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Need Transmission Advice

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,714
If you insist on running a c-4 with miss matched gearing then you better have a really big aftermarket tranny cooler. or go back to 29 inch tires. You hurt that Bronco C-4 beware they are getting harder and harder to find one to replace it. Ford C4 were retired in 1981 that's over 40 years ago. 45 years ago in the 1977 bronco. Cant just run down and pick one up these days.
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,735
Loc.
Ridgefield WA
If I remember right, someone was making a planetary gear setup with lower first & second gear for the C4. It would be interesting to find out how that would work out.
 

Broncobowsher

Contributor
Total hack
Joined
Jun 4, 2002
Messages
33,193
If I remember right, someone was making a planetary gear setup with lower first & second gear for the C4. It would be interesting to find out how that would work out.
I recall they had some excessive wear issues. And it still won't fix the poor gearing at cruise.
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,714
as for a lower planitary it comes from the AOD check with Broader but it doesnt help with the bad gearing in high gear.. its very expensive. want to cheap out just swap the gear in the rear axle and remove the front drive shaft then you will have a 2wd Bronco with the right gearing.
 

Broncobowsher

Contributor
Total hack
Joined
Jun 4, 2002
Messages
33,193
Don't think the C4 low planetary is from an AOD. 1st gear ratio is nearly identical. Add in the planetary design is completely different (Ravagnau vs. Simpson)
 
OP
OP
SVTY SVN

SVTY SVN

Contributor
Jr. Member
Joined
Jan 6, 2022
Messages
75
Loc.
LA/TX
I have a C4 with 33s and 4.11 gears and couldnt be happier... Since this is new to you, just checking off some boxes.... What trans cooling do you have going on? I know its overkill but I have both the rad cooling and external cooler going on. Since automatics seem not to be your preferred choice, are you sure that it is at the proper level (check isnt the same as checking the oil). Lastly, what fluid is in it? Beyond the concern of old burnt fluid, an original unrebuild C4 should be using "Type F". If you have something else in there it will slip. If it has been rebuild, most people will tell you to use modern Mercron or Dextron.
Eoth,
Appreciate your follow up. I too have been reviewing things for an easy fix before I turn it over for a rebuild. Regardless, thanks to everyone’s input, I’m realizing that the most direct path with the highest ROI is to hang onto the C4 and regear (and sneak some lockers in). Glad to hear that you are enjoying the 4.11s and 33s.

Recently replaced the radiator with a toms 3-core aluminum (w shroud) and have trans cooler lines attached to that. Btw, how/what order are your coolers hooked up?

After several successful drives it vented fluid for first time after a drive and reversing up inclined driveway. Then after a professional service (not full flush, unfortunately) to remove some of PO’s pepto bismol fluid it was shifting into and out of gear better but eventually vented again reversing up driveway. I serviced again the next week myself with type F fluid and found a 1/4” piece of clutch or band material and tiny remnants in pan. I did overfill it here bc although the engine was idling at operating temp, the transmission apparently was not yet. It shifted even better and gave a few good drives around town. But after slightly longer 6-8mile drive, vented fluid again traveling forward and lost torque until it cooled down.

At this point I’m hesitant to drive it and cause more damage. Verified cooler flow at radiator already but planning to verify flow into trans (is there a measure to determine adequate flow btw?), change filter/screen again and re-service. May be too late but cheap and easy. Anything else I should look at?

Thank you.
 
Last edited:

brewchief

Sr. Member
Joined
Feb 11, 2007
Messages
833
If the fluid looked like pepto it probably had water in it, water will cause the clutch material to separate from the steel it's bonded onto, plan on a rebuild at this point.

