C6 Cooler Lines Fitting Size

[CV355]

I'm measuring 0.498"-0.500" OD on the existing flare-style fittings for hard coolant lines, but it does not appear to be a tapered thread.  Are C6 coolant lines 1/4 NPSM?  I don't have a thread gauge for this unfortunately. 

[DubyaTF]

    Mine was 1/8" NPT. I used two of p/n 220646N from Summit to build 6AN hoses for my cooler.

[CV355]

    Mine was 1/8" NPT. I used two of p/n 220646N from Summit to build 6AN hoses for my cooler.

Hmm...  that's around a .400 OD.  Sounds like they changed over the years.  I might have to hit up one of my machinist buddies to see if they have a set of pipe thread gauges. 

Update:  I went out and chopped off the old fitting from the hard lines, lifted the car up and tested it.  It does not fit the new transmission whatsoever.  I measured the ID at 0.340" which indicates 1/8NPT, so you are correct DubyaTF.  I will have to go with a swivel street 90 to avoid hitting the floor panels on mine.  Still, glad I asked as I was finding conflicting info online.  1 or 2 threads per inch difference can turn a good day bad in a hurry.  I need to get some ID thread gauges...

Well, if anyone navigates here with the same question (regarding C6 coolant port fitting sizes, specifically):
0.500 OD fitting / 0.440 ID Port = 1/4 NPSM
0.400 OD fitting / 0.340 ID Port = 1/8 NPT
Outlet = Towards torque converter (forward)
Inlet = Towards tailshaft (rear)

[Rory428]

Its been over 20 years since I owned a C6, but I do know there were different size cooler line fittings on the side of the case. no idea whet year(s) the change occured, but on the long shaft 75-76 FE PU C6s I had, the fittings were smaller, 5/16" tubing with 1/2" size nuts, while the earlier versions I used, had 3/8" tubing with 9/16" nuts. No idea what the actual thread sizes in the cases were, as I used the original fittings, and made new steel tubing lines. I do know the later, small fitting were pipe thread, but I seem to recall the earlier C6s had straight threads with gaskets. I do recall the rear fitting on my 428CJ 69 Mach 1 used a 90 degree elbow with a jam nut and a O ring, so the rear cooler tube went straight back, rather than take a 90 degree curve. Maybe Ford felt there was not enough room in the transmission tunnel for curved tube?

[CV355]

Its been over 20 years since I owned a C6, but I do know there were different size cooler line fittings on the side of the case. no idea whet year(s) the change occured, but on the long shaft 75-76 FE PU C6s I had, the fittings were smaller, 5/16" tubing with 1/2" size nuts, while the earlier versions I used, had 3/8" tubing with 9/16" nuts. No idea what the actual thread sizes in the cases were, as I used the original fittings, and made new steel tubing lines. I do know the later, small fitting were pipe thread, but I seem to recall the earlier C6s had straight threads with gaskets. I do recall the rear fitting on my 428CJ 69 Mach 1 used a 90 degree elbow with a jam nut and a O ring, so the rear cooler tube went straight back, rather than take a 90 degree curve. Maybe Ford felt there was not enough room in the transmission tunnel for curved tube?

I suspect I'll have to do the same- there isn't much room in there for fittings without interfering with the floor pans or tunnel.  I saved the old cooler lines (which I assumed would still fit just to mock up for AN lines), and of course, they did not fit.  In fact, the new C6's case appeared to be drastically different than the previous in the servo area.  I may have to do a loop on the return line.  It's ok though, I have 20' of PTFE braided steel line coming in today.

[cammerfe]

This might be completely erroneous, but as I remember, sometime back in the early '70s, a guy I worked with at T&C Livonia told me his T-Bird simply quit moving as he was driving down the street and wanted to know if I might be able to help.

I looked, and found a streak of trans fluid leading to where the car sat. A quick look underneath found a severed cooler line. He told me he remembered hitting something in the street that jumped up and hit the underside of the car. As I remember, I used a piece of replacement brake line from the local auto part store and a pair of unions to bridge the gap where I cut away the smashed spot. The greatest amount of cost for the repair was the trans fluid.

