• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

BN1 Mechanical Brake Switch

Share this page

A

Adelaide

Freshman Member
Country flag
Offline
I have a 1953 BN1 that I rebuilt over 12 years and have had on the road since 2002. I have used silicone brake fluid since I rebuilt the car and I have had no problems other than having to replace the hydraulic brake switch several times as it requires significant pressure on the brake pedal to activate the lights.

This appears to be a common problem with hydraulic brake switches when using silicone brake fluid.

I would like to fit a mechanical brake switch but it is not a simple job as unlike the six cylinder models, on the BN1 the brake pedal pivots on a shaft under the floor.

Has anyone fitted a mechanical brake switch to a BN1 or BN2 and if so what sort of switch did you use and how did you fit it?
 
Adelaide said:
I have a 1953 BN1 that I rebuilt over 12 years and have had on the road since 2002. I have used silicone brake fluid since I rebuilt the car and I have had no problems other than having to replace the hydraulic brake switch several times as it requires significant pressure on the brake pedal to activate the lights.

This appears to be a common problem with hydraulic brake switches when using silicone brake fluid.

I would like to fit a mechanical brake switch but it is not a simple job as unlike the six cylinder models, on the BN1 the brake pedal pivots on a shaft under the floor.

Has anyone fitted a mechanical brake switch to a BN1 or BN2 and if so what sort of switch did you use and how did you fit it?
Click to expand...
I've had the same experience with ester-based (non-silicone) fluids and I believe the problem is inherent in the nature of pressure switches: the membrane through which pressure is exerted simply hardens up with age and as time goes on becomes less and less pressure-sensitive.
 
Could one like this be used? Fits under floor.
Hella Brake sw.jpg


Danny
 
Thank you Michael and Danny for your responses.

Michael I suspect that you are right about the membrane in the hydraulic switches as I have had to replace them regularly and they seem to work alright for a while and then you have to stand on the brakes to make the light come on. I think a mechanical switch would solve the problem as I am never quite sure if the lights are working or not.

Danny I have a similar switch on my BSA Golden Flash and thought I could use a similar one on the Healey. The problem is that switch has a pull action and the brake pedal under the floor pushes forward from the footwell floor and there does not seem to be any room behind it to fit a switch. If I fit a push-in switch in front of the pedal it is very exposed to the elements.

I was just wondering if anyone had managed to fit something that was effective and neat.

Cheers Jock
 
As you can perhaps see from my owned vehicles I vintage race (the Elva and the Ginetta). Before each race all cars must pass tech and one of the things they check for is brake lights. Yet it is very common for me to see cars whose brake lights are not working on the track and that is because when they go thru tech they stand on the pedal and the lights come on, whereas in normal braking with moderate pedal the switch does not close. I regard the pressure switches as maintenance items to be changed annually on all my cars.
 
Hi Michael. As I am at a bit of a loss on how to neatly and effectively fit a mechanical switch to my Austin Healey BN1, I think I will have to do the same as you and make changing the hydraulic switch an annual maintenance job. I have searched numerous websites and forums and although fitting a mechanical switch to the later six cylinder models is a common modification, nobody seems to have come up with a modification for the 4 cylinder models with the under floor mounted pedals.

Thanks for your input. Cheers Jock
 
Crusin' thru the photos banner I recognized the switch Danny suggested. Same one is used on early (pre-1968) Lotus Elan headlight pods to turn 'em on when the pods are fully "up". With a floor mounted pedal box it would likely not be a good alternative. Could a pedal extension to trip a N.C. micro-switch be something better? Bracket under dash to hold the switch in place, extension on the pedal to detent the thing when in the 'brakes off" position? Just thinkin' aloud.
 
I have thought about installing a mechanical switch under the dash with some sort of bracket attached to the brake pedal but have not yet come up with anything that is neat and effective.
i may have found a solution by using an early model Harley Davidson hydraulic switch. It has the right thread to fit the Healey and I am told that silicone brake fluid is commonly used in older Harleys in the USA.
I have acquired a Harley switch that I will fit when I get home from an extended camping trip and will post the results when I have tested it out.
Cheers Jock
 
I know this is an old thread but I think I may have solved my problem and thought it may be useful to share the results of my research.

