brake issue - suggestions?

[Saffy]

1995/96 300TDI 110

I am having to occasionally double pump the brake peddle before it is firm. Is fine for awhile then is slack again. Other than the first slack peddle there is no obvious reduction in braking performance.

No fluid loss what so ever. No tell tale dribbles on the brake pedal.

Vacuum pump appear to have good suction, no leak in pipe or coupling from pump to servo.

Brake fluid hoses are not ballooning.

Is this a servo issues or master cylinder seal breakdown, or something else? Any fault finding tips before starting to replace parts?

cheers

[ben_haynes]

clamp of all the break hoses then if it does not go hard then it is marster cylinder but if it goes hard then take one clamp off then you will find one that goes soft then it will most likly be the slave cylinder / caliper or a Brake hose collapsed inside

[Tommo]

change your fluid is worth a try.  after a while it absorbs moisture ad becomes all mankey and useless.

[biggerlandy]

its ascorbic

[Saffy]

its ascorbic

hygroscopic even :D

(I had to look it up)

It is possible the fluid may be passed its best as I do not recall renewing it and no idea of its age before that.

[extreme90]

check wheel bearings
this is the tell tail sign  
i had a broken up inner bearing ont front axle of my 90, and it took me ages to figure out what it was

pump the breaks up, 100 yards down the road in stright line its fine

go 500 yards or turn, had to pump the breaks again

dan

[davidlandy]

I would second the wheel bearings as TBD has said- the disc moves side to side on the bearing and forces the pistons back a tad - the result is that you have to pump the brakes to get the pedal back.

Its happened to me a few times!

[Saffy]

check wheel bearings
this is the tell tail sign  
i had a broken up inner bearing ont front axle of my 90, and it took me ages to figure out what it was

pump the breaks up, 100 yards down the road in stright line its fine

go 500 yards or turn, had to pump the breaks again

dan

I would second the wheel bearings as TBD has said- the disc moves side to side on the bearing and forces the pistons back a tad - the result is that you have to pump the brakes to get the pedal back.

Its happened to me a few times!

:idea:  :!:  ok cheers had not thought of that,  I will check because I repacked grease on the front bearings about a week ago and maybe they are not adjusted correctly or have slacked off.

[extreme90]

check wheel bearings
this is the tell tail sign  
i had a broken up inner bearing ont front axle of my 90, and it took me ages to figure out what it was

pump the breaks up, 100 yards down the road in stright line its fine

go 500 yards or turn, had to pump the breaks again

dan

I would second the wheel bearings as TBD has said- the disc moves side to side on the bearing and forces the pistons back a tad - the result is that you have to pump the brakes to get the pedal back.

Its happened to me a few times!

:idea:  :!:  ok cheers had not thought of that,  I will check because I repacked grease on the front bearings about a week ago and maybe they are not adjusted correctly or have slacked off.

dont forget the rear axle

you need to remove the half shaft to check them properly  
as it takes most of the play out

dan

[Saffy]

check wheel bearings
this is the tell tail sign  
i had a broken up inner bearing ont front axle of my 90, and it took me ages to figure out what it was

pump the breaks up, 100 yards down the road in stright line its fine

go 500 yards or turn, had to pump the breaks again

dan

I would second the wheel bearings as TBD has said- the disc moves side to side on the bearing and forces the pistons back a tad - the result is that you have to pump the brakes to get the pedal back.

Its happened to me a few times!

:idea:  :!:  ok cheers had not thought of that,  I will check because I repacked grease on the front bearings about a week ago and maybe they are not adjusted correctly or have slacked off.

Cheers guys your diagnostic was spot on! Front nearside bearing had loosened right off with a lot play :shock:  Now adjusted with brand new lock washer fitted. Brakes back to normal.

[extreme90]

check wheel bearings
this is the tell tail sign  
i had a broken up inner bearing ont front axle of my 90, and it took me ages to figure out what it was

pump the breaks up, 100 yards down the road in stright line its fine

go 500 yards or turn, had to pump the breaks again

dan

I would second the wheel bearings as TBD has said- the disc moves side to side on the bearing and forces the pistons back a tad - the result is that you have to pump the brakes to get the pedal back.

Its happened to me a few times!

:idea:  :!:  ok cheers had not thought of that,  I will check because I repacked grease on the front bearings about a week ago and maybe they are not adjusted correctly or have slacked off.

Cheers guys your diagnostic was spot on! Front nearside bearing had loosened right off with a lot play :shock:  Now adjusted with brand new lock washer fitted. Brakes back to normal.

good to hear  8)

[Eck-T]

thanks for the tip on wheel bearings, i have been chasing brake fade for ages, changed fluid, changed seals in master cyl without success, just checked and replaced rear wheel bearing on drivers side, it was knackered, only got one new bearing though, will now order another 3!
cheers