Thread: No drive

One cannot make assumptions about the drivetrain in these things, as so many people (incl. myself) change things around - but for the fact the MY suggests you should be 3.9 ZF4HP22 and BWTC, can we make a generally safe assumption that's what's in the vehicle?...

1. established that the transmission barely functions, is overfull and smells (oil)
2. no drive in forward gears
3. barely moves (sporadically) in R

I'm going to suggest pump failure. Not that I can guarantee that to be an accurate from a couple thousand km away.

Pump failure would impact the ability for the A clutch to engage, and also for general inability to rotate the internals with an amount of sufficient torque to drive the load imposed by the vehicle..

Bear in mind, this is without any real testing, and there could be a number of internal issues, but the flow diagram is esentially simple. Pumps can rotate and fluid can flow, but if the fluid is not flowing at the correct volume and pressure, nothing will work.
Slipping clutches, or stuck components or even something broken previously that we are not aware of.
Stuck valves in the valve body can cause issues, which can mask problems also- like diverting (bypass) fluid and then you have internal leaks past seals etc, due to age, lack of use etc.

For example, an unrelated transmission (mercedes 722.3/4/5xx series) have some common issues with no reverse - and it's usually the pump seal oring. One day you start the car, put it in R and instead of engaging within about 1 second, pump's working on the Reverse piston, but seals kaput and fluid gets past it and effectively there's no reverse. it's enough to destroy the case if not immediately attended to, due to rotating steel contacing the alloy housing.

Just be aware that 90% of auto trans failures are due to worn seals or contamination of fluid from lack of routing maintenance. Age, yes, but the words routine maintenance also covers that, because routine maintnance also covers rebuilding the transmission when it has been observed during maintenance windows that there is excessive wear, deterioration of mechanical parts or debris/contamination in the fluid.

The vehicle has sat for a long time which doesn't help. Overfull, doesn't help. Seals can bind, or shrink or plain just fail over time. The ATF can in some cases accelerate this, but let's just agree to understand that an overfull transmission is not a good thing, like an overfull sump in the engine.

If you are going to do an R&R on the transmission, before you do, drop the sump off. if your torque converter has a drain plug, remove that and drain it also (not all do) then take the fluid filter off the trans valve body and toss it. Have a REALLY GOOD look around and observe how much friction material contamination is there. anything more than the finest grey dust means you have clutch pack delamination. If that's the case, stop there and do not proceed - just pull the trans. If there is only the smallest amount of grey dusty deposits in the remnants of fluid, clean it with Acetone or brake cleaner from all the immediately visible areas, let it evaporate and dry, put a new filter and gasket on the pan, put it back on fill it with the correct amount of fluid and then test operation.

Worst case is you get nowhere (literally) and that means you definitely have an internal issue with the trans. (assuming you cannot see any rotation from the output shafts, is what I am referring to). If that's the case, all you have lost is some fluid. Then it's time to strip it down overhaul with a full kit and new frictions and steels.

If you get somewhere, then you need to gently coax this back into life very carefully, by allowing it to properly come to temperature, then using each gear manually to ensure you get fluid flowing correctly through each of the circuits in the valve body. Do that for a few hours and then check the fluid. If it's not contaminated, run it for a week and then drop the fluid and filter (again) and when refilling, use an antiwear additive and a seal restorer like the liquimoly trans restorer - but do not leave it in there any longer than one oil change (6 months or 10,000km) because long-term the seal stuff can lead to deterioration (swollen seals soft etc, you get the picture) it's meant to be used for the duration of a fluid change. Long-term, a product like AW-10 antiwear, has proven to be extremely effective, so long as the dosage is strictly adhered to. 'less is more' in the case of ATF and friction modifiers.

Ultimately, the best solution is rebuild the transmission, however, that is an expensive undertaking whether you DIY it or you pay someone else to. And, if it's a 4hp22, then you'd absolutely want to hybridize it with some 4hp24 internals to make it stronger, regardless.

It all adds up to $$$$ and time.

Rebuilding transmissions is not some secret or obscenely complicated process that so many places and people suggest.
YES, you need some tools. Invest in them and it will repay.
Cleanliness is of the utmost importance, and in the strictest sense. clean clean clean and then clean some more. spotless is the understatement. Like any hydraulic system, contamination will kill it in no time flat.

measuring needs to be exacting. not 'close enough'
torque specs, clearances and shimming, - all of that must be exacting.

Other than that, it really is not as difficult as people make it out to be - and if you want to know the dirty truth - YES, you can rebuild one in the slap-dash method to "get you home" by throwing a kit at it, if nothing is broken internally, like sprag clutches or drums or splines or gears. So long as there's no physical damage to internals, no nasty scoring, no gouging and no excessive wear, you can strip and rebuild in a day.
New fluid and filter after 1000km (or less if you can afford bulk ATF) and you'll probably have to not touch it for a very very long time.

It's always best to be clean though, and thoroughly diligent with all the factory specs.
ATSG manual is a good starting place, plenty of exploded diagrams online to show you how it's all put together, but essentially, decide if you want to persist with that or buy another transmission if you need to get moving on a lower budget or are time pressured.

ZF4hp22.pdf

zf 4hp22 ATSG.pdf

EDIT: just in case someone needs the EH info
4hp22-eh.pdf

A web resource for interest's sake:
Chris Cowdery Global Presence

4hp-22 step-by-step (9 pages of internet time you won't get back)

Here is another, manual with step by step instructions.
ZF+4HP22+Transmission+Repair+Manual.pdf