Just to reiterate, my problem was that I had experienced difficulty in sourcing a hydraulic brake switch for my 1953 Austin Healey BN1 that could be used with silicone brake fluid. Although Hella make a switch that fits, they advise that the switches are unsuitable for use with silicone based brake fluid. I have used these switches in the past but it would appear that the silicone makes the diaphragm go hard which results in the need for excessive pedal force before the brake light comes on. In the past I have had to replace the switches at regular intervals to maintain acceptable brake light performance.

After exhaustive research, I have found a Harley Davidson hydraulic brake switch that neatly fits the Healey and I understand could be resistant to silicone brake fluid. Although Harley Davidson do not specifically claim that the switch is silicone compatible, I have been led to believe that silicone brake fluid is widely used in Harleys in America so I am hoping that they will last much longer on the Healey.

The switches have the correct thread (1/8" x 27 NPT male thread) and blade terminals for the Healey but are a little smaller than the Hella models. The part number is HD72023-51 and they suit the 1971 - 2007 Big Twin and the 1979 - 2003 Sportster Harley Davidson models.

I guess only time will tell if it lasts the distance but they are easy to fit a relatively inexpensive.
 
Jock, I appreciate your problem but I donā€™t think it is caused by the silicone brake fluid. I have had silicone brake fluid in my BJ7 for about 15 years and have never had to change the brake switch. Maybe a new source for the switch might solve it.
A small joke I tell people when they tease me about Lucas electrics. I tell them it canā€™t be Lucas electrics, when I restored this car all the parts came from China.
 
Hi Vette. I'm pretty sure it is the switch as the operation of the brake lights improves dramatically when I first replace the switch and besides, Hella say their switch is not compatible with silicone.

Do you know what brand of switch you used when you restored your BJ7 some 15 years ago? If it came from China the material they use for the diaphragm may be silicone friendly!
 
I would have suspected that most diaphragms would benefit from silicone.
I will look for a receipt of course 15 years can certainly change a manufacturing process.
 
I'd be willing to bet that some of us who think our brake switches are just fine would be surprised to see how things are actually functioning--that is, when we apply pressure to the brake pedal in a real-life gradual manner rather than when we stomp on the pedal while in the garage to test their function. Silicon or esther, the issue is the membrane's losing its elasticity, etc. etc. See my post #5.
 
FWIW, many years and miles ago I replaced the M/C in my BJ8. The new cylinder came with a label stating: "Warranty void if silicone brake fluid used." I installed it and topped-up the reservoir and bled with my usual DoT5. It's worked fine ever since (prob 10yrs/50K miles). There seems to be a "we have to use what they used in 1967" mentality--justified in rare instances--with fluids; I've had some interesting conversations with owners over "you gotta use straight-weight, non-detergent 30W motor oil in the gearboxes," even had to show them the later manuals that 'authorized' 20W-50 motor oil (showing that even BMC could change with the times). I've used MT-90 in both my gearboxes/ODs, and their operation subjectively improved (yes, it's a little harder to contain it). Same with points, even though electronic points--e.g. Pertronix--perform better and require zero maintenance (and it's getting harder to find quality points). Do the concours judges look under distributor caps?

Silicone fluid got a bad rap early on--even Norman Nock reversed his position--but I think the formulations were improved over time. My BN2 has DoT3/4 in it, because my dad insisted on it, and I've had lots of issues--mainly gelling--with it.
 
vette said:
I would have suspected that most diaphragms would benefit from silicone.
I will look for a receipt of course 15 years can certainly change a manufacturing process.
Click to expand...
There is also a small, but non-zero chance of DoT3/4--it's flammable, DoT5 isn't (under normal conditions)--igniting if it comes into contact with the electrical components in the switch. A few years ago there were some instances of fires in Ford Rangers and Explorers caused by the switch in the M/C that disengages cruise control when brakes are applied cracking and coming into contact with the BF (at least one house was burned to the ground; fortunately the family dog alerted the sleeping family to the smoke). I think there was a recall, but I never received a notice for my '96 Ranger; it gets parked outside because there's no room in the garage or carport anyway.
 
Last edited:
John Turney said:
DOT 5 will burn if exposed to hot exhaust gas, like a unsealed seam in a header pipe.
Click to expand...
Well I suppose thatā€™s another good reason to make sure your hydraulic system is leak free, besides the want for brakes.šŸ˜
 
Back
Top