top drive

top drive

Well-Known Member
so thought i had my brakes sorted after changing servo and adjusting it up....(for those that dont know , both calipers have new pistons and seals , all brake pipes are new cunifer , all the flexies have been switched to gwyn lewis braded hoses , the rear shoes , drums and slaves are all new and working (and adjusted up right) theres a new servo , new master cylinder and fresh fluid bled through) - it passed an mot like this and does brake well, but im a bit fussy !

and they are amaizing when i give them a shove- they will stick you through the screen sharp.

how ever prolonged soft braking or cadence braking the pedal goes hard and the brakes go wooden and seem to fade - no matter how much more effort i put into shoving the pedal....

the servos working - it holds vac for ever when engines off (which it didnt with the old one - because it was cracked where the MC bolts on) and the hose from vac pump will suck to my hand when engines running - how hard should it be to pull off ?
when i press the pedal with engine off to use the vac then hold my foot on and start the engine - the pedal drops.

im wondering if in multiple braking situations like above - if im using all the vacumm up and the pump cant keep up ?

does the Vac pump off a 19j fit ? got one lying about , tempted to fit it when i get home for diagnosis purposes ......

Any other ideas ? am i just being paranoid - is this normal from this type of brake set up......
 
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I had this when I fitted cheapy pads on a camper van years ago.
Came to head going down dynas mowdry (spelling is wrong) scared the bejesus outta me.
Replaced pads and all good.
Worth a try if the servo proves good.
 
just cant handle the heat or what ? ive had pads glaze on me on bikes - and tend to find they lack bite as well as prolonged stopping power.

these things bite like a bastard.

how ever - the prospect of 25 quid on a set of mintex does fill me with more joy than 80 quid on a pump :(

will see when i get home
 
top drive said:
just cant handle the heat or what ? ive had pads glaze on me on bikes - and tend to find they lack bite as well as prolonged stopping power.

these things bite like a bastard.

how ever - the prospect of 25 quid on a set of mintex does fill me with more joy than 80 quid on a pump :(

will see when i get home
Click to expand...
It's a possibility, normally the pedal goes spongey but your braided hose may be masking that.
 
Mine felt a bit like this when I adjusted the rod that sticks out of the servo so it was a bit too long. It was fine for occasional braking, but repeated application on a drive round town mean that the pedal felt very hard and was acting very high up. Plus they were binding a bit. Didn't you mention in another thread that you've got them set so there's not much free travel on the pedal? Try backing the adjuster down a few turns and see if it makes a difference. There should be plenty of suction from the pump - just pull the hose out of the servo and listen to the air whistling in!
 
You remember correctly brown

How ever i did adjust that up nicely. - i had as you describe the rear drums were binding on after 30 minutes driving.

I should add that give it 30 seconds after they have gone wooden and press again - they bite like a bastard again.....

But if i press 4/5 times in quick succession they go hard and feel like they are not stopping me ....

Oh and no whistle when i pull the hose .... Its more like a limp meh suck..... Will try swapping it out with my other one
 
Sounds to me like vacuum pump isn't keeping up with demand and your exhausting the servo vacuum 'reservoir'
 
Yeah thats where my powers of deduction was pointing me. But its been wrong before.

Shall report back when i get it done.
 
yep thats the one - how ever if i pull against the wheel and really stamp on it they still lock up. suggesting its lack of servo assist. .... did an experiment on a closed road last night - into neutral - left foot pushed the brake 3 or 4 times untill it went hard - then revved with the right foot while pressing the brake with left and the asssistance came back - so its either the vac pump or the hose r the 1 way valve
 
I had exactly this problem with a faulty servo a couple of weeks back. The vacuum pump wasn't producing enough vacuum to compensate for the servo leak.

Yours seems similar but different, your vacuum pump isn't providing enough for full servo assistance for repeated braking.

An option for you to double check, would be to buy a vacuum gauge, test the vacuum pressure of the pump, and bang the figures up on here. Then you can rule out if it's faulty or not before forking out on something!

Hope this helps
 
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