924Board.org

!tom · Posted: Fri Jun 24, 2011 5:25 pm Post subject: Part issues

As some of you may have clued in, I'm in the middle of a 5-lug conversion. Since the front donor rotors were worn beyond the minimum thickness, I placed an order for 4 new rotors, figuring I might as well replace everything.

This is what I ordered.

Turns out they don't fit.

They don't fit for two reasons.

The holes for the studs are a bit too small to fit over the knurls on the studs. I'm guessing the studs were replaced at some point with longer studs (same length as the front studs, but they don't have to go through the thick aluminum, so the usable length is longer). This would be easy to remedy with a drill. I measured the dameter of the holes, and it appears as though they are ~0.1 mm smaller in diameter than the old rotors that fit.
The big issue is the hole in the middle of the rotor to center it on the hub. This hole is WAY too big on the new rotors. It's around 10 mm larger in diameter than the old rotor (that fits properly).

The 5-lug donner was apparently a 931.

What gives with the hub hole in the rotors? Am I supposed to be able to use these rotors even though the hole is way too big to center properly?
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78 924 NA
5-lug

emoore924 · Joined: 13 Apr 2004 Posts: 2822

Sounds like the wrong rotors to me. I thought the 924/931/early944 vented 5-lug rotors were all the same so what you show in this link I thought would fit. Maybe you have a conversion from a later (85.5+) 944 or something. Maybe put some pics up of what you have and we can have a look.

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

On my car that is currently apart, the rotor fits somewhat loosely over the studs and on the hub. It is effectively centered by the two screws that hold it to the hub.

*clicky*

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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

emoore924 · Joined: 13 Apr 2004 Posts: 2822

Here's a pic of late rotors someone is selling on pelican. Is this what you have?

http://forums.pelicanparts.com/porsche-924-944-968-used-parts-sale-wanted/603937-fs-2-brand-new-front-slotted-frozen-rotors.html

Shurick · Joined: 15 May 2005 Posts: 524 Location: Russia, Moscow.

5-lug 931 had the same rotors and steel trailing arms that had the early 944. and 924S got the updated aluminum trailing arm and rotor from 944 85/2.
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WBR, Shurick
'79 931 -- intercooled K26-3060-6.10 turbo @ 1.2 bar, EFI+EDIS, 951S brakes, stripped interior, 951 look.
'86 924S -- R.I.P.
https://www.instagram.com/ru_pacecar/

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Disagree. 924, 924S, and "early offset" 944 all use the same rotors.

And FWIW, 924S got rear hubs and trailing arms from the 86 951, giving it late offset with skinny body.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

!tom · Posted: Sat Jun 25, 2011 6:21 am Post subject:

!tom · Posted: Sat Jun 25, 2011 7:14 am Post subject:

My hub is designed for a rotor with a 90mm diameter hole in the middle. That's the size of the donner rotors.

The ones I linked to above have a 103mm diameter hole in the middle.

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78 924 NA
5-lug

!tom · Posted: Sat Jun 25, 2011 7:17 am Post subject:

Shurick · Joined: 15 May 2005 Posts: 524 Location: Russia, Moscow.

!tom · Posted: Sun Jun 26, 2011 5:59 pm Post subject:

Problem solved, inasmuch there wasn't really a problem in the first place. The rotor still centers itself on the outer edge of the hub.

The old rotors had two flanges used to center it, but that's redundant. The new ones have just one, which is good enough.

The issue I mentioned about the studs was a non-issue; it was the rotor hanging up on the hub on the inside, rather than hanging up on the studs. A whack with the palm of my hand got it to go on all the way, showing how the outer edge of the hub really is centering the rotor.
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78 924 NA
5-lug