Hey everyone, I really appreciate your help with this. I just rebuilt my automatic 2wd C6 for a 1970 F250. I bought a stacked plate transmission cooler, and my plan is to run my transmission lines through the radiator first and then through the cooler and then back to the trans. I will also be running a filter, and potentially putting in a temperature gauge. I will also be flushing the cooler in the radiator prior to installation. My question is, what are your recommendations regarding The actual transmission line. I could buy new, pre-bent ones, versus just getting the 5/16 tubing and bending/flaring it myself, versus putting in braided hose, which seems like it would be the easiest option. Also, if I do end up doing the braided hose, any recommendations on the best way to do the fittings? Thanks again for everyone’s help!

 

I went through this recently, take a look in my build thread for details.
I skipped radiator loop and used just a LARGE cooler (6L diesel). 5/16 custom hard lines.

I suggest bending your own 5/16 lines and re-using the fittings you have.

If braided lines, you will likey have to use AN fitting. The hose is REALLY EXPENSIVE. There isn't really an 'AN5' so you would have to go to AN6 (3/8). trans fitting are 1/8 FPT.

The exhaust will be close so hard line have a benefit here.

 

The radiator loop is a key component of fluid temperature control. Unless you are running a inline transmission thermostat then you need the radiator loop. The radiator loop provides much more stable temperatures and eliminates the chance of under temperature transmission fluid.

 

I agree with you 'gashog, and intentionally did not suggest OP use rad or not.

But like many things in life, it is also dependent on the specific application, environment and other variables. My trans builder was VERY adamant about NOT using the radiator loop for my truck (big tires, big power) in extremely hot climate. Why? because heat is #1 killer of transmissions.

For a stock application, I would leave rad loop in.

 

I am in California where it doesn't freeze. I am not sure where in Utah the OP is located.

Version 1: I ran the stock lines from the C6 to an Aluminum radiator. Out of the radiator to a rubber hose adapter and then to a filter. Then rubber hose to stock line to return to C6. Trans Temp ran high in the 105F summer, at a stop light it heated up because the lines and transmission are soooo close to the exhaust. Driving it ran 200F and stopped it would climb to 230F max (temp sensor is at the EXIT, so much hotter than the pan). Transmission shop said it was fine and when they resealed the transmission from a leak, they said the internals were excellent. Trans Shop owner strongly suggested a nice cooler and to REMOVE the lines from the radiator. He said after 50 years in the business he said that MOST complete trans failures are from radiators leaking into the tranny fluid. (Of course this is his opinion)

Version 2: I didn't like the 230F (at the exit). Kept the same setup, changed to AN6 lines and fittings everywhere. Could NOT find a good place to put a transmission cooler in the front of the Radiator and AC Condenser (big one from Vintage Air). So I added a frame mount Scoop Cooler from Derale. Expensive stack/plate cooler that mounts to the frame with a mini scoop that draws fresh air. Dropped temps 10F.

Version 3: Rerouted AN6 lines. Skipped the Radiator. So now it is C6 to Filter to Cooler and then back. Same Temps but takes MUCH longer to get near 200F because the Radiator isn't warming the tranny fluid.

Version 4: Pulled the Scoop cooler and installed a LARGE fan stacked plate cooler under the cab between the frame and the body. WOW what a difference. Even at 105F, the transmission stayed around 190F (at the transmission exit). Also added a second sensor at the return to the C6. This was 170F when cruising on the highway, and 185F with the fans off and stopped. On a hot day, it still climbed at a stop light from the exhaust heat near the sensor, but not nearly as bad. I ended up fabricating an exhaust tunnel type insulator (DEI material) from the passenger downpipe to keep it cooler. Helped a ton but DEI stuff is not cheap.

Where the AN6 lines cross over the exhaust, I also added DEI heatproof sleeves for protection.

If I did it all over again (which I am SURE I WILL). I would run two coolers. One passive but in front of the radiator/condenser. Thin but 13x9. Then a second thermostat controlled fan unit under the cab. I still wouldn't go back to the radiator thou. My truck runs 185f and is a fuel injected 390 so the computer controls the radiator fans. It reaches temp quickly because of the startup fuel maps pour fuel in. So with it in the radiator, the trans temp would come up with the engine temps. I like it to stay cooler longer. Most 20 mile trips, the trans temp never reaches 200f at the exit.

Just my experience. I am meticulous and fabricated all the brackets, lines, etc... I will say that AN lines help me sleep at night. My fuel injection, coolers, trans lines, etc. all AN lines and when you connect them and snug the fittings, they just don't leak.

Good luck

 

Thanks everyone for your help. It was my first time rebuilding an automatic, and will be my first time reworking cooler lines. I snapped one of the fittings off one of the lines as I was pulling the tranny. So in answer to your questions, I live in Utah so it definitely gets below freezing in the winter, can get fairly warm in the summer, usually just above 100. When I bought the truck, the previous owner had bypassed the radiator and was just running to a small fin cooler that he had attached to the front grill with some wire. Probably no wonder the trans went out. So I’m not sure what the situation is with the radiator cooler, was just planning on flushing it and hooking it up again. But now I am wondering if there’s maybe an issue with it? Should I take it to a rad shop and have them test it? It’s had no coolant issues. I’ve heard so many opinions saying use as much metal line as possible, he had the original lines plumbed to the cooler with small pieces of rubber hose right at the end. Then hard line with fittings into the transmission.

Do you recommend both hardline to the radiator and then hard line from the radiator to the auxiliary cooler, if possible? Obviously hard line back to the trans as well. I’ve got a little tube bender and a double flare kit.

Just also want to make sure I also get my filter and temperature sensor in the right places in the circuit.

