brakes pulsing

[68 Wagon]

I've got 4 wheel discs on my 72 VG30 510. Stock 280zx front, maxima rear with ss braided lines in the rear. Brand new 280zx master cylinder. They work great but "pulse" when you stop.....kinda like something is bent or wobbly in the rotor or something but I have checked all this out and everything is running true. I used the stock proportioning valve as it has 5 lines going into it and the zx pro. valve has 4. I am wondering if the valve is cycling too fast or something and causing this pulsing?

[tr6racer21]

Still sounds like a rotor is slightly warped or caliper not secured properly. Is this a new system, or an older install that has developed this issue? If you haven't done so already use a dial indicator to measure runout on the rotors. You may need to use the lug nuts to secure the rotors tight to the hubs while doing this without the wheels mounted. Check that the caliper mounting is also tight and that you have enough thread depth on the caliper bolts before the shoulder...ie. if you run out of threads and the shoulder bottoms out before the caliper tab is tight you will have pulsation issues. Maybe others can speak to the pro. valve possibilities.

[68 Wagon]

Couple years old. Been doing it since jump. It's done it with the original 280zx rear calipers and my home made rear mounts and with the Maxima calipers and their mounts from Datsuns.com. So maybe a rotor is warped or one of the mounts is goofy. I have a magnetic indicator and will check front and rear rotor runout. The caliper mounts are secured well with no bolt bottoming problems.

On the proportioning valve it occurred to me that I might be able to remove the rear nut on the 280zx valve and replace it with the rear one out of the stock 510 valve. That would then give me my needed 5 lines. Winter projects for sure as Monday we are supposed to get snow.

Scott

[datzenmike]

I don't think the 510 has a proportioning valve does it? Front/rear bias is achieved by the rear wheel cylinder diameter sizing. Could you be thinking of the pressure switch that warns of a system failure?

The master cylinder should have a disc brake residual valve in the front if running rear discs.


As to the pulsing, one or more of the rotors needs to be trued up. It may have some pad transfer or uneven wear on it.

[bertvorgon]

No proportioning valve on the 510.

The "distribution" block on the driver side strut tower is a "shuttle" valve, which, if one of either the front or rear circuits gets a leak, it triggers the brake warning light.

If the rotors are true, then likely as Mike says, there is either a weird area on the rotor(s), from either heat or pad transfer, or corrosion, with pad(s) sitting in one spot for a along time.

[68 Wagon]

Thanks guys for the tutorial. I just had it all apart and all rotors are nice and smooth. I'll get it up on the lift and check run out and really look at everything.

[yenpit]

Did you powdercoat any of the hubs or rotors or ?? Paint lays thin, and typically pretty evenly. Powdercoat lays thicker, and can be UN-even in thickness. If you powdercoated any of the mounting surfaces of the face of the hubs or the backside of the rotors, for example, even when torqued down, powdercoat can cause a very slight off-kilter mating of machined surfaces. I have always taped off those surfaces when powdercoating, or scuffed 'em back down to raw metal.

[McWicked]

This won't help but...

I have noticed that every time somebody has a problem with pulsating brakes, the first solution that gets floated out is "you got warped rotors". This indeed can cause those symptoms, but in my personal experience... it's never been the actual root cause of the problem. Never. In over 20 years of dicking around with my own cars, girlfriends' cars, friends' and co-workers' cars... it's never been warped rotors. It usually ends up being something like a bad bearing, bushings or ball-joints. Hell it's even turned out to be bad tires.

Just doing my part to add to the confusion.
-McWicked

[James]

I've had warped rotors…..Not on a 510 - but a volvo 850 wagon…..warped multiple times (turbo car which I drove hard - went away when I upgraded to larger discs which dissipated the heat better).
On my 510 I thought I did, but ended up being a loose axle nut.
Drums can also go out of round a bit (get them really hot then pull the brake and let them cool). Can add vibration.

You are correct though, that the cause is more likely something else…...

[okayfine]

Well, we can share all sorts of experiences. But we need the OP to jump back in and let us know the braking system is in good shape beforehand, exactly what checks he did, what results he got, etc.

[Byron510]

The dial indicator will not lie!

For the record, I've never seen a warped rotor on any of my 510's either. Big my Mazda 5 has had this issue twice, which really starts my mind working negatively about materials being utilized in my brake system. But one thing is for sure, my bloody little mini-mini vacation has a brake surface even area about 8X that of my 510. The vans rear rotors dwarf my 510's front rotors. And this diameter is what makes the rotor more susceptible to warpage.

Byron

[Sleepys-14]

I work in the auto industry, so I can tell you from first hand experience that OEM(factory) rotor are made in a much more controlled environment. They are much higher quality, and rarely have thickness variations. I can say the exact opposite for aftermarket rotors. 25% of the time aftermarket rotors have .001-.003 thickness variation right off the shelf. 50% of the time warp within the first 10k, and the other 25% of the time are fine. Im just saying the quality is not there with the cheaper rotors. What rotors do I run, you ask? Advanced auto el cheapo's. Out of the 3 sets of front rotors I had on the car this summer, I've had to resurface 2 sets. And in the rear, I had to resurface them before I even put them on the car because they had .002 variation off the shelf. Just my .02.

