Anyone here clever with braking systems?

Clarkey

Clarkey

Clarkey

Soldato
Joined
18 Oct 2002
Posts
18,306
I fitted upgraded brakes on the Silvia and they just suck, I've used up all of my knowledge (not much) and don't know where to go from here.

What I did..
Stock brake system 15/16" master, 280mm front, single piston (57.1mm) sliding caliper, 258mm rear, single piston (38mm) sliding caliper.

Replaced the fronts with Mazworx CTS-V conversion. V1 CTS-V caliper (brembo 4 pot, 40mm & 44mm pistons), Evo 324mm discs and pads.
After this, the pedal was incredibly sensitive and it would lock up the fronts and cause an ABS frenzy just by breathing on it, not good.

Binned the master and fitted a BM57 17/16" one from a 300zx. Pedal feel is much better now but ultimately the fronts locking is still a problem.

Rear upgrade time, binned the stock setup and on went the 300zx setup. Now it's a 297mm disc and 2 pot caliper (38mm).

I was hoping that the big rear setup would balance it out and make it better, but honestly it hasn't, at all. When you get into the pedal at all, it still just locks the fronts easily and the ABS has a party.

The master cylinder and rear is all stock 300zx, so if we compare the front setup to the 300zx one..
Piston area is up by 8.3%
Disc diamater is up by 15.7%
Surface area of the pad is up by 19%

I don't know the maths to work out how that affects the actual braking torque, but I guess it's quite a bit more and that's why it's locking so easily.

I guess I have 3 options here
1. Increase the rearward bias. This means either disassemble the MC and shim the proportioning valve to move the knee point higher, or changing for a Navara MC with no prop valve and then using an external one on the rear line.

2. Reduce the front line pressure, this is by far the easiest option, just buy a wilwood valve and plumb it inline. Problem is these valves tend not to have a linear reduction (they have a knee point), and I don't know how it would affect the pedal feel.

3. Bin the front brembo setup and go with a stock skyline GTS setup and matching MC. This will work, but I'd like to keep the Brembo set if I can make it work, it's really beefy and should resist fade well on track (that's why I upgraded to start with, stock was hopeless on track). Also they look great, and were brand new so I know they work properly.

Any advice would be welcome, I've spent a lot of money on this and I'm pretty disappointed right now and don't know which way to go for the best.
 
The smaller pistons will travel further in your new brakes with the same amount of brake force as you used on your old brakes which moved less. If that makes sense.
 
thedinks said:
The smaller pistons will travel further in your new brakes with the same amount of brake force as you used on your old brakes which moved less. If that makes sense.
Click to expand...

No, it doesn't. His new calipers have about 8% more piston area, which means the pistons will move about 8% less for a given volume of fluid and provide about 8% more force on the pads for a given amount of pressure.

Of all the options, I would go for the Navara MC with a separate proportioning valve. Does the Silvia have any kind of load sensing valve on the rear as standard?
 
No load sensing no. I think I agree with trying to increase the rear pressure. There is in fact another way that people have messed with this which is slightly experimental. You can shim up the spring in the prop valve part of the master cylinder and this will increase the knee point of it. Alternatively, some people have shimmed it to the point where the spring is coil bound and thus locks out the prop valve and then fitted an external one.
 
Dogbreath said:
No, it doesn't. His new calipers have about 8% more piston area, which means the pistons will move about 8% less for a given volume of fluid and provide about 8% more force on the pads for a given amount of pressure.

Of all the options, I would go for the Navara MC with a separate proportioning valve. Does the Silvia have any kind of load sensing valve on the rear as standard?
Click to expand...

Misread it! I guess I should read the OP better before posting :)
 
Is your Silvia a track toy or is this just for fast road use? its only ~1250kg so with good pads the stock brakes aren't that bad unless yours is at silly power.

For my S14a temporary daily driver and primarily track use car. Initial track/airfield days with just the stock brakes using Mintex 1155 pads were good, I didn't experience any fade/issues in 20 minute stints
The pedal feel was/still is dreadful, and as I bumped the power up I also upgraded the fronts to use 330mm discs using the DB-Power spacers for the stock calipers, and also 300zx rear brakes.

In the dry I haven't had any issues with locking up the front, I've tried both the standard BM50 and BM57 finding the BM50 to actually suit me better even if the pedal feel is spongier with it.

What tyres are you using?
 
It's a bit of a dual duty car, I use it daily but I take it on the track when I can. Going to do donington next month but right now I don't have much confidence in the braking.

Bear in mind that my car was originally an NA so it never had the Sumitomo 4 pots. It has all the usual suspension work, BPU engine mods 300hp, AD08R tyres. I found that I had severe fade after just 1 lap and no brakes at all after 2 laps of donny. It was obvious that an upgrade was needed and this setup had been done in the states with good feedback, it was good value and meant I didn't have to use 15 odd year old used parts, so I did it.

Next week I'll have a play with the prop valve, see what's what with that.
 