Sent from my SM-T510 using Tapatalk
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,714
On my C-4 I do not run the cooler in the radiator as here in so cal we don't do freezing but we do run in the hot desert in the summer. on the C4 the tube closest to the bell housing is hot fluid out the tranny line at the passengers side rear is the line coming out of the cooler. if you run the tranny line into the external cooler first you cool the fluid and then the fluid is cooler than the radiator so it puts in very little heat into the radiator then coming out the fluid is as hot as the radiator. this is good for freezing weather. if you put the cooler after the radiator cooler your putting very hot tranny heat into your radiator and sending heated fluid into your external tranny cooler and your auxiliary cooler is trying to cool the heated oil and then dumping it in to the tranny. one way adds heat to the radiator the other way does not. this may be very important if your running an air conditioning condenser up front where added heat is a problem.
 

Broncobowsher

Contributor
Total hack
Joined
Jun 4, 2002
Messages
33,193
The in radiator cooler is still a very good item to have installed. If you have a high load condition with little or no vehicle speed the water can sink a LOT of heat. The air cooler can only dump heat as a factor of air flow. Other forums I am in there is a known issue with the in radiator cooler manufactured wrong and it will leak in time. The fix was to just bypass it. Everyone was told to do it, everything is fine, it is just an extra cooler. Then suddenly people started frying transmissions. Cool weather, fan clutch not needing to pull a lot of air. Not enough vehicle speed for ram air through the cooler. Steepish grade that lasted a fair distance. Suddenly you hit the right conditions, transmission is cooked. Now the warning message is out, undo the bypass. Get a new radiator that doesn't have the leak issue and get the cooler hooked back up. All it takes is that one drive on that one road doing normal driving and it is fried.
 

jamesroney

Sr. Member
Joined
Sep 11, 2007
Messages
785
Loc.
Fremont, CA
Good evening. Thanks in advance for any advice you can offer.

Sadly, our recently purchased EB now has a transmission that is slipping. Not something I wanted to deal with right off the bat but here we are.

Stock 302, C4, 3.50 gearing, 33” tires w 15” alloys, 80/20 highway/off-road use, sea level, flat earther. Like the current gearing span of 3.50s and the look of our 2.5” suspension lift w no body lift. But not completely opposed to 1” body lift if need be.

We actually prefer driving manuals and love their rugged simplicity but bc we’re not positive we’ll keep this EB, hesitant to go through hassle of conversion that might result in lesser appraisal.

Considering options to include rebuilding C4 myself though no experience, shop rebuild, RAT/RAN conversion, new process trans bc of granny gear and/or other options.

Open ended question I realize, but what are your thoughts? Thank you.
OK, here I go...
Everybody knows that I hate automatic transmissions. All of them.
BUT, if I were you, I would rebuild your C4.

Stop wasting money trying to patch it. The instant a C4 starts to slip is the day that you should stop driving it. A master rebuild kit costs about $90.
The only thing wrong with your transmission is that it can't build pressure, because a lip seal behind a piston has failed. Stop trying to find ways to spend more money. There are many, many, early broncos with C4's and 3.50's. You KNOW what's wrong with yours. So you don't need a torque converter, and you don't need a valve body, and you don't need a governor, or a modulator. Don't need bands either. It's the worlds easiest rebuild.

If you take it to a shop, they are going to charge you for a complete rebuild, and replace everything. Including the stuff that doesn't need replacing. That's how they stay in business. If I were building your transmission, and I had to give you a warranty...I would replace everything, and you would pay for it. because I can't afford to do it twice.

But If I owned it, I would yank the C4, pull the valve body and front pump, re-seal the pistons, and run it. I would probably even re-use the ATF at this point.

C4 is a robust transmission, and as simple as an automatic can get. Spend $100 and install the rebuild kit. Then drive it and decide if you like it. Then upgrade if necessary.

Done.
 

Eoth

Contributor
Bronco Guru
Joined
Mar 10, 2004
Messages
1,642
Btw, how/what order are your coolers hooked up?
Radiator then into external...Typical transmission temp range is from 170-220. My logic is that my thermostat is set at 190 so I send it there first and it warms up or cools down depending on what is going on.... So in a "perfect world" it leaves my radiator at 190 and goes to the external cooler where it knocks off another ~20 degrees. Thats puts me towards the bottom of the range. Some people get concerned with transmission fluid getting too cold, but that isn't a factor until you are talking about winter weather (below freezing). Mine is a "fair weather driver" only.
 

