M35 Brake Bias After R34 Conversion

[Thrifty]

Hi Guys,

I recently converted my NM35 from the factory front brakes to calipers and rotors from a R34 GT-T. I used the factory lines and removed the restrictors from the calipers.

After the conversion the brake bias seemed to be hugely out, I assumed this was due to the master cylinder not being able to keep up with the front brakes and fitted a BM50 from a S15, this improved pedal feel but the bias is still completely off.

e.g. after a normal around town drive the rear rotors would be 70 degrees while the fronts are 40, after a hard drive the rears will be 150 degrees and the front 70. The front rotors are glazed while the rears look like they are doing all the work and have a nice wear pattern.

Im beginning to wonder if removing the restrictors in the calipers is what is causing this problem.

Has anyone else had this problem, and what did you do to fix it ?

[scotty nm35]

Sounds like you haven't bed the front pads in correctly.

I had nice front bias with the sumitomo's, running the factory master and stock rear callipers.

I have now too much rear running the Brembos. You can change the bias using pad compound to some extent I found.

[iamhe77]

M35 master cylinder not keeping up with R34 brakes?

It keeps up fine with my Z34 Akebono's so perhaps yours was on its way out?

[PN-Mad]

Well, for a start, the Silvia BM was the wrong direction. They run a higher level of rear pressure before bias is stabilised. Nissans run 0.4 rear to front as a rule I've read.

I can't say I have the same issue. I have r32 gtr calipers on mine, with restrictors removed, and it brakes fine. Had it on the track, and didn't notice any terrible front or rear bias.

[Daleo]

I have been for close on 2 years running the exact same setup as you are running with absolutely no bias issues.
Mine pulls up hard & straight time after time with excellent pedal travel & feel.

The "restrictors" you speak of; are simply the double flare brake line seats for the GT-t OEM lines; they do not do any kind of restricting at all.

Are you absolutely sure you have the calipers on the right way up (bleed nipples at the top) and have introduced no air into the system, or the ABS module?

Sometimes silly things can bite you on the arse; you would be shocked at how many peolpe have intalled the Sumitiomo calipers upside down.

[scotty nm35]

Sometimes silly things can bite you on the arse; you would be shocked at how many peolpe have intalled the Sumitiomo calipers upside down.

Or how many workshops have...

[M35woah]

What does it feel like when the bias is not balanced?

Aren't the rear calipers getting hotter than the front because the rears are smaller? Isn't one the reasons of going larger calipers is that they won't suffer from fade as quick as the stock brakes will?

Did you measure the temperature of the rears before you did the conversion?

[scotty nm35]

Measuring the temperature of the brakes will only waste your time, the rear disk mass is much less than the 34gtt disk and will heat quicker, it will also cool quicker. (as Matt was getting at)

I would be looking at your pads, what compound are they? What brand?

[Thrifty]

I have been for close on 2 years running the exact same setup as you are running with absolutely no bias issues.

Mine pulls up hard & straight time after time with excellent pedal travel & feel.

The "restrictors" you speak of; are simply the double flare brake line seats for the GT-t OEM lines; they do not do any kind of restricting at all.

Are you absolutely sure you have the calipers on the right way up (bleed nipples at the top) and have introduced no air into the system, or the ABS module?

Sometimes silly things can bite you on the arse; you would be shocked at how many peolpe have intalled the Sumitiomo calipers upside down.

It pulls up straight, but the pedal is very light for around half of the stroke before the brakes start to drip fairly hard.

Yep, made sure the calipers are the right way up. I was actually suspicious of the problem being air in the ABS module. We have bled the system around 3 times now and each time get some air out.

I'll vacum bleed the system and see if that improves it.

[Thrifty]

What does it feel like when the bias is not balanced?

Aren't the rear calipers getting hotter than the front because the rears are smaller? Isn't one the reasons of going larger calipers is that they won't suffer from fade as quick as the stock brakes will?

Did you measure the temperature of the rears before you did the conversion?

The main reason I think the bias is out is because I can lock up the rear brakes on it, easily. The wear on the rear is also quite pronounced while the fronts just look glazed.

Im going to vacum bleed the whole system and look in to getting some decent pads, it currently just has whatever the local repco had on the shelf (probably crap)

[scotty nm35]

Yep, plenty of air in the system by the sounds.

You need to clamp the lines before you rip the stock calipers off, otherwise the air can get into the ABS unit as you found.