spongy brakes & used dot 5.1 fluid

[bmw9818]

quick question, recently when im driving my car my brakes are terrible, its the original 28year old master cylinder on there, so im replacing it as im hoping its that

basically my calipers are all brand new all four ends, new discs/ ebc pads lines are all good & ive got braided flexis cant see any obvious leak,

however just came across the wiki it says to not use dot 5.1 brake fluid as it can damage the seals?

when i refurbed the braking system i topped it up with dot 5.1 as i was going nurburg, didnt help a lot anyway tbh as my brakes failed after 4 minutes

but could the fluid have damaged the seals in the calipers? its been around 3 years since i went, i have been noticing fluid in the reservoir going down significantly as well,

[paultv]

It's an interesting question, can you use DOT 5 without issue?

Paul

[steve_k]

Strange one this is,

I've been using dot 5.1 for nearly 10yrs in both my e30 & my daily,

Never had any problems with I damaging the seals on either & never heard anything about not using it either,

Hopefully someone with a fair bit more knowledge See's this thread.

[arrisbmw]

i didn,t think you were suppose to use a modern silicon ? based product with 30 year old rubber seal.
I only ever use dot4 . I guess if everything is new including the master cylinder be o.k.
what spec does wiki say on here aways go by that......,,,,, hayne manul states sae j 1703 or dot 4.

[arrisbmw]

this may throw some light on the issue DOT 5.1, like DOT 3 and DOT 4, is a polyethylene glycol-based fluid (contrasted with DOT 5 which is silicone-based). Polyethylene glycol fluids are hygroscopic and will absorb water from the atmosphere, which is necessary to prevent sheer and undiluted water in the braking system,[citation needed] which is very corrosive. Water droplets can also freeze in the pipes, thus blocking the system

so looks like 5.1 is o.k as it just has a higher boiling point. than dot 4 . not sure about dot 5 though

[bmw9818]

Hmm I've changed my master and the brakes are still the same, takes a while to stop, plus there no obvious signs of leakage,

Assuming my servo has had it or one of the vac pipes

[arrisbmw]

you can test the servo. pump the pedal 5 times until it goes hard, start the car and the pedal should fall slightly showing the servo is o.k

[paultv]

Have you got ABS??

Paul

[bmw9818]

hmm i dunno, might be cause i hardly driven it in two years, literally done a 1000 miles from start of 2016 to this year april,

did lemans in it and some spirited driving later seems to be biting ok/ has improved but still a slight delay,
or might just be me!

but nah no abs in it

[ChrisHC]

My brakes felt very poor, eventually cured by adjusting the rod that runs across the car from the pedal to the master cylinder. This is what the wiki says:

Brake Pedal

The brake pedal forms part of the pedal box, and it may surprise you to know that it is how the brakes are activated by the driver. It is connected to the master cylinder through a pull rod, which can be adjusted to control pedal height. There's a small rubber buffer on the lowest part of the bracket that holds the brake light switch, and the rod should be shortened until the arm of the pedal all but touches this buffer.

To adjust the brake pedal, slacken off the lock nuts and turn the pull rod using a 7mm open-ended spanner on the flats near the clutch pedal to adjust, until the brake pedal only has a small bit of upwards free movement to its stop. One end of this rod has a reverse thread, so turning it changes its length.

Be careful though. If you over-tighten things, so that the pedal is touching the buffer and moving the master cylinder push rod, the brakes are likely to lock on.

[paultv]

Also DOT 5 is silicon and DOT 5.1 is Glycol with a higher boiling point (than DOT 4) and is non silicon.

I asked about the ABS as the pump unit is full of tiny fine filters which fill with crud, vastly reducing fluid flow as they block up. This is why ABS delete "appears" to improve braking.

This shows up as very hard to bleed calipers, extreme pressure required to get a dribble of fluid.


Paul