C4 Burnt Fluid Help

[SC74]

I had a C4 rebuilt by a reputable transmission man several years ago. I am not pointing any fingers and if I pull it back out it will go back to this same guy.

This Bronco may get 200 miles a year on it, so let's say the transmission has less than 1,000 miles on it total - mostly back road cruising on a pretty Saturday. Several weeks ago, I was asked to go on a 300 mile "ultimate adventure" style ride. Of course I was in!

In my prep for the ride, I noticed the trans fluid was a brown color but didn't really smell. It has good hard shifts so I didn't think much of it. During the ride, I noticed a leak under the truck at a stop and it was a dark fluid that my friend thought was thin gear oil, but when I showed him the dip stick he agreed it was tranny fluid. We topped it off and finished the ride, still shifting fine. Now the fluid STINKS like it has been toasted. It's also low again so there is a leak (or could it have been coming out of the vent?). The fluid was above the cross member and we couldn't see where it was coming from.

My question.... should I service it with all new oil and keep on trucking, or should I pull it and start from scratch again? I would try this if it weren't for the leak that would require pulling it anyway, unless you say most likely it was out of the vent.

What would cause it to smell so bad? I do run a cooler that's mounted on front of the radiator, but I do not have a temp gauge on the transmission. When we noticed the leak, we were on the Blue Ridge Parkway where there were a lot of steep grades and the tranny was having to work hard.

Thanks in advance for your help!

 

[bronconut73]

After many miles of mine staying red and not smelling burnt it just recently started to on my trip up to Super Cel.

It could be that mine and yours have never had to work so hard before.....
I am going to drop the pan and replace some of my fluid in the process. Will report back.

 

[surfer-b]

You can try and change the fluid and filter but I would guess if its dark and smelling burnt the clutches are toast, even if you do change the fluid it want fix the leaking prob. I would pull it and fix it for good, I know its kinda PIA but its like I tell myself, its much easier to work on it in my garage than it is on the side of the road.

 

[B RON CO]

Hi, as mentioned drop the pan and change the fluid and filter. If you find crap in the pan you will probably need a rebuild. Just as important is to find and fix the leak. It could be as simple as snugging down on some bolts. Good luck

 

[Rustytruck]

check the oil in the transfer case to see if the tranny fluid is mixing with gear oil. Are you forcing your tranny to work harder by running in 4 high instead of 4 low. Another area of concern would be tire diameter and axle gearing miss-match forcing the converter to heat up pulling the extra load. Cooking the fluid is never good.

 

[Viperwolf1]

My guess is not enough (or any) cooling. Leak is probably from overheated fluid coming from the vent. Drain it and replace. Make sure you have flow in the cooler circuit (could be a bigger problem). Put a better cooler on.

 

[Yeller]

It's either not enough cooling or a bad converter,not both. I always feel that reman converters are a crap shoot, seems about 1 in 10 is junk

 

[SC74]

My guess is not enough (or any) cooling. Leak is probably from overheated fluid coming from the vent. Drain it and replace. Make sure you have flow in the cooler circuit (could be a bigger problem). Put a better cooler on.

I have considered checking flow through my cooler also. It is mounted to the front of the radiator, but no fan on it. I think I am going to do what you recommend and flushing it all out and seeing what happens. I am thinking the vent was my leak too, since it happened to be when the tranny was working hardest on the scenic highway.

It's either not enough cooling or a bad converter,not both. I always feel that reman converters are a crap shoot, seems about 1 in 10 is junk

Now this seems like my luck! I did replace the TC when I put the trans in last time. Would the tranny still act normal until this point? I will say, since new, the fluid has not been bright red. It's also only been used on 10-15 mile cruises around the house since then and not given an opportunity to overheat so much as this past adventure.

 

[SC74]

I would pull it and fix it for good, I know its kinda PIA but its like I tell myself, its much easier to work on it in my garage than it is on the side of the road.

LOL this is how I convince my wife of so many "upgrades!" That and safety are my go-to's!

 

[SC74]

check the oil in the transfer case to see if the tranny fluid is mixing with gear oil. Are you forcing your tranny to work harder by running in 4 high instead of 4 low. Another area of concern would be tire diameter and axle gearing miss-match forcing the converter to heat up pulling the extra load. Cooking the fluid is never good.

I think the overheating occurred on the scenic highway running 40-50 MPH, but constantly shifting with the grades and curves through the mountains between 2nd and 3rd.

I am very familiar with that double lip seal that separates the oils. In fact, that's the reason I had this transmission rebuilt last time, and on a different bronco as well.

I have 33's with 4.10 gearing.

