Today I began installing the front 1990 grand am brake upgrade on my 86GT. The machined fiero hubs were bought from a member in the Mall. The rotors I bought are Wearever YH141376 and are for the 1990 Grand Am WITHOUT the WS6 package and do not clear the machined hub.

What is the dimension the hub is supposed to be machined to? Currently it is about 5.5" while the inside of the rotor minimum hub clearence is about 5 1/8".

Do I have the wrong rotors or is the hub supposed to be machined further down?

That appears to be the correct part number for the brake rotor. You have to turn down the Fiero hub to fit the inside diameter of the G/A rotor, with a little bit of clearance just to be safe. About 0.010" of clearance should do the trick.

It sounds like they just cut the rotor off (all that is needed for the Lebaron or C4 brake kits) and didn't turn them down to fit inside the Grand Am rotor.

Who did you get them from?

If you send them to me, I can turn them down to the right dimension for a Grand Am kit for $50 shipped. They will fit in a medium USPS flat rate box.

Hubs for the Grand Am kit:


Hubs for the LeBaron, C4 or C5 kits:

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fieroguruperformance.com

Thanks bummer that I didn't test fit the rotor before installing the bearings (grease). I should have a friend with a lathe to machine the parts but if not I'll get in contact with you fieroguru

Well I found a few things out when chucking these hubs up in the lathe. First one of the two wasn't even initially machined centrally from the factory. There is an obvious "wobble" as it spins (viewing from the backside) where the thickness is not consistent. It goes from 0.2 inches to 0.4 inches roughly in thickness on the backside. Even the other hub measures at roughly 0.4xx inches and I am afraid any more machine work will leave too thin of a wall.

I'm currently working on uploading some pictures to show my issues and will be contacting the forum member who sold me them to see what we can do about the product I currently have. One of them seems pretty off to be balanced properly and I don't think it's useable for any brake upgrade.

**Looking again at the pictures fieroguru posted, maybe I don't need to worry about the thin wall and just cut more material off to remove the wall entirely. This would reduce the "uncentered" cut that the hub came with initially.



You should be able to see the difference in the hub on the left if you look at the outer wall thickness around it's circumference.

[This message has been edited by KaijuSenso (edited 05-28-2014).]

Man, that looks to Me like that hub is Unusable ! that'll be so unbalanced there will be No way to rebalance it.

Many cast parts are not completely uniform or true as they are cast... while you might not like the look of these, you will be hard pressed to buy new ones that are cast "perfectly". I buy a lot of new hubs from my local Napa and see some from time to time that have the same "as cast" irregularity.

Once the hubs pictured are turned down to fit inside the Grand Am rotor, the thin side of the outer ring material will be completely removed and the thicker side will still have material in the outer ring. On the hubs I machine for the Grand Am swap, I take the rear portion of the hub down and completely remove the outer ring and only leave the 5 support spokes. Doing it this way isolates the remaining "as cast" imbalance to the center hub surface.

Rotational vibration comes from 3 main factors: mass of the imbalance, distance from the imbalance from the rotational center, and rate of rotation. Since this additional weight will be quite small, about 1" from the rotation center , spin at about 880 rpm at 60 mph (24" tires), I doubt there will be any noticeable vibration.

If you wanted to, you could take the hubs in and have them rebalance by removing material from the exposed webs.