TorqueFlite 727 Burned Front Clutches

[Fish Bite]

I could use some help diagnosing an issue with my first 727 rebuild. It's a 1964 cable-operated that I rebuilt last year. I used Alto Red frictions and Kolene steels. The front clutch has four frictions and 10 springs. The snap ring is wavy. I cannot find my build notes, but I recall the clearance was in somewhere around 0.060". It definitely wasn't outside of the factory spec range, which the book says is 0.024" - 0.123". Tom Hand's book that I also referenced has the range listed at 0.082" - 0.151". I measured the clearance by sliding the feeler gauge between the pressure plate and the peak of the wave for the widest gap. Everything air-tested correctly.

Here's the issue. The transmission shifted really well with no issues. Somewhere around 150 miles of use, I smelled burned fluid. There wasn't an immediate thing that happened that would pinpoint when the clutches burned. I dropped the pan and didn't find any clutch debris in the pan or filter, so I changed the fluid and put another 300 miles on it with crisp shifts. I pulled the engine and transmission to paint the car, and I decided to pull and inspect the clutches. The outside of front drum and low/reverse drum show no signs of overheating, and the kickdown band looks great. I haven't pulled the guts back to the low/reverse band, but the drum looks fine when I push the band to the side to get a glimpse. The rear clutch frictions are a uniform red with no sign of slipping, and the steels are flat with no abnormal wear. The front clutches are fried. The pressure plate on the side that faces the first friction has a small spot of light brown discoloration from heat, but it doesn't go through to the other side of the plate. The friction that rides on that is still red with only a faint black smudge ring. However, the other side of that friction and both sides of the other three frictions are black, cracked, and flaking. One of the steels is cupped into a slight cone. The current clearance is 0.092", but it isn't accurate for what it was since friction material has been removed and the one steel is cupped.

Here are two significant variables is considering diagnosis:

1. Unbeknownst to me, the shifter cable groove that locks into the rooster comb via the locking wire was worn enough to where on a hard press of the 2 shifter button the cable could pull out. At some point during tuning (I don't know the exact miles), I was wide-open throttle from launch, and when I pushed the 2 button at 6,500 rpm, the cable only partially pulled the rooster comb forward before pulling out of the lock when the shift was only partially complete between 1 and 2. The engine RPM jumped, and the transmission acted like it was in neutral. After coasting to a standstill, I was able to reseat the cable into the locking wire by mashing the neutral button a couple times. When I got home, I removed the cable and filed the groove edges to repair that issue. I don't recall if I smelled burned ATF at this point.

2. I have a cable-operated throttle-pressure setup on the transmission/engine that I adjusted properly per the instructions. However, again unbeknownst to me, at some point the return spring down at the transmission lever came loose to where I was driving around for an unknown amount of miles with the transmission lever potentially not returning fully to its off position. At one point, I noticed that the transmission in 3rd/D wouldn't auto shift from first into second until 55 MPH under moderate acceleration. To get it to shift, I had to roll off the throttle at 30 MPH where it would unload and then upshift. After I got home, I inspected everything and found the spring had come loose. Once I attached the spring and bent the hook to where it couldn't come loose again, the transmission shifted as it should when at running temp, but I noticed it would shift at a higher MPH when it was cold until it warmed up.

So I am not sure if the burned frictions/steels were caused by a rebuild issue on my part, by the transmission becoming stuck between the 1 - 2 shift, or by driving around with the kickdown return spring disconnected. I'm going to order a new set of front steels, frictions, and seals but am concerned I'll have the same issue if I'm setting up the clutches or something else incorrectly. Thanks for any help.

 

[AbodyBB]

I’m recalling a comment from almost 30 yrs ago so I cannot be entirely sure of what exactly was said. But I was told that the forward clutches are third gear. Third gear depends on the kickdown for proper line pressure. Without the spring the kickdown will remain in a position that drops line pressure. The lack of pressure means less force on the clutches and of course slippage.
On reassembly ensure the kickdown is assembled correctly and will travel to the furthest position in WOT and returns the the forward position completely whit the throttle closed. To eliminate any other issue put a pressure gauge on it when you first drive it. 60-90 psi is what you’re looking for.
Be sure the governer is free as that is what has taken out two of my transmission builds in the past.

 

[Fish Bite]

I’m recalling a comment from almost 30 yrs ago so I cannot be entirely sure of what exactly was said. But I was told that the forward clutches are third gear. Third gear depends on the kickdown for proper line pressure. Without the spring the kickdown will remain in a position that drops line pressure. The lack of pressure means less force on the clutches and of course slippage.
On reassembly ensure the kickdown is assembled correctly and will travel to the furthest position in WOT and returns the the forward position completely whit the throttle closed. To eliminate any other issue put a pressure gauge on it when you first drive it. 60-90 psi is what you’re looking for.
Be sure the governer is free as that is what has taken out two of my transmission builds in the past.

You're correct that the front clutch controls direct drive and reverse and definitely relies on throttle pressure signal for proper governor function. I haven't checked pressures, but I'm going to buy a pair of gauges and do so with the car in the air once I have the engine/transmission installed. I wish I checked those pressures before pulling the transmission, but it seemed to be shifting fine to where I didn't expect the issue aside from the smell of burned fluid.

