4l80e slipping in reverse, grinding in 1st.

[CumminsFever]

1994 k1500 4l80e, controlled by us-shift controller. Trans is from a newer truck, it has the extra bellhousing bolt hole for ls motors.
I rebuilt it 2500 miles ago with a Jakes kit, designed for 1000+ ft lb torque. It's rollerized input/output, 34 element sprag, accumulator delete, dual feed direct.
I put it together with absolutely zero issues, it's performed flawlessly... until today.
Drove across town, went to back up, reverse gave the dreaded grab/slip/grab/slip. On the drive home, I noticed 1st gear has a grinding noise that instantly ceases upon shift to 2nd gear. Shifts are firm like they've always been, temps are normal, no other symptoms. 1st doesn't slip, just grindy noises that are about the speed of the driveshaft... it seems.
Pressure is good, meaning it follows the tune, from 30 at idle position, to 180 from 50% throttle on up.
Fluid is full.
Of course I know it's gotta come out and get fixed. Something is grindy, that's more than a valve body drop will fix.
Anybody with ideas on where to look when I get in there or what may have happened?

 

[NickTransmissions]

1994 k1500 4l80e, controlled by us-shift controller. Trans is from a newer truck, it has the extra bellhousing bolt hole for ls motors.
I rebuilt it 2500 miles ago with a Jakes kit, designed for 1000+ ft lb torque. It's rollerized input/output, 34 element sprag, accumulator delete, dual feed direct.
I put it together with absolutely zero issues, it's performed flawlessly... until today.
Drove across town, went to back up, reverse gave the dreaded grab/slip/grab/slip. On the drive home, I noticed 1st gear has a grinding noise that instantly ceases upon shift to 2nd gear. Shifts are firm like they've always been, temps are normal, no other symptoms. 1st doesn't slip, just grindy noises that are about the speed of the driveshaft... it seems.
Pressure is good, meaning it follows the tune, from 30 at idle position, to 180 from 50% throttle on up.
Fluid is full.
Of course I know it's gotta come out and get fixed. Something is grindy, that's more than a valve body drop will fix.
Anybody with ideas on where to look when I get in there or what may have happened?

How many miles on the transmission since you rebuilt it last?

Any racing/high performance, etc?

Did you replace the L/R band or was the old one reused?

Lines and cooler(s) were flushed and/or new?

Drop the pan and look for kibbles and bits...Also may be worth checking the L/R servo for seal damage.
For planets (damaged or otherwise), check the vertical travel on each pinion...if far enough out of spec, sun-planetary-ring gear service packs will be out of mesh.

Just some quick thoughts...

 

[CumminsFever]

It's rite at 2400 miles since the rebuild. All new seals, bushings, bands, clutches, steels.
Yes, it does see some power, engine is capable of 1000ft/lb torque. I get spirited on the go pedal at times, but not regularly. Daily driving type of thing, no racing or towing.
Cooler lines are 3/8, replaced when the rebuild took place, cooler in front of rad is new, hayden brand. Never run over 215°.
Today I notice the grindy noise is also present for reverse. The grab/skip/grab/skip seems to be gears, not hydraulic.
I'm suspicious there's a planetary with teeth that are missing.
Do reverse and 1st share planetary? I've done some reading, and it appears the 1st gear planetary COULD be a weak spot?
There's also 1 other detail. Upon rebuild, my 1-2 shift was a tire chirping shift, I drilled the separator plate hole a bit too large. About a month ago, it softened. Still firm, but not tire chirping. I don't know if it's connected to this issue today or not.

 

[NickTransmissions]

It's rite at 2400 miles since the rebuild. All new seals, bushings, bands, clutches, steels.
Yes, it does see some power, engine is capable of 1000ft/lb torque. I get spirited on the go pedal at times, but not regularly. Daily driving type of thing, no racing or towing.
Cooler lines are 3/8, replaced when the rebuild took place, cooler in front of rad is new, hayden brand. Never run over 215°.
Today I notice the grindy noise is also present for reverse. The grab/skip/grab/skip seems to be gears, not hydraulic.
I'm suspicious there's a planetary with teeth that are missing.
Do reverse and 1st share planetary? I've done some reading, and it appears the 1st gear planetary COULD be a weak spot?
There's also 1 other detail. Upon rebuild, my 1-2 shift was a tire chirping shift, I drilled the separator plate hole a bit too large. About a month ago, it softened. Still firm, but not tire chirping. I don't know if it's connected to this issue today or not.

Please quote my post if you would like me to response - otherwise I prob won't see it...


Your gear train will likely need to be replaced...Reaction and output carrier specifically...I'd pay close attention to the orientation of the sun gear and if the beveled side of the splines are facing rearward or front (they should be facing rearward)...Second, I'd assess the spacing between the reaction and output carriers - too much slop here is a problem for anything high performance/RPM/power....At 1000 HP you ideally want a billet input shaft and super drum w/a 36 element super HD sprag as well along with a case saver for the Ctr support/intermediate clutch lugs in the case. Set rear gear end play to .006-.010 and front end play about 2x gross overall travel (i.e. front ep should me measured net of rear end play).

What's your stall speed?

What was the clearance in the intermediate clutch pack?

Line pressure: 30 PSI is low - should be 2x that or so but line rise sounds like it's where it should be...

 

[CumminsFever]

Please quote my post if you would like me to response - otherwise I prob won't see it...


Your gear train will likely need to be replaced...Reaction and output carrier specifically...I'd pay close attention to the orientation of the sun gear and if the beveled side of the splines are facing rearward or front (they should be facing rearward)...Second, I'd assess the spacing between the reaction and output carriers - too much slop here is a problem for anything high performance/RPM/power....At 1000 HP you ideally want a billet input shaft and super drum w/a 36 element super HD sprag as well along with a case saver for the Ctr support/intermediate clutch lugs in the case. Set rear gear end play to .006-.010 and front end play about 2x gross overall travel (i.e. front ep should me measured net of rear end play).

What's your stall speed?

What was the clearance in the intermediate clutch pack?

Line pressure: 30 PSI is low - should be 2x that or so but line rise sounds like it's where it should be...

Thank you for the tips, I'll be diving into this mess in a day or 2.
I don't remember what the clearances were anymore, I had set them according to the specs from Jakes.
I do have billet input, and the overdrive hub that is on the back of the input. (I think that's what it's called)
Stall is 2200.
I can easily adjust the idle (no throttle) pressure. The pressure ramp is not a straight line. It ramps to 100psi at 20% throttle, then a straight line from 100/20% to 180 at 50%.
It is diesel, so I don't spin rpm to get the torque. While I can rev to 5k, I keep it limited to 4k.
Your advice and input is extremely appreciated!