AOD Overheating - fixed

All,

We had overheating issues with an AOD transmission on my 74 Bronco. We looked at all kinds of potential causes. We checked to make sure cooling lines did not run near any hot surfaces. Checked the TV cable and the pressure. We’re using the correct throttle cable “geometry” for our carburetor. In the end the solution was a second radiator for transmission only that does not share with the engine’s main radiator. Based on my experience I would expect anyone with an AOD to have a similar issue. I think you should count on running a secondary transmission radiator.

For anyone considering the AOD here is my .02 input, our configuration for reference and the solution we went with.

Firstly I recommend the AOD. We bought a new/reconditioned AOD and used an adapter from Advanced Adapters for the AOD and Dana. You will need to buy or fabricate a brace to hold it in place since its longer than the stock transmission. In my case we replaced the manual 3 speed with this. It shifts smoothly and its pretty quiet and for what we use the bronco for it’s a great choice. This is the AOD not the AODe so it has no other external electronics or computer attachments. It did run hot however and I would be surprised if everyone else doesn’t have the same experience. When I installed it we added dedicated pressure and temperature gauges for the transmission. I recommend that too. These classic Instruments gauges are good and they will light up red when you get to extremes on transmission pressure or temperature.

Here is our engine setup:
Mostly stock, flat tappet original 302 with no EFI. It’s a Holly 4brl, carb with some short hooker headers and an MSD ignition. Otherwise pretty stock. We added a new aluminum radiator and the Transmission shared the radiator with the engine at first. The fan is stock with the stock belts.

Symptoms/Problems:
When driving on longer (30min +) trips the transmission heats up and eventually runs at over 240 degrees and we need to sit and let it recover before moving again. We tried limiting the use of over drive, checking the transmission levels, looking for issues with the lines running near heat sources etc. Making sure the pressure and kickdown looked right etc.

Solution:
Finally I decided to separate the Transmission cooling from the main radiator. I used this Fluidyne unit from summit. It was expensive (I think) but its worked out great.

https://www.summitracing.com/parts/FLD-DB-30110-8AN


Pictures
We mounted it in front of the main radiator and we had to take the grill off to be able to drill and fit it properly but its been worth it so far and for other reasons we needed to be able to get the grill on and off so we took the opportunity to put new front fender bolts and clips in. Here are some photos on how we mounted it. We did have to grind a little metal to get the fittings to clear some spots.

https://74bronco.shutterfly.com/pictures/162


Results:
The results have been great/dramatic. The temp holds a under 160 degrees in all conditions now. Really happy with it so far.
https://74bronco.shutterfly.com/pictures/162#158
https://74bronco.shutterfly.com/pic...-SFLY-43737-3178588440&clickId=3178588440#161

Doesn’t look too bad (subjective) from the front grill.

Where is the in radiator cooler located? I remember there is a company making aluminum radiators but they were putting the cooler on the hot side of the radiator, not the cold side. You may have just been fighting a bad build design.

In general I like a 2-cooler setup for the transmission, with one of them being an in radiator cooler. As small as that in radiator cooler is, you can't beat liquid to liquid heat transfer. I've seen plenty of oil to air only coolers not cut it in high load low speed conditions. Just can't dump the heat. That is why I like the in radiator using the water as a huge heat sink. But that is the cold side of the radiator.

I don't know where inside the main engine radiator the Transmission portion might be but it does enter and exit from the back (engine facing) side of the radiator on the passenger side. Would surely be a poor design if its coils are only on the back side.

This new setup is working great but I haven't tested it in all situations.. for around town and highway use its really good. here is a picture of the temp gauge after an hour around town..

https://74bronco.shutterfly.com/pictures/158

I haven't watched it yet under slow speeds and heavy load which is where I would expect your two-cooler setup might have some advantage but for what we've been doing I think having the engine cooler shared with the Transmission is actually transferring heat to the Transmission instead of helping to cool it.

The in transmission cooler isn't tied to the cores, it is tied to the tank.
Is the cooler in the same tank as the upper hose (hot side) or the lower hose (cold side).

sorry i’m not following the conversation
in the prior setup the transmission lines were plumbed into the back (engine side) of this champion radiator with the barbs you can see in this photo

https://74bronco.shutterfly.com/pictures/164

since it’s on the passenger side of the radiator in the back I assume it’s what you are calling the cold side.

whatever side it is, for this champion radiator, it’s not doing it’s job.

https://www.championradiators.com/Ford-Bronco-radiator-3-row-1966-1967

I thinks it’s this radiator can’t remember if it’s 2 or 3 core. the fan is belt driven not electric

Yes that is the cold side of the radiator.

This is the one built wrong and has the cooler on the hot side.
https://www.championradiators.com/Ford-Bronco-5.0-conversion-radiator-1966-1967

Out of curiosity, where do you have the transmission temp sender? In the pan or in a cooler line?

bottom of the pan.
https://74bronco.shutterfly.com/pictures/165

by the way, you posted my link back to me saying it was the radiator that was built wrong. I think the radiator I have is a good one

never mind I see you did post a champion radiator but with the input/output lines reversed
anyway the champion i have does a poor job even if it’s transmission lines are plumbed properly.