[68 Wagon]

An update; I too thought let's start small and work up. No powder coat on anything by the way. LF .002 run out. RF 0 run out. LR .011 run out, RR .008 run out. I wire brushed and emery clothed the rotor and hub mounting surfaces on the LR and rechecked run out. It measured .004, quite an improvement. I will do the same to the RR and see what effect that has. I "think" I bought the rear rotors from Rock Auto and picked a Raybestos or Beck Arnley mid grade price range. I try and steer away from the cheapest parts just because they may be junk but the post regarding warpage on many aftermarket rotors may be what happened.

I have always just replaced stuff when doing brakes and then driven the cars. But on this one I had read somewhere that braking could be improved if the pads were seated in by braking hard from speed a bunch of times etc. So I did this. I am wondering now if I warped the rears right off the bat.

I will put it back together, road test and get back to the forum with results. The rear wheel bearings are new too by the way.

[datzenmike]

But on this one I had read somewhere that braking could be improved if the pads were seated in by braking hard from speed a bunch of times etc. So I did this. I am wondering now if I warped the rears right off the bat.

This may be what can cause pad transfer. Extremely hot rotors with new pads resting against them. If doing this to 'cure' the pads with drive them for another 20 min with out stopping even for a second to let them cool down. Don't know if this is true but I've heard of sudden extreme panic stops doing this to slightly older pads that were never fully cured.

This may not apply to today's pad formulae.

[bertvorgon]

Each manufacturer has different criteria for bedding in new pads/old rotors...new pads/new rotors, or combinations thereof.

A lot of today's pads are pre-cured, to try to eliminate this problem, but, the quality of the rotor material has a huge effect on how the brakes will feel. Checking the manufacturers site is the best.

After market stuff is crap for the most part, as I too have experienced "warped" rotors on our GM tracker, when we put aftermarket on. And we are NOT hard on brakes. Same with my old Aerostar, went through rotors like crazy, they were just plain too small for a vehicle that size.

New rotors should be lightly sanded is what I have always done. HOT pads sitting against a rotor are bad. I'm with Mike, do some good hard stops, but plan on being able to drive a reasonable distance to let natural air flow cool everything down.

I have NEVER warped rotors on my 510, and I can guarantee you they have been NUCLEAR.

Maybe get some #80 grit paper and put a good cross hatch on the rotors, give a pass on the pads, and try again.

I pulled this from TIRE RACKS site for you.....


Brake Pad and Rotor Bed-In Procedures


All brake pads must be bedded-in with the rotor they will be used against to maximize brake performance. The bedding-in process involves a gradual build up of heat in the rotors and pad compound. This process will lay down a thin layer of transfer film on to the rotor surface. Following the bed-in procedures provided by the manufacturer will assure a smooth, even layer of transfer film on the rotor and will minimize brake judder. Here are a few things to keep in mind when installing new rotors and pads:

When installing new pads, the rotors should be new or at least resurfaced to remove any transfer film from the previous set of brake pads.

It is critical that the installer clean any rust, scale, or debris from the hub mounting surface thoroughly and check it for excessive run-out with a dial indicator gauge before installing the rotor.

The new rotor should also be checked for excessive run-out using a dial indicator gauge before the caliper and pads are installed. If a rotor has excessive run-out of over .004" (.10mm) it should be replaced.

If your new rotor has excessive run-out, please contact our customer service department for a replacement rotor. Do not install and drive using the rotor! Rotor manufacturers will not warranty a used rotor for excessive run-out. Running with excessive run-out on the hub or rotor will cause vibration issues.

Failure to follow these procedures may result in brake judder, excessive noise, or other difficulties in bedding-in the new brake pads. The pads need a fresh surface to lay down an even transfer film. Residue from the previous pad compound on the surface or an irregular surface on a used rotor will cause the pads to grip-slip-grip-slip as they pass over the rotor surface under pressure. The resulting vibration will cause noise and telegraph vibrations through the suspension and steering wheel. This vibration is known as brake judder or brake shimmy. This is typically caused by an uneven transfer film on the rotor surface or an uneven surface on the rotor not allowing that transfer film to develop evenly. This is often misdiagnosed as a warped rotor.

Bedding-in new pads and rotors should be done carefully and slowly. Rapid heat build up in the brake system can lead to warped rotors and or glazed brake pads. Most brake pad compounds will take up to 300-400 miles to fully develop an even transfer film on the rotors. Following are the recommended bed-in procedures from each manufacturer:

AKEBONO

400 to 500 miles of moderate driving is recommended. Consumer should avoid heavy braking during this period.

ATE

400 to 500 miles of moderate driving is recommended. Consumer should avoid heavy braking during this period.

BREMBO Gran Turismo

In a safe area, apply brakes moderately from 60mph to 30mph and then drive approximately 1/2 mile to allow the brakes to cool. Repeat this procedure approximately 30 times.

HAWK

After installing new pads make 6 to 10 stops from approximately 35 mph with moderate pressure. Make an additional two to three hard stops from approximately 40 to 45 mph. Do not allow the vehicle to come to a complete stop.When completed with this process, park the vehicle and allow the brakes to cool completely before driving on them again. Do not engage the parking brake until after this cooling process is compete.

NOTE: Hawk racing pads (Blue, Black, HT-10, HT-12) may require a different bed-in procedure. Contact your sales specialists at the Tire Rack for racing application information.

POWER SLOT

Follow the brake pad manufacturer's recommended break-in procedure taking care not to produce excessive heat in the system. Avoid heavy braking for the first 400-500 miles.
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