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Just venting here----and trying to help out anyone else trying to order some stock, disk brake rotors for a '75 Z (or any other '70-78 plus Z).

 

I tried ordered online stock replacement rotors for my '75 z from Rock Auto and what they sent was a rotor with a bolt circle diameter of 4.055 9 4 1/16"). The box was marked with the part number from Centric that matched their online listing number for a '75 Datsun 280z. So to return them I had to answer several questions one of which was does the part number on the box match the description that is posted online, so I went back and studied the description and under info it reads that the bolt hole center line  was 4.055", which I didn't catch because to my knowledge there is only one bolt hole centerline for the early Z's (4.5").

 

There is no way to contact Rock Auto and notify them that they have a mistake in their online catalogue (I checked and all the other lines of rotors for the '75 and they all listed 4.055 as a centerline, so I sent them back and ordered from Parts Geek.

 

I ordered Raybestos rotors (part num. 412570) for a '75 Datsun 280z and just got them in today and guess what, bolt centerline diameter is 4.055", so these will have to go back. If you read their small print it states that they will not cover return shipping even if the part does not fit. This is getting expensive.

 

So I drove down to O'Reiliy Auto parts and tried to order a pair of rotors for a '75 Datsun 280Z and before ordering, I asked what the bolt center line distance was and ----------yep, he said 4.005". So I whipped out my phone and did a search for what the bolt center line distance is for a '75 Datsun Z and showed him three different sites verifying 4.5" as correct. I asked him how they could go about getting me the correct rotors and they shrugged their shoulders. 

 

So I drove over to an old established Auto supply store/distribution warehouse and, you guessed it, they listed  the rotors cl as 4.055 but the counter guy looked up a number of suppliers and found an old listing for a Raybestos rotor for a '75 Z with 4.5" a bolt centerline distance and a part number of 9064R----- but they were no longer a supplier for them and therefor could no longer get them for me.

 

So I came back home and looked up what NAPA had to offer and NOOOOOOOO, they listed the 4.055 cl, just as all the others.

 

Has somebody supplied all of these outlets with inaccurate information regarding these rotors bolt hole centerline distance?

Is there some Datsun of this vintage that these incorrect rotors have been mistaken to fit the Z?

Has anyone else had problems with ordering stock rotors from one of these sources?

I am currently discussing this issue with my counsel (Mr. Beam, that's Jim Beam) and thought I would post this situation.

 

 

PS. I will be in LA next week and will stop by MSA and pick up a pair.

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I just got on Rockauto and looked at several and even the 1980 280ZX shows 103 mm (4.055") as the wheel bolt circle diameter.  You've supplied numbers but have you tried the rotor on the hub?  Stuff happens.  Not really sure what the issue could be.  Hard to imagine that all of the rotors, from 240Z to 280ZX are the wrong size.  They all show 103 mm as the size, at least for Raybestos parts.

 

Could you share those three links?  They'd be good to see.  Might be that one is measuring bolt (actually lug) centerline diameter and one is measuring lug hole inside edge diameter.  Might actually be  two different, but correct, measurements.  Maybe the rotors actually fit.

 

1 hour ago, Cruzzar said:

did a search for what the bolt center line distance is for a '75 Datsun Z and showed him three different sites verifying 4.5" as correct

 

https://www.rockauto.com/en/moreinfo.php?pk=391343&cc=1209316&jsn=2073

 

https://www.rockauto.com/en/moreinfo.php?pk=1075555&cc=1209158&jsn=2143

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The mounting bold diameter for the rotors is correct at 103mm. The rotors don't slip over the wheel mounting studs like in newer model cars they bolt to the rear of the hub. The mounting bolt pattern to attach the rotor to the back of the hub is 4x103.

 

Source - I produce brake kits for the S30 and have personally measured the rotor mounting bolt diameter.

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Sounds like you've got at least a couple sets of the correct rotors by now.  4 x 103mm (4.055") is indeed the correct hole spacing for the rotor mounting, and has nothing to do with the lug spacing for the wheel studs (4x114.3mm), as confirmed by the others.  

 

If you don't have the FSM yet, you can download it free at:  http://www.xenonzcar.com/.   Front rotor replacement is covered in the "Front Axle" chapter.

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I have the rear hubs apart so the stub axle is available and it definitely does not fit into the 4 holes in the rotor. The centerline distance between the opposite holes where the lug studs goes is too short ! My measurement indicates about 4 1/16".

 

Lowrider, thanks for the clarification,  I have not taken the front end apart as I have just gotten this Z from a friend who has had it stored since '94 and am replacing all the brake workings. I just jumped the gun in assuming that they fit in the conventional method.  Do I have enough egg on my face?

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3 hours ago, lowrider said:

The mounting bold diameter for the rotors is correct at 103mm. The rotors don't slip over the wheel mounting studs like in newer model cars they bolt to the rear of the hub. The mounting bolt pattern to attach the rotor to the back of the hub is 4x103.

 

Source - I produce brake kits for the S30 and have personally measured the rotor mounting bolt diameter.

 

I had forgotten about that myself.  Rotor bolts (not lugs) on one side and wheel lugs on the other.   Seems to the source of the confusion.

image.png.e540d2c5f9943e5667d0caae122ba613.png

image.png.84006da8c59596a56ef1d4a3c8c90ccc.png

 

 

 

Edited by NewZed
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So just to clarify, as your first post says you bought factory replacement brake discs for a 75 280z.  You are installing a msa rear disc conversion kit & the recommended 280zx rear rotors do not fit over the hubs.  You have confirmed part numbers & tried multiple sources.

It sounds like you are getting front rotors, can you post a picture?  

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I ordered two sets of rotors. One pair for the stock '75 Z font end and one pair for the rear Nissan Maxima upgrade. When I opened the boxes I grabbed my rear drive axles that I had apart to replace the carrier bearings and made sure the rotors fit the stud pattern. The rotors for the back fit just fine when I lined up the studs. The stock rotors for the front did not fit over the studs as I had thought they should. What I did not know is that the rotors bolt on the front hubs and do not fit over the studs as most conventional rotors do. As I posted  earlier I am slowly rebuild the brake system on the Z that has been parked since '94 and when I ordered rotors for the back I also order new rotors for the front. I have not disassembled the front suspension yet so I was not aware of how the rotors mounted. When I opened the boxes I incorrectly assumed (sic) the wrong method of installation . Had I broken down the front end I would have remember and noted that the rotor hats bolt on the back side of the spindle and not slid over the studs.

My original post dealt only with the front rotors since that is the only disk brake option on a stock '75 Z. I did not mention the rear conversion to avoid responders getting confused with what I was asking for. The confusion I was having is that the mounting bolt pattern for the front rotors is 4 on 103mm (4.055) which is correct when you bolt them on and not try to slip them on over the studs that are on a 4 on 114.5 mm bolt pattern.

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