1974 R90/6 Brake Failure Light

[DRRAOULDUKE]

Pulled my 1974 R90/6 out of the shed today. Started right up and everything seemed okay except my brake failure light is on. Rode through my subdivision for about three miles, front and rear brakes both work??? I tried doing a search under airheads for "brake failure light" and got a Brazilian hits on every variety, year, and model of BMW bike before posting here. I would love to hear thoguhts/ideas/suggestions from those more technically proficient than me on what could be causing this.

Thanks in Advance,

 

[manicmechanic]

Check the fluid level in the brake reservoir under the fuel tank.

 

[DRRAOULDUKE]

Will do

Thank you very mcuh for your reply

 

[PGlaves]

People might ask themselves, "Why is there a wire connected to the lid on my master cylinder, under the tank?" Or, "What is that brownish white thing that dangles from that lid?"

The answers are that the white thing is a float and the wire connects to a switch that causes the warning light to glow when the brake fluid level is low.

 

[dennisdarrow]

The next thing to check is where did the fluid go????..........Check out the frame tube under the MC and the relays etc........That fluid had to go somewhere and the typical thing that happens is a seal has bit the dust......God bless.......Dennis

 

[DRRAOULDUKE]

All good ideas - thank you-what Brake fluid would you recommend

Is any of the newer synthetic stuff better than the original OEM?

Kind Regards,

 

[PGlaves]

Is any of the newer synthetic stuff better than the original OEM?

Kind Regards,

All brake fluid is synthetic. The term is marketing hype. Use ONLY DOT 4 fluid, Not 3, not 5.

 

[DRRAOULDUKE]

Seal Replacement

The next thing to check is where did the fluid go????..........Check out the frame tube under the MC and the relays etc........That fluid had to go somewhere and the typical thing that happens is a seal has bit the dust......God bless.......Dennis

How difficult is it to replace these seals? Want to get it accomplished before our riding season ends in Northern IL

TIA,

 

[dennisdarrow]

For some, like me, it's a pain to get those seal in the master cylinder right. Others do it with no problem. You can get a master cylinder rebuild kit from your dealer that includes the seals and a new piston. Lots of threads about doing this or even some Utube stuff. Do hone the cylinder.....I never got it right so I ended up sending off the master cylinder to a fella who rebuilds them. That was 2 years ago maybe 3, and no problems. That cost perhaps $100 VS $400 for a new MC...........Good luck in getting it done before the snow flies.......Dennis

 

[brook.reams]

MC Seal Replacement

How difficult is it to replace these seals? Want to get it accomplished before our riding season ends in Northern IL

TIA,

Here is a link to a write-up I posted when I rebuilt mine.

• 34 BMW R75/6 Rebuild Master Cylinder & Disk Caliper

I hope this helps. It's not hard to do this job, but there are a number of small parts and the instructions, and particularly the diagrams, that come with the rebuild kit are useless which is one reason I documented what I did. The other is I like documenting what I work on so next time I don't have to think too much

Best.
Brook Reams.

 

[lkchris]

It's not a brake failure light--it's a low brake fluid light.

Obviously if the level is low enough the brakes won't work ... a failure.

But, it's not any indication that pads are worn, master cylinder doesn't function properly or anything except fluid level.

This light is there because the master cylinder is out of sight hidden under the gas tank.

When BMW changed and mounted the master cylinder on the handlebar, the light was deleted.