Sinking brake pedal

[AndyBaur]

As per a couple of other posts, I have a sinking brake pedal. The booster seems ok (pedal isn't heavy) & the brakes work fine in normal use.

I only noticed when I kept my foot on the brake on a steep downhill T-junction. In the safety of my driveway I experimented further. The pedal will go all the way to the floor under moderately heavy pressure but acts normal when released. There is no sign of a leak & the m/c reservoir level stays correct.

Is this a dodgy m/c or some other aspect of the system ?

[e21-Mark]

Master cylinder is most likely.

[Gazman]

Sounds like one of the two problems I have with my brakes. I believe this problem will be resolved with the master cylinder refurb and my heavy brake peddle, I think, is down to a faulty brake booster. There are some e21 master cylinders on eBay at the moment.

[AndyBaur]

There are some e21 master cylinders on eBay at the moment.

I think one of those might be the way forward.

The car spent 4 or 5 years languishing in a barn before I recommissioned it. I put new seals & pistons in the calipers & was wondering if the m/c would be ok. I need wonder no more.

The question is, how old are these m/c's - are the seals age hardened? Would a seal kit for my m/c be better? How much is a seal kit anyway?

[e21-Mark]

Cylinder seals hate not being used and nearly always fail once you start using them again. If the internal bore is OK and not scored etc, you should be able to get new seals from either main dealer, or any decent motor factors. Once you have bore size, rebuild kits can usually be found as the same cylinders get used in several cars.

http://www.powertrackbrakes.co.uk/wcylinder.html

[Jeroen]

One more to add to the Directory I guess!

[e21-Mark]

Scratch that. Powertrack no longer supply any e21 seals etc.

[Jeroen]

[AndyBaur]

Ok, priced a seal kit from BMW - £80 but on back order. W & N do the same part no. for the same price.

But what if the bore is rusty? This thread mentions a bore honer.

Obviously a new/reconditioned m/c would be better. W & N do a RHD one for £164.30 but we all know the issues with W & N quality.

Bigg Red's website is off-line at the moment.

Does anyone have any other recommendations? I'm starting to get desperate!

[e21-Mark]

You could try 07867 868899 as they were breaking a tidy 320. Or try www.pristinebodyworks.co.uk, Big Bavarian Beauties or Fritz bits for a used part? I'll have a look in my lock-up tomorrow, on the off chance I have an old one laying about you can have? It's certainly worth ringing Mick @ Pristine, as mine was replaced with a 535 item, so the original could be laying about?

If the bore of yours is rusty, wrap some similar sized dowel with emery cloth and spin in between the palms of your hands, to remove any surface corrosion. One removed, clean it out with fresh brake fluid, assemble the new seals and Robert's your Dads brother.

Final alternative is find an old style motorfactors and take them the cylinder, to see if they can match it to an alternative from another car. As I said before, I seem to recall a MK2 Golf one being similar? I think it has 4 outlets, instead of 2, but you can black off the extras with a couple of small bolts. Or maybe use the internals in your old cylinder? Most 20mm ATE twin outlet m/cyl would be worth a look I imagine?

[AndyBaur]

Thanks for the suggestions Mark.

With the idea of a Mk2 Golf m/c in mind I've been looking at the ATE website.

The E21 m/c is:

--- a 20.64mm bore, 3 port, Thread M10x1, Length 1: 18.8mm, Length 2: 162.5mm

Early Golf:
--- a 20.64mm bore, 4 port, Thread M10x1, Length 1: 32.4mm, Length 2: 114.9mm

Late Golf:
--- a 20.64mm bore, 4 port, Thread M10x1, Length 1: 35.4mm, Length 2: 109.7mm

I have no idea what the different 'lengths' mean - does it affect pedal travel or front/rear balance? I guess you could blank off one of the ports but which one? Easier going for a standard E21 m/c.

The appeal of a complete unit is not having to strip the old one down, just a straight swap over.

I'll call some of the people you mentioned.

[Gazman]

Fritz bits are getting my original master cylinder reconditioned with a stainless sleeve inserted, so no more rust in the bore in the future. I haven't got the master cylinder back yet or a final cost but Richard at Fritz bits thought it would be about £100 done ? Might be worth considering it ?

[AndyBaur]

Well I've had no luck in tracking down a seal kit from anyone but BMW.

I guess I'll pull the m/c off the car & strip to assess the condition of the bore.

Fitting a LHD m/c looks to be a bit of a faff but not impossible. I can't figure out why BMW felt the need to make LHD & RHD units when one would have done the job.

[cbear1288]

This may sound silly but have you searched your vin on real oem? Also is this any help?
http://www.ebay.com.au/itm/BMW-320-E21- ... e8c&_uhb=1

[cbear1288]

or this?
http://www.ebay.com.au/itm/34311156133- ... 422&_uhb=1