Torque for bolts on adapter to a TH350

[dremu]

I'm redoing my Doubler and fixing some leaks while I was in there -- Greg72's fricken MightAsWell-itis hit me hard today

The adapter from the NP203 to the TH350 has the four bolts that hold it onto the tailhousing, and apparently they are supposed to have O-rings under their heads. There's a machined space in the adapter that would take the O-ring.

I did some searching but couldn't find a specific torque to tighten these guys down to. I hate to deform the O-rings, so I suspect the usual torque for a 3/8" bolt would be too much. OTOH, it's nightmarish to get in there to re-tighten them, so I wanna make sure they're on properly.

Any ideas?

-- A

 

[4xcrazy]

tight

 

[diesel4me]

Only specs my old books have for t-case to tranny are 35 ft lbs..this was for a TH-350 to a NP-205...most torque specs for bolts by size listings also say 35 ft lbs is the usual rating for a 3/8" bolt..

I'd be careful if your threading into aluminum,like on the tail of a TH-350..best to make sure the transfer case is shoved tight against the tranny and well supported,so the bolts aren't forced to draw them together at an angle..those bolt holes can be easily stripped,and there isn't always enough meat left around them for a heli-coil to be used sometimes..

 

[dremu]

Only specs my old books have for t-case to tranny are 35 ft lbs..this was for a TH-350 to a NP-205...most torque specs for bolts by size listings also say 35 ft lbs is the usual rating for a 3/8" bolt..

I'd be careful if your threading into aluminum,like on the tail of a TH-350..best to make sure the transfer case is shoved tight against the tranny and well supported,so the bolts aren't forced to draw them together at an angle..those bolt holes can be easily stripped,and there isn't always enough meat left around them for a heli-coil to be used sometimes..

In this case there's the adapter that bolts to the tailhousing (bottom of pic)

and it has a lip to hold it in there... but yeah, I'd forgotten about the TH350 case being aluminum. I'll be extra careful there.

I was just glad I have a local transmission parts house that had the square-cut O-ring for the TH350. (Also nice that I can just show them the old one and say "Turbo 350", and not go through the "What year is your car?" crap you get at the chain stores.)

-- A

 

[4X4HIGH]

Aaron, there should only be the large O-ring that goes around the circumfrence of the adapter where it mates with the trans case. The torque value for a 3/8" bolt is 33 ft/lbs for grade 5 bolts or 47 ft/lbs for grade 8 bolts and this is the dry torque value.

 

[dremu]

Aaron, there should only be the large O-ring that goes around the circumfrence of the adapter where it mates with the trans case. The torque value for a 3/8" bolt is 33 ft/lbs for grade 5 bolts or 47 ft/lbs for grade 8 bolts and this is the dry torque value.

It took me three reads to get that you meant transmission case and not transfer case. You have to be careful not to confuse me

I'm happy to believe you -- the O-ring idea I found on a Pirate thread, which doesn't make it true -- but my particular adapter does have this machined lip smaller than the diameter of the bolt head:

Which just screams "O-ring" to me.

-- A

 

[diesel4me]

I never saw any o-rings on the bolts when I took the Np-203 out of my 77 GMC in favor of the Np-205 I saved from another truck I had with a TH350--that doesn't mean GM might not have ever used some though..square cut ones would work better maybe--possibly some small block valve stem seals would fit there good?..

I remember having "fun" trying to locate that square cut TH350 o-ring for the tail end once when a friend and I swapped a used one into his truck and the old one was not useable..didn't want to use blue goop there and risk a leak--we tried two tranny shops and a few parts stores,none had them listed separately and the tranny shops didn't happen to have one hanging around..in desparation we even tried looking for o-ring stock to make one from,all we could find was round,not the square type....

While we were digging thru drawers in his shop hoping to find something suitable that might work,I saw a pile of old oil filters in the corner,lying in the roll around drain bucket..saw the gasket on one looked "close",and after prying a few off,we found one that fit nicely,and it worked OK,we expected it to not last,but it never leaked!..

