BN1 - Questions about tracing overdrive faults

[matt78]

Hi.

I'm currently trying to understand what's happening in my new (for me...) BN1, esp. regarding overdrive.

Since I bought it, OD has been out of service, and I think that it is linked to an electrical issue (blown fuse). I've checked the throttle switch and the two relays R1 and R2 w/o finding any fault, but when it went to two other components, it wasn't the same fun :

1) top gear switch (on the 'box) : whatever the gear lever's position - 2nd, 3rd, as for any of neutral, 1st or reverse - there's no contact between the two terminals, so I conclude that the switch is always open and therefore faulty --> Am I correct ?

2) OD solenoid : it doesn't react when directly feeded by 12V between its wire and its body (except sparks at the junction...), and offers the same resistance (i.e. none) with the plunger in low or high position, so I conclude that one of its internal windings is shorted/grounded --> Correct ?

3) I also guess that in this case, it could be the cause of the fuse blowing, still correct ?

In addition, during these tests I noticed 2 other curious fittings :

4) on the right side of the OD, there is some slack (rotation) between the lever used for valve setting and the shaft, because (I think) the split pin securing it is of too small diameter. I suppose that matters for a centering use, right ?

5) on the left side, there's no stop screw under the operating lever (actuated by the solenoid plunger) : I'll try to fit one, but is there any chance that it might have caused an issue in the OD operation ?

Sorry for all these - maybe stupid - questions, but I'm in a fix...
Thank you in advance for your help.

Matt

 

[Healey 100]

Matt:

These are all great questions, I can offer a few of the answers:

The 2-3 contacts should definitely be closed when the gearshift is in second or third gear. I have defeated this switch on my car by simply shorting the wires together to bypass it. You may be able to repair it by adjusting the plunger but the switch is not really designed to be serviced and they are hard to find. Fortunately, this switch is not essential to have a functional OD. You do have to be careful if you stop and reverse the car with the OD engaged as the OD cannot be reversed when engaged and doing so may damage it.

The solenoid should have very low resistance (way less than 1 ohm) with plunger out and much more (10 ohms) with the plunger in. There is a tiny contact in the top of the solenoid that opens to switch off the low resistance pull-in coil. If this contact isn't working (stuck closed) you can blow fuses -- the low resistance coil draws lots of current and normally only operates for an instant when the od first engages. Or, if either coil is shorted the solenoid will not engage and will draw lots off current. Fortunately there are now reasonably priced repro solenoids available from the usual sources. Sounds like you may need one.

Since you have the doghouse over the transmission off, I suggest you drive the car up to about 30 mph and manually actuate the OD by rotating that external lever on the right side of the OD, just to make sure the unit is working OK mechanically. If not, adjust all the stops and linkage until it definitely engages. Be careful to not get wound up in that spinning driveshaft!

Good luck, hope this is helpful.

 

[EV2239]

Solenoids do fail fairly frequently, or that was my experience when we used these cars as regular transport back in the sixties.

 

[MikeAH100M]

When it comes to OD issues, I always refer to Norman Nock's 12 or so articles in the Tech Talk book available from British Car Specialists. Great step-by-step troubleshooting and correction. www.BritishCarSpecialists.com

 

[PHulst]

My overdrive didn't work because the bushing in my shifter wore out, and the end of the shaft didn't move the lever over enough to depress the top switch inside the transmission.
I know that's a long shot, but easy to tell if you remove the shifter and verify that all is well with the shift rod itself and the control lever inside the transmission.

 

[matt78]

Thank you all for your answers.
Today, I bought a new solenoid (its plunger seems to be of one piece, w/o any possible adjustment ?!?), and a new top switch - hope my shifter isn't faulty as PHulst one !
Regarding this switch, there is no washer fitted underside (previous "mecchanics" put some silicone paste...) : I guess I should use the isolated washer # 866-295 pictured in the Moss catalogue (for example) for adjustment purpose, but still don't understand why - is the stroke of the rod such a small one as to necessitate so fine a tuning ?
I'm leaving for a biztrip, so could only do the job on next W.E. I'll keep you posted :joyous:

 

[PHulst]

I believe that the washer is just to make future removal easier, as well as prevent any oil from seeping out when the transmission is active.

 

[glemon]

As I recall you don't adjust the solenoid movement, you adjust the rod an lever the solenoid moves for a set range of movement, the adjustment is in the manual. There is also a cool little centrifugal switch in the system, you have to over a certain speed for the overdrive to turn on, then another switch measures throttle and won't let you turn it off without being on the gas a bit. The centrifugal switch is pretty reliable, but thought I would mention these other possible sourges of electrical failure. Knock on wood, I have never had a mechanical failure with a Laycock overdrive, but have had many electrical ones. Luckily those are the cheaper and easier fixes (once diagnosed, the figuring it out part can often be a PITA).

