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Discussion Starter #1
I have a 4L60 that I believe is centrifugally applying the reverse input drum clutches. The trans was brought to me due to no 2-3 shift at wot. I figured the 2-3 clutches were toast and maybe a pressure leak somewhere. During teardown I found the direct clutches show some heat but definitely not burned up to the point where it would slip that bad. It is an 8 clutch pack build. Further inspection revealed forward clutches to my surprise are totally fried. After that I found the reverse input drum clutches are toasted as well. I originally built this trans over 2 years ago but it hardly ever gets taken to the track. The reverse piston was keyed to the drum with a steel and the piston has a .0625 bleed hole in it. I also cut a groove across the bleed hole on the piston so it would vent even if the steel was seated tight against it. The snap ring is intact also. I suspect the drum is applying with rpm. This car has a 4800 stall and shifts at 7000 rpm. All the shaft sealing rings were replaced by me and they all look new. It has a transgo HD2 shift kit. I cant find any evidence of a cross-leak anywhere.
I feel compelled to drill more bleed in the piston. Do any of you think this would be beneficial or is there something else I could try?
 

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Discussion Starter #3
I'm trying to wrap my mind around exactly what that drum is doing in 1st gear or 3rd gear. I want to think its not actually a centrifugal apply issue as much as it is an excess of fluid flow due to the higher line pressures associated with the shift kit. Some fluid flow is always going into unused circuits correct?
Another thing, the steel that is locked to the piston has chewed the shit out of the drum splines. The other steels are beating up on the splines too. I realize in this situation the steels can hang up and drag the clutches but I wonder why the steels are eating at the drum splines so bad.
 

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From memory The Reverse Input Drum spins Anti Clock Wise at .9 Engine Speed in 1st.
Stationary in 2nd and 4th.
1:1 in 3rd.
They suffer terribly from Centripetal apply after 6000rpm
We generally block the Factory Piston Hole, drill 2 x 0.030" Bleed Holes 180.Degree apart and enlarge the Feed Hole in the Separator Plate.
 

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I found stronger springs help with both rpm apply and spinning the retainer on the snap ring.
 

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The splines on the forward frictions show more wear than I am used to seeing also. The forward steels aren't eating into the input housing.
Usually worn/stripped splines on the FF are from excessive end play.
 

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A common denominator for burned forwards/reverse as well as slips/no third is low line pressure.
Bad EPC, stuck boost valve, control issue etc.

Gregg Nader
Sonnax Tech
 

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Discussion Starter #12 (Edited)
A common denominator for burned forwards/reverse as well as slips/no third is low line pressure.
Bad EPC, stuck boost valve, control issue etc.

Gregg Nader
Sonnax Tech
I considered low line pressure at first but it was the appearance of the direct clutches that made me think otherwise. They each had a thin dark line around the inside circumference of the friction. Other than that the direct frictions looked great. The steels looked good also.
The forward frictions are black and are worn slick. The reverse frictions dark as well but aren't as bad as the forwards.
I'm just thinking out loud here but is it possible the forwards were slipping on the 2-3 shift instead of the direct clutches. The 1-2 shift wasn't as firm as it had been either at wot.
The reverse steels eating at the drum splines may be due to the 2nd gear servo. It is a big TCI servo with no spring cushion. I figure the band was violently locking that drum on the shifts and the steels were beating on the drum. Then the steels were hanging up in the drum causing the reverse drum to drag. The reverse clutches have more surface area than the forwards so the forwards burned up worse. Once again just thinking out loud.
I have since swapped over to a 4L80 in this car and am selling this trans. I have gone all the way through it and installed a corvette servo instead of that big TCI servo. The owner is fully aware of the transmissions history and never plans to spin it to 7000 rpm. Thanks again every one for your replies.
 
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