 

[Yeller]

Yes the tranny could still act normal. Pull the pan, if it's not full of metal (a little bit is normal) I'd look into cooling. I'm going to get flamed for this (and remember I used to make my living as a tranny guy) if your cooler is of adiquate capacity mounted in front of the radiator is just fine, no need for a fan. I got tired of having cooler issues so I started using OEM ones for 7.3 super duties and my cooler issues disappeared, the units off of a 6.0 work great too but are just sized large enough to complicate mounting. No matter what you do be sure to have the largest cooler you can fit in the space. Don't fall into the trap of "over cooling" we're not running when it 40 below outside so it ain't gunna happen.

One thing to remember.... Fin and plate coolers are very difficult to impossible to fully clean without a hot oil flusher, and then if it's really bad still not happening. There are a lot of shops out there that do not have a hot oil flusher l, compressed air and solvent are not adiquate

And with 4.10's and 33's gearing is not an issue causing excess heat.

 

[SC74]

Update... With some help from Yeller, I've found that the transmission isn't getting fluid to or from the cooler. Both lines barely dripped when unhooked from the cooler, even with higher RPM and the modulator line removed. It looks like I've got a project this weekend now pulling it out to dig a little deeper into it.

I'll keep the thread going when I find out what's happening.

 

[Viperwolf1]

In a C4 there are a couple cooling circuits check balls located in the pump stator. Those balls can get stuck and block the cooler circuit. They were eliminated when the C5 was introduced. I always remove the check balls on a C4 during a rebuild.

There is a good chance you can unstick them by blowing compressed air into the front cooling fitting.

 

[SC74]

In a C4 there are a couple cooling circuits check balls located in the pump stator. Those balls can get stuck and block the cooler circuit. They were eliminated when the C5 was introduced. I always remove the check balls on a C4 during a rebuild.

There is a good chance you can unstick them by blowing compressed air into the front cooling fitting.

I may try this, BUT.... if the fluid is cooked (worst I've ever smelled oil), is it worth it? Also, the transmission builder who built this is known for racing/hotrod transmissions and I wonder if he wouldn't have done the same. He's hard to get on the phone, but maybe worth a 45 minute ride to go ask him.

 

[needabronco]

Try what Viperwolf said to do and change the fluid. If it doesn't work your out an hour and a few quarts of atf. If it works you saved a grand or more in a rebuild... I aleays do a little more homework before condemning a transmission. I'd even go further and cleanout the valvebody while the pan is off but that's just me.

 

[Broncobowsher]

If the transmission still shifts right and doesn't slip you should be able to fix the cooling problem and put fresh fluid in and be done. If it got hot enough to hurt itself it will show up in excessive slippageor bad shifting.

 

[September 1972]

Leave the fluid alone if it shifts good, if the fluid burned so what. Oils are attracted to heat and the heat is the friction plates. The oil inside the plates exceeded it's smoke point so the oil component stuck to the plates and the remainder turns brown. The plates have protection and they are smoother now. New fluid is highly detergent so it's going to dissolve the nice oil film that was burned into the now smoother plates. Since new fluid has the full lubricity the smoother plates may slip, they may have slipped the first time. If it slips again since the plates are smoother it's really going to burn the fluid and the plates may fail.

A cooler as suggested is the only maintenance required. Put one way valves that open at 1.5 PSIG to prevent drain back. An old condenser is great for a tranny cooler!

Is there a inline filter in the line returning from the radiator or cooler? It's not possible to clean metal from the previous failed transmission out of the cooler tube or cooler because the metal sticks like glue to the inside tubes. Change the filter in a 1000 miles and cut it apart and see how much metal there is. If there is a lot then keep changing it because you do not want the filter to go into bypass and dump it's metal load into the transmission.

Why is the warranty on new cars 3/36 and they recommend changing fluid at 36? Nothing is as good as factory fluid. They want the tranny to outlive the warranty and some guys tow and are lead foots.

Another important reason not to change tranny fluid is contaminates find their way inside during a fluid change. One piece of lint can ruin a tranny. I learned this 45 years ago in tranny school. I have never lost a transmission, but I never changed the fluid either.

My suburban 4 by 4 has 195K and I have driven it hard, it has the hot motor and hauls ass. The fluid is bright red when I checked it years ago. I don't bother to check it any more. If a solenoid goes out or otherwise I have to crack it open, the exterior will be washed dinner plate clean and that fliuid is gold to me, it's going back in, no matter what it looks like. It shifts like a rock and I want to keep it that way.

Those guys that take care of their vehicles may disagree. Have you noticed that those guys that don't take care of their vehicles don't have problems like those that do? Cooling systems is what you want to keep on top of, leave the sealed hydraulic unit alone.

 

[Crawdad]

SC, you going to the fella up in Spartanburg that I'm thinking of?

 

[SC74]

SC, you going to the fella up in Spartanburg that I'm thinking of?

Cook's Racing in Cowpens. It's second generation now and Mr. Cook isn't there, but I know of a lot of people running and abusing the transmissions that still come out of there. Like I said, mine will go back there too! They also built the C4 in my crawler and anyone that has seen me wheel knows how I treat it ;D