vt951

I just got done replacing the front rotors on my '86 951. The FSM lists torque spec for the hex bolts that hold the rotor to the hub as 23 Nm (17 ft-lb). This seem really low to me, considering that other than the press fit, these bolts are the only thing to transfer torque from the rotors to the road during hard braking. Anyone run into this in the past and have an opinion as to why the torque spec would be so low? Thanks!

austin944

I think the lug nuts are actually what holds the rotor firm against the hub, not those little screws.

shiners780

Sounds about right. Keep in mind the rotor is sandwiched between the hub and wheel which is torqued to 94+/- ft/lbs. I know some people who don't even use those rotor bolts at all.

schwank

I've done multiple 944's and the brakes on my boxster. The two screws only hold the rotor on when the wheel is off, so they don't have to be very tight. On all of my cars the screws are Phillips head. I don't torque them just make them reasonably hand tight. The lugs/lugnuts, which are tightened to 92 lb-ft, are what actually provide the main holding force.

I've never had single issue with these. They can't really back out because the wheels hold them in.

vt951

You guys are all thinking of the rear rotors. The front rotors are bolted on the hub, and are NOT sandwiched between the wheel and hub (at least on '86, not sure about other years).

Edit: it looks like on 87 and newer, the front rotors are sandwiched like you're saying... on 86 and earlier, they are not sandwiched.

So, my question still stands, should the bolts that hold the front rotors to the hubs on an '86 951 be torqued to only 17 ft-lb?

Darwantae951

Wow, I never knew that early cars were like that. Mine rest on the studs and are held in place by the wheel. I don't know why the torque is so low, but if it's in the manual then can you really argue with them? Looks like there should be a lock washer, and the stress isn't really placed on the nut, but the body of the bolt as the wheel rotates. Just make sure that you have good hardware (or new hardware) and you should be good.

-Darwin

Darwantae951

BTW, did you have to remove the entire hub from the spindle to do this?

-Darwin

Everyone, here is his setup:

xsboost90

yeah those are very low torque spec- and if you over torque they will snap off or warp your rotor possbily- I put mine at about 18lbs just to spite the manal. No problems.

vt951

Yup, had to remove the hub. Wish I could go back in time 25 years and ask Hans and Franz what they were thinking.

vt951

Thanks Dan, good to hear that. I overtightened them first to make sure the press fit between the rotor and hub was seated completely, and then untightened and torqued to spec. Hopefully it works.

dye46

This thread never mentions the torque spec for the 5 bolts that fasten the rotor to the hub from the back side (early cars).

So, what torque did vt951 actually use? 17 ft-lbs?

odonnell

Correct, it's 17 ft-lbs. I use washers, new M8 bolts, and blue loctite when I do them... cheap insurance. I don't think there are washers there normally.

dye46

Thanks, but that sounds a little low to me....only 5 ft-lbs more than the tiny allen head screw that locks the hub nut onto the spindle.

17 ft-lbs still sounds like the torque for the little screws that secure a rotor that mounts over the lug studs, keeping it hub-centric when a wheel (which provides the real clamping force) is removed.

Sorry to be a skeptic, could someone quote from an official source, or explain why such a low value?

thomasmryan

section 46-7 and 46-8

http://www.9ss1.dk/porsche944/garage/vol3/vol3.html

V2Rocket

they're only M8 screws, so much over 17lbft would break them...

the hub is secured with those 5 AND the big collar nut on the spindle...it's not going anywhere.

though it does make you wonder, why do we need M14 wheel studs..lol