 

[busybrit]

The first thing I do when an overdrive isn't working is check the oil. But it sounds like you have a direction of attack which is electrical, as some of your components sound faulty to start with. One thing I also do to trouble shoot the system is to drive the car with the tunnel off and have my son manually move the lever on the right side to turn the overdrive on, but be careful doing this, make sure you're moving forward.

 

[matt78]

I'm back, with facts and... new questions

Following all your advices:
1) I manually tested the OD by actuating the lever when driving the car : everything was OK, OD going in and out perfectly (important relief...),
2) I replaced the burnt solenoid, set the lever and fitted the missing stop screw at the bottom. Having shorted the centrifugal switch in order to test the system with the car at rest in my garage, I tested the whole system and simulated the different events : the solenoid behaved as expected, taking into account the events (shifting out of 2nd or 3rd, throttle action...) --> OK (didn't drive the car, but there was no more blowing fuse, so I suppose that this problem, at least, is solved)
3) tonight, I replaced the gearbox switch that was actually faulty (quite surprising to have 2 faulty elements : the switch AND the solenoid...), and tested again all the system.
Unfortunately, the switch is now effective, ** BUT ** only when in 2nd or 3rd gear I keep pulling the gear lever to the left, beyond its normal position, as if something was worn as described by PHulst :mad-new:

So, here are the questions :
a) where may I find a picture of the mechanism inside the gear box which actuates the switch ? Can't understand how it works, because on the exploded view of the parts catalogue, I can't see the control lever PHulst is talking about...
b) The washer sealing the switch to the case is rather thin, and I wonder how I could get a thinner one to shim the switch - and if it would be enough, thinking to the rather long travel of the gear lever knob required to get the switch on...
So, is there any way to put an additionnal part between the switch mobile part and the control lever, in order to "shim" it and compensate the slack ? I'm especially thinking about this short additionnal part falling into the casing, causing a huge mess...

I'm not really confident in leaving the gearbox switch shorted, and relying only on the centrifugal one to avoid any damage to the OD (even if a speed test would theorically prevent shifting into reverse...), but I don't really want to undertake a transmission out job...

Thank you again for your replies.

 

[British_Recovery]

See if you can get the switch to go deeper into the mounting on the gearbox. I believe the cross shaft ( part 17 in the parts manual ) pushes against the ball on the switch.
Bob

 

[matt78]

Already checked this point : today, I fitted the switch without any seal, and it wasn't deep enough because I still needed to pull the lever in order for the switch to be actuated.
I thought that I might get the switch basis machined, so it could go deeper inside the gearbox. Therefore, I dismantled the faulty previous switch to measure its inner thickness. Unfortunately, there's not enough material left for machining it :-(

Do you know of another type of switch with a deeper contact ? I'm really fed up with the single idea to dismantle the gearbox...
If there's no other way, I'll left it electrically shorted and will rely only on the centrifugal switch, but it isn't 100 % safe against shifting rearward...

 

[oxford]

Hi
I don't know all that much about BN1s as I own a BN4, but shouldn't the overdrive only work in 2nd and 3rd gears?
Matthew

 

[British_Recovery]

Refer to the service manual for initial gearbox tear down instructions. You should be able to determine wear on the parts without removing it from the car. Shift lever removal is the first thing. Then drain the oil, if you think the gear lever control box can be removed in place. This should expose the cross shaft socket lever, which might be worn.
Good luck,
Bob

 

[matt78]

Thank you for this information.
I had a look this afternoon, but the control box seems to be definitely too close from the chassis member : I think I won't be able to move it far enough on its left side to clear from the cross shaft and the gear lever socket... did anybody already succeed in doing this ?

I suppose that when this kind of issue happens (gear box not activated in 2nd or 3rd ratio), the culprit is the wear of this gear lever socket ? Or is it combined with gear lever's wear, so that the two need replacement - more logical from a mechanical point of view, maybe ? Don't even know if they can be sourced.

 

[pan]

Disconnect the rear mounts, then the transmission can be raised with a jack enough to allow removal of the gear change housing.

 

[matt78]

Thank you all for your help.
Having had a look at the prices and availability of some parts like the gear lever socket, I'll first try to keep doing without the gear switch - relying only on the centrifugal switch and my awareness.
Should I be brave, I'll use the Pan's trick to extract the housing and go further.

Matt