Q45 Brake problem's got me stumped

Post by **cgh1** » Fri Jan 03, 2003 4:56 pm

I have my father-in-law's 1996 Q45 to look at a brake issue and am scrathing my head over it.

Any application of the brakes above 50MPH results in a shaking of the car. The faster you go before applying brakes the more violent the shake. At 60MPH and a goo firm application of the brakes the dash and steering wheel are shaking like made until the car gets down to about 45, at which it's smooth from there on down. I think the issue is up front, since the steering wheel is shaking the most and I don't get that seat-of-the-pants feel like a problem coming from the rear.

At first I figured warped rotors. I pulled off the wheels and checked on things and it appears the car has fairly new rotors and pads up front and fairly new rotors and a good bit of pad left in the rear. The rotors show no sign of wear and appear to be straight as new.

Any ideas?

Before I pull off the pads to have a look at them I want to get proper torque specs on the lugs nuts and caliper pins. Could anyone help me with these numbers as well?

Thanks in advance for any help!

Post by **Chally** » Fri Jan 03, 2003 4:56 pm

Without hesitation, Machine the Rotors!They might look OK, but are very definately warped.

Post by **Q45tech** » Fri Jan 03, 2003 4:56 pm

The spec is 0.0028" runout not many can differeniate 50 times this by eye......they look ok?

Post by **texasoil** » Fri Jan 03, 2003 4:56 pm

you definitely need to check the runout on th ebrake rotors using a dial indicator. Eyeballing it is not nearly sensitive enough.

Also remove, clean, regrease the bolts/pins on which the calipers float Often those do not get properly cleaned and re-lubed, resulting is lots more brake vibration (shudder) cause the calipers do not float freely.

Post by **cgh1** » Fri Jan 03, 2003 4:56 pm

They "look" OK but I know that seeing is not always believing when it comes to rotors and sight vs. feel. The thing that strikes me is that they look brand new. My father-in-law does not remember when they were last serviced but he is dangerous just looking at a tool (any tool!) and does not keep track of any of that sort of stuff. The owner's manual's not even in the car...and he lives 3.5 hours away so I can't just run over and get it.

At any rate, the front pads look new as do the rotors all the way around. As thick as these rotors are, and as slow as pops drives, I can't imagine him building up enough heat to warp the darned things. That's the part that's got me stumped.

I hadn't thought about caliper mounting being off (thanx texasoil!) but will have to check that too. Is there a place here, elswhere on the web, or could someone help me with torque specs on these things? Having no service manual (or even owner's manual!) really sucks when trying to do these kinds of things. The last thing I want to do is have a caliper mounting pin or some other critical part mis-torqued to compound this problem or create others.

Thanks All!!!

Post by **911/Q45** » Fri Jan 03, 2003 4:56 pm

Slow drivers are often left foot brake guys and ride the brakes, leading to overheating and warped rotors. Caliper mounting bolts and pins are 70 ft lbs.

Post by **cgh1** » Fri Jan 03, 2003 4:56 pm

Thanks for the info 911/Q45!

I've ridden with my f-i-l many times and he seems to be short and hard on the brakes instead of long and lean (this doesn't mean smooth though :-O) ...at least while I'm in the car. his driving style may be comepltely different when I'm not around, who knows.

Looks like there'll be some dial gauge use these rotors' future.

Can you tell me to what torque the lug nuts are supposed to be tightened?

Thanks again!

Post by **Chally** » Fri Jan 03, 2003 4:56 pm

In all seriousness, if you don't know what torque to set ANY brake part, DON'T touch them. Take your car to a brake specialist & get them to do the whole job. I don't mind DIY's, but when it comes to brakes & steering, I'm all for the specialists to take over. Without either of these 2 items wroking properly, you will eventually crash!

FYI I have a spare set of discs that I change over about every 3-6 months, as the front discs warp regularly.

Post by **cgh1** » Fri Jan 03, 2003 4:56 pm

I don't mind DIY work either and do it regularly (on brakes) on my Vette - but I know all the torque specs. That's why I haven' t moved on this car yet. I don't want to change anything until I know how to put it all back - properly. Speaking of which, I'm really surprised that the caliper pins are 70lb-ft. Man, my Vette's only 23. The caliper mounting bolts I can see (Vette's 125 on those) but the pins... They must like you to put your guts into it on these cars!

I am trying to avoid the expense of labor here as we only have 1 Infiniti dealer and they rape people on service work.

Post by **Chally** » Fri Jan 03, 2003 4:56 pm

Good, it seems as if you may be able to handle it OK.

The Slide pins have a torque of 61-69ft/lbs & the caliper bolts have a torque of 53-72ft/lbs.

Stuck slide pins can cause the disc to get hot & warp, so make sure they are lubricated properly, but you still have to machine the discs.

Good luck.

Post by **DAEDALUS** » Fri Jan 03, 2003 4:56 pm

Lug nuts are 72-87 ft-lbs. If you have trouble getting the rotors off, use a couple of screws in the 2 holes near the lug holes to separate the rotors from the hubs. The rear rotors use 8mmx1.25, but I think the front rotors use 10mm screws, maybe 10mmx1.25 or 10mmx1.50. Sorry, can't remember.

Post by **cgh1** » Fri Jan 03, 2003 4:56 pm

Cool!Great info guys - thanks!

Q45 Brake problem's got me stumped

Q45 Brake problem's got me stumped

shudder on braking

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