I have the line pressure and throttle pressure adjustments set at the factory specs. The 1965 factory manual calls for 54 - 60 psi of line pressure at 1,000 RPM with the transmission in direct drive and shifted into 3rd/direct drive. With full throttle pressure, the psi should be 90 - 96 psi just before or at kickdown. The front servo release pressures should follow the line pressure +- 3 psi.

What has me thinking the issue might be in the reverse circuit is that the front and rear clutches rely on the same line pressure when the transmission is in 3rd/direct drive. If the mechanical line pressure were too low, I would expect both the front and rear clutches to show signs of slipping, but the rear clutch looks fine. However, I wonder if the additional force on the rear clutch provided by the Belleville spring is enough to stop the rear clutch from slipping whereas the front clutch doesn't have that extra force multiplier?

If direct drive line and front servo release pressures check out, which I won't know for a while, I suspect the reverse line pressure might be too low. My manual calls for 240 - 280 psi at 1,600 RPM.

 

[AbodyBB]

Sadly my information source passed away a couple years ago. I do recall that he did say that the fronts are the ones that get burned. I don’t remember what he said about why the rears don’t.
If the fluid circuit feeds the rear clutch first then it would be more likely that pressure drop would cause front to slip while rear remains engaged. I don’t have my service manual in front of me to verify the circuit.
But I can be very confident that a kickdown issue always burns the fronts.
I replaced clutches and the same issue returned. What I found was that the pressure loss allowed the governed to remain in one place where it got stuck.

 

[Fish Bite]

@oldkimmer, in your experience, would incorrect throttle pressure adjustment burn up just the front clutch with no damage to the rear clutch or either bands? Would the transmission shifter momentarily sticking between the 1st and 2nd gear detent at 6,000 RPM shift cause the described damage? I appreciate any input you have.

 

[oldkimmer]

Yes, just the front clutches can burn up. Not the 1-2 shift. 2-3 shift if slipping will burn them up. The rear clutches are applied in all forward gears and are not as prone to burning up unless u have really low pressure or low fluid level. Kim

 

[Fish Bite]

Yes, just the front clutches can burn up. Not the 1-2 shift. 2-3 shift if slipping will burn them up. The rear clutches are applied in all forward gears and are not as prone to burning up unless u have really low pressure or low fluid level. Kim

Thanks @oldkimmer. Since the frictions/steels overheated badly, I'm going to replace the springs and piston seals just to be safe in case they got hot. I mocked up the drum with new thin Alto red frictions and Kolene steels and can fit 5 at 0.082" clearance. I was planning on increasing the springs to 12 with the 5 frictions since the transmission has a 3.8 kickdown lever and Fairbanks shift kit set up for stage 2 performance street (OEM pressure regulator and converter springs, pressure regulator set at 1-3/16", restrictor in the front clutch oil passage). Does this plan of 5 frictions and 12 springs sound reasonable?

I could use your advice on testing the pressures. Once I have the engine/transmission back in the car, I'm going check all the pressures with the rear wheels off the ground per the factory manual. If I find that the 2-3 line and/or front servo pressures are off, do I need to worry about frying the forward clutch during this pressure test? I've never performed a pressure test before, so I'm trying to get a handle on how much I can play with adjusting the throttle pressure cable and thumbing the lever during testing with the rear wheels off the ground without damaging anything.

 

[Bewy]

The front piston seals can get damaged during installation; they then leak, causing pressure loss. Clutch plates then burn up because they are slipping.

 

[RustyRatRod]

@oldkimmer, in your experience, would incorrect throttle pressure adjustment burn up just the front clutch with no damage to the rear clutch or either bands? Would the transmission shifter momentarily sticking between the 1st and 2nd gear detent at 6,000 RPM shift cause the described damage? I appreciate any input you have.

You bet. That's how it works. With no or too little throttle pressure, there's not enough pressure to hold the clutches together. It will burn the highest gear first (3rd) because it takes more power to pull high gear so there's more leverage on the high gear clutches. If it's left like that, 2nd will be next and then first. That's why the kickdown linkage is so important and must be adjusted correctly.

 

[Fish Bite]

The front piston seals can get damaged during installation; they then leak, causing pressure loss. Clutch plates then burn up because they are slipping.

I was extremely careful during installation and used a rubber seal tool to chase the seal into place, and the air test didn't show any signs of leakage. I inspected both seals when I disassembled the drum, and I don't see any signs of damage.

 

[Fish Bite]

You bet. That's how it works. With no or too little throttle pressure, there's not enough pressure to hold the clutches together. It will burn the highest gear first (3rd) because it takes more power to pull high gear so there's more leverage on the high gear clutches. If it's left like that, 2nd will be next and then first. That's why the kickdown linkage is so important and must be adjusted correctly.

Thanks. When I get everything put back together and installed, is testing the pressure between 1,000 and 1,600 rpm and fine tuning the throttle pressure linkage with the rear wheels off the ground something I don't have to worry about burning up the direct clutches?