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Todd100's Ph1 GSi

nige-p

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did you have the brackets made up todd,

ive had a set of these calipers sitting around for years waiting for some time to attempt to fit them but i want to do it with the 308 discs but im sure i will have to run wheel spacers if i use standard vaux discs, what size where the sierra discs
 

Todd100

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I made the brackets myself, the discs are mainly to get the caliper further in for fitting with standard wheels, the Sierra discs are 283mm
 
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Hi!
Yea I know what you mean, the pedal is just spongey in comparison to a modern car. I have this dream of fitting a motorsport master cylinder in the OE place haha
Sorry for interrupting I would like to add my experience.
I really hated the standard brake pedal feel on my MK3.
After some investigation and the ABS removal I found that the bulkhead flexing is the most obvious cause of spongy pedal feel IMO.
I made a custom bracket (from 5mm thick base plate which reinforces the bulkhead) for a Mercedes Girling booster and also added another bolt for holding it to the bulkhead. Then mated it with E34 M5 25,4mm master cylinder.
The ratio of the pedal remained stock, I also used the standard rod that pushes the servo and modified it to fit the Girling booster.
The booster diameter is 225mm approx which I found that has enough helping power and not too much (before I had 275mm which was too much I hate to easy brake).
Now the brake pedal modulation is very good, it has a precise point where it stops and then you can adjust the stopping power with the force you exert and not the bulkhead distortion eats up you force. Front brake is 288mm Vectra with 57mm piston, nothing special.
It was a bit complex to make but worth the effort.
This is the bracket that holds the booster and the MC, tilted as the standard one.
IMG_20211012_140010.jpg
 

Todd100

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Thanks for the input, it's good to hear another person's opinion, do you have any pictures or the master cylinder /servo fitted and pictures of how you strengthened the bulkhead at all? Do you know what mercedes the servo was from?
 
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Thanks for the input, it's good to hear another person's opinion, do you have any pictures or the master cylinder /servo fitted and pictures of how you strengthened the bulkhead at all? Do you know what mercedes the servo was from?
I can take pictures of the servo, but if I remember correctly it was a Merc 190 booster, I found it on the internet that it accepts girling master cylinder of the M5 which I already had. Both of them are aluminium so saves a good amount of weight especially with the ABS removed.

Anyway I think what You need to consider is this: all the power you exert on the brake pedal need to go to the brake calipers via the leveraged hydraulic system. So all the flex you have between these two points acts as a power loss. My first post was not exactly on point because not only the bulkhead flexes (it flexes less) but the standard brake booster holder flexes a lot more which is made out of ridiculous thin sheets and it is a horrible design, as we know it. Also the unfortunate placing of the steering rack makes it hard to place it close to the bulkhead.
BFD09F39-3100-4178-A849-2C6C4DC5C145-MEDIUM.jpg
You can check for yourself, someone pushes the brake in your car and it does the same:

In an MK3 it moves a minimum of 10mm. Obviously seperate pedal boxes get rid of these effects, but it is another story.

The holder I posted earlier has a thick baseplate of 5mm and a 4th bolt that connects it to the bulkhead (despite the limited space), this is it. And you can see finished holder, the 190 servo and the finished assembly:

IMG_20211011_131801.jpgIMG_20211012_123543.jpg190 brake booster.jpgIMG_20211119_213600.jpg
It was pretty hard to get the angle right as the standard one is also tilted upwards as I wrote earlier. (My motronic wiring is a mess right now on the picture I know, it is obviously not a showcar :) )

So in my opinion maybe it is better to get a bigger standard vauxhall master cyl and create a proper, rigid holder that connects multiple ways to the bulkhead and therefore it is a lot less prone to flex as the standard one.

It worked out quite well for me. Maybe later I will go for a fully machined aluminum holder and some more refinement on the bulkhead.
These are my 2 cents :)
 
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Todd100

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Really interesting info, thankyou,

The mounting is a lot better on RHD cars as it doesn't have all of the thin steel supports, it's a cast aluminium 2 piece bracket.

But I will definitely be looking into how much the bulkhead flexes and will see if I can strengthen that up for sure!
 
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Sorry about it, I didn't know the RHD is different and it is really a lot better, I've just searched.
Anyway it is a good idea to check if it flexes :thumb:
 

DavebGsi

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Let us know what you find Todd, interesting info, never really thought about this being an issue, the pedal is naff on a mk3 though!
 

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