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Does anyone know what the differences are in terms of fitment? I've got to make a decision to go to an aftermarket axle or stay with the 9 bolt (another posi cone rebuild is in order), and finding a rear axle that uses third gen brakes is apparently impossible.
oser, for example, sells an axle to fi the 93-02 rear brakes, but not one to fit thirdgen rear brakes, I cant imagine why. I recall these setups being nearly identical, but I've never actually looked at a 89-92 10 bolt disc brake setup, 89-92 9 bolt disc setup, and a 93-02 disc brake setup. I'm sure someone has posted something along these lines already, but my search skills just arent good enough.
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
I believe the 4th gen style is slightly larger size calipers of the same design(PBR) and use a larger rotor. I had the old 9 bolt diff and iirc the rotor size is 10.5, the newer size is 11.5. I personally like having the bigger rotors/calipers. The 4th gen stuff still has support for aftermarket axles and its why I choose to use it and retain my factory wheels.Im running the s60 rearend instead of the moser. Im not 100% sure thats the reason but the 3rdgen stuff vs 4th gen are not directly the same physically.
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
Pretty sure the difference between 89-92 and 93-97 rear discs is the diameter of the rotor, and the 4th gen calipers have the cooling/stiffening fins milled smooth across the top of the caliper.
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
82-88 rear disc are not worth talking about imo. Heavy, prone to leaks, calipers freezing and on and on.
89 is the only year with the 9bolt, larger rotor and aluminum pbr caliper. Has 2 different caliper mounting brackets, early 2 piece (dust shield) and late 1 piece no dust shield.
90-92 have the same brakes as 89 but bracket for 10bolt. Somewhere in late 91 the calipers gained a round vibration dampener. It continued through 97 but sometime on the 4ths it changed and faced forward.
93-97 lost some of the fins on top of the caliper (for wheel clearance i'm thinking), have a couple different rotor designs but are same size. Also, the rotor and bracket have a specific offset in some years iirc.
98-02 got a thicker (larger diam?) rotor, different pbr caliper look, internal parking brake, more complex and more weight
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
Originally Posted by 86White_T/A305
I believe the 4th gen style is slightly larger size calipers of the same design(PBR) and use a larger rotor. I had the old 9 bolt diff and iirc the rotor size is 10.5, the newer size is 11.5.
My 9 bolt has the 89+ disc brakes on it. They are not 10.5” delco-moraine calipers. They are 11.75 or something close to that. Hence why I see no need to upgrade these.
But it sounds like the reason they won’t work is the rotor is a different size on the 93+ cars.
So I’m guessing there are no backing plates available for a ford 9” rear and the 89-92 brakes?
Last edited by InfernalVortex; 12-30-2019 at 08:39 PM.
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
I have Bear backing plates on my big bearing ford 9" rear and 13" 2 piece rotors with my stock 89 formula calipers. I'm sure they make them for stock size rotors too but I used my stock 89 backing plates on the 9" with stock rotors.
rear disc are the same diam for 89-97 but the offset is is different from 3rd to 4th gen rotor
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
My 9 bolt was original to my 86,probably why it had smaller rotors. So if the calipers are virtually the same minus the cooling fins, the only difference is the rotors offset from 3rd to 4th gen. Could a spacer to correct the offset be the solution. Assuming the offset is to bring the rotors further out? Chance are its not :P
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
It appears the 4th gen rears have 11.530 inch diameter rotors. 3rd gen PBR rears have 11.665" rear rotors. So the rotors are .165" smaller, and the calipers are ever so slightly clearanced as well. Probably to fit stock 15" wheels with the new 4th gen offset.
Also was able to verify on Rock Auto that the caliper bracket is the same. So it looks like the only difference is .135" of rotor diameter. That probably means the caliper bracket mounting bracket holes are .0675" closer to axle centerline, so barely more than 1/16 of an inch.
Not sure if the aftermarket axles come with backing plates, but I am guessing they do and that's the issue. The only other question is the rotor hat offset from the rotor surface... rock auto is showing some odd discrepancies, as usual, but it looks like all are in the 1.9-2 inch range. So I dont even think the offset of the rotor is different.I wonder if the 4th gen backing plates on an aftermarket axles could have their holes elongated just enough to fit...
