Brake pedal on 1978 244DL
 

Hi All,
My 1978 244DL failed its M.O.T. with the rear brake balance being under 30%.
I have replaced the rear discs and pads and the shoes were in good order so were reused.
I took the car for a test drive and all seemed well with the car stopping nice and straight.
Once in my drive way I sat listening to the radio with the car in neutral, engine running and my foot hard on the brake pedal. Slowly the pedal started to sink to the floor but the car remained on the hill and did not roll forward.
I removed my foot from the brake pedal and then pushed it down very hard again and again the pedal slowly started to sink to the floor.
As far as I am aware I did not break anything whilst fitting the discs and I pressed the pedal a few times before I took the car out for a test drive to settle the new pads and operated the hand brake a few times to settle the old shoes.
As it was now dark and I had to go to work I have not investigated further.
Do I have a master cylinder problem or a leak some where else? What should I suspect?

RE: Brake pedal on 1978 244DL
 

Hi Neil,
That sounds very much like a knackered master cylinder assumming you have no fluid loss.
If the fluid level is dropping but no visible leak it's odds on the servo nbg.
Regards.
Vaughan

RE: Brake pedal on 1978 244DL
 

Hi Neil.
Sorry i am unable to give any technical advice although in my experience of brakes it sounds like either there is something missing at the disk i.e. the pads letting the pistons in the caliper compress too much which i think is unlikely if youve looked over it or as vaughan suggests the master cylinder is knackered.
Anyway my reason for replying-i have two cars here for parts and a garage full so if you need anything give me a shout and i can probably post them(well the master cylinder anyway as the servo is a tad big)
Best Regards
Ben
82 242
82 244
89 245
91 245
96 850

RE: Brake pedal on 1978 244DL
 

It sounds like the master cylinder leaking internally. This often happens after any major work even if the fluid circuit has not been disturbed. What happens is that either pressing in the caliper pistons to fit the new pads sends old dirty fluid back up the pipes, or else the pedal inevitably gets depressed further than normally and so runs the seals down on to a section of bore that may be a bit rusty or have dirty deposits. Either way the seals get damaged slightly. The brakes may work but as you have found the pedal slowly sinks to the floor.

I wouldn't bother with trying a used MC - they are quite cheap new from Europarts or German-Swedish.
It will need bench-bleeding. With skill and luck you can replace a MC without letting in any air so not needing to bleed the whole system.
If you let in air near the MC you then get involved in the pain of trying to bleed the rear pressure relief valves or re-setting the dreaded 'octopus'.

Good luck - if you find you do need to replace the MC and need more tips do ask - I have quite a good success record (ie 3/3) of replacing MCs without re-bleeding!

RE: Brake pedal on 1978 244DL
 

I would'nt advise fitting a new master cylinder without bleeding the entire system properly.
Your brake fluid needs changing every couple of years as it absorbs water (being hydroscopic) and will corrode internally, calipers,pipes and master cylinder.
Plus the water content drastically reduces the boiling point of the fluid which can lead to entire brake loss after a sustained heavy braking session.
Just take a look at the old fluid when you bleed it.
It looks like someone has washed some potatoes in it.
Vaughan

RE: Brake pedal on 1978 244DL
 

Thanks guys.

Looks like the master cylinder has had it and I will fit a new one and bleed the system complete and have fresh fluid all round. I'll let you know how I get on.

RE: Brake pedal on 1978 244DL
 

Just to clarify what I meant. When I said you can get away without bleeding the system I didn't mean don't flush it through. I just meant don't at any stage introduce any air. You flush the old fluid out with the new behind it until each bleed nipple in turn runs clear.

RE: Brake pedal on 1978 244DL
 

Please explain how to not get any air into the system when changeing the master cylinder.
I should know now before I start work.

RE: Brake pedal on 1978 244DL
 

Disconnect each pipe at the MC and immediately plug with a bit of tapered wood, eg one of those golf things. Remove the MC.

Start with the new MC on the bench. Fill it up, and gently press the plunger to encourage fluid down into the chambers, taking out the plastic plugs for a bit. The when you have got as much fluid in and air out as possible, fit it into the car.
Remove one of your pipe plugs, and see that it is still brimming with fluid. Inject a bit more if not. Quickly pull the plastic MC plug and connect up the pipe, but don't tighten fully.
Repeat with the other. Loosen one coupling a bit more, and very gently depress the pedal a bit. Keep the reservoir topped up. Watch/listen for fluid bubbling out of the leaking connection. Don't press too much so that you risk pumping any fluid/air down the pipes, just enough to let it weep out of the joint - like doing a house radiator. Tighten the connector. (Lots of rags underneath )
Repeat with the other pipe.
Then slacken one a little bit, and press harder on the pedal just to see if you have got all the air. Repeat, then tighten fully.
With luck the pedal will now be rock hard.

RE: Brake pedal on 1978 244DL
 

Thanks For that. Will hopefully have the time to purchase Master Cylinder tomorrow and will fit it over the next day or two. When fitted I intend to change all the fluid but your tip should ensure that no air gets in and fresh fluid shouldkeep the system working for the next couple of years.