks; I think they just let 'em hang.
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I have a cage, the frame is boxed in strategic places, and the motor mounts and motor mount cross member are all custom fabricated. I'm good to go. Nothing to do with luck.

I have broken adapters in the past on a stick and automatic, but also discovered broken driver side motor mounts and felt that this was why the adapter broke. I replaced everything and also added a motor limit strap and never had anymore problems. These were street legal trail trucks.

[SunSoaked]

Originally Posted by DirtyLarry

Congratulations with your luck guys. GM stopped tying the tcase to the frame in ’73 for a reason. As I have mentioned in other threads, that reason was related to broken trans to tcase adapters on manual trans trucks and broken bellhousings on automatics due to tcase mount. That was straight from a retired GMC truck engineer that 3 of us members personally know and worked with for several years.

Manual trans rigs have a higher fatality rate of the adapter just due to the greater torque load passing through the driveline and the design of the adapter itself. Automatics didn’t suffer much of adapter (there isn’t much to a TH350/NP205 adapter to begin with) issues but more of cracked transmission bellhousings due being twisted apart by that bracket holding the tcase to the frame.

Think about it, the engine will want to twist with the rotating mass. The engine, trans and tcase all need to rotate together as one assembly. With the tcase to frame bracket in place the powertrain is restricted and something will eventually be twisted beyond its giving point and break. The weakest link is the trans to tcase adapter on 465 rigs and the thin aluminum bellhousings on TH350's in the torque converter area of the bell. The carnage will be worse and happen quicker with worn engine mounts that allow excessive torque rotation. I would imagine a good set of Energy Suspension polyurethane engine mounts would mitigate powertrain movement if one must keep their frame mount.

One thing is for sure, when the day comes when your lucky horseshoe gets lost and you notice a trans fluid leak on the ground then find that nice crack in your adapter or find a broken bellhousing on a 69-72 automatic 4x4, I bet this thread will quickly come to mind and the frame bracket will find its way into the iron pile.

Ya, what he says

[DirtyLarry]

Originally Posted by OLDCHEV4X4

I have broken adapters in the past on a stick and automatic, but also discovered broken driver side motor mounts and felt that this was why the adapter broke. I replaced everything and also added a motor limit strap and never had anymore problems. These were street legal trail trucks.

Dang, I have never even heard of an automatic adapter breaking as there isn’t much too them. They are very short (~3.5 -4”) and robust while the manual trans adapter design is long and rather delicate (~6.5”). If anything breaks on an automatic it is usually the auto trans bellhousing just above the torque converter. If you are using a tcase to frame bracket, I suppose anything could break but again, it is usually a bellhousing. I briefly had a '69 K5 in high school with a broken bell housing. I always wondered why it broke and years later I now know why. On the other hand, the early figure 8 manual trans 205 adapters are famous for breaking even without a tcase to frame bracket. The tcase to frame bracket will cause it to break sooner.

TH350/205 adapter. TH400/205 bracket very similar but has two more bolt holes on the trans side


SM465/205 adapter. It is long and rather fragile

[Burt4x4]

I tell you what DL ~ if'n it ever breaks you'll be the first to know
If'n you never hear about it then it never broke and your theory didn't apply to my rig and the way I have set it up....when my 454 raps, the engine doesn't move in between the frame...the WHOLE truck rocks
Ask anyone that has wheeled with me..I ain't no tenderfoot slowski I like to hit it and if my stuff ain't broke by now...well I doubt it is all luck, maybe some tho hehee


Good Times!!
Burt

[RANDY COX]

HHHm glad I saw this thread cuz on my truck it doesen't have that bracket on it.I thought i was gonna have to find one..cuz to me it looks like it would help hold the transfer-case.So sounds like if I don't put it on there I'll still be good to go......to put on or not to..Is the question...

[RANDY COX]

on my 70 Burb 4x4 I had to replace the adapter from tranny to transfer,cuz after I got to checking it.Found that it was cracked,the adapter didn't have the extra casting or webbing or what ever you call it,it was more smooth.guess it made it weak..

[burnin oil]

I wouldn't worry about the transfer case not being supported. My old blazer had a built 400sb with the 465/205 drivetrin. Never had a problem breaking a bellhousing or adapter. By the time the truck was scrapped I couldn't get the instument panel out from body flex and the frame rails sat at two different hieghts. The floor was even bent on both sides of the transmission tower from torqueing the drivetrain so hard! I went through 5 motors, 2 front axles, 2 rear axles, 3 front drive shafts, 17 rear wheel bearings, can't remember the number of clutches (broken dampening springs), and never broke a mount or adapter. Trans and tranfer case took it all. Just putting a little personal experience out there.

[DeerMeadowFarm]

Well, I'm going to dig up an old thread as I am in the process of figuring out what to do and what the PO did. I have a (presumed) 74 one-ton frame with a SM465 and 205 combo. I pulled them out of the truck this weekend and the adapter housing was broken (see pic)


The only thing supporting the trans/TC combo were two rubber mounts on this (bent-up) cross-member; located in the two big holes.


I was trying to find a new cross member and a new adapter housing but you guys are saying I don't need to support this at all? I can leave it all off? Sounds weird to me to have the transmission and TC hanging just by the motor mounts essentially?
Help please!

[Dale99]

No, you need the trans crossmember. I may actually have a NOS one. I dont remember what years it fit.

They are saying that is ok for the TC to hang off the rear of the transmission.

[DeerMeadowFarm]

OK, my TC adapter housing was bolted to that cross member. Is that right?

[Dale99]

yes, adapter, spacer, coupler.... whichever you choose to call it.

[DeerMeadowFarm]

OK. Do you have one? Any pictures?

[Dale99]

Adapter, no. I "might" have a NOS crossmember.

[special-K]

All my trucks have been put together the way GM built them. I have never had a problem caused by this side bracket. It "gives". If you are torquing so hard on your rig that the transfer case mount causes breakage,something should break. And,if it didn't break from that,it will break from something else. Nothing allows your drivetrain to twist in the frame as far as it wants. There has to be a limit. If you wheel hard enough to break something because of the transfer case bracket,but don't have one installed,you'll be breaking something else. I've seen clutch linkage drop out of a '77 K30. If nothing breaks,that's where you're riding on your luck. After 40 years of use,all these stock set-ups aren't together still by luck,just by type of use. You can break anything on a 4wd if you try hard enough...including the parts others design as an "improvement"