Please help (brakes)

bad driver · Unread post by **bad driver** » 19 Jan 2005, 17:00

I have put a full gti6 brake setup on my 306td. It has new flexi's, new master cylinder etc.
Anyway when the engine is off the brakes are pretty much solid as you would expect but as soon as the engine is running the brake pedal travels almost to the floor. I have bled it several times using a pressurised kit and theres definatley no leaks or air in the system.
Is it possible the master cylinder needs to be the same as the gti6 master cylinder to displace more fluid or something?
If it does then will the gti6 cylinder fit onto the same servo or is the servo different as well?

turbolag · Unread post by **turbolag** » 19 Jan 2005, 17:05

It's possible. Calipers are designed to work with a certain servo/pump & master cylinder combination. Bigger calipers often mean bigger (or more) pistons means a larger displacement of fluid is required and the 306td might not be up to it.
To be sure, bleed it the old fashioned way without the kit (using air to expel air always made me suspicious), chock the brake pedal down with a bit of wood and leave over night in a garage with the reservoir cap off. If that don't do it then you've got possible compatibility issues.
Some caliper swaps work well(MG ZS brakes onto Rover 400/200s are popular) but some require transplant of the entire setup to work effectively.
Good luck.

bad driver · Unread post by **bad driver** » 19 Jan 2005, 17:14

I have tried the old fashioned way and also tried the chock down trick. Sadly no luck.
Any idea if the cylinders use the same servo?

bikeboyz · Unread post by **bikeboyz** » 19 Jan 2005, 18:22

There are 4 Master cylinders for the 306
1.4 models
1.6-1.9 models
2.0i with ABS
ABS models not 2.0
They are all different part numbers so not interchangable, this looks like part of your problem. You say its fine until the engine is running. Diesels of course have an engine driven vacuum pump and petrols dont - wether that is a problem too I dont know.

bad driver · Unread post by **bad driver** » 19 Jan 2005, 18:29

They are different part numbers as they have different size pistons inside. Also ABS models have 4 pipe connections where non abs has 2. Usually however the 4 pipe types come with 2 blanking off screws as there are various types of abs.
Anyway thats not the issue. I know now that I need to use the 22.2mm cylinder and from what I have been able to establish it will fit onto my servo, the 306 has 2 different size servo's. Mine is the larger 225mm type and I would imagine the 22.2mm cylinder will use the larger servo.

bikeboyz · Unread post by **bikeboyz** » 20 Jan 2005, 05:19

Why did you change the old master cylinder? I assume you put another diesel one on?

bad driver · Unread post by **bad driver** » 20 Jan 2005, 18:21

Long story with the brakes, basically the car failed MOT before the new brake setup due to the rear drivers side brake. It was kind of on and off constantly. As though the drum was out of shape. It had 3 brand new drums, new stub axle, new backplate,new shoes, new flexis, new cylinder, new brake lines and new master cylinder. None of which solved the problem. I then had an accident on the way home from its 4th MOT resulting in damaged front bumper, smashed splitter and smashed sideskirt. At this point I decided I would take her off the road and do a bit of a rebuild.
So anyway, thats how it came to have a new master cylinder for the old setup and ultimatley what led to deciding to go for a disc brake rear, which led to going to a gti6 front setup which is now leading to a new master cylinder.
I have now found out from others that have done the gti6 brake conversion that the best MC to use is that of a 406 2litre. Its a 23.8mm cylinder and fits to the servo for definate. Everyone using it says they have minimal brake pedal travel so sounds like the best option.

Dave Burns · Unread post by **Dave Burns** » 21 Jan 2005, 02:50

Hmm...I fitted disc brakes to a 205 diesel from a 205 GTi and had no such problems, the pedal was allways right up at the top and hardly moved, I'd have another look for air first because all though the pistons are much larger in a disc setup, they only move about 1/2 millimeter, so practically nothing compared to a drum brake.
When you bleed the brakes retract the pistons fully so as to give any air much less of a hiding place in the caliper.
Dave