Any trans guys?? 4l80e problem
 

Here's the deal. 2 years back I bought a 2500 suburban with 454/4l80e with a known bad trans. I figured I would try and rebuild it myself. The original trans was recently rebuilt but what I found was whomever put the pump back together put the small gear in backwards which caused it to bind from the torque converter smashing it into the back of the housing thus pumping a nice mixture of oil/metal throughout the trans. OD one way sprag(?) was demolished and everything got hot due to no fluid. I cleaned the hell out of everything that was still good and bought some hard parts/steels and clutches from a much newer used trans along with torque converter. Also bought all new gaskets o-rings, pistons(?) from fatsco. Put everything back together along with trans cooler and radiator and it worked beautifully for a few months (2500 miles a year tow/emergency vehicle only) then I lost engine braking in 3rd, then 2nd etc.. Just recently, the truck didn't want to move until higher rpms, like a snowmobile. Glanced down and trans temp was high. Checked fluid and was near two quarts low. Put new fluid in and temps came down. And was able to make it home. (75 miles away, no towing).

Here is the current situation.. Truck goes into drive fine, engages strong with no slippage. Reverse engages with high rpms, but doesn't slip once engaged. No engine braking/drops to idle when coasting. Doesn't upshift without backing off gas slightly. Fluid is clean and not burnt at all. Truck has 223,000 miles but trans since rebuild has approx 4,000. Has a transgo shift kit. (previously installed/shift have been soft but solidly engaged)

Any ideas? I will try and get pressure readings today but feel as if it's a bad converter.

What year?

98

What year hard parts did you put in? This stuff changed every few years. It does sound like you might have a convertor problem but it would act the same ebgaing fwd as reverse. How is the shift into 3rd gear? I would suspect a 3rd gear/direct clutch problem causing your soft reverse if you tell me it also flairs into 3rd (same clutches used for reverse as 3rd). The reverse servo pistons also are very prone to cracking on the newer (including yours) 4l80e's, the after market has addressed this with a heavy duty billet servo piston. We just fixed a 98 (in the vehicle) that had a real soft reverse because of a cracked piston. After wards we did a line pressure test on it and cold iit had nice pressure going into reverse but hot it was over 500 psi, changed the boost valve in the pump (in the vehicle) and it was fine. You mention you have the transgo kit installed, if the whole kit wwas installed there will be a pressure relief valve onn the valve body with a little plunger, a gold plate and a tiny spring, if you have a boost valve problem you will heear a faint buzzing coming from the trans as it is lifting all the time hot, post more info and I will try to help you motre, Smitty
Fatsco is the most exspensive place to buy parts from, if you have to go back into it and need stuff you can pm me and I will try to help you by getting you wholesale prices on what you need, !

Artic, thanks for your help. Not 100% sure but I believe the hard parts I installed were from an 05. Overdrive planetary set, forward drum, converter, steels and clutches. Today when I started the truck after weeks of sitting, reverse worked great as did forward. The bands were still in excellent shape as the trans was just rebuilt. Manual second band was also the upgraded part (1/4" wider). It will not shift with out letting off the gas or it hits the rev limiter, same with down shift there for I can give you an accurate description as to the 2-3 shift. After it was hot I had to feather the gas to get reverse to grab. Have zero engine braking in all gears. Didn't get pressure gauge yet.

Taking it for a drive now to get exact symptoms in each gear.

George

OK, just took truck out and beat the hell out of it.

Cold
Reverse engaged immediately
Forward engaged immediately
Shifts OK when under light/no throttle
Full throttle stays in lowest possible gear until rev limiter

Warm/hot
Reverse doesn't engage until given throttle
Forward engages soft
All gears work but hard to differentiate between 1st and 2nd.
2nd feels as if its slipping, 3rd feels strong until it downshifts.

Was able to get trans hot quickly in second. Temp sender into test port on side of trans. 190 degrees when usually 140. I know that's not a great place but I never welded pan to accept sender.

Sounds like the one way roller /stator failure in the tq convertor , unusal though for a 4l80e to have convertor failure. There still might be a underlying lube flow problem, there were slight running changes going from 98 to 99 to the 2000 stuff, we recently had a 99 apart next to a 04 and the tube that drives the low sun gear was .040 longer, center support was slightly different, I'm not sure how much can be interchanged unless you changed everything, Smitty

Would a pressure test confirm/rule anything out?

could it be the shift selaniod acting up ? just guessing , becasue my 96 had the same issue and my trans guy fixed it ...5 min or so !

A pressure test on the reverse port cold/hot would confirm alot. If pressure is low in reverse hot, you have a oil flow problem, if pressure is good in reverse hot but it won't engage unless you throttle it I would think you might have a convertor problem. The fact it has a hard time engaging forward and reverse hot tells you its not a clutch pack issue as they are different clutches. You can tell if the low/reverse band has a problem by taking truck up to about 25 mph in low, let off gas and see if it compression brakes, if it coast like its in neutral, the servo is cracked, leaking or band is gone. If it goes into 3rd soft (flare at wot) and reverse the direct clutches are going out. Off the top of my head I think you should be seeing 180 psi plus in reverse hot with a little throttle but check your reference material if you have any, Smitty