BW35 Gear Box Inhibitor Switch Fault

[johngilroy]

Hi Guys, I have a Stag with BW35 gear box which will only start in the driven gears i.e. 1, 2 & D. When its in neutral and park the starter motor will not operate, the reversing lights are also off, this is leading me to believe that the inhibitor switch is faulty and needs replacing. Its obviously not very safe to start the car in 1, 2 & D position as you need to keep your foot on the foot brake and knock it into neutral as soon as it starts. I've removed the access panel on the passenger side foot well and its obviously very tight to work in this area. Can anyone give me guidance on how to fit & set up a new switch? Any help would be gratefully received.

[DJT]

Hi, and welcome.

The test and setup procedure is described in th Repair Operations Manual Section 44.15.14. Just ignore all the preamble about lowering the 'box, etc. You can start at step 9 and carry out the operation through the inspection cover. Not easy, but doable and saves a heap of work.

If you don't have one, you can download an early version of the ROM here: http://www.grampianstags.net/restorations.htm

[rwdstag]

At least it’s not a type 65 I just paid £80 for one ouch
easy to change though

[wilf]

I recently did this very job.

My inhibitor switch had fallen apart - the swaging of the ally base had "released" the bakelite top part. Took a while of intermittent operation before it finally failed. (switch basically fell in two halves)

Had to rebuild the switch, then carefully work out the motion involved and adjust it - under an hour in total, through the access panel in the transmission tunnel.

Tip - put the bare base, with the operating pin in it, back onto the 'box, then move the gear lever around while feeling how the pin moves, to work out the motion involved, it really helps, when coming to adjust it, to have a clear mental picture of which contacts are being made and when.

Also take a good note of which contacts work the reversing lights and which the starter, as if you get them the wrong way around you will ever adjust the switch successfully.

Forgot to say - if your switch is Fubar, then you can get new ones, but use the old one as I suggested to understand how the mechanism works.

[SteveD]

My inhibitor switch and reversing lights didn't work but I could start the car in park or neutral. I got a new switch from LD parts. The one had the plunger bit stuck down where the aluminium threaded part had worn. I put the new switch in and undid it until the reversing lights worked having previously worked out which contacts did the reversing lights. Now the reversing lights work but the inhibitor part is still not working. Any ideas please?.

[wilf]

Sure you have the right connection for the reversing lights?

And I would suggest it still is not adjusted correctly.

[SteveD]

Sure you have the right connection for the reversing lights?

And I would suggest it still is not adjusted correctly.

The reversing lights only come on when reverse is selected.

Is the inhibitor switch wiring an open/break or closed/make connection when in gear so I can test the wiring off the switch to make sure it's not been messed about with?

[StagJonno]

Inhibitor switch contacts are closed when P or N; open when in gear, according to my Mk2 wiring diagram.

Jonno

[wilf]

As you push the operating plunger into the switch, it "makes" first one, then the other, set of contacts. The "height" of the cam that pushes the switch plunger upwards is different for P/N and R. That is how the switch "knows" what contacts to "make".

I simply can't recall which are which, but the fact that your reversing lights come on when the selector is at "R" does not automatically mean the switch is properly adjusted, nor that you have the right pair of contacts selected for the reversing lights. You could try the other pair of contacts and see if the lights come on in P and N.

[thebadleys]

Is this diagram of any assistance in this issue.

BW35 Inhibitor Switch.jpeg

Nigel

[sujitroy]

I have a BW35 and never could get that switch right. It was a pain to do from that hole in the tunnel. In my case, my Stag starts in N and P and D.( can be hairy in D) The reverse lights worked when the shifter was in reverse but now the lights only go on when shifting between Park and Reverse.

I'll get to it some day.

Sujit

[wilf]

Nigel - that diagram really helps.