crbxmlp

hello, friends. I installed a 4l80 in an old chevy pickup, overhauled by myself, amateur me, hahaha. gears are controled whit switches, full line pressure, first three gear works fine, very fine, loved the feeling of it over the previous th 700.. shifts are harsh but fine, (I am making a pwm controller to take care of that in the near future) but when 4th gear kicks in, immediatly drops out, like going neutral, droped v-body, valves seems with no play or stuck. checked check ***** positions, seems ok. checked 4th piston feed bolt, seems ok, checked piston whit air, also ok. the thing I noticed is both accumulators pistons are thigt, like impossible to pull out by hand, could this be the problem? when I driped the v-body, fluid looked brand new, no debrids or overheat smell. I have read the treads with similar problem, but my tranny does not present the problems listed in those, tanks in advance.

performabuilt

iTrader: (25)

It is possible the input front sprag is not holding what happens if you try and start in 4th gear switched and position.

crbxmlp

Both switches on, car goes forward but kinda limp. I put a new sprag because I broke the original during the teardown. Could the races of the rollers be the problem? Or the líp seal of the sprag housing? Thanks Thank in advance

clinebarger

The O/D Roller Clutch overruns in 4th gear/4th clutch applied, You would have issues in reverse if the roller clutch wasn't holding.

Did you check the 1-2 Shift Valve Spring? A broken spring here can cause the 1-2 shift valve to "Balance/Neutralize" in a position where the 2-3 Drive oil will exhaust....Releasing the Directs (3rd) & the Intermediates (2nd) Giving you a Overdriven 1st gear (Forwards & 4th Clutch applied) which can feel like a neutral condition at higher speeds.

Some paper & rubber kits are coming with a stronger 1-2 shift valve spring now.....I had to learn/diagnose this the hard way.

crbxmlp

Reverse is fine. Guess I have to drop v-body again yo make Shure. Thank you for the info

clinebarger

Remove Shift Solenoid "A", Use a Awl or pocket screwdriver & actuate the 1-2 shift valve......The valve should have spring pressure against it & return back to the roll pin everytime.

crbxmlp

you know? I forgot to say, but some times when selecting 3rd after 4th gear fail, it feels limp, and some times it runs in 2nd even when only switch 1 is on. the failure you´re saying seems more certain now, it seems to me you have solved my problem, going to check this week end and leting you know, thank you

crbxmlp

can inverted springs cause the issue?

crbxmlp

well, IT WAS the issue, my friends, problem solved, tanks, clinebarger, your post was the key for solving this.