Serious Pulsation With New Rear Rotors (Q45)

[carcrazyguy]

I was doing some brake work on the car (94 Q45). I put new pads, boots, lube slide pins, etc.Anyway, I noticed that rotors on the rear were getting thin...nothing horrible but thin none the less (original w. 200K). I already had put front rotors on this car a couple years ago so they were fine. So I bought a new pair of rear rotors...and installed them.Now, once I test drive the car, the brakes pulsate like crazy.

I put the old rotors back on and everything was fine.

Upon searching I could not find anyone with the exact same circumstances, but similar. Here are the diagnosis from the old posts - hub warp in one case and new rotors needing time to wear in on the other. However, when I put the front rotors on a few years ago, there was no issue at all with them needing a "break in". Any ideas?

[Q45tech]

Aftermarket rotors are known for not meeting specs out of the box, why there is a picture/proceedure for measing runout in the FSM brake section.

If they exceed the 0.0028" spec you can feel it in drivers seat fore/aft motion as you slow down.

[maxnix]

Must measure hub and rotor runout or we're just guessing.

[carcrazyguy]

If they exceed the 0.0028" spec you can feel it in drivers seat fore/aft motion as you slow down.

Yes, that is what it feels like. Will they "wear in" over time or will I need to have them cut or lathed? Could this be a hub issue?

Quote »Aftermarket rotors are known for not meeting specs out of the box[/quote]Are OEM (Nissan) rotors 100% right out of the box? The (aftermarket) set I put on the front were smooth from day one...was I just lucky?

[Q45tech]

When a customer insist on aftermarket we insist on a PAID mild retrueing of the brand new units before installation. Unless it is a ultra premium unit like power stop.

Faster to just do a mild cut out of the box than to set up and measure runout.

1mm wear limit = 0.0254" and a mild cut is 0.003" you can see that 8 mild cuts would not wear rotor to minimum.

The metal box that catches the slivers of rotor metal, weighs a lot and needs emptying frequently.

Over it's entire life the 1mm per side of a front rotor wears off 0.7 pounds of metal [rear about half that]..........only 2-4% reduction in new vs worn out weight

[bullittandy]

Yes, that is what it feels like. Will they "wear in" over time or will I need to have them cut or lathed? Could this be a hub issue?

Are OEM (Nissan) rotors 100% right out of the box? The (aftermarket) set I put on the front were smooth from day one...was I just lucky?

They won't get any better and since the originals were smooth you might throw those back on. I've bought two sets of aftermarket for my 97, one was decent and one was awful. When i bought a set of brembo's from Nopi they were great from the start. I do think you got lucky with the other aftermarket set.

[carcrazyguy]

Here is another idea I had...let me see what you guys think. If I were to put the original rotors back on, yet in a different position would this not tell the tale?I had always put the rotors on exactly the same with the two puller holes and the big hole at the same place in repsect to the studs (you can see the age markings on the hub)In other words, if I put the old rotors back on differently and the brakes are still smooth, would I not then know that the new rotors are suspect. On the same lines, if doing this caused the pulsation I would then suspect the hub...correct?

[goody90q45]

If you're going to swap rotors why not take the new set while they're off the car to your local brake shop and have them measured. This wouldn't take a shop but a couple of minutes and probably wouldn't cost you either.

[carcrazyguy]

If you're going to swap rotors why not take the new set while they're off the car to your local brake shop and have them measured. This wouldn't take a shop but a couple of minutes and probably wouldn't cost you either.

I guess I could try that, but in my area, it is unbelievable how unknowledgeable tire or brake shops are, and even the "pros" at dealerships and specialty shops. For whatever reason the only shops that flourish here are really old school. New ones will pop up and dissapear within weeks.A couple examples of recent issues: 1.When I bought aftermarket wheels recently it took me a month to find one that (kinda) knew how to balance an aftermarket wheel (with an overbore hub) and they went out of business. Worse yet, no local shop had even heard of a stick on wheel weight, and I had to stop them from hammering a weight on the wheel's front edge!And brakes - forget about it. I never found anyone that could measure / cut the rotors / hubs on my previous Z32 (which require on car lathes). Naturally they had never heard of such a thing.When I do use local shops (as a last resort) I often end up having to explain things to them - and I really don't know squat either, so they are in really bad shape. See my issue...

[carcrazyguy]

On a slightly different note, what is the trick to getting the brake grease inside the slide pin boots. I got some in when I did the brake job, but made a mess of it!

[Q45tech]

I usually replace the boots and slide pins [plus shim set] on my vehicle every 2nd set of pads...............80k is long enough to expect these things to function.

Cleaning things up takes longer than just replacing the old scored/dirty/ items.

Be sure to rebuild/replace calipers [clean bores, polish pistons, replace piston seals] PLUS HOSES every 150k increment.

[carcrazyguy]

Update, I put the old rotors back on in a different position and even tried swapping them from left to right and there was no vibration, so I believe you guys were right in that the new rotors were not true.So for now I will run the original rear rotors, and keep the new ones I bought...until maybe I can find an "on car" lathe - wouldn't that be nice!

Also, about the last question, is there is a way to get grease down in the slide pin boots periodically (between brake jobs). I was thinking of maybe a syringe? Any ideas. I had replced everything as you recomended but made the mistake of putting it all back together before I put grease in the slide pin boots - so I ended up making a hella mess trying to do so without dissasembling everything again.