 

[Tnsejed]

That little machined section is most likely a relief so that the flange of the bolt is contacting the surface, and not the rounded section of bolt left from machining the shaft to flange extrusion.

I've never seen orings under the heads of the bolts myself.

 

[dremu]

That little machined section is most likely a relief so that the flange of the bolt is contacting the surface, and not the rounded section of bolt left from machining the shaft to flange extrusion.

I've never seen orings under the heads of the bolts myself.

Makes sense, especially as IIRC the bolts that were there had a pretty good flange and weren't just hex head bolts. Don't know if they're original or not, of course.

However, the thought plickens -- really does look like there's supposed to be something there. From the horse's ass mouth (the illustrated GM parts book)

#7 is the guilty party.

Of course I can't find it in group 4.515 in the parts book, which is annoying, but I'll keep digging. Maybe it's supposed to be a lock washer like #6 and somebody was lazy typing it up

And yeah, I'm prolly overanalyzing, but it's something to do while the paint dries and I wait for parts. Anyway, I'll post up as I find more.

-- A

 

[mudjerk]

Hello, im new to this and cant really figure out how to work this forum but I have a transmission question I was hoping someone could help with, 91 k5 w/700r4

 

[dremu]

Hello, im new to this and cant really figure out how to work this forum but I have a transmission question I was hoping someone could help with, 91 k5 w/700r4

Probably best to start a new thread:

as this thread is about a very specific issue on an entirely different transmission (and the answer is likely that Emu is fussing too much!)

It's also helpful to put specifics in the subject line, like "700R4 shifts wrong" (or whatever your problem is) instead of just "Question" (I hate those ) or "Transmission question" (still too vague.)

Oh, and welcome to CK5! Lots of good info and good folks here.

-- A

 

[dremu]

After frustrating myself with the parts books and stumping a very helpful guy at the dealer, I'm gonna just try normal boring O-rings:

The machined lip is ~.050" deep, so I 'm going with a ~.075" thick O-ring that's right about .375 ID and .500 OD, i.e. 3/8x1/2". I'm thinking that when the bolts are torqued to normal spec, the flange head will cover up the O-ring and deform just it enough to fill the countersink.

I betcha that 99.9% of the time the bolts' flange head will seal well enough that this is never an issue ... but I always enjoy digging through the parts books. For a while

Thanks all!

-- A

 

[Tnsejed]

Yeah that part schematic shows something there. Good find. I never would have guessed it.

 

[jekquistk5]

I would just dab some right stuff on there and call it good

 

[blazer74]

I think (not 100%) this is what your looking for gm 8621767, national or timkin 342805 or skf 4911. also fits other apps on our trucks. its like .093 th x.687 od x .5 id
Probably not worth it, about 4 bucks a piece.
Id use high temp red rtv in there.

 

[dremu]

I think (not 100%) this is what your looking for gm 8621767, national or timkin 342805 or skf 4911. also fits other apps on our trucks. its like .093 th x.687 od x .5 id
Probably not worth it, about 4 bucks a piece.
Id use high temp red rtv in there.

1/2" ID is high for a 3/8" bolt though.

I'm also annoyed that Rockauto lists it as an oil seal, so they show a generic oil seal picture for what should be basically an O-ring. Aargh.

We'll see how my generic O-rings go with regular torque. Can't leak any worse than it did before

-- A

 

[blazer74]

Yup too big, those old parts manuals aren't very clear.

 

[Bevis]

I know this is several months old, but how did the o-ring work out for you? While looking at my mounting plate for my TH350/NP203, thought there should be something there too. I have a Transmission leak that is at the plate, if left park.

 

[dremu]

I know this is several months old, but how did the o-ring work out for you? While looking at my mounting plate for my TH350/NP203, thought there should be something there too. I have a Transmission leak that is at the plate, if left park.

Thus far all good. Maybe it was replacing the big square O-ring, maybe it was adding these, but I don't have the giant bloody drip out of the tranny any more.

-- A

 

[Bevis]

After closer inspection, my 4 bolts have a small washer like on them. Wonder if thats what they are calling the seal in the diagram posted above. I'll get a pic of it when I go out to the barn later.