Choice of Auto trans for 750 ft.lbs FI BBC set-up

[1969CamaroRS]

OEM fittings are definitely not NPT, so if you got a 4l65E from GM, the fittings (snap in type) are straight thread.

Its a built trans from a pretty well known transmission builder (not going to name names). But it definitely looks like a NPT fitting as it has a taper, and still has some thread sealant on it.

It doesn't help when vendors advertise the wrong part or mislabel the correct part.
Many vendors sell the right fittings but still call it NPT, when it is not NPT.

Definitely, thanks again for setting things straight.

[Jake's Performance]

Once again,
GM hasn't used NPT for decades.
There are many transmission builders who don't know the difference in the fittings or just do things the hack way if they do.

It's my personal preference to do it right and use the correct fittings. I use the Russell fittings made for the application. They don't cost much more than any AN fitting so why risk it?

[1969CamaroRS]

Once again,
GM hasn't used NPT for decades.

I don't doubt what you are saying, just that the source of the confusion was my trans came with the wrong fittings.

Thanks

[Jake's Performance]

Any reputable shop SHOULD be aware of the difference in threads, and if they aren't using the right parts, it calls into question what else they aren't doing right IMO.

I would be asking them if they know, and if they do, why they don't use the proper fittings.

[Steve Chryssos]

Put it this way. I won't recommend the 612000 in the future. But I won't be pulling apart any of my three house cars just to change fittings either. One car is six years old. The others are three and two years old. The wrong fittings are sealing. Probably the result of very soft aluminum used in the fittings and common sense used when tightening along with teflon sealant. No leaks, no cracks.

Doesn't change the fact that they're wrong. They'll get changed eventually.

[Jake's Performance]

Steve,
I would probably not change those fittings, the threads may be "stretched" now and putting a NPSM fitting in may not thread tightly.
It would be a "feel" thing, if the NPSM threads OK, it would probably be OK.

I know of some big name builders who use NPT, it just seems cheezy to me to do so when the proper fitting is readily available. I ordered 2 sets last night because this thread reminded me that I am out of stock.

A NPT with taper fit into a tapered hole gets the full interference fit so will seal quite a bit of pressure. I'm sure all of us are using NPT to run air in our shops, water into our houses, etc. Relatively low pressure applications like the cooler lines on a trans.
However threading the tapered fitting into a straight cut hole limits how much interference fit you get. Thread sealant will help seal it but then you have potential contaminants in the ATF.

The NPT will usually work, as proven by your experience and others, however when it doesn't the scenario is it doesn't seal, so the end user tightens them a bit tighter, and they still seep, so a bit tighter will fix it right?

Now Mr. Transmission guy gets the blame for the leaky transmission, bad case, and costs incurred when he did nothing wrong but the customer was ill informed (all too often by the internet or another vendor) and didn't have the common sense to realize that threading a fitting into an aluminum case at gorilla torque specs isn't wise.

When you quote a customer $150+ for a core even on a TH350 (which is a losing deal for the transmission shop but that's another story), and the customer is wondering why you are charging $150 for a case when he can buy a rebuilt TH350 for $300-400 at Jim Bob's transmission shop and then $200-300 to recase it they start screaming.

I pay ~$100-150 for TH350 cores but it takes 3-4 usually to get ONE good core to build because the cases are usually bad from low support wear, I won't build one using an excessively worn case.
A 4L80E core is $300 for an early model or $700 for a late model by the time I pay transport costs (I'm local to the suppiers).
Usually they are good but I have a $300 core in the shop right now that has a ruined case from the "runaway pressure" problem the 4L80Es had.

Also,
On late model 4L80E's (97-up) you must use the fitting with the tube on the rear fitting. That limits your options. I can modify the Russell/ATI fittings to work or you can use the Sonnax piece to convert to inverted flare. If you install a regular fitting in the rear, the trans will be toast in short order. Expensive toast...