 

Pcmdub it looks like you are recommending braided line with AN6 fittings. But also using heat shield material where it gets close the exhaust. FYI my application will be a 460 with some mild upgrades, Probably 450 hp max when I’m done. I built the transmission in anticipation of that. So not doing any heavy racing or towing, just a fun and fast daily driver. tires are just barely bigger than stock.

 

I'm close to re-doing my radiator and transmission lines and will be doing the following:

• new pre-bent lines from the transmission.
• short length of flexible hose from hard line to radiator.
• flexible hose from radiator to aux cooler, mounted in front of the radiator.
• flexible hose from aux cooler to hard line.

i'm retaining the radiator cooling because water cooling is a lot more efficient than air cooling. yes it only gets down to the temp of the water but that's fine.
the aux air cooler is to bring down the temp more, since from what i've read, you can't really get too cold when it comes to transmission fluid. I'm in a climate where it rarely dips below freezing anyways.
I'm using flexible hose to deal with any vibration or movement.

 

I like the flexibility of flexible lines. They are pricey to do, but have great flow characteristics over hand bent lines. Some of the pre-bent lines are really nice if the bends are super smooth. Also, I didn't like the lines going perpendicular to the radiator right down the middle. I tucked all of my lines down the frame to look cleaner and make it easier to work on the engine.

With a big 460 engine, I would suggest making the engine bay as clean as possible. Hard lines are tried and true. Use some welding rods and lay out your pattern first. I would stay away from the headers/exhaust, and left or right of the starter (so you can replace it when needed). Get the biggest cooler you can fit in your application and you won't have to worry about it.

 

So the more I think about it, the more I am moving towards doing AN lines/fittings. I think it will give me a clean look, and I can try to route away from the exhaust, and I’m hoping the bigger diameter will help out with the temperatures. I want to make sure I get good line, so I’m not going to go the eBay route.

Do you have specific AN line that you recommend? If I get a good set of cutters, I can trim it to fit right?

where in the line do you put the filter? I’ve seen some suggest doing it after the cooler, and some that suggest doing it after the output from the transmission.

Also, with the temperature sensor/gauge, where do the sensors get installed? I’ve tried to look it up and I’m not finding much information for an older transmission that doesn’t have an actual test port built into it. Do you just do a T-fitting from the cooler output of the transmission? Do you have a source for that as well?

Sorry for all the questions. I really do appreciate all your help.

 

Also, this is the trans cooler that they gave me at my transmission shop that I ordered all my parts from. It is a Hayden 1679, which they show as extra heavy duty for heavy towing, motorhomes, large travel trailers, etc. 11 x 11-1/8 inches. The thing that concerns me is that the fittings are three eights inch push on, wouldn’t I want some kind of threaded fittings? Thanks

 

AN6 is plenty for the C6 transmission.

Trade the Hayden 679 for the Hayden 689. Same size but the 689 comes with AN6 fittings. https://www.summitracing.com/parts/hda-689

When cutting, I use a band saw and then clean up the ends with a tool. Much easier that the sharp cutters, but you can also just grab tape and a hack saw.

I was always told to filter your oil when it is hottest. So I put the filter first (out of the trans). Either way will be fine thou.

Temp gauge is easy. Many suggest just using an adapter in you oil drain plug. I wanted more info, so I ran two temps at the trans output and input. Overkill thou. I like this fitting because it is simple. https://www.anhosefittings.com/an-ma...sor-ports.html

You will probably need STRAIGHT fittings in/out of the transmission, and NPT fittings to go in/out of the Radiator. I say probably because some C6's have 1/4 and others have 1/8" fittings. However, most people thing they are tapered (NPT) but I have been told and SHOWN by a transmission shop that they are indeed straight. The shop said several people have cracked the casing from overtightening NPT fittings (who knows). I used NPSM and no threadlocker or sealant, no leaks at all. Here is the Transmission side. https://www.redhorseperformance.com/...ng-black-2pcs/

 

Nice. Thanks. Is that website the same source that you used for all your hose and fittings? I just wanna make sure I don’t spend a load of money on crap.

 

Ughh. Fittings...

I think the saying "you get what you pay for" really fits this situation. I tried to cut a few corners with Amazon/Asian made parts and really paid triple to fix the problems. Had some thread break off in parts etc...
I like the name brand fittings when they matter. Redhorse (local hot rod shop carried these), Earls, Russell, etc. The temp sensor port was more difficult, so I searched for hours and found anhosefittings for those parts (great quality but remember that anodized aluminum doesn't ground so you may have to ground your temp sensors). I try to order all black fittings (not flashy) but I see the benefit of silver/blue fittings because you can quickly find any pesky leaks fast.
Now for the actual hoses and AN fittings, you can find a bulk kit of 30 feet of hose and connectors (usually 4 90s, 2 45s, and 2 180s) for fairly good prices on Amazon. Yes they are not name brand, but I have used a 30 kits from amazon for these parts without a hitch. (Well, honestly, I had one 90 elbow leak from the swivel side).

All in all, buy good parts and save the headaches.

 

OK, so I’m getting ready to buy everything that I need. I just want to make sure that I get this done correctly. So from what I understand, I will thread on those straight fitting to AN6 adapters into the transmission case, then immediately to that adapter (on the output side) do I thread on the sensor adapter? Or do I space it out with a little hose first? Then i’ll probably run a little hose to the frame, and then at that point put in an in-line magnetic filter. It looks like all of the filters are just hose barb/push fittings, so I’m assuming those are OK to just keep like that with clamps. Have you had any leaking from the filter connections? Everything else seems pretty straightforward. Thanks again for all your help.