Broncobowsher

Contributor
Total hack
Joined
Jun 4, 2002
Messages
33,193
Radiator then into external...Typical transmission temp range is from 170-220. My logic is that my thermostat is set at 190 so I send it there first and it warms up or cools down depending on what is going on.... So in a "perfect world" it leaves my radiator at 190 and goes to the external cooler where it knocks off another ~20 degrees. Thats puts me towards the bottom of the range. Some people get concerned with transmission fluid getting too cold, but that isn't a factor until you are talking about winter weather (below freezing). Mine is a "fair weather driver" only.
Slight flaw...
The thermostat is controlling the hot side of the radiator. Transmission cooler is in the cold side of the radiator.

The whole cooling system isn't running a single fixed temperture. Hot water leaves the engine, cools in the radiator, goes back in the engine again to be heated. How much split is there between hot and cold sides? Depends. Lightly loaded, cold day, nearly no flow through the radiator, water coming out will be nearly as cold as it is outside. Working hard, thermostat wide open, blocked airflow so the radiator can't get rid of the heat, engine temps climbing out of control, the water on the cold side of the radiator can be nearly as hot as the engine. And that is a bad thing as there is no cooling going on, just heating.

The aftermarket Champion radiators, with the reversed fittings, design flaw in they keep the cooler in the original location which is now on the hot side of the radiator.
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,714
My set-up running only an external cooler never hits 160 I have a gauge monitoring the temperature. it has been running over 30 years and almost 100,000 miles since I rebuilt it when I was a young kid. the Valvoline type F fluid is as clean and red as new.
 

Eoth

Contributor
Bronco Guru
Joined
Mar 10, 2004
Messages
1,642
Slight flaw...
The thermostat is controlling the hot side of the radiator. Transmission cooler is in the cold side of the radiator.

The whole cooling system isn't running a single fixed temperture. Hot water leaves the engine, cools in the radiator, goes back in the engine again to be heated. How much split is there between hot and cold sides? Depends. Lightly loaded, cold day, nearly no flow through the radiator, water coming out will be nearly as cold as it is outside. Working hard, thermostat wide open, blocked airflow so the radiator can't get rid of the heat, engine temps climbing out of control, the water on the cold side of the radiator can be nearly as hot as the engine. And that is a bad thing as there is no cooling going on, just heating.

The aftermarket Champion radiators, with the reversed fittings, design flaw in they keep the cooler in the original location which is now on the hot side of the radiator.
No argument, I certainly oversimplified things. As a person with an aftermarket reverse flow radiator my engine has never exceeded 206 degrees with a 190 degree thermostat. I also agree that the trans cooler ideally should be on the drivers side. Without boring everyone with details, my thermal camera says my external trans cooler is consistently a bit north of 100. Everything is happy.... :)
 

Broncobowsher

Contributor
Total hack
Joined
Jun 4, 2002
Messages
33,193
My set-up running only an external cooler never hits 160 I have a gauge monitoring the temperature. it has been running over 30 years and almost 100,000 miles since I rebuilt it when I was a young kid. the Valvoline type F fluid is as clean and red as new.
Profile shows 4.11s with 33s. Goes to show what proper gearing will do for a happy transmission.
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,714
yep and the fact that the C4 doesnt use clutches in the converter producing additional heat in the tranny like the new model transmissions do
 

Broncobowsher

Contributor
Total hack
Joined
Jun 4, 2002
Messages
33,193
The lock up convertor actually make the modern transmission run cool. I know of a few modern transmissions that have fluid heaters. So on a long cruise down a cold highway the transmission will stay warmed up and not run too cold. I never thought I would see automatic transmissions that ran too cold and needed heat from the engine to keep them warmed up. The slipping of an unlocked convertor is what makes lots of heat.
 
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