I think Tim is showing you that company’s radiator that isn’t a good design. Thanks for the input and maybe if it heats up under a load I vote for what tim said about running them both.

Right
i’d be interested to know if anyone has had success running an AOD without a secondary radiator? if so I would like to know what brand and sku radiator that was and if the fan was stock/non electric. i’ll climb to Alice’s restaurant up skyline next weekend and see how it does.

I think the engines radiator is making the transmission temp hotter not cooler.

FWIW, I have a 74 also with an AOD. Did the same as you on the install so it's set up correctly, but I’m using a TV rod vs. the cable and a 2bbl 2150 with the AOD linkage. The 74 is basically stock (2.5 suspension and 1.0 body lifts) with the original 302, Mallory ignition, and had a C4 stock set up before the AOD swap. The AOD lines are run into the stock radiator where the C4 lines were. All the rest, fan, etc., is stock as well. I did have to route the fuel line out farther away from the engine as I was getting vapor lock in the summer but doubt that had anything to do with the AOD install. I can’t say for certain that the AOD is not running hotter than it should as I don’t have a temp gauge on it; something I probably need to add. I’ve not experienced any issues shifting, etc., so far and I’ve been running the AOD for about 2+ years now. And the engine is not running any hotter than it did with the C4.

Great proof point Grinch. Almost identical.
I have a 1" body lift, no suspension lift - only real difference seems to be the champion radiator (I went from manual 3 speed to the AOD)

Im curious how far do you drive? I've run fine for 2+ years with the AOD nothing noticeable until I started to extend it on longer drives that I noticed it.

First time I noticed it was an hr drive down to Morgan Hill (was on the drive to your place Doug) and the temp was too high. I caught it and even without a temp gauge you would notice smoke from the transmission fluid overheating at about 40minutes out on highway speeds (for me that means like 60/65 Mph).. Short drives were fine. In all situations there was never any problem shifting.. I noticed smoke and the high temp on the gauge and once I was aware of it I can see the pattern. We never encounter it on typical use driving scenarios.. around town, back and forth from home to Stanford (15 miles +/-) all fine.. go 40 minutes or an hour and the temp starts to climb.

Are you driving more than hr or more at a time?

Maybe the champion Radiator is poor at cooling the transmission or.. this particular radiator really requires a non stock fan or electric fan to be effective. IDK)

RE: the AOD rod, I might look into that. Not for the heat but because I think its better than the cable. For the cable I had to add a return spring because the cable was not returning all the way.

So, yes I do drive it more than an hour at a time often, but not at 65 mph for the whole time. The road into town is 55 so I’m usually doing 60+ and then in town it’s 45 or 35 mostly and I downshift to 3rd. Depending on where I go, most roads after the city limits are 70 mph. And it’s hills mostly around here, and once it begins to climb it downshifts to 3rd or I do it manually especially if it’s going to be a lot of up and down.

It’s a 4.11 stock rear and I’m running 265/75R16 tires; so top end is about 65; 70 if it's downhill .....maybe. Avg mpg is 10+.

Recently, I did pull over after a long uphill climb and get out and ‘sniff’ for anything burning, but so far nothing…which is good news.

As to the TV rod, here’s the place I got mine http://www.kickdownrods.com Go to their ebay store and they show two for the AOD; one for the 2bbl and one for the 4bbl. I did have to remove the spring to complete the install adjustment for the correct location at the correct line pressure. But after it's set there's no movement. Which is what I liked best over the cable.

Next I’m going to get the temp gauge anyway, cuz now this has got me thinking.

oh good.
your investment in the temp and pressure gauge will be good for me
if you are going an hour at highway speed using only the main radiator then something is better about your setup than mine was.

I will go back and check my gear ratio. I checked and posted it here in the forum a long time ago and now I can use the forum to remember my own setup.
ill re:check my gears and tire combo and post them.

i’ve been slowly (over years) preparing to drive this one from the bay area peninsula out to lake tahoe. So the AOD was part of that even though I put it in there a few years ago or so.

Right now - The new dedicated radiator is really working well but I haven’t pushed it hard and in theory chaining it to the main radiator should be “better” but I think no way with this champion radiator. Looks like this below:

For the gauges - I like the classic instruments gauges.

So if your setup works well then my theory for now will be
1) something is not right with the champion radiator- maybe fluid not circulating or not enough volume
2) maybe the champion radiator really needs an electric fan
3) something not right with the AOD/TV during overdrive but I have no shifting problems and a nice ride.. could be the transmission at highway speed is sitting right in the RPM range (2k or 3k for slipping and causing heat.. idk) but it runs smooth and i’m not noticing any drama at speed, I love it.
4) maybe... the entire system now has more fluid in it.. the new secondary radiator took an extra quart and when I disconnected the main radiator nowhere near a quart came out and that was suspicious to me. like the volume of that transmission cooling portion of the main radiator was crazy small.


but right now my transmission is running very cool. 140 to 150

one thing I should add is that we never shift it out of overdrive we always just put it in drive and go.. let the AOD do everything, even on hills. So if we drive out to Alice’s we just put in D and go.

