Brake Bleeding After New Servo & Master Cylinder

[JeffW]

Hi

I replaced my master cylinder with a new Lockheed one (not TRW) and a rebuilt servo from the usual trusted supplier.

I have filled the reservoir with new fluid and started to bleed the brakes, offside rear first. There is fluid at the drum, as when I slacken the nipple fluid comes dribbles out, however when I pump the pedal only some small air bubbles appear in the reservoir but no fluid is coming out of the rear bleed nipple.

Any idea what I have done wrong? There is no fluid leaking anywhere.

Thanks
Jeff

[DMT]

Hi Jeff

I just did mine this afternoon, The stag system has two separate linked cylinders and air gets stuck in between.

I have a vacuum pump ( from Amazon) which I fit on the wheel cylinder and start to pump. This seems to fill / prime the master cylinder and some fluid comes out into the pump bottle with some air. I found that if you then pump the brake pedal it will pump fluid through and I continued until the pipe at the pump had no air.

Dave

[trunt]

I use a pressure bleeder, it screws on the cap and pushes the fluid through the system. but if you don’t have one I have got over this issue before with my finger.. but it’s messy!

I think it’s because when you lift the pedal it sucks air from the brake line rather than fluid from the reservoir but that’s just a theory,

Remove the pipes to the brake lines and get someone to depress the pedal. Seal the line holes in the master with your fingers as they release the pedal, do this over until fluid starts squirting out. Once it’s squirting then you can reconnect the lines and it should work from there..

[sujitroy]

Has the shuttle moved in the PWDA? I have a YouTube video on how to keep it centered with a small screw and regular bolt.
Sujit

[Lingen]

Sujit.
For future reference, the position of the shuttle is irrelevant when bleeding the brakes. It is only part of a switch mechanism, and has no effect on the flow of brake fluid through the casting. It may need to be centralised though after bleeding to get the switch working properly again.
Mike.

[JeffW]

Thanks all for the tips. Will try again today and see where I get to. I have a cheapo vacuum version arriving today from Amazon so I will see if that gets things going and if not gloves and fingers!

Thanks again
Jeff

[Phil S]

When I trained as a mechanic (just after Noah fitted an engine) we were trained to bleed the shortest line first then go to the next shortest.
always worked very well.
Until I started using a vacuum bleed, no looking back after that.

[Niallcat]

I was always taught furthest brakes first, possibly makes no massive difference but gives a routine to get them all done.

[bullstarz]

Always start at the furthest first brake from the master cylinder. Unless you have twin master clyinders (opposed to a tandem) where you have to do a front and rear at the same time.


But before you even start bleeding you have to ensure there is fluid in the master cylinder. Just crack open the brake unions on the master cylinder and wait for all the air to be explelled untill just fluid come out.


I've just replace my rears calipers all the brake lines and master cylinders on my Stag. It took an age and loads of fluid to bleed. My vacuum bleeder didn't do the job correctly. So I ended up doing it the old fashioned way, with a one way value into a jar of brake fluid. These valves are about £6 off of Amazon

[JeffW]

I got the vacuum bleeder from Amazon this morning but it's junk. The smallest nipple attachment is still too big for the Stag rear drums so it wouldn't build up a vaccum.

Moving on to the finger test, I undid the front pipe on the master cylinder and fluid squirted immediately. However when I removed the rear (closest to the servo), no fluid squirts no matter how many times my friend pumped the pedal with my fingers in the master cylinder. There is no fluid loss at all, just the occasion burp of fluid coming up into the rear compartment.

I am at a complete loss! Could there be something wrong with this new master cylinder?

Thanks
Jeff

[DMT]

My vacuum unit from Amazon seemed pretty poor until I noticed the 90dep fittings. They fit fine even on the rear cylinder nipples.

I found that when using the vacuum it sucked air in from round the loose nipple BUT I found it did prime the master cylinder.

I started with the vacuum unit then pumped the pedal, this gave me a nice full pipe from the nipple to the reservoir to see any trapped air.

Dave

[trunt]

Don’t forget that the front section is the rear brakes, rear section the front brakes From what you are saying the rears seem to be pumping.. try that vacuum pump on the front brakes like Dave suggested.

[JeffW]

Don’t forget that the front section is the rear brakes, rear section the front brakes From what you are saying the rears seem to be pumping.. try that vacuum pump on the front brakes like Dave suggested.

That's the odd thing - the front is squirting fluid fine, yet nothing reaches the rear brakes. I'll try the fronts as DMT Dave suggested.

Thanks
Jeff

[JeffW]

My vacuum unit from Amazon seemed pretty poor until I noticed the 90dep fittings. They fit fine even on the rear cylinder nipples.

I found that when using the vacuum it sucked air in from round the loose nipple BUT I found it did prime the master cylinder.

I started with the vacuum unit then pumped the pedal, this gave me a nice full pipe from the nipple to the reservoir to see any trapped air.

Dave

Hi Dave

Yes, I tried those but all I got was a squishing sound (likley air around the nipple) and no vacuum. No fluid moved at all.

I may try an Eezibleed if all else fails.

Thanks
Jeff

[DMT]

Jeff Did you get the pipe connections on the vacuum bottle the right way round? I believe there is a non-return valve in one leg.

I managed to get up to 25"hg with mine.

Dave