I lost reverse and overdrive is slipping and humming at low speeds on my 4.3L two wheel drive '97 sonoma! Does this mean a whole new rebuilt/swap transmission or can it be something less such as a

This could be anywhere in the drive-line. Process of elimination would be the best approach. From your symptoms it sounds like the bad vibration is noticed at low speeds. There are many moving parts within this system. Were there and recent repairs performed? New tires could cause a vibration, if the tread is aggressive. Damaged wheel-bearings, defective components inside the rear differential (suspect low fluid level, damaged ring and pinion or bearings), defective U-joints, or internal transmission failure. You didn't mention if the truck was 2wd or 4wd. If the vehicle is a 4X4 then you will need to inspect the transfer case, the U-joints in the output shaft, and the front wheel bearings. I'm not sure how far you want to go with the diagnostics. Please write back if you have other questions or to give an update to how the repair is going, good luck.

Are you sure it's not in 4 wheel or do you mean that it's just not switched to 4 wheel? Sounds like a bad indicator switch in the transfer case which is indicating 4 wheel low to the ecu which might not allow overdrive due to speed constraints of the 4 wheel low system.

I have a 92 Crown Vic first and second works fine reverse works fine when it shifts in the third gear it goes to slipping and overdraft can you help me fix this problem thank you

it may be a bad transmission modulator valve located on the side of your transmission,vacum operated. a sudden downshift or forward shift when unexpected is sign of a bad modulator valve or a vacum leak to the transmission.best to shop around for a garage w/references when it comes to transmission work though. check all the vacum lines to your transmision,you need to look on the underneath side of your truck on the side of transmission for a loose or disconnected vacum line on the side of the transmission. when you feel the vacum line,follow it to the top of engine,the vacum line is about 3/8th line,and may be disconnected or losing air. to make this short,when you drive the car,start out in low gear and shift the transmission,manually from 1st to 2nd to 3rd does it do right with no slipping? if it does this right and shifts great manually,the modulator valve on the side of the transmissions bad,or a bad vacum leak in-between.thank you for choosing fixya.com

Sounds like the low one way clutch is bad. The trans will need rebuilt or replaced. After you get some speed in low1 like to 15 mph, shift to low 2, then at 25-28 shift to drive, then at 42-45 shift to overdrive. Will the trans hit all the gears when you do it this way?

You broke the low one way clutch. The trans will need rebuilt. The truck should be drivable if you take off in Man 1, shift to Man 2 at about 12mph, then shift to drive at about 27, then shift into overdrive at about 42.

Your transmission needs rebuilt...the overdrive cain has gone bad, and if thats the case the whole transmission needs serviced or replaced.

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reverse band is a goner

You probably need a new, used or rebuilt transaxle installed. I would have a junkyard swap one in if the cars is in good condition, or sell the car for parts if it needs lots of work or has high miles.

There isn't a modulator on this trans as it is electronic

You can have first gear going forwrd but no reverse. It is possible. The low/ reverse clutch isn't needed to go forward.