Early/late front rotor interchange

[cat herder]

My 1980 ElCamino needs front rotors soon... OK, it needed them like 15 years ago. This is not a brake conversion thing, just stock replacement stuff.

Question(s): Is there any benefit to the '82-up rotors with the bigger outer bearing? Does the '82-up setup fit on '81-down early spindles? Inner bearings are the same, outer bearings are the same ID but larger OD but I don't know if the inner-to-outer spacing distance is the same. Anything else I need to know if I were to do this, or is it a nothingburger with no real benefit and I should just use the correct catalog parts and not worry about it?

 

[abbey castro]

Avoid trying to guess at what fits or doesn't fix. Stock replacement is all you need.

 

[pagrunt]

Plan & simple, '78 is the odd ball year, '79 & up all fit but '79-'81 have inch studs with '82 & up use metric studs.

 

[cat herder]

So, don't upgrade anything, just use what the catalog says? This is my first car and I don't want to mess anything up...

Just kidding, I bought this car as a roller nearly 30 years ago and it's been through more engines than I have fingers. I just thought that as common as these cars are that someone would be able to answer without me having to resort to buying parts and test fitting everything myself. Yes, the car still has the same grooved-up rotors on it now as it did when I bought it. Somehow they haven't gotten any worse in all that time.

pagrunt, thanks. I totally overlooked the stud issue. I was too focused on the outer bearing difference. And there is a bearing difference - the outer bearing outer race OD is bigger on the '83-up. The outer bearing inner race ID is the same on both versions.

1978:
Outer Diameter (IN) 1.781
Inner Diameter (IN) 0.75
(rotor bore is the same, spindle journal is smaller)

1979-1982:
Outer Diameter (IN) 1.781
Inner Diameter (IN) 0.8437

1983-up:
Outer Diameter (IN) 1.9687
Inner Diameter (IN) 0.8437
(rotor bore is larger, spindle journal is the same)

 

[scoti]

The rotors don't fit the same on the spindles.

You need the correct rotor for the early spindles & same for the later ones. If you try to put the later 'metric' rotor on the earlier spindle, you won't be able to seat the castle-nut/cotter key combo. I've read/heard it's 78/79 & then '80-up. I've also heard 78-80; '81-up. So, to dumb it down, just use a replacement rotor that correlates to the bearings.

 

[pagrunt]

Make it simple, using Rabestos p/n's from Rock Auto here is the break down.
5064R, '82 to '87/'88, 12mm studs
5038R, '79 to '81, 7/16" studs
5034R, '78 only, 7/16" studs
If I had my GM parts books handy I would used that for their p/n's plus add the spindle's p/n.

 

[cat herder]

So the factory changed the outer bearing in '83 for no reason? There was no problem they were trying to solve there? So no benefit to changing a 1.781/.8437 bearing to the later 1.968/.8437?

Factory changes designs all the time based on issues that show up in the field. Using later parts on earlier vehicles to solve or prevent potential problems is, I thought, as common as dirt. Guess I've been modifying cars wrong for 30 years.

I'm not saying I WANT to do this, I was just asking if it was commonly done. I guess not.

 

[pagrunt]

So the factory changed the outer bearing in '83 for no reason? There was no problem they were trying to solve there? So no benefit to changing a 1.781/.8437 bearing to the later 1.968/.8437?

Factory changes designs all the time based on issues that show up in the field. Using later parts on earlier vehicles to solve or prevent potential problems is, I thought, as common as dirt. Guess I've been modifying cars wrong for 30 years.

I'm not saying I WANT to do this, I was just asking if it was commonly done. I guess not.

FRom what I've seen with me replacing my complete '81 from with one from an '86 including the complete front suspension & steering parts is the spindles are the same. I put the rotors & bearings listed for '81 on with no issues with fit or function. As noted earlier, when in doubt always look up your specific year.

 

[64nailhead]

So the factory changed the outer bearing in '83 for no reason? There was no problem they were trying to solve there?

Sounds like you’ve never owned a Ford.

 

[ck80]

So the factory changed the outer bearing in '83 for no reason? There was no problem they were trying to solve there? So no benefit to changing a 1.781/.8437 bearing to the later 1.968/.8437?

Likely no, they weren't.

Automakers ALWAYS like to save money. When one part can be used across more car lines, with more interchanges, the more money they save both from setup costs for manufacturing runs, and, needing to keep less stock on-hand. Why pay for double storage space, double inventory taxes when 1 part can go into 2 applications instead of one? Then imagine if you can use the same part for even more applications.

Go compare how many different applications the different parts fit. Look at models phased out, models added.

parts get changed ALL the time to neither solve a problem nor improve performance.

Factory changes designs all the time based on issues that show up in the field. Using later parts on earlier vehicles to solve or prevent potential problems is, I thought, as common as dirt. Guess I've been modifying cars wrong for 30 years.

Possibly yes, if your criteria for making a mod is seeing there was a change during production and assuming it was to correct a problem or improve performance in every case the part was changed during production.