300zx brakes knock sound??

[i2ice4m3]

Hey all! Two problems:1) I installed the z brakes 2 weeks ago and i've just started to brake hard with them. When i stomp on them, I hear a single knock sound coming from the brakes-i think it's the passenger side brake. Anyway, it knocks once and then slows down fine. This happends each time i step on it hard. If i slow gradually and then progressively harder, no sound. 2) The brakes dont feel as responsive as i expected-my friend replaced his brake pads and rotors on his stock 240sx brakes, but his car seems to stop a lot faster. My brake pads are new, caliper used, and the rotors were resurfaced when i got them. By the way, the rotors were redrilled to a 4 lug pattern and a 1/4in spacer was used to clear the z brakes. I was thinking the rotor might be moving around. Thanks a lot guys and happy driving!

[YamaOni]

What size is your Brake master?

[Dori Dori]

Did you use shims on the pads? If not, they could be moving around.

As for how the car feels...what kind of pads did you use? What kind of fuid? I'm assuming your lines are SS, so that's not an issue. Is your master cylinder stock? If your friend is using more aggressive pads, then his car may have more initial bite. His pedal may feel better too if he is using SS lines and some good fluid. And if your m/c is stock, it may be having a hard time moving 2x the # of pistons.

[i2ice4m3]

hey thanks for replying guys. The brake master cylinder is a stock 240sx one. And Yes, i did use shims on the pads. The lines are SS. I didnt know brake fluid mattered- i used some super-tech brake fluid from wal mart with some castrol brake fluid. Castrol is rated for dot 3 and 4, while the super tech is dot 3. It seems like the master cylinder makes a whole lot of difference..since it's moving 4x the number of pistons right? I think the stock caliper uses a single piston- i only saw one pot. Could it be the rotor also? i'm picturing the lug holes in the rotor hitting against the stud everytime heavy braking occurs. Also, should i worry about pistons themselves? Thanks for the help!

[Dori Dori]

Brake fluid does matter. One thing worth noting is that I've always been told never to mix brake fluids. Now, I don't know why or how true that is...it's just something I don't do. Anyway, if you want something good, I reccommend Motul. I used Motul 600 in my WRX and loved it.

As for that clicking sound, I really hope it's not a poor redrill. If it is, I don't know how long those studs will last considering studs break pretty easily. Check to see if the rotor moves around on the studs. Also, are your calipers rebuilt or taken from a junk-yard?

Oh, and it's 2x the pistons.

Stock 240: 2 2 1 1 = 6

300zx: 4 4 2 2 = 12

[i2ice4m3]

ahh..silly me to think the stock front brakes are single piston. anyway, i'll try changing the brake fluid to a better type. I havent seen motul on store shelves. Also, the calipers are from a junk yard. Do they need to be rebuilt? how much does that run usually?

[Dori Dori]

Rebuild kits are like $25/pair I think. Not sure though. You can also order a new set from Discount Auto. They'll charge you a core fee, but you get it back when you return your calipers. It'll end up costing you around $25/caliper I believe. So your rotors checked out OK then?

You'll probably need to order the Motul online unless you have a motorcycle shop or a race shop near you...sometimes they'll carry it. Super Blue is also a good choice.

[i2ice4m3]

I'll have to investigate the brakes when i get home. I'm thinking about selling them too, since I need the money and stock brakes will work just fine for my street application- i shouldve gotten my priorities straight before i did the upgrade. Anyway, Thanks a lot guys for your help!

[18hr]

one more thing that you will want to look at is what tires you and you friend are using. If you are using a tire that has a 400 treadwear and he is using something with a 140 treadwear, his car is going to have more bit (he has more grip).

Everyone always forgets that you need good tires to make your brakes and suspention work. If you have bad tires you going to get bad resoponse, if you use good tires you get good response. Even the D1 drifters in Japan uses race tire, they don't just run out and get the cheapest tire they can get.

[i2ice4m3]

thats true, but i dont think that has to do with my situation since i cant even get the tires to screech by applying the brakes. maybe less than all 4 pistons per caliper are working? is it possible the pistons get "stuck"?

[Dori Dori]

Even though your tires aren't screeching, they are still very important in stopping distance.

I really think you should get some rebuilt calipers or rebuild your own. Also, did you ever figure out what was clicking?

