In this thread I look at Rockauto to get dimensions for GA hub....
Then later I figured "What is Fiero hub dimensions?" Why? Because these # will tell you dimensions needed to make hub centric shims. And is not a typo... I mean Shims.

# you need is "Brake Pilot Dia" and Different between both #s is 0.021" (for rear Fiero hub)
0.021/2=0.0105"

So it look like if you wrap 0.010 shim stock, wire, etc, around Fiero's hub and now you are hub centric for GA rotors. (Remove rust etc...)

30 AWG Wire is 0.0100" (Source: Wiki)
Coat hub w/ glue then tightly wrap wire. Only need to wrap about 1/4 inch on hub...

At least will help in back... Front need different shim.

I think for front, GA Brake Pilot (2.295) - Fiero Wheel Pilot (2.244) = 0.051 / 2 = 0.0255

22 gauge wire = 0.0253"

Why do I need to center my rotor? 0.025 and 0.010 is small but off center rotors can mess w/ wheel/brake balance at highway speeds. (Back rotor maybe ok. 0.010 is very small) + GA rotor are heavier... Hub centric rotors will stop that.

Hub #....

84-87 Fiero (rear hub)
MOOG Part # 513011K
Wheel Bolt Quantity=5
Flange Dia=4.921"
Bolt Circle Dia=3.937"
Bolt Size=M12X1.5"
Wheel Pilot Dia=2.244" <-- Hub Centric for Wheel.
Brake Pilot Dia=2.274" <-- Hub Centric for Rotor..
Flange Offset=1.66"
Hub Pilot Dia=2.795"
Splines=33

84-87 Fiero (front rotor)
CENTRIC Part # 12162018
Wheel Pilot Dia(Hub Reg)=2.24" <-- Will be Hub Centric for New Rotor.
Brake Pilot Dia=N/A
Part off Rotor section so hub area will meet GA Flange Dia (=4.921" Proper Diameter so that any GA rotor will fit!)

90 GA
MOOG Part # 513017K
Front Wheel Bolt Quantity=5
Flange Dia=4.921" <-- Proper Diameter so that any rotor will fit!
Bolt Circle Dia=3.937"
Bolt Size=M12X1.5"
Wheel Pilot Dia=2.244"
Brake Pilot Dia=2.295" <-- Hub Centric for Rotor.
Flange Offset=1.749"
Hub Pilot Dia=2.894"
Splines=33

What some # means...


------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

[This message has been edited by theogre (edited 11-17-2011).]

WOW! I never looked into all this when I did my GA upgrade. I just slid the calipers on and bolted up my wheels. They spin perfect and have NO vibrations. That car rides wonderfully. I don't think it's a big issue.

errant post

[This message has been edited by weaselbeak (edited 10-15-2011).]

quote Originally posted by jwrape: WOW! I never looked into all this when I did my GA upgrade. I just slid the calipers on and bolted up my wheels. They spin perfect and have NO vibrations. That car rides wonderfully. I don't think it's a big issue.

Vibration can be too small for driver to notice, even at highways speed. (And some are racing and see speed higher than highway...) You suspension will notice if you have off-center rotors.
Also, Some lugs/holes are tighter fit... So off-center error can be smaller than expected but lug holes aren't meant to be use as center point for rotors.

Many will do the job just like you. Some have vibration problem. (Search in archives.) Some just want hub centric rotors. This method & info should work/help.

[This message has been edited by theogre (edited 10-15-2011).]

well. Looks like TheOgre was right.

I'm having vibration issues with the new Grand Am Rotors-Calipers up-front swap.

I've re looked at everything and even after tighening the spindle nut to 12ft lbs (while spinning the rotor) and then backing off and re-tightening nut by hand, still the issue continued.

I even tried keeping the spindle nut @ 12ft lbs torqued, and that seemed to help a little, but still the vibration issues continue.

The problem is the slop in the fitment of the grand am rotor with the old machined front rotors/now hubs. There is too much play in the rotor with it not being centered. Add that the stock 14" fiero gt wheels don't center properly against the hubs and grand am rotors, and hence the vibration.

TheOgre is right. We need to properly center the grand am rotor around the fiero hubs. With that said we need to run hub centric rings around the od of the front hubs to keep the rotor snug.
Might as well buy some hub centric rings for the wheels as well.

Looking @ Ebay now...tons of them on there. Just got to get the right sizes.

Dave M.

Theogre,

Since you are dealing with diameters, won't wrapping wire (or shimstock) around the hub result in a new diameter equal to the old diameter + 2 X the wire diameter?
If that is correct, then you need thinner wire or shimstock.

Larry

ooh this might be my problem!!!! i have the ga brake upgrade in the front and am having major issues with wobble. so .025 or 22gauge wire around my hub before i put on the rotor to center the rotor and the tire correct? or after the rotor is on?.

quote Originally posted by imacflier: Since you are dealing with diameters, won't wrapping wire (or shimstock) around the hub result in a new diameter equal to the old diameter + 2 X the wire diameter?

For front, GA Brake Pilot (2.295) - Fiero Wheel Pilot (2.244) = 0.051 / 2 = 0.0255

Diff in Diam = 0.051
0.0255 is for wrapping shim/wire to fill up the area.

quote Originally posted by mmeyer86gt/gtp: So .025 or 22gauge wire around my hub before i put on the rotor to center the rotor and the tire correct? or after the rotor is on?.

before rotor goes on. Only need to wrap hub in 2-3 turns of wire

All,

This is an Experiment because no-one else bothered and/or posted the dimensions to buy/make rings. Worse, many are told to use inside of GA rotors Hat area as machining measurement for Fiero hub... Big problem... Doing later brake job and maybe new rotors won't fit. People have gotten burn by this issue.

