Vw 412 engine and gearbox trouble

[Autostyle]

Hi there.

I have a vw 412 le fuel injection with an automatic gearbox. I have 3 problems that I need assistance with.

1) The car experiences a lack of power at low speeds,usually till 60km/h. This is experienced most when going uphill.

2) After some time of driving when I stop at a robot or stopping in traffic, the car switches off most of the time. The car does restart easily. However when I restart the car the car takes off very slowly.

3) The gearbox has a kick whenever i pull of or when the gear changes. I have checked gearbox oil and it was significantly short but the problem is still there after topping up.

Any help or advice would be appreciated. Thanks

[raygreenwood]

There is a lot to look at. To start what year is this car and because Australian cars may have a few differences.....which fuel injection system do you have? All except 1974 should be D-jetronic. The 1974 into early 1975 should have been L-Jetronic.

First the transmission fluid. Were you low on transmission fluid.....meaning the red Dexron fluid that is checked with the dip stick?....if so its very important to ask.....are you leaking visibly anywhere?

If you have no visible leaks....stop driving the car at all for the moment. You need to also check the GEAR OIL.
These transmission used fairly normal hydraulic fluid in the gear change section and that is what you check with the dipstick.....and only when its running.

The problem is that the final drive section....the differential.....use 90 weight gear oil. With age the seals between the gear change section fail and transmission hydraulic fluid will leak into the differential and contaminate the 90 weight gear oil......and very quickly it will destroy the differential. Spare gears are rarely available except used.

You need to STOP....put the car on level ground and remove the side fill plug from the differential section of the transmission. If oil starts pouring out heavily.....the level is too high and its a sure sign the seals have failed. Its not expensive or very difficult to replace them but the transmission will have to come out. Its mainly an external job.

These seals had problems in all of VWs automatics through the 1970s and 80s even in the water cooled cars. Audi issued an technical service bulletin that they should be replaced at 7 years or 70,000 miles. You should do these.

The other item that can cause fluid loss without any external leakage is the vacuum modulator. If the diaphragm in the vacuim modulator fails....it allows fluid to leak into the vacuum hose on the lower right side of the transmission and it is sucked through the engine and burned. Because that also means the vacuum modulator is not functioning....you will have poor shifting.

You should look for a spare and buy one anyway because they are hard to find. If you pull the hose ofc and fluid drips out....there is a part of your problem.

The stalling and low power. In either of the fuel injection systems....you are not allowed to have ANY vacuum leaks.....not one.....not even a small one. With D-jet.....the system is vacuum controlled. Any minor vacuum leak is seen by the MPS....as a throttle input and it will run poorly, run rich, stall snd have poor idle and poor power range.

The engine needs to be in good shape to operate the automatic. This means no large variances in compression.

Your tune up needs to be excellent and exactly as factory. Timing must be set with a strobe as per the book....because the fuel injection timing (which uses separate trigger points in the bottom of the distributor)....is dependent upon having the ignition timing set exactly like factory.
Your fuel pressure must be stable and must be fairly exact. Factory setting is 28 psi. You can go as high as 30 psi but no higher. You must not drop below 28 psi.

There is a lot of little details. Start with this and post some pictures and details. Ray

[KTPhil]

Stalling, low power off idle, and rough shifting are all symptoms of vacuum leaks, which will affect both the engine and tranny, and how they interact. As suggested, a thorough tune-up and vacuum leak check should precede any attempted repairs.