Brake switch replacement- help please

I need to replace the brake pressure switch on a morris 1000. I seem to recall somewhere reading that if the front of the car is elevated then the switch can be replace without bleeding the system. I would be very grateful for advice as to whether this is a practical and safe short cut or a dangerous false recollection.

Many thanks Jonathan

I need to replace the brake pressure switch on a morris 1000. I seem to recall somewhere reading that if the front of the car is elevated then the switch can be replace without bleeding the system. I would be very grateful for advice as to whether this is a practical and safe short cut or a dangerous false recollection.

Many thanks Jonathan

Sounds absolutely bloody stupid to me. When you take the switch out there's nothing between a normally sealed system and fresh air. I'm sure if you're incredibly careful you could manage it, but it's the sort of thing where saving half an hour bleeding the system isn't worth the risk of not getting it right, IMO.

I can think of a safer way of doing it, but I'm not going to advise anyone to do something potentially lethal.

Use this as an opportunity to renew the fluid :)

If the fluid is dribbling out then no air will get in, with the new switch in it can be used as a bleed nipple you can then check for any air bubbles coming out with an assistant pushing the pedal, if the pedal still feels good afterwards then it will be ok.

mrcheerful

"mrcheerful ." realised it was Sun, 28 Aug 2005 20:52:05 GMT and decided it was time to write:

Fluid dribbling out must be replaced with something. Most probably air.

It'll be draining through from the master. But the point is, getting the new switch in without trapping air under it might be a problem, making sure the whole of the hole is full of fluid (and not diagonal as the car is at an angle) might be a problem, and really why cut corners like this?

Chances are, if the OP wants to avoid bleeding thebrakes to fit a switch, then they may not have been bled recently anyway. So now presents a perfect opportunity to do so and get the old cruddy fluid out the system. Or at least it's a chance to bleed the front system, there should be no need to do the rears provided the fluid doesn't run low (bit of plastic over the filler cap will help there).

In the event of any work to the braking system hydraulics it is simply foolhardiness NOT to do a full bleed on the entire system. If there's one thing you want to be 100% sure of on a car, it's brakes.

Alex

But since many people do more damage working on their car, why give them at least 3 or 4 points to strip threads etc.

Although fluid dribbles out when the switch is removed, it does so because gravity is pulling the fluid out, the fluid is being replaced from the master cylinder reservoir, once that is empty fluid will enter the system, not before. It is quite easy to change master cylinders in the same way.

mrcheerful

I have never owned a Minor, so can't be sure, but don't the pedals pivot under the floor rather than from the bulkhead like most cars? This suggests that the master cylinder is under the floor (like the Triumph Mayflower) and is lower than the brake light switch. I can't see how leakage can be replenished from the master cylinder under those conditions.

Jim

I can't remember minors very well either, but if it has a remote reservoir that will be higher, or a remote reservoir can be rigged using an old cap and some tubing. I fully agree that the nice way to do this job is drain the system, change the switch, fill and bleed, however many people are scared of that and look for ways round.

Thinking back, did they have the reservoirs under the floor carpet?

mrcheerful

Absolutely correct. The master cylinder is under the floor with an access point under the carpet. Ingenious but exposed to road dirt and a PITA to service (though the latter applies to most brake cylinders anyway ;-)

Jonathan ( snipped-for-privacy@aol.com) gurgled happily, sounding much like they were saying :

Why on earth would you want to?

It's not exposed to road dirt. It's enclosed in the box section that carries the engine mounts, and front suspension etc. Mike.

My mistake. I've not done anything to mine, couldn't be bothered to crawl under the car to check, just reached for the manual... I'll check better next time!

many thanks for your advice.

Jonathan