julianf

Well-Known Member

• Apr 5, 2019

• #1

Ok, so ive not driven the 101 since last year.

Started it up today, very first pulse of the key, so happy there.

But one of the fluid reservoirs was empty - the front brake one.

No peddle either.

So i dig about for some DOT4, thinking ill top it up, pump away, and see whats leaking.


I do just that, get a good peddle after a bit of pumping, top up the resevoir again, and go for a crawl about underneath. Nothing to see.

Get back in the cab - reservoir now overflowing, and the peddle isnt there again. Pump it and it comes back after a bit, the level in the reservoir goes down, but then the same again. Looses peddle, fluid rises.



Ive owned the truck about 20 years. Always the same master until about 3 or 4 years back, when i changed to one of those modified s3 ones (basically IIRC, so you can use the servo from the s3, but the modified cylinder is tapped to 101 thread)

Im guessing this must be a master fault, rather than the pistons. Im also wondering why only the front brake reserve fell. Back system is still on the level.


Any ideas?

 

R

rob1miles

Well-Known Member

• Apr 5, 2019

• #2

The first job is to find where its gone, could it be in the servo?

 

J

j_g_uk

Well-Known Member

• Apr 5, 2019

• #3

Perhaps you pumped brake fluid through against the air pocket in the system and then when you stopped, the air pressure pushed it back into the master cylinder reservoir?

 

J

j_g_uk

Well-Known Member

• Apr 5, 2019

• #4

If it’s been sitting there a while then the leak might be very slow and not immediately apparent? You didn’t bleed any if the brake cylinder?

 

julianf

Well-Known Member

• Apr 5, 2019

• #5

I've ordered a new master, as, the way I figure it -

If I pump to get a firm peddle and then press and hold the peddle, it's firm, then fades quickly whilst the level rises.

So its got to be the master. If it was anything else then I might get fade, but the level wouldnt rise again.

Where the fluid went though, who knows. It's not leaking now though. As mentioned above I'll probably find it in the sevo and then have to order another one of them too!

Thanks to all for advice.

 

C

Colthebrummie

Well-Known Member

• Apr 6, 2019

• #6

You might be right but I would have tried bleeding the system before buying a new master cylinder, they ain't cheap. Don't buy a britpart one.

Col

 

tottot

Well-Known Member

• Apr 6, 2019

• #7

As Col says,bleed the system. Once the fluid level drops below the resevoir air will get into the system. A very slight loss of fluid over some time will be hard to detect,more so with drum brakes. Get the air out and give the brakes some use. It may be fine but keep an eye on the brake units for signs of fluid loss.

 

julianf

Well-Known Member

• Apr 6, 2019

• #8

If the system had have drained down to the point where there was air below the master, then would it leak back up again, through the master?

What I mean is, when I pump away to get a firm peddle, and then the pressure comes back up, through the master - I can totally see how, if there is air below, I'm compressing it and that's wanting to push the fluid back up, but should it be able to push around the master seals like that?

You might be right though. I know that the master won't be sent out until Monday, so I may drop them a line just to hold it until I've had more of a play.

 

C

Colthebrummie

Well-Known Member

• Apr 6, 2019

• #9

I have a piaggio scooter. If I leave it unused for a long period the brake levers have no affect, they go back to the handlebars with no pressure. When it first happened, I drained all the fluid out, refilled and bled. Now, I have discovered if I keep pumping the lever and then use a clamp to clamp it to the handlebar the pressure returns after a few hours. This trick also seems to work on my series if I don't use it for a few months, except of course, I use a hammer to wedge the brake peddle down and leave it overnight. Try it, it might work.

Col

 

S

suburban

Well-Known Member

• Apr 6, 2019

• #10

Colthebrummie said:

This trick also seems to work on my series if I don't use it for a few months, except of course, I use a hammer to wedge the brake peddle down and leave it overnight. Try it, it might work.

Click to expand...

heard of similar for a clutch that is difficult to bleed, wedge pedal down overnight.

 

Shippers

Well-Known Member

• Apr 7, 2019

• #11

suburban said:

heard of similar for a clutch that is difficult to bleed, wedge pedal down overnight.

Click to expand...

That's what I did on my 101 after replacing reservoirs and slave cylinders...