mdarney

I am trying to fix my rear hatch motor but I have gone through the wiring diagram and I am confused. The motor works fine with the hatch open but when you close the hatch the switch disconects the motor so it won't work. I have looked at the wiring diagram and I can not tell if there is supposed to be a circuit to loop the motor and bypass the switch. Why is the motor switched off when the hatch is closed? Help. -Mark

1985 928s 5 speed

chaadster

In my experience, the hatch release system is the single, most complicated and difficult-to-work-on system on the 928. Good luck.

I have noticed that if there is too much pressure on the hatch motor drivetrain (such as when the hatch is closed), it will not be able to move, and so seems to do nothing. You're sure the motor see's no power when the hatch is closed?

Sorry I can't be of any real help.

Alan

Do your interior lights work from the door switches? if not fix them and all will be good.

Alan

mdarney

Alan, no they don't. Can you explain how does this matter? and how do you remove the switches? -Mark

1985 928s 5 speed

Mike Frye

Really!???

Alan

The way the hatch release motor works is a little non-intutive.

It runs for 2 quite seperate reasons:

1) The initiation circuit

2) The parking circuit

The initiation circuit is fed by the interior light supply, via the hatch pull switch(es) to the motor and the motor ground is vis the switched interior light switch ground.

To operate correctly the following have to be working:
The interior light fuse
The hatch pull switches
The interior light switch ground must get connected to ground
- a. the interior light door switches must trigger the (delay) relay switching
- b. The rear hatch switch (open) drives this with a direct switch drive

If any of these are not functional your hatch switch(es) will not initiate a release cycle.

The interior light "feature" ensures you can only open the hatch when a door is open - so its locked out when you are normally driving.

The motor will continue to run for as long as you pull the hatch switch - but without any other circuits operating the hatch motor will stop as soon as you let go. It may stop at a point where the hatch cannot be latched closed...

The parking circuit is rather simpler - it is designed to run whenever the motor is not in its park position - its sole purpose is to cause a motor cycle - once initiated as above - to continue all the way to the park positions (hatch unlock tab in the fully disengaged position). When it gets to this point it stops driving the motor - of course it will keep running if you are still pulling a switch.

It accomplishes this with an integrated circuiar track with a wiper driven by the motor and a break in the track at the park position. You can see & clean this easily if you disassemble the motor.

The parking circuit - only - is fed by the dedicated 1A fuse on the CE (fuse) Panel.

If that fuse is bad your motor will stop as soon as you let go the hatch switch, if your motor continues to run cycles after you release the switch - your circuiar track has likely become continuous across the gap from smearing - usually cleaning restores operation.

The switch tops spin off the body anticlockwise. Some seem to have issues with these - there is a little lock hole in the side. All mine have always come off with a sharp twist to initially break them loose... and no need to use the lock hole. I don't think you need to remove them though - focus on the interior lights.

Alan

mdarney

So Alan, if I understand this properly the ony reason the motor works with the hatch closed is this is the only working ground so I need to get the door and glove box door switches working. They have 12.7 volts to them so I assume the ground is the issue. Mark

Alan

Yes - all the switching for the interior lights is on the ground circuit - see if either door will switch the lights (twist the pin around back & forth a bit to see if that helps) - if even one works intermittently its the pin switches at fault - if neither works it may be the delay relay (if equipped).

Currently only the direct drive hatch switch is allowing the switched ground to get grounded - (goes off as soon as the hatch is closed) - normally the interior light and delay will keep this grounded.

Its not very helpful to only have the hatch opener operate when its already open huh?

Alan

imfinlay

Great write-up! I' ve been unable to find the 1A fuse on my '89 UK car. Where the **** is it?

Alan

On the CE panet (the main fuse panel) but it may have been replaced with a 3A or 5A because 1A's are rather hard to find. Fuse # 26


Alan

j.kenzie@sbcglobal.net

Wow Alan. That's the best write-up on the hatch motor I've seen. I've done a decent amount of work on mine but I still learned things because of the way you explained them.
Thanks

mj1pate

...I have two issues:
1) The hatch release system fails to release the hatch, even though the release mechanism goes through the motions that it should. Perhaps the nylon latch tongue is worn(?)
2) After operating the the release system for any where between 1 and 10 cycles, the interior light fuse blows. I suspect that a piece of metal has made its way loose into the motor housing (gear housing looked clear) or a diode in the gear housing has blown.

Are new latch tongues available? Does anyone have part numbers for the diode and transistor in the gear box? I would liike to rebuild this unit, when I put it back in.

Thanks

Mike

jpitman2

A friend called recently with a failed hatch release - the bush between the link to the motor and the cast arm on the receiver had broken up and allowed enough slack that it could not release the catch. I lent him a spare reciever I had, and turned up a couple of brass bushes (5mm ID, 7MM OD, ~2.5mm long IIRC) to relpace the missing (probably plastic) bush. I then drilled the arm pin and tapped a 2-56 thread, and retained the arm with a washer and a 2-56 bolt from my modelling kit. I suspect that a careful search of tube sizes (in any material) in good hardware stores might yield something suitable also.
jp 83 Euro S AT 50k, dont have no steenkin' electric release.....

Alan

Mike - OK so this issue is purely mechanical it seems.

Mine did this too - My solution was to wrap the release tongue with several Zip ties to increase its protrusion into the hatch receiver to better release the lock pawl on the lock.

This has actually been working for 5 years now with no other changes!

See the photo - the black cable ties - go all the way around the lobe - with the joint out of the way at the back. You need decent strength small ones - with the smooth side out - cinch them up tight. I could probably have fitted 1-2 more on there... If I was doing it again I would.

Alan

jpitman2

Mike, Check for ANY slack in the linkage - it wont take much to reduce the travel of the trigger such that it wont work anymore.
jp 83 Euro S AT 50k