Inhibitor switch stopping reverse engagement?

Philippe Holland

Philippe Holland

Member
Hello, I've been having problems engaging reverse with my BW35 auto and thought it was a gear lever/rod adjustment problem because the gear lever bush was shot and there was a lot of slack. I've changed the lever mechanism but still no reverse. All the other gears engage with a positive click except reverse.
When I put the car 'in reverse' with the ignition on the reverse lights do not light up.
How much gear engagement responsability does the inhibitor switch have? Could this be the source of my problems? It seems to have a pretty good coating of oil on it....but £76+ for a new one....ouch!
Any ideas out there?
Many thanks, Philippe
 
I doubt the inhibitor switch will cause failure of reverse, if you've sorted the linkage, check the fluid level, and if this is correct, do a road test and see if you have lost any other gears.
The inhibitor switch only interrupts the starter circuit and operates the reverse lights. If the starter only works in park or neutral, that part of the switch is ok.
As for the switch, if req'd, try a s/h one, they don't give many problems.
 
I thought it was a long shot! Strangely enough when trying to engage reverse there is a lot of travel between D and P where reverse should be and there is not a definite 'click' at the lever or 'thunk' in the box, as when the other gears engage.
It looks like my last minute used gearbox find from Beaulieu is about to go in!
 
If both park and drive engage it can't be a linkage problem, because reverse can only be between those two. It will be an internal fault.
As a matter of interest what series number of gearbox have you bought?
 
The old box has serious signs of gasket sealent around the filter pan as well as around the drain plug, so maybe something was amiss and badly repaired and/or the plug thread stripped...
How long should a good amateur need for a box swop providing there are no rusty exhaust bolts etc to deal with?
 
Sorry mate, that's one thing I can't help you with. Take your time, don't rush it and take as long as it takes.
The exhausts can be the most time consuming bit of the whole job. That's why I used to like doing them on the P5B, no exhaust to worry about :)
 
It's only the down pipe nuts that give real problems, where the front pipes join the centre box are easy to cut off. Buy your self some brass nuts to put back and kiss those troubles goodbye in the future!
 
Years ago I saw a BW 35 box where a roll pin had broken in the internal selector mechanism and that caused gear selection problems
 
That problem won't cause the symptoms Philippe has. With reference to the selector mills pin snapping inside the gearbox, this was the subject of a recall on the 65 box fitted to the SD1, and when it failed it allowed the car to be started in gear even tho' the selector was in park or neutral. Not to be recommended!
 
Before you start changing boxes, see if you can find a BW service manual, I think Haynes used to produce one some time ago. The problem you describe sounds like a fault in the valve block or in a mechanical part of the selector mechanism rather than a fault in the transmission itself. Although not much broadcasted over here, in the US where auto trans is the norm, many of this type of fault can be rectified by a competant home mechanic without removing the box from the car.
 
As I suggested earlier, a road test to see whether top gear is faulty as well will tell you a lot more. If it's reverse only it's worth taking the sump off because it will be a rear band related fault which you stand more chance of curing without removing the box. Top and reverse points to rear clutch and is less likely to be curable with the box in situ. I think the box in question has already had someone who doesn't know what they're doing messing with it, so may be better to cut your losses and fit another box. (although personally I'd never fit a s/h box of unknown quality, most of the people that sell them say it is a good box when they wouldn't know a what a good box is, as they havn't got the knowledge to recognise faults that are developing)
 
If everything goes ok you should do the job in a day - it took me around 4-5 hours but the exhaust did come off easy... you can do the job up on ramps (the drive on kind)
I'm not that sure if this will help but try to get a factory workshop manual before you start, as it may be something you can fix (not being following all the thread so if you've already had the sump and valve chest out and cleaned it sorry!) without swapping...
 
OK, its time to get serious here...I've soaked all visible nuts and bolts with WD40 and swept the garage floor...coffee, music and a good buddy on standby...so will get the hands dirty at the weekend.
If it all goes well, there will be plenty of beer drunk in the evening...if it all goes badly there will be plenty of beer drunk.....

Funnily enough, the official workshop manual does not mention adjusting the rear band, but the BW manual that I downloaded does..

A roadtest is out of question to test all the gears due to a faulty brake servo...Parisians kindly leave a maximum of 10cm when they cut into your 'safety zone' and I do not fancy stuffing 'Enzo' up the back of a yacking 'Petasse' Clio driver on her mobile phone...
Anyhow, if my new used box is no good atleast the manifold bolts will be easy to undo again!

Or maybe I should do that final road test?..I think I'll watch 'Lock Stock and two smoking barrels' first though just to get into the mood...just incase a moron cuts me up!

Wish me luck gents
 
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