KS

[Falcon67]

Having made replacement AN fittings for C4s, I think you will find both.  "Most" C4s use a 1/8 NPS thread with an o-ring.  "Some" later models use a 1/4 NPS with either an o-ring or a gasket.  C6 I believe is similar and varies depending on the model and year.  I would guess mostly 1/4 NPS. I could never find a chart or even consistent examples in the wrecking yards.  Note that some people get away with forcing a NPT into the ports, but you can crack the case so it's not advised.  You can modify a 1/4 or 1/8 NPT fitting with an appropriate NPS die. I would buy bunches os -6 AN x 1/8 NPS fittings and re-die the threads and cut an o-ring groove and they's work great for converting to braided cooler lines.

[RustyCrankshaft]

Just put new fittings in my 73 C6, as far as I know all C6's used 1/8" NPT thread and most of those ran adapters to go from 1/8" NPT to 5/16" inverted flare to take the "tube" fittings.

I used 1/8" NPT (-4) to JIC and built a set of stainless braided hydraulic hoses for the truck for durability.

[djburton]

Every C6 I worked on had straight pipe threads,some with O rings,some with a flat fiber ring,some 1/8,some 1/4 to a female inverted flare.A pipe thread fitting will screw in but you could risk cracking the case if screwed in too tight. If yours is 1/8 in,Summit has fittings that connect these to 3/8 hard line which I prefer for added cooling compared to the braided stuff.

[RustyCrankshaft]

Every C6 I worked on had straight pipe threads,some with O rings,some with a flat fiber ring,some 1/8,some 1/4 to a female inverted flare.A pipe thread fitting will screw in but you could risk cracking the case if screwed in too tight. If yours is 1/8 in,Summit has fittings that connect these to 3/8 hard line which I prefer for added cooling compared to the braided stuff.

That's interesting, I've never seen a C6 case with anything other than 1/8 NPT thread in the case, not that they couldn't exist I've just never seen one. I have seen FMX's and such with other options. All of the C6's I currently have are 1/8 NPT. The factory fitting measured correctly for 1/8 NPT. I've never measure the case threads tho.

I didn't use anything from summit to plumb my cooler, the braided hose I used was hydraulic PTFE, no significant cooling difference between hardline and the braided in this case.

[Falcon67]

> I've never seen a C6 case with anything other than 1/8 NPT thread in the case
That is interesting.  I wish I had a C6 case here to look at, but haven't had one around for a long time.  All C4s and even the one out of the 78 T-bird has 1/8 NPS + o-ring fittings. I have air pressure tested my modified AN +o-ring fittings to near 100 PSI without any issues.  The NPS+O-ring seal really well, even hand tight.  On mu dragster I switched to all o-ring type fittings a couple of years ago.  Way less hassle that pipe thread. 

LOL, when you run a 4000 or 5000 or 6000 flash converter, the cooler lines don't amount to much.  In any event, I'd say the cooler at the end of the lines makes more impact.  I can run hose a lot easier than hardline. I almost never used hardline for anything in the last 20 years. 

[RustyCrankshaft]

> I've never seen a C6 case with anything other than 1/8 NPT thread in the case
That is interesting.  I wish I had a C6 case here to look at, but haven't had one around for a long time.  All C4s and even the one out of the 78 T-bird has 1/8 NPS + o-ring fittings. I have air pressure tested my modified AN +o-ring fittings to near 100 PSI without any issues.  The NPS+O-ring seal really well, even hand tight.  On mu dragster I switched to all o-ring type fittings a couple of years ago.  Way less hassle that pipe thread. 

LOL, when you run a 4000 or 5000 or 6000 flash converter, the cooler lines don't amount to much.  In any event, I'd say the cooler at the end of the lines makes more impact.  I can run hose a lot easier than hardline. I almost never used hardline for anything in the last 20 years.

I was talking about a factory C6 case. I've seen lots modified to other things. I prefer ORB fittings when I can use them.

I agree, the amount of cooling from the lines themselves is pretty small. I also agree hose (if it's good quality) is usually a good way to go, I've seen more hardline failures for various reasons than hose (many of which were caused from the last professional repair work done).