How does one determine the required torque for a particular bolt, when the bolt/fasteners is not the same size as originally called out in the parts catalog and the specified torage in the service manual?

My auto transmission fluid pan bolts are much larger than originally called for. If I remember correctly they are either a 13mm or 14 mm head bolt. Originals were much smaller. The original little one's didn't fit the holes, so there must have been a change at some point. Even more strange is there seems to be no record from GM of the bolt change.

So since I have what I have, I'm trying to figure out what the correct torque should be for these large bolts.

 

Wouldn't the torque amount be the same since you are fastening the same parts? I wouldn't think the bolts' head diameter should make any difference, but that's just my best guess.

 

I was thinking one has to consider the material the bolt threads into, as well as the specific bolt. I suppose on some applications its possible to damage the threaded receptical before the bolt snapped. But I would certainly believe that a 14mm takes more torque than a 8 or 9mm bolt.

 

If that were the diameter of the bolt, yes. standard torque is determined by the diameter of the bolt (not head size) and the material it is made from. When you start talking about the material it is threaded into you now need the specific torque from the MFG.

 

We're not talking about head bolts. Exact torque on transmission pan bolts doesn't matter.

Most torque specs are there to discourage overtightening. Just get the pan snug and the bolts tight enough to not back out.

 

We're not talking about head bolts. Exact torque on transmission pan bolts doesn't matter.

Most torque specs are there to discourage overtightening. Just get the pan snug and the bolts tight enough to not back out.

Now throw in cork or rubber gasket and what do you have ?
The same thing snug only.
Retighten after about 5000 miles.

 

Well I suppose my first error was letting the dealer service it and install a new filter. It never leak one drop in nearly 10 years, now its been back to the same dealer five times as the bolts keep loosening up and causing leaks. Each and every time they charge me for a new gasket as they say gaskets aren't covered by a warranty. Honestly I just getting tired of taking it back to them paying more money for more poor quality work.

So I was thinking I'd buy a new gasket from Chris and do this myself.

Oh since I don't have calipers to measure the width and thread of the bolts I just used the head size as the best description of how different the bolts are. I reviewed the manual specific call out for the bolt dimensions and I know the one's installed in mine are not even close. Plus I ordered a set of new one's and when I compared them they are much different. Since the pan housing is setup for the different larger bolts it not indicative of someone putting the wrong bolts in. Its apparent that these are the correct bolts for the transmission.

But one can't figure out what to torque them to. (And I'm not following my comical brother's comment to tighten until the pop then you know how much not to tighten them....LOL)

Anyway so I'm thinking of doing this myself and perhaps using locktite on the bolts to see if I can stop them from loosening up. If they'd just stay tight there would be no leaks.

 

You can find the torque values for metric bolts at: dodgeram.org/tech/specs. Use the LocTite, too. (Personally, I would just snug 'em up w/LocTite). Good luck.

 

As simplistic as it seems, I'm going to have to go with shotchkiss...

The facts seem to indicate that new bolts were used which have larger heads. There's no evidence that larger BOLTS were used in this application. It's not uncommon to buy the same size bolts with heads of different sizes....

Larry
code5coupe

 

Torque spec for a '89 700R4 pan bolt is only 8 ft-lbs or 11 N-M, if that helps any.