Help With Long Brake Pedal Problem

[thomasrally 3]

Hoping someone here might have some idea what the hell is going on with our brakes which are basically crap, have alot of travel (good 3"-4") and braking is far from good either, we're running out of ideas.

 

Since the day I bought the car the pedal has been absolutely crap, we've changed the front calipers, discs and pads - no difference.

 

We've changed the master cylinder twice - no difference.

 

Changed the back pads - no difference.

 

Disconnected the tilton bias valve and bled everything to death - no difference

 

Also if I hold the hydraulic handbrake on to lock the back wheels and press the brake pedal down, it doesn't want to move the handbrake whatsoever as if there's no pressure, BUT the handbrake does lock the back wheels, this should I'm told try to force the handbrake when depressing the brake pedal?

 

The ONLY time I ever had a decent pedal was we'd literally just put a brand new master cylinder on, bled everything through and great - a pedal.........next day took it for a drive it was back to its normal crapness

 

Just for clarification we're running a 1600 205gti with 1900 rear beam, the master cylinder is plumbed in as below when looking from the front of the car - is this correct??

 

Back left (closest to servo) - Blanked off

Back right (closest to servo) - Through hydraulic handbrake to rear brakes

Front left (furthest from servo)- Front drivers side caliper

Front right (furthest from servo) - Front passenger caliper

 

Any ideas?

[powermandan 0]

i seem to be suffering the same thing as you although i have a cable handbrake. Compared to the 309s brakes my 1.6gti brakes are poor.

 

Ive changed the master cylinder for a newer scrappy one also, the best i can manage from mine is tyre squeal when im standing on the brakes

 

Next thing i was going to do was temporarily remove the rear compensator and see if i can lock any of the wheels.

 

What you could try also is temporarly blank the rear braking circuit off and see if you can get good performance out of the front.

[DRTDVL 4 1 Cars]

what master are you running?

[Jrod 7]

My opinion is that the servo rod needs adjusting.

[shalmaneser 26]

So you've changed all the front brakes, rear pads and the master cylinder? Time to look at the servo maybe?

 

which rear callipers are you running at the rear? can you measure the piston diameter - some 306 ones are bigger but look pretty much identical although this is unlikely.

 

Are you running 1.9 or 1.6 calis at the front? are you running a compensator/bias valve at all - I'm not overly familiar with hydro handbrakes but could too much force be going to the rear?

 

either way the obvious culprit is the servo.

[thomasrally 3]

im using a brand new 1900 4 port master cylinder from shenpar, the rear left closest to the server is blanked off, the right goes to the rears and front 2 furthest from server go to the front cals.

 

Brake pedal is the same whether the engine is running or not too, the rears im pretty sure are standard 1900 cals but if you have a size i can measure them to make sure, theres no other valve or compensator valve in the system anywhere, the line runs from the master straight to our hydraulic handbrake and then the rear

[brumster 135 1 Cars]

Just as a note, without any bias adjustment you *might* want to put some brake proportioning valve in the rear circuit anyway - gravel or tarmac?

 

But that's by the by for now... if it doesn't improve with the engine running then that does seem to suggest a servo problem, but then again lack of servo shouldn't make the pedal *long* - it should pump up. What about my suggestions on the BR forum, do you think you could easily bypass or rule out the m/c in the rear circuit used for the hydraulic handbrake?

[Jrod 7]

As I said, the servo rod. This is the gap between the servo and master cylinder. If the gap is too big the pedal will have to travel a distance before it engages the master cylinder. The distance will just as big whether the engine is on or off.

[brumster 135 1 Cars]

I'd agree, JRod, but isn't the rod length fixed as part of the master cylinder? Is it adjustable? Otherwise the suspicion is simply wrong m/c (with incorrect length rod) but from memory when removing my standard setup on the car a few years back, I don't recall any adjustment on it, just a pointed end with a circlip to hold on the pedal?

 

edit: No, just dug it out, the rod and the m/c are clearly separate.

 

So maybe what we've got here is a 1.9 m/c but with a 1.6 (or some other model) servo rod?

 

Let's have a look at the parts CD :-

 

4 different servos listed, rod seems to be integral part (no separate parts listed). Mainly injection non-abs, an ABS-listed one and then carb/diesel. Maybe an ABS/carb/diesel servo has a different rod length and that's been installed some time previously?

 

We need someone to confirm what the rod length should be, of course don't have mine handy any more though, only the m/c.

Edited April 28, 2010 by brumster

[Anthony 1,002]

The ONLY time I ever had a decent pedal was we'd literally just put a brand new master cylinder on, bled everything through and great - a pedal.........next day took it for a drive it was back to its normal crapness

That suggests to me that the rod isn't the problem, as if it was, you'd have never got a decent pedal, surely?

 

I'd personally suggest that it'll be something to do with the hydraulic handbrake setup - remove the rear line from the MC and put a blank in there, and see if that gives you a decent pedal following a quick re-bleed. If it does, then it's got to be something amiss with something on the rear brake circuit.

[thomasrally 3]

Cheers lads plenty to check out there, we're going to have a good bash at it later today hopefully!

 

Just to throw something else into the mix as I'm not quite 100% sure whether our front calipers are 1600 or 1900 ones, would that make any difference? Also are the servo rods the same length in both versions?

[brumster 135 1 Cars]

I can't say for definite that the slave volumes between 1600 and 1900 calipers are different, but given the different part numbers and designs I would say it's almost certainly the case. You wouldn't want to mix 1600 and 1900 system components, given they're listed separately in the parts manual at least. Maybe someone can confirm, but I would really look to keep the system married up - so use a 1900 m/c with 1900 calipers and rear disks, 1900 servo, etc.

 

edit: This got me searching and it seems plenty of people have moved from 1.6 to 1.9 front brakes without issue, and the implication in their posts is they haven't swapped the m/c. So maybe the piston size/volumes are identical (or near enough)?

Edited April 28, 2010 by brumster

[yeti-dj 7]

I have in the past on my 1.6 gti used 1.9 front callipers and a 1.9 rear set up and still used the 1.6 M/C and compensator with no problems other than the rear locking a little to easily..so mixing components i dont think will give you such a bad pedal feel.

 

I also agree that the best bet is to blank off the rears and bleed the fronts and see if they feel better and then have a look at the hydraulic handbrake and see whats going on there..

 

good luck...

[Anthony 1,002]

1.6 and 1.9 MC are the same - it's just that the 1.6 one only has 3 outlets.

 

My car started up as a 1.6 and is now pretty much a complete 1.9 in terms of the braking setup (still retains the 1.6 servo, compensator and brake line setup, but otherwise using 1.9 front and rear calipers) and all is fine. I've never noticed any difference in pedal travel between 1.6 and 1.9 front calipers, and usually if anything, fitting 1.9 calipers on the back improves matters (as the drum self-adjusters rarely work properly)

[brumster 135 1 Cars]

Interesting - thanks Anthony. Didn't realise that, then the search certainly suggested what you're saying. Good news then, that rules out incorrect m/c to caliper ratios (assuming it's a GTi m/c I guess)...

Edited April 28, 2010 by brumster

[thomasrally 3]

Plenty of food for though. think we'll try pressure bleeding the system first of all to completely rule out any airlocks then try blanking off each brake line one at a time to see whether we get a good pedal

[TT205 42]

If engine on/engine off makes no difference - have you checked vacuum hose?