Why only an Experiment? I just restore my OE brakes last year... I'm very happy w/ the results and not in any hurry to "upgrade."

Notice to that all of dimension are hub dimensions. Rotor's hub hole is slightly larger on purpose.

You may need a thinner wire/shim for Tolerance. Dimension is simple GA - Fiero = Difference / 2 = needed shim size
Need a different shim for use in another rotor? Just look up hub/axle info of that car. Check Rockauto... (Rockauto is source for info above...)

I'm not sure how you attach shim/wire. Glue in short term.
Solder/etc? Maybe heat can damage the hub. But make wire into a tight ring and slip onto hub would work.

This shim/wire can come out... install tire w/o center cover on and pull shim/wire out thru hole if you're worried. 1-2 ounces at center shouldn't unbalance the assembly.

Info should help for buying rings.

I've update first post to include some front rotor dimensions.

Note... When using lug centric to install tires... Needs Cone lugs and Tire can't see any load until lugs are tight.

Hi Guys

Did some investigative work.

According to my Vernier Caliper. my stock 85 v6 front hub is roughly 56.28mm or 2.23" wide in diameter.

While the Grand Am Brake Rotor's center hole is 58.08mm or 2.28" wide in diameter.

So there's a gap of 0.05" or 50 thousandths.

That's not really enough for a problems. The Problem is that with the Grand AM Rotor sitting on top of the fiero front hub (formerly the stock fiero front rotor, the original center hub is covered by the rotor so there is no lip to hold the stock 14" Fiero wheel on center while tightening the lug nuts.

The answer would definitely be to have a hub centric ring around the hub on the spindle, but there is nothing to hold it in place after.

I spoke to FieroStore.com and they said they don't machine anything off the face of the front Fiero discs when they apart the rotor off and make them into front hubs. They did say that with the Grand AM brake swap up-front, the brakes go from a formerly hub-centric based to a lug centric setup.

I am going to try using some wheel spacers 5x100 (10mm wide) that have a hub centric ring on there, to see IF it solves the vibration issues.

Will keep everyone posted.

p/s tried 0.025" = 0.6mm MIG wire around the gap of the brake rotor and spindle hub. It helped center the brake rotor, but the problem lies with the wheels not be centered against the rotor.

Dave M

i went and put some 20gauge wire between my hub and rotor without taking off the rotor and it solved my shimmy problem. i am sooo happpy and the fix only cost .50 so now i need to looking to get a ring / sleve for my hub for my rotor so it stays centered!!

well... read up about center bores and the hub centric vs lug centric Logic:

"The centerbore of a wheel is the machined opening on the back of the wheel that centers the wheel properly on the hub of a vehicle. This hole is machined to exactly match the hub so the wheels are precisely positioned as the lug hardware is torqued down. Keeping the wheel precisely centered on the hub when it is mounted will minimize the chance of a vibration. Some wheels are vehicle model specific and will come from the factory with a bore machined to match that vehicle. Some wheels are designed to fit multiple vehicle models and will use a centering ring system to reduce the bore size to match the hubs of different vehicles. These rings keep the wheel precisely positioned as the lug hardware is torqued down.

Some wheels are non-hub centric by design. These are known as lug centric wheels. With these wheels it is critical to torque the lug hardware with the vehicle on jack stands, off the ground. This allows the nuts or bolts to center the wheel and torque down without the weight of the vehicle pushing them off center."

So I put the car on jackstands and took out all the wheels and then slowly centered all the lug nuts by hand, and then had a buddy push the brake pedal while I torqued the lug nuts 100 ft lbs.

Took the car out for a spin...Vibration issue continues : (

Again the problem to me appears to be that the back fiero spindle-centerbore (with Grand Am Rotor in place) is 0.380" tall, and up front, what's left peeking/portruding fwd is only 0.125"... No room for the wheel to be centered on the lugs.

David M.

Personally I haven't had the problem. However, it occurs to me that wire is not necessarily the best answer.

I have lots of guitar wire in various gauges. You go to a music store and you can buy the wire from .009 through to .017, or spun wire from .022 up to .056

It seems to me that aluminum muffler tape might be better. It seals on with heat and you can layer it up pretty precisely. It also won't shift like wire can do.

Just a thought.

Arn

quote Originally posted by n_tensetuning: Took the car out for a spin...Vibration issue continues : (

IF diameter on flange area > 4.92" then flange might not sitting on flat area in hat on rotor.

Did wheel or tire change? Tire are old? Hit something?
Can be a tire problem...
Rotate wheels see if that help/changes
Check Wheel balance. (Even got new tires...)
Check tires for broken belts. If sidewall have a depression running bead to thread then likely has a bad belt.

Can do more but need to "break" tire bead...
Tires and many wheels have off center construction. Most time is not a problem but If they both are mounted with "high" spot aligned...
1. Mark tire and wheel.
2. Break bead.
3. Rotate tire 180* around wheel
4. Inflate.
5. Balance the assembly.

[This message has been edited by theogre (edited 11-19-2011).]

There is something else that is a bit of a mystery to me Ogre.

My wheels have conical lug nuts. They self center. So how can the wheel get out of true with the spindle?

Arn

Right, you are talking just the rotor getting off alignment, not the wheel. Oops.

[This message has been edited by Arns85GT (edited 11-19-2011).]

quote Originally posted by Arns85GT: My wheels have conical lug nuts. They self center. So how can the wheel get out of true with the spindle?

Cone's self center only with wheel don't see any load... Loading wheel, like dropping jack to stop wheel spin when torquing lugs, cause lugs/bolts to slightly bend and other interference.

I have lug centric wheels. Method use is in brake upgrade article. (Need to put in Tire article soon.)

I saw your oopp... but a good Q.