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Discussion Starter · #1 ·
I have a 9c1 rear that i was wondering would it bolt up directly to rms?are the two rears the same length? Any help will be appreciated thanx!
 

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[From memory] I think the RMS uses the standard sedan axle. The 9C1 axle is a little narrower. It is not a big difference, but if you are running larger rims/tires then it might be a concern. Pre-crash there was someone that put one in his RMS. He had SS wheels/tires and had clearance issues [tires occasionally rubbing on the inside of the fender wells]. He put in spacers and it was good enough.

- The axle mounts are the same.
- The disc brakes will swap directly over to your RMS axle.
- If already have posi (and it works), the 9C1 posi is the same unit. [There is a market for good used posi's if you decide to get rid of either or just keep it for when (not IF) your posi goes out.]
- There is not much difference between 2.93 and 3.08 to justify the cost of swapping the internals. [If you have 2.72 gear, it MIGHT be worth it.]
-If you go to the 3.08 gears, your speedo will be off a little. It requires a PCM flash/tune to correct it. [LOTS of advatages in doing this, if you have not done so already.]

If you have the clearance between the inside of the wheel wells and the tires, then its your call whether to swap the whole axle or just pieces.
 

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Discussion Starter · #3 ·
[From memory] I think the RMS uses the standard sedan axle. The 9C1 axle is a little narrower. It is not a big difference, but if you are running larger rims/tires then it might be a concern. Pre-crash there was someone that put one in his RMS. He had SS wheels/tires and had clearance issues [tires occasionally rubbing on the inside of the fender wells]. He put in spacers and it was good enough.

- The axle mounts are the same.
- The disc brakes will swap directly over to your RMS axle.
- If already have posi (and it works), the 9C1 posi is the same unit. [There is a market for good used posi's if you decide to get rid of either or just keep it for when (not IF) your posi goes out.]
- There is not much difference between 2.93 and 3.08 to justify the cost of swapping the internals. [If you have 2.72 gear, it MIGHT be worth it.]
-If you go to the 3.08 gears, your speedo will be off a little. It requires a PCM flash/tune to correct it. [LOTS of advatages in doing this, if you have not done so already.]

If you have the clearance between the inside of the wheel wells and the tires, then its your call whether to swap the whole axle or just pieces.
good info!

heres my situation:

I bought a 9c1 rear adn swapped it into my wagon to be able to use adapters for these boyd coddingons i had. i no longer have the wheels. I want to put my ss wheels back on the wagon but they dont fit now because the 9c1 rear is too narror. i really dont want to run spacers anymore.the 9c1 rear thats in my wagon needs to be rebuilt. I have all the parts including new ring and pinion for the rebuild. my plan is to get the rear rebuilt with new posi and gears, then swap that rear onto the roadmaster sedan once ive found the ss rear. im just worried about clearance issues with the SS wheels on the sedan
 

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Some of this already mentioned, just repeating for clarity.

Wheel opening of the RMS is basically the same as 91-92 Caprice, all used the NARROW housing.

RM's used only 8.5" ring-gear axle, so no driveshaft issue.

The only thing that has to change physically will be the park brake cable setup, which is specific for disc brakes.

9C1 used 3.08 or 3.23 ratio, so you will have to update the PCM for correct speedometer calibration.

Having a used 9C1 axle can be a mixed bag--take a good look at the condition of the rotors, calipers, pads and especially caliper brackets--slide pins have a history of seizing and the brackets do wear at the pad contact areas, and it may be a good plan to just replace them.

The hose to each caliper, if original, should be replaced.

Inspect the axle hard line to make sure it's not damaged or crimped in any way.

Might as well check the axle shafts, wheel bearings and all seals--pinion and both axle seals.
 
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