Brake light switch - have I got it right ?

[JohnboyLandy]

Hi All,

I recently reassembled the brake light switch that sits at the top of the pedal box, and I put the "lever" back how it was when I took it out, i.e. with the lever coming underneath where it swivels as opposed to coming out on top of where it swivels - can someone just confirm this is correct ?

Also, then switch itself could go into either hole, so which is correct out of these two photos, A or B ?
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Any and all help appreciated.

Thanks
John

[S3ute]

Hello from Brisbane.

The lever appears to be correctly fitted in your photos - i.e. correct orientation.

The switch usually fits in a single central hole on the top plate.

Not sure if that second hole has something to do with the later models that had the brake fail warning light. My truck hasn't got that feature but eventually will if that proves to be the case.

No doubt a genuine guru will come along with some better insight.

Cheers,

Neil

[JohnboyLandy]

Hi Neil,

Which of my pics looks more like the switch position you describe as "single central hole", my "A" pic or "B" pic ?

Thanks
John

[S3ute]

Hello again.

Photo B.

The brake pedal tower that I am fitting came off a 109” truck with single circuit brakes. The switch is fitted into a threaded hole in the centre of the top cover plate. This is the only hole in the cover.

I seem to recall reading somewhere that the two holed covers had something to do with dual circuit brake models. Could be wrong there, of course.

I also seem to recall an earlier post where it was suggested that the better alternative to screwing around with the top mounted switch is to fit the switch assembly from an earlier model Series 2A. This is mounted inside the driver’s footwell and directly operated by the foot pedal. Apparently less sensitive to adjustment and gives the option of fitting simpler but more reliable switches.

Cheers,

Neil

[S3ute]

Hello again.

Back for an equivocal answer on your original question.

I am in the process of fitting a dual circuit brake master cylinder in my 88” truck - where previously no such part resided. The brake tower that I am using came from a six cylinder truck that only had single circuit brakes. So, that top plate has just the one central hole for the switch.

Now, in my earlier response I mentioned that the top plate with two holes - as shown in your original post - might have had something to do with dual circuit brakes. Apparently correct from perusing the parts manual. The rotating plate that activates the switch is apparently also different because the two variants have different part numbers.

This is where the equivocation comes in - the diagram in the manual suggests the middle hole in fact has a blanking screw to seal it and the second hole closer to the edge likely takes the switch. The vagueness there is because it doesn’t actually show the switch and bugger knows why you would add a threaded hole and then plug it up...

Whatever, if the last bit is anywhere close to the truth then your photo A would be the correct one.

Cheers,

Neil

[JohnboyLandy]

Hi Neil,

I ended up installing the switch as per my picture B (near where the arm pivots). From what you describe, the manual is suggesting switch installation like my picture A, i.e. away from the level pivot.

I deduced that picture B was better, as you want to the switch to make contact early in the pedal movement range, and switches don't have a lot of mechanical movement in the plunger once they have made contact, but there's still quite a bit of range left in the pedal movement after the switch has made contact, and that needs to be catered for so the force applied to the pedal is not being applied to the switch plunger, and I figure that's why the lever is made from a springy steel, so it can flex for the remainder of the pedal movement after the switch plunger has reached the end of it's movement.

Putting the switch in the hole as per my Picture A, would restrict the amount of flex on the spring steel lever.

I hope my logic makes sense.

Cheers,
John

[S3ute]

Hi Neil,

I hope my logic makes sense.

Cheers,
John

John,

Hello again.

Probably nothing wrong with your logic.

My earlier comments were based purely on looking at a fairly incomplete picture in the Series 3 parts catalogue (1L 06 RHS). That illustration had the two hole plate for dual circuit brake models but didn't actually show the switch in it - so, had to infer where it might have been supposed to fit.

Had been hoping that a genuine guru might have emerged by now to set us both right.

Cheers,

Neil

[S3ute]

Hello again from Brisbane.

Following on from the previous sequence of posts I am keen to know the specific role of the threaded holes in the top plate on the pedal tower for trucks fitted with a servo and dual line brakes. The Series 3 parts manual shows this as a different part to that for single line models with two holes rather than a single hole. It also has a different part number for the switch activating lever.

I am presently installing a dual line system in my 88" and the pedal tower was sourced from a wreck that only had a single line circuit. After considering a few other threads on longevity and ease of maintaining brake switches I am inclined to install the switch activating set up from a Series 2A and not use the tower set up anyway. So, unless the second hole does something that is unrelated to activating the brake switch I will keep the single hole plate and plug it.

Any insights?

Cheers,

Neil