First off I would bin the ABS, I detested it on my Silvia and it was far too sensitive

You've got an mismatch between the master cylinder and calipers, I'm not convinced that chucking on more rear bias is the solution

Matching the master cylinder will be better, if you're using your car for track work you're probably going to want to be able to bias your brakes around anyway and you don't want end up where you can't put anymore front bias on because of this issue
 
Why? Clarkey and many others know what they're doing - it will still have to pass the MOT - and will currently pass, he just finds the front over biased and wants to sort it out. What's the problem? :confused:

Even if we're not talking about brakes, changing an oil filter, or other engine bits are easy if you have the right tools, why wouldn't you want to do it yourself if you are mechanically minded?
 
Which pads are you using on the front? Some do have very hard initial bite that may be causing the lockups.
 
I just used db powers 330mm grooved brembo discs with spacer for stock 4 pot calipers on my 200 with red stuff pads.

Nice and simple and on track they are perfect, i had to remove the abs as it kicks in too early imo and since then had no bother.
 
Last edited:
howler said:
First off I would bin the ABS, I detested it on my Silvia and it was far too sensitive

You've got an mismatch between the master cylinder and calipers, I'm not convinced that chucking on more rear bias is the solution
Click to expand...

:confused: The system is currently causing too much bias to the fronts, or from an alternative perspective not enough to the rear.

Increasing bias to the rear is the easiest fix for this, he certainly doesn't want any more front bias.

snapdragon69 said:
Jesus wept. No wonder the EU want to ban people from working on their own cars.:eek:
Click to expand...

Don't judge other peoples abilities and knowledge by your own.
 
snapdragon69 said:
Jesus wept. No wonder the EU want to ban people from working on their own cars.:eek:
Click to expand...

Can you imagine how many cars would be scrapped if people couldn't work on their own cars themselves and had to pay a garage (who can often be inept) large amounts of money rendering the car uneconomical to keep on the road.

My car would have been history if I had to pay a garage as the work would have cost many times more than the value of the car, it still has to pass an MOT like Freefaller said so what is the issue?
 
Dogbreath said:
:confused: The system is currently causing too much bias to the fronts, or from an alternative perspective not enough to the rear.

Increasing bias to the rear is the easiest fix for this, he certainly doesn't want any more front bias.
Click to expand...

No it's not, there is too much effort going through the front brakes as they are locking far too easily, I would say it isn't a question of bias given the changes that have been made
 
Clarkey said:
I fitted upgraded brakes on the Silvia and they just suck, I've used up all of my knowledge (not much) and don't know where to go from here.

What I did..
Stock brake system 15/16" master, 280mm front, single piston (57.1mm) sliding caliper, 258mm rear, single piston (38mm) sliding caliper.

Replaced the fronts with Mazworx CTS-V conversion. V1 CTS-V caliper (brembo 4 pot, 40mm & 44mm pistons), Evo 324mm discs and pads.
After this, the pedal was incredibly sensitive and it would lock up the fronts and cause an ABS frenzy just by breathing on it, not good.

Binned the master and fitted a BM57 17/16" one from a 300zx. Pedal feel is much better now but ultimately the fronts locking is still a problem.

Rear upgrade time, binned the stock setup and on went the 300zx setup. Now it's a 297mm disc and 2 pot caliper (38mm).

I was hoping that the big rear setup would balance it out and make it better, but honestly it hasn't, at all. When you get into the pedal at all, it still just locks the fronts easily and the ABS has a party.

The master cylinder and rear is all stock 300zx, so if we compare the front setup to the 300zx one..
Piston area is up by 8.3%
Disc diamater is up by 15.7%
Surface area of the pad is up by 19%

I don't know the maths to work out how that affects the actual braking torque, but I guess it's quite a bit more and that's why it's locking so easily.

I guess I have 3 options here
1. Increase the rearward bias. This means either disassemble the MC and shim the proportioning valve to move the knee point higher, or changing for a Navara MC with no prop valve and then using an external one on the rear line.

2. Reduce the front line pressure, this is by far the easiest option, just buy a wilwood valve and plumb it inline. Problem is these valves tend not to have a linear reduction (they have a knee point), and I don't know how it would affect the pedal feel.

3. Bin the front brembo setup and go with a stock skyline GTS setup and matching MC. This will work, but I'd like to keep the Brembo set if I can make it work, it's really beefy and should resist fade well on track (that's why I upgraded to start with, stock was hopeless on track). Also they look great, and were brand new so I know they work properly.

Any advice would be welcome, I've spent a lot of money on this and I'm pretty disappointed right now and don't know which way to go for the best.
Click to expand...
i should have a spreadsheet with the math to spec braking system if that would help you
 
howler said:
No it's not, there is too much effort going through the front brakes as they are locking far too easily, I would say it isn't a question of bias given the changes that have been made
Click to expand...

Braking force is a finite amount, if you send bias to the back then there's less for the fronts?
 
The braking effort is too high, not unbalanced from front to rear

Sending the bias further to the rear may fix the problem initially but you'll probably find the rear brakes are doing a lot more than they should. When you hit the brakes hard on track the rears will have too much bite and are likely to lock
 
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