I was driving on the freeway, floor it and the trans downshifts then less than a second later upshifts. I was able to drive it home but it eventually lost all forward gears regardless of the shifter position.

I finally opened up the trans and found the input drum lugs for the forward clutch snap ring all broke off letting the backing plate hit the ring gear.



Did letting the trans downshift from 4th cause this? If not how can I prevent this in the future?

Everything is stock except the Transgo-HD2 shift kit.

 

Did you put the spring kit in at the same time as the shift kit?? And were the factory cushion springs still in there.... Imput drum is known to have issues anyway....

 

I didn't install the springs, I only did what I could with the trans still in the truck.

I didn't remove any of the factory cushion springs, and per Transnsgo instructions, I added a spring.

 

This sounds like it was a 4-2 kickdown?

All I can say is I got about 1 month of usage outta my stock tranny once I started 4-2 kickdowns.

Hell, RPM doesn't recommend them with their fully built trannys.

 

Yeah, that's what I did. Guess I learned the hard way not to do that. The trans had a lot of miles on it and I planned to rebuild it but I didn't plan on breaking it first.

 

Sounds like a good excuse to get the sonnax drum....

 

I looked into the Sonnax drum, too much $ and overkill for my application.

I did look into the Sonnax reinforcing kit with the sleeve and piston, would this be a good thing to do?

 

Not a lot of money if you want it to live.

 

Anything to help that weak *** input drum...

 

I have the sonnax drum in my trans, haven't broke it yet, have been beating the snot out of the truck every weekend at the track and DD as well, my trans is fully built minus billet input/output shafts. The drum is a good piece of mind, like stated in op, if you want the trans to live it is a nice investment