my bonnie tranny 4T60E ,was slipping a little in the lower gears. reverse was fine . I put in a lil lucas no slip in and a week later it stopped slipping in forward gear ,but now all of a sudden i have no reverse,and when i put it in reverse its like the emergency brakes is on, it torques up and bumps into reverse but it wont move,like it locks up? anyone have any ideaswhat could be the problem any ideas would be much appreciated,TY for your time. David

First of all, how many miles are on it?

If its a high mileage trans, I would suspect the clutch'* are getting worn out or the filter is getting clogged up. I heard replacing the filter and putting in Dextron VI helps.

well the engine has like 217k, but the tranny was replaced with a rebuilt one about 10 years ago,and i changed the tran pan filter and oil about 180 or 190k , the car always shifted great until recently, like i said reverse was fine never slipped ,forward gears were slipping a little so i put some lucas no slip in , now forward gears are fine ,but no reverse,i know wierd right!i am gonna try replacing filter again and adding new dextron vi,also isnt there an inline filter coming from tranny or coolant line?i was thinking it might be clogged as well not getting enough hydralic pressure.ill do the filters and all 1st see what happens. i heard also might be electronical , like and actuater for reverse ? ok mike for your time will let you know how i made out, David

My transmission started slipping a while back, it slipped from 3rd to 4th, and reverse barely worked, I dropped the pan and the transmission fluid was pretty dirty looking, luckily it was not burnt, I did find pieces of my forth clutch thrust washer in the filter, it was clogging the fluid flow, so I replaced it with Mobil 1 Synthetic, and I added some LubeGuard Automatic Transmission Fluid Protectant, afterwards reverse started working like normal, and it shifted from 3rd to 4th gear without any problems.
For now it is fine, but I know eventually I'll have to have it rebuilt.
I'd drop the pan, and change the fluid like you plan, and see how it goes from there.
Don't forget to inspect the pan well, maybe even drag a rare earth magnet through the old fluid, and see if you have any metal bits or shavings, also inspect the pan magnet to see if it has more than the usual looking goo on it.

Here are links to the only additive I used.

LUBEGARD Automatic Transmission Fluid Protectant

Like William suggested, a filter and oil change with an additive may get you by for now, but please keep in mind anything you do at this point is likely to be a temporary solution. You can delay the inevitable but you probably need a transmission rebuild.

hey mike, i am finally getting around to doing my bonnies trans , you said in reply to use dextron vi ,, but it says in repair book only to use dextron iii , is there something special about dex vi??

ive dropped the trans pan and fluid looked almost black , not burnt, but i found alot of sludge and a lil metal flake on magnet in pan. so i want to get my best chances of fixing the reverse problem and some of the slipping, so i wanna use the lube guard like you said ,but im a lil confused about fluids1st mobil 1 synthetic is this a dextron trans fluid they also make besides eng oil ? 2nd the repair book says to use dextron iii only , i didnt know there was a dextron vi and is it ok to use in my 1997 bonnie??

the dex vi is the new stuff its got a different additive package. and its backward compatible. but im with roy if you got blackness and metal flakes in the pan you are wasting your money. that new dex is expensive.

i got my 98 bonny trans rebuilt by a&m in fancher for under 1000, a little messy but worth it for half price of everyone else

nevermind i thought hamilton was by rochester

Taken from a wikki article.

The fluid specification for Dexron-VI was introduced in 2005,and was first used as the GM factory-fill automatic transmission fluid for model year 2006. All Dexron-III licenses expired permanently at the end of 2006, and GM now supports only Dexron-VI fluids for use in their automatic transmissions.[3] Fluids asserted by their manufacturers to meet Dexron-III standards continue to be sold under abbreviated names such as Dex/Merc, but the licensing system no longer exists. These fluids are not regulated by GM.[4] Dexron VI is of a slightly lower viscosity when new compared to the prior Dexron fluids (a maximum of 6.4 cSt at 100°C for Dexron VI and 7.5 cSt for Dexron III), but the allowed viscosity loss during use (from shearing of the ATF) is lower for Dexron VI, resulting in the same lowest allowed final viscosity for both Dexron III and VI (5.5 cSt).[5] The intent of the lighter viscosity is to gain an incremental improvement in fuel economy by lessening parasitic drag in the transmission. Since Dexron VI is not allowed to thin out (lower its viscosity) as much as Dexron III during use, it requires the use of higher-quality, more shear-stable (thins less in use) base stocks (the base oils, to which additives are added to make ATF).[4]

Basically it is backwards compatible with Dextron iii, and it is a lot better.

When I changed my fluid it was dark brown, almost black, luckily it did not smell too burnt.
I had the usual grease built up on the pan magnet, so the greasy residue you seen is normal, and if you only seen one metal flake you may be ok for a while, but a rebuild will be inevitable as already mentioned.
After a fluid/filter change my reverse worked normally again, and the car shifted very well, I do not run it hard though, so if it runs well after you change the fluid, then take it easy till you can get it rebuilt.