Last edited by InfernalVortex; 01-01-2020 at 11:32 AM.
Reason: fixed some maths
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
I am doing something similar now, i just got a used 12 bolt from a 4th gen and i used to have the 9bolt from an 89 trans am. I took some pics to show the differences. I ordered 95 LT1 calipers, rotors and pads and they look almost identical to the 89 pbr's. new LT1 rotor on inside, old 89 pbr rotor on outside old LT1 rotor on right, old 89 pbr rotor on left, notice the steep step in the LT1 rotor LT1 rotor on right, 89 pbr rotor on left, notice the bolt holes in the LT1 rotor are larger and the machined lip on the 89 pbr rotor on the inside vs LT1
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
Originally Posted by InfernalVortex
It appears the 4th gen rears have 11.530 inch diameter rotors. 3rd gen PBR rears have 11.665" rear rotors. So the rotors are .165" smaller, and the calipers are ever so slightly clearanced as well. Probably to fit stock 15" wheels with the new 4th gen offset.
Also was able to verify on Rock Auto that the caliper bracket is the same. So it looks like the only difference is .165" of rotor diameter. That probably means the caliper bracket mounting bracket holes are .0825" closer to axle centerline, so between 1/16 of an inch and 3/32", not sure how much that matters.
Not sure if the aftermarket axles come with backing plates, but I am guessing they do and that's the issue. The only other question is the rotor hat offset from the rotor surface... rock auto is showing some odd discrepancies, as usual, but it looks like all are in the 1.9-2 inch range. So I dont even think the offset of the rotor is different.I wonder if the 4th gen backing plates on an aftermarket axles could have their holes elongated just enough to fit...
I still have all of my brakes apart waiting on some new brake hardlines that go across the axle and rubber hoses, as mine split after 30 years, lol. Let me know if you need pics of anything, i have my 89 9 bolt rear sitting outside and the 12 bolt in the car and all calipers and brackets still.
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
If you look at the 3rdgen rotor, it has a lip on the outer edge of the pad surface not being used. My guess is that the smaller outer diam won't make a difference at all other than removing a bit of weight.
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
I didn't link the pics I uploaded them to 3rd gen site. I still have the passenger side to bolt up, but from what I can tell, the calipers look to be the same. My backing plate on the 12 bolt is thicker so I had to get longer bolts for the caliper brackets.
keep in mind I am using an aftermarket rear with the LT1 backing plates. If you look on the strange website they say the 3rd gen brakes wont work and you need to convert to Lt or Ls brakes but I don't think they researched that 89 to 97 calipers are the same.
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
Originally Posted by 89gta383
I didn't link the pics I uploaded them to 3rd gen site. I still have the passenger side to bolt up, but from what I can tell, the calipers look to be the same. My backing plate on the 12 bolt is thicker so I had to get longer bolts for the caliper brackets.
keep in mind I am using an aftermarket rear with the LT1 backing plates. If you look on the strange website they say the 3rd gen brakes wont work and you need to convert to Lt or Ls brakes but I don't think they researched that 89 to 97 calipers are the same.
This is what i was suspecting, it looks like you confirmed it! Your picture does show that the PBR rotor is ever so slightly larger, which matches what I saw on Rockauto. You gotta let us know if you're still able to use it. But even so, rotors are a lot cheaper than the rest of the brake setup.
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
I bolted the pbr caliper to the lt1 bracket, remember these are aftermarket brake backing plates. I put a small washer between the caliper bracket and backing plate to space the caliper out the correct distance. 89 pbr caliper on backing plate stange LT1 backing plate
Re: 89-92 vs 93-97 rear brakes and aftermarket axles
A torsen for the 9-bolt? I've read that they exist, but do not fit 3rd gen axles, not convinced they fit the 3rd gen housing either. This is years old info, though, I havent look into it in a long while. Can you show me this?
12-30-2019, 04:56 PM
