e38 brake fluid change, master cylinder

[richyb]

I am planning of renewing the brake fluid on the 740iL on Friday and I'm a bit concerned about creating master cylinder problems. Basically I think its been atleast a year and maybe even 2-3 years since the fluid was changed. Now I've chnaged brake fluid a dozen or so times but its always only been on vehicles with a year or less old fluid in it. I think it needs to be done but is it likely a fault will occur once the fresh fluid is in and what should I look out for? Is it just the usually spongey feeling or more serious? Any advice welcomed. Thanks.

[phelix]

Pardon my ignorance but is there something unusual about the E38's brake system?

[richyb]

No. Maybe I'm wrong but from doing some research online there are a lot of cases of master cylinders developing faults after fluid is changed when the old fluid has been in there a substancial period of time (3 years for example which maybe the case in my vehicle). Just looking for other peoples views on it?

[Mroad]

The only general problem I know of that can crop up on an old system is when the master cylinder seals no longer seal after a bleed.
It can happen when the pedal is pumped when bleeding and pushed down passed it's normal 'maximum' pedal travel limit. This means the seals in the master cylinder also go passed their normal travel limit and get 'roughed' up by normally untouched areas of the cylinder wall.
The answer is to either not to go mad on the pedal when bleeding (pumping quickly can also reverse the seals so should be avoided) or just use a pressure (e.g. Gunson Ezibleed) or vacuum bleeder (e.g. Mityvac).

[phelix]

I wouldn't wrry about the master cylinder - if it's marginal the problem will emerge sooner or later in any case.

My suggestion is to use a Gunson Eezi-bleed but don't put fluid into the bottle - just use it to pressurise the MC. You need to keep a close eye on the level but it saves the cleanup and greatly reduces the potential for spraying brake fluid all over the place.

[Stu R]

Just did mine last week, can't say I had any problems and it'd obviously been in there a while, judging by the colour. Last reciept & stamp was a smidgen over 2 years back.

[richyb]

I'm using a eezi-bleed as opposed to the two man set up. I'll give it a bash and let you all know how I get on. I'm doing the pads all round, oil and filter, rear diff oil and fuel filter as well if I have time. Just hoping the weather is going to stay nice for Friday.

[Stu R]

We should go halves on an E38 only garage Rich!! I've got all the same jobs on the hitlist, some complete, some left to do, with the fuel filter, diff oil, gearbox oil, all the filters and so on getting done this week. Gearbox sounds like fun, 7.5 litre capacity!

E-z-bleed kits don't half make it a lot easier.

Once that lot is out of the way the real fun begins

[richyb]

Stu R said:

We should go halves on an E38 only garage Rich!! I've got all the same jobs on the hitlist, some complete, some left to do, with the fuel filter, diff oil, gearbox oil, all the filters and so on getting done this week. Gearbox sounds like fun, 7.5 litre capacity!

E-z-bleed kits don't half make it a lot easier.

Once that lot is out of the way the real fun begins

Tis a shame there is a few hours drive between us or we could have had a few E38 task days. I've looked into the transmission fluid change but its still something I'm not confident about yet. I was thinking about doing some suspension work at some point too, probably traction struts and wishbones up front and wishbones at the back. Ideally want to get some standard E38 wheels on it first. I really want to find some original 16" if possible but they are hard to source. 2 new PDC sensors, rear diff, oil and filter, fuel filter, new pads and fluid is the plan for Friday.