[i2ice4m3]

The sound the brakes are making are more of a thump- a brief, low-pitched "GuNGk". Not sure how to describe it but thats the best i can do :P . I think i feel the pulse through the pedals too. Could it be a piston is "stuck" and engages later than the other pistons and when enough pressure builds, it "shoots" out and hits the brake pad? It could explain why progressively hard braking doesnt make that noise.

Yeah i'm pretty set on rebuilding the calipers myself. Anybody ever done this? I'm at college right now so i rarely have time to go home, where i have the tools. Car's with me though, so i can do all the driving i want to try and troubleshoot. Anyway..thanks yall! By the way...i'm about to win a 300zx brake master cylinder off ebay. Hope that thing helps too...and i hope it works!

[Dori Dori]

I don't know what to tell you about that sound. Rebuilding your calipers is a good choice.

Also, about what you're feeling in the pedal, maybe you have air in your lines? If you are changing the master, you'll have to bleed the lines anyway. Good luck.

[Drift Machine]

By the way...i'm about to win a 300zx brake master cylinder off ebay. Hope that thing helps too...and i hope it works!

Yeah, too me that seems like it could be your problem.

[i2ice4m3]

hey guys i sold the z brakes...I figured there is no need for some huge brakes for street. Anyway, upon installation of my stock ones, I noticed I could lift the front passenger strut/spring assembly easily. I tried on the other side, but it was stiff. I believe the culprit behind that "knock" sound is a blown strut. When i braked hard, the weight transfers to the front and then strut gets compressed. Well thats my theory...what do you guys think?

[C-Kwik]

Actually, I'd check to make sure all the suspension parts are bolted on tightly. A blown shock would not make it any easier for you to compress the spring. Chances are something might be loose.

As far as the comment about mixing brake fluids, if they use the same base, it is okay to mix. Most brake fluids(Dot 2-4) are based on Glycol. Even some synthetics(Dot 5.1). Silicone based fluid(Dot 5) is not compatible with glycol based fluids.

Lastly, pedal feel tends to suck with a stock 240 master cylinder. It will require a longer pedal travel before the same pedal pressure is felt. But, because of the higher clamping force and larger diameter, you essentially get more brake torque. I can lock mine up quite easily if I try. If you could not lock your brakes, you may have had air still in your system. And a stuck piston tends to get stuck in the out position, which causes the pads to drag on the rotor. The fluid pressure can usually pop any siezed piston out. But there won't be enough force to suck a siezed piston back in.

[i2ice4m3]

A day before i put the z brakes on, I changed the two lower frame braces where the T/C rod attaches. In the process, i removed the sway bars and also the T/C rods. Maybe something with those components. I'll have to investigate it. I dont get how braking abruptly would cause that jolt. If it were loose suspension components, the jolt should occur whenever the suspension is traveling. Regarding the suspected blown strut, my impression of wheter a strut is good or bad is whether it will rebound when it is compressed. They are tokico blues, by the way. Well thanks for your time and input!

[C-Kwik]

A loose caliper can easily cause that. I just fixed this exact problem on a friend's car over the weekend. And it's likely a loose suspension piece may cause noise during suspension movement, but I wouldn't rule it out.

Shocks don't cause rebound. Compress a spring and the spring itself is what causes the rebound motion. Shocks only slow movement of the spring to control oscillation. If your shocks are blown the car will want to bounce on the springs. Or rather it will bump(compress), then rebound, then bump, then rebound, etc... A good suspension should settle very quickly in most scenarios. Optimally, with little or no oscillation...or bump, rebound, stop.

[i2ice4m3]

How do you define "loose caliper"? If you are talking about the two 19mm bolts that hold the caliper assembly to the spindle (i think its the spindle), I bolted them tightly. How did you fix the problem? Also, I have gas shocks-do they work the same way as oil shocks? Thanks a loT!

[C-Kwik]

take your wheel off and grab a hold of your caliper. Try to wiggle it back and forth. If it moves, your caliper is loose. If thos 19mm bolts are tight against the caliper, there should be no problems switht he calipers.

This does not apply to sliding calipers though.

[i2ice4m3]

I had my friend move my car back and forth, braking hard. After braking from a forward motion, i notice the whole suspension/wheel assembly moves forward, as if pivoting on the strut mounting plate! This motion is minute, but one can see it- the way the wheel looked while undergoing hard braking was abnormal. Also, while turning i sometimes hear that clunking noise-but dont feel it much. The only thing I can think of that would allow the suspension to move that way is the T/C rod bushings being shot. I have the whiteline bushings sitting around...but its SOO hard to get the old bushings out!