Those with J30/Q45 brakes inside please

[ZiG]

So I just did the q45 front brake upgrade on my ABS S13. Rebuilt the calipers, too. Now my problem is the pedal feels too soft for my liking. At first I thought I just didn't bleed them well enough, so I did it again and they still feel the same. I can put the pedal to the floor (with the engine running) if I really push on it.. Has that been the experience of others, too? Most people say the stock MC is 'fine' but I dunno. Would a 300ZX BMC be too much for these brakes or should I go with a Q45 BMC instead?

[ZiG]

wow.

maybe i should summarize:

will a 300zx bmc be too big for a q45 front brake swap

[R-Yahne_240]

dude your fine make sure your brakes are throughly bled the size of your mc will not effect your pedal feel just how much pressure will be applied to the hydrolic system

air compresses so if its in the system it will cause bad feel

ps if the mc is bad that will distroy your vaccum pressure draw from the motor and not allow proper pressure to be applied to the brakes

[ZiG]

Huh.. from the terminology used in the articles I have been reading, I was getting the impression that the mc does indeed change the pedal feel.

I should like to use a z32 mc, but my fear is that it will be too large, causing the brakes to hit their normal locking point with the pedal only pushed in like an inch (and that the mechanical gain caused by the difference in piston cylinder diameters will become such that it takes much greater force on the pedal to generate the same pressure at the calipers).

[mopower13]

I do alot of research before changing things on my car especially major things like brakes and every brake swap I have read said you should go with the coresponding mc but I was looking at the z32 swaps you may want to check those forums.

[R-Yahne_240]

i did q45 brakes on my car with the 5 lug conversion and no problem with the floating calipers z32 have fixed calipers soo maybe they are a different

ps your mc is shot if you can put the pedal to the floor with it running allowing stupid feel

[pmkls2]

mc size directly affects pedal feel, travel, effort, whatever you want to call it. If the pedal feels spongy with the brake upgrade then yes you can go to a z32 mc. There are 3 different sizes that you can choose from. I believe that a 1" would be the next size up for an abs equipped s13. For the record it doesnt negatively affect the vehicle keeping the stock mc it just changes the pedal feel and each driver has their own preference. some people even do a z32 conversion and keep the stock mc and the brakes work ok the pedal is just way too soft. As for myself, the stock pedal is spongy enough with the stock calipers. I tried a 1 1/16 z32 mc with my stock calipers and it was too stiff so i went back to stock for now. In any case, the decision is up to you. If the pedal feels too soft go with the next larger size mc. You will have to do the research to find out which z32 came with what size mc, but advance auto parts lists the sizes on their website so all you need to do is start looking up mc's for a '90-'96 300z and find the one that lists a 1". You also need to double check the factory size of your mc. I believe the abs cars have a 15/16" mc. I know for sure that my non-abs s13 has a 7/8" mc. Your factory mc will have the size in inches in the side the lines come out between the mounting point and the rearmost brake line. If yours is a 7/8" you could go with a 15/16" mc but like I said before I think thats what you have and the 15/16" mc is harder to get. HTH,Phil

[R-Yahne_240]

dude spongey is different then soft

spongey means air in the lines soft just means soft

if the pedal is going to the floor something is wrong not just a "bad feel" problem

[pmkls2]

dude spongey is different then soft

spongey means air in the lines soft just means soft

if the pedal is going to the floor something is wrong not just a "bad feel" problem

Firstly if you read his original post he said his pedal feels too soft I am the one who used the word spongey as I fail to see the difference. Regardless on many unmodified cars with a properly operating brake system the pedal can be pushed to nearly or all the way the floor with less effort than one would imagine depending on the system design. I know these facts as I have been an auto technician for 10 years and am GM and ase certified to repair brake systems. Secondly I did leave out 2 vital pieces of info that I believe he has already covered. First he believes he has properly bled the system of air and although some abs equipped vehicles can be a bit difficult to bleed simply replacing calipers shouldnt allow air to enter the system that far up the lines. Second I took it under assumption that the mc was in proper working order. With those 2 factors out of the way the pedal's "soft" feel comes from the leverage principle that a hydraulic system operated under. By replacing the calipers with units that have a larger volume it now requires less effort to depress the pedal and exert x amount of clamping load, but subsequently it also takes more pedal travel in order to do so. By increasing the diameter of the mc bore it requires less pedal travel to displace the same amount of fluid, however it also requires more effort to exert the same pressure on the other end of the system i.e. the calipers.

[pmkls2]

oh and by the way ZiG the only problem you would encounter with a z32 mc would be the pedal feeling too firm. By going with a larger mc you lose the mechanical advantage and therefore it is actually herder to make the brakes lock up.