Trans installation question

K

Ken B

Well-known member
Oct 9, 2002
16,834
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Well I re-installed my trans a couple of days ago. Then I ran around with a torque wrench tightening everything up. There are three 7/16" bolts on
the rear of the trans that mount it to the vertical bracket with the rear trans on it.

The version of the manual I have says they are 3/8"x 16 bolts and are torqued to 55 ft-lbs. They are really 7/16" bolts so the book is in error on
the size. They go through the bracket and thread in to the aluminum rear of the trans. 55 Ft-lbs seems awfully high to be threading into aluminum.

Then I got thinking that maybe GM put Heli-coil type inserts in to those aluminum holes so it could be tightened to 55. I can not see in there now
because I have the trans installed.

Does anyone know it there are heli-coil type inserts in there?


--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
> Well I re-installed my trans a couple of days ago. Then I ran around with a torque wrench tightening everything up. There are three 7/16" bolts
> on the rear of the trans that mount it to the vertical bracket with the rear trans on it.
>
> The version of the manual I have says they are 3/8"x 16 bolts and are torqued to 55 ft-lbs. They are really 7/16" bolts so the book is in error
> on the size. They go through the bracket and thread in to the aluminum rear of the trans. 55 Ft-lbs seems awfully high to be threading into
> aluminum.
>
> Then I got thinking that maybe GM put Heli-coil type inserts in to those aluminum holes so it could be tightened to 55. I can not see in there
> now because I have the trans installed.
>
> Does anyone know it there are heli-coil type inserts in there?

We have a th425 here out of an Eldorado that has no insert in the threads, just threaded aluminum. The bolts are 7/16.
--
Wally Anderson
Omaha NE
75 Glenbrook
Megasquirt III injection
Bob Stone hydroBOOOOST
Manny reaction arm system
Branscombe Kelsey Hayes park brake
http://wallyandsue.blogspot.com/
 
None of the ones I've messed with (more than I wanted) had anything but a threaded case.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
Thanks guys. What you do think about 55 ft-lbs torque into aluminum 7/16 - 14 UNC (course) threads?

I just found a bolt chart on line that says grade 2 - 24 ft-lbs, grade 5 - 37 ft lbs and grade 8 - 52 ft-lbs. No where in the chart do the address
being threaded into aluminum.

Maybe I am being overly pessimistic, but unless I find something to the contrary I think I'll go with 25 ft-lbs. I am not worried about the bolts. I
am worried about the aluminum case threads.

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Just "turn 'em ' till they're tight", Ken. I want to watch you get a
torque wrench up in there anyway. :-)

Have you followed my suggestion to drill an access hole in the step riser
behind the top left bolt? Sure makes that go in a lot easier. Before
that, I'd sometimes spend as much time on it as the rest of the
installation.

HAPPY NEW YEAR!

Ken H.

On Tue, Dec 31, 2019, 7:21 PM Ken Burton via Gmclist <

> Thanks guys. What you do think about 55 ft-lbs torque into aluminum 7/16
> - 14 UNC (course) threads?
>
> I just found a bolt chart on line that says grade 2 - 24 ft-lbs, grade 5 -
> 37 ft lbs and grade 8 - 52 ft-lbs. No where in the chart do the address
> being threaded into aluminum.
>
> Maybe I am being overly pessimistic, but unless I find something to the
> contrary I think I'll go with 25 ft-lbs. I am not worried about the
> bolts. I
> am worried about the aluminum case threads.
>
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I bored the hole in my step. Saves half an hour per install. And I simply apply blue LocTite to the bolts and snugged them up nicely. I'd be
interested in someone else's luck with 55 ft lbs into that case, preferably tested on a broken case. Then if it takes the threads out, no loss and we
have the answer. When I got the coach, it had some transmission shop's label on the bumper, and had only two bolts tight on the bellhousing. One
missing, the rest finger tight. Ran it two thousand miles home that way without it falling out. Currently the mount bolt for my compressor which
goes into the intake has stripped the threads. Since it's winter I haven't addressed it, and probably won't unless or until I need the dash air.
Given the length of the bracket to that bolt, there's a pretty good level to put stress on it. I suspect a helicoil is in my future.

--johnny

--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
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