COM takes a while to warm up

[Yadkin]

I rebuilt the tranny myself about three years ago using an aftermarket kit. The clutches are made of some type of fiber. The car sat for a long time waiting for the engine builder and body man. I originally filled the fresh unit with Valvoline Type F. During the break-in process I had several leaks in the cooling circuit and pan so ended up diluting it with no-name brand Type F from O'reilly.

The first issue that I had was stalling when putting into any gear. Sometimes chirping of the tires. I chalked it up to needing to be broken in, specifically the clutches. After less than 50 miles that issue went away.

Next I noticed that the transmission was taking a long time to warm up and getting progressively worse. Basically it doesn't shift into 3rd until warm. Over the course of 1000 miles or so it got excessive so I dropped the pan and found that the filter was clogged with clutch material. I smelled a slight amount of burn odor, but the fluid was clean. New filter, new Valvoline fluid and the transmission worked perfectly. Except for the warm-up issue.

I'm not sure if my current warm-up issue was there at the last service or not. I've put about 1200 miles on the car since then and the warm-up period is consistent at about 4 miles. It will shift into 3rd right away at low speeds with no load, but above 40 mph or so it stays in 2nd. After warm-up, the transmission shifts like a dream. Nice firm shifts, no slamming into gear, very predictable shifts and quiet operation.

I guess my question is, is this warm-up period (summer here) considered normal?

 

[Yadkin]

The issue got worse over the weekend after I paid a visit to my neighbor who lives on a long, steep gravel road. The transmission clutches got a workout, and apparently shed more fiber onto the OEM filter. Warm-up the next day was well over 4 miles.

I've decided to drop the pan again, convert the OEM filter into a pickup, and install a remote oil filter in the supply line of the cooling circuit. This will allow me to change out the filter on a routine basis as as better protect the transmission itself. I've designed the system to use the same filter as the engine.

 

[makrie]

I wouldn't have the expertise or ambition to rebuild an automatic transmission as you already have! Chasing these symptoms unfortunately will likely lead to transmission failure which is probably how your journey began.

Since a good transmission still up-shifts when “cold” what comes to mind is the change of oil viscosity. Thinner oil might allow flow through a partially clogged passageway or one of the valves in the valve body is sticking. This mimics a low fluid level or a clogged filter you're finding which I'm assuming is due to the excessive wear stuck in first gear.

Not having had this issue myself, a quick google search found several discussions on C4 C6 transmissions pointing to the pressure regulator, governor, vacuum diaphragm, linkage, band and/or servo possibilities. Sorry there isn't a single answer out there so it becomes a process of elimination.

In your search for guidance don't limit to Thunderbirds alone as these transmissions were used across the Ford line. You might find the resources you need in one of the other Ford forums. Best of luck and hope to see your Thunderbird on the road soon!

I've included a photo of the Cruise-O-Matic diagnosis guide from the 64 - 65 Service Manual.

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[Yadkin]

Well, my theory of a clogged filter screen does not appear to be correct. I removed the pan and drained all the fluid out of the case and torque converter. It's more brown than red after about 1500 miles. There was a thin layer of black on the base of the pan and inside the filter. The filter was free of clutch fiber material, no clogging on it at all.

I've been using Valvoline Type F for the last change- the oil that I just removed. I don't know if that is the issue. I've heard some folks suggest changing to Mercon but that shouldn't cause the problem that I have been experiencing. Maybe I need to bu a different brand.

Another issue- unrelated. I had used a rubber gasket that I cannot find the receipt for so don't know the brand name. I used a thin layer of RTV black on both sides and torqued it to 1/2 of the OEM value. It was the first time in 30 years that the gasket had not leaked. I had a Felpro fiber gasket in my parts bin so used that, same technique. It fell apart when I reached 6#-ft. I removed the pan and searched for the good brand, and I hope that I found it: Autocrafters. I have not used that site and there is little description of the gasket, but the filter looks like the one I just converted over to a pick-up.

 

[Yadkin]

I installed a remote filter and converted the OE filter to a pickup by removing the fine screen. I found a nice spot on the left, symmetrical with the engine oil filter about the oil pan.

 

[HeadacheGuy]

Don't want to to Be the one with the bad news here but drop the transmission and start over. The clutch pack material means something is badly wrong.... To low or high of control pressures etc.Torque converter should have never let the first problem happen. Actually sounds like a band hung up or too tight but regardless clutch pack material is debris in the system. If normal means anything mine shifts too hard totality warmed up. Shifts like a dream when cooler. Good luck

 

[Yadkin]

It seems to be shifting a lot better now. Warm-up is about two miles, and after warm-up shifts are predictable and firm. The filter should do a good job protecting everything from debris and clean up any small particles that are still inside.

 

[makrie]

I have to concur with HeadacheGuy's suggestion...start over. Hagerty has an interesting artcle on rebuilding one of these transmissions "https://www.hagerty.com/articles-videos/Articles/2017/05/24/Redline-Rebuild-Revisited". At least compare to the work you've already done and see if you might have missed something.

 

[Yadkin]

The transmission was running fine when I rebuilt it, just leaking at the front seal that turned out to be a badly worn front bushing. It was perfectly clean inside with nice red color to the fluid. I didn't disassemble any of the major components like he did, just the clutch packs. Since the problems are repeatable and due to temperature it's obvious that viscosity is playing a major role. Maybe some clutch pack material stuck itself to the band clutches and has changed the friction characteristics. I think now that the packs are broken in and I have a 20-ish micron filter on the system the warm-up issue will go away with miles as the material washes out of the bands.

No need to spend a lot of time and money re-rebuilding it until that theory is debunked.

 

[Yadkin]

Here's a drive I did today documenting the issue.

https://www.youtube.com/watch?v=zSqcU02rabM