W123 Brake fluid change - anything to look out for?

[neilrr]

Tomorrow I'm changing the brake fluid on my '82 230E. I've never done it before & wonder if anyone who has can tell me if there's anything to watch out for, or, is there an order in which it's done.

Any tips most welcome please.

TIA.

 

[bolide]

I'd start with the n/s/r wheel (assuming it's a RHD car) and try and gravity bleed it. Clean & remove the brake fluid reservoir cap, check the fluid level & top up if necessary. Then clean & open the bleed nipple slightly with a length of hose attached and see if brake fluid starts running out. If it does, get your assistant to top up the reservoir continuously until you see nice, new brake fluid running out. Then do o/s/r, n/s/f and o/s/f

Check the front calipers to see if they have multiple bleed nipples. If they do, do the uppermost ones first

The reason to gravity bleed, and not pump the pedal, is that on some cars you introduce air into the servo & ABS and it tends not to come out again. If it won't gravity bleed I'd get an expert to do it with a pressure bleeder

Once you're done, and the pedal has hopefully returned, adjust the handbrake. I assume the W123 has rear discs. If it does the handbrake adjustment won't affect the pedal. If it has drums it will

If your reason to change the brake fluid is a soft pedal then you may have a leak, bad servo or bad master cylinder (or any combination thereof) and I wouldn't assume bleeding will cure the problem. In fact I wouldn't assume anything at all with brakes, particularly on a heavy car like a W123. Finally I'd have all four wheels off before you start and have a good look for fluid leaks. Once you start bleeding you won't know if the fluid round the nipple is from a leak or from bleeding, so check them all first

That's how I'd approach it, but then I normally get experts to do it for me. Hopefully some of them will chime in and correct any mistakes in my plan!

Nick Froome
www.w124.co.uk

 

[nickmann]

You can get a pressure bleeder for about £20 or so. You use the pressure in one of your tyres, perhaps the spare, to power it. It makes for a quick and easy job. If you go this route just check the working pressure for the device and drop the pressure in your tyre accordingly.

 

[grober]

Flexible brake pipes

The other thing to check for on a car of that age is that the flexible brake pipes are in good nick, dont look damaged or perished. If the car's been looked after they may well have been replaced at some point. If the pedal is spongy as bolide has said you can sometimes track down the location of the problem by isolating each caliper or drum piston/s by clamping each flexible brake pipe in turn (this assumes they are in good nick in the first place) If you sucessfully isolate the faulty unit you should immediately feel an improvement in pedal firmness. You can then investigate/repair/bleed the offending unit. Brakes are essential to safety so you got to know what you are doing. If in doubt take it to a good independant.

 

[neilrr]

Thanks to everyone.

I'm pretty sure it's only water in the fluid. I noticed the cap on the reservoir has been overtightened and cracked around 60% of the circumference, leaving a 1-2 mm gap. I don't know how long it's been like that, but a good long while at least. I think the brake fluid has picked up moisture & has lost it's efficacy.

A friend who is a retired garage owner is helping me & he'll tell me if it's more serious than that.

I bought the car from the original owner with a v. good service history & under 90K miles so I know it's been looked after. It went through it's MOT last year needing nothing save a big rubber band to hold 1 side of the exhaust up & no other advisories.

Getting her ready for the big day, 150 123s booked & more (like me!) expected to show up on the day -

NATIONAL W123 DAY

HIGHCLERE CASTLE, NEWBURY, BERKSHIRE
JUNE 18TH 2006

Mark Cosovich has organised a special day for all UK owners of W123's. It is celebrating the 30th anniversary of the launch of the W123 in the UK. It will be a real family day out with activities for children as well as adults. There will be prizes, technical advice and an "American picnic" (everyone to bring some food). All Mercedes cars will be welcome but only W123s will be display parked. The cost will be £10 per car. It should be a great day out !!

Members of the MB Club will have had an application form in their copy of the Gazette. You can also book a place by giving Mark a call. But if you cant get through to him then let me know and maybe we'll be able to organise a block booking!