Drove up to Alice’s and back today on 280 at high speed.
that is about a 20mile drive half highway and half climbing. takes about 40minutes
the transmission stayed under 180 for the trip. IDK that still seems hot to me for such a short drive but it’s way better than it was. I would hit 220
easy on the drive and 260+ on the drive to morgan hill which is twice as far. Hottest temp today was at highway speed on the return drive.

not sure what i’ll do next. probably watch it for a while then maybe chain it back to the radiator, maybe.. then maybe look at a new or different primary radiator. if I don’t like what i’m seeing there

are the champion radiators considered good ? I bought this one mostly because a
lot of the after market radiators had logo’s painted on them that were visible through the front grill which was annoying.

but now I have the transmission radiator visible there as well so IDK
i’ll try the drive down to morgan hill at some point and see that we stay under 180. but i’m really trying to get the system ready for the 4hr drive and climb to tahoe. that’s going to be interesting - long climb up through the sierra mountains and it’s at altitude with the 4brl carb not fuel injected. at 5-10mpg for 220 miles one way. altitude will hit about 7K I think, i believe the town of Truckee is at around 5500 altitude. we should all take bets on my over/under chances of making it.

I need to fix the oil sending unit (again) and fix the timing chain gasket(s) before trying it..

here’s a video - wife open highway on 280
today for the 4th of July

https://youtu.be/CpkHJOtbEGM

Mike,

Sorry, just got back from a road trip to Idaho... Kind of stepped away from all things on line...
You are welcome down here in MH any time.

Looks like you have been busy! Thanks for the Video you sent too.

CA650 said:

For the gauges - I like the classic instruments gauges.

Click to expand...

i have an AOD ready to be installed. i got a custom valvebody that allows a solenoid to lock out overdrive in case it shifts back and forth at a certain speed. it the only electrical component in the trans. i still need to drill the case for the wires to the solenoid.

where did you get your gauges and what line did you tie them into?

that transmission radiator looks good. Did you also run it through the main radiator also or just through the trans cooler by itself?

thanks,
mad

CA650 said:

anyway the champion i have does a poor job even if it’s transmission lines are plumbed properly.

Click to expand...

That small fan isn't helping...

904Bronco said:

Mike,

Sorry, just got back from a road trip to Idaho... Kind of stepped away from all things on line...
You are welcome down here in MH any time.

Looks like you have been busy! Thanks for the Video you sent too.

Click to expand...

thanks doug, we have been busy. i’m collecting the parts for the timing chain gasket job.. the front grill come on and off with ease now so that hurdle is solved. i’ve got the gaskets, timing chain set from edlebrock, the 28oz harmonic balancer and im ordering a new bolt set for the cover and im trying to locate the right shade of ford blue for my engine so I can paint the cover when I get in there. I did manage to hose something up on the turn signals when I put the front back on.. the turn on but don’t blink anymore.. no idea why since they worked before i fckd with it and now the don’t and wired and grounded them the same way they came off.. so idk. but I bought a new turn signal blinker relay so maybe that’s it.


stil don’t have a solution for the oil sending unit extension. the wild horses extension isn’t going to work so I just plugged the hole in the block for now and i’m running without the gauge for a while.

otherwise all goood

Madgyver said:

i have an AOD ready to be installed. i got a custom valvebody that allows a solenoid to lock out overdrive in case it shifts back and forth at a certain speed. it the only electrical component in the trans. i still need to drill the case for the wires to the solenoid.

where did you get your gauges and what line did you tie them into?

that transmission radiator looks good. Did you also run it through the main radiator also or just through the trans cooler by itself?

thanks,
mad

Click to expand...

Mad, good luck with the AOD it’s a great mod. I think that and the hood shocks (instead of the metal stick to hold your hood up) are my two favorite bronco mods of all time.

Re the gauges: im a fan of Classic Instruments gauges. you can get them anywhere. https://www.tomsbroncoparts.com/category/66-77-ford-bronco-gauges-instruments

I think I bought mine direct from classic instruments. The transmission temp and the transmission pressure both will flow red at the extreme end of their scale and they look good and retro. They connected right up to the AOD. I can take some pictures for you but there is a pressure port and there is a sensor in the bottom of the pan for temp which you can see in an earlier post in this thread. Not hard to hook up. The pain in the ass with the AOD setup was the adjustment of the TV cable and kickdown for the carburator if I remeber right - but if you install your pressure gauge that will help because you need it to set the shift points. but once installed I haven’t touched it and it’s great.

for the radiator - that is the whole debate in this thread. right now I have only the external fluidyne radiator connected and it is not chained to the main radiator in any way.. my opinion right now is that tying the main radiator to the auxiliary transmission radiator is NOT helpful in my case. but i’m not your bronco expert i’m a moderately technical trial and error experimenter. you should trust others in this forum before you trust me.

I noticed someone earlier in this thread mentioned that my stock fan was “small”. So i’m going to start googling for larger fans that sounds like something worthwhile regardless. If anyone has an opinion on which one to get id like to hear it. I have the stock fan shroud right now but i’m ok swapping that too if something is better.