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Discussion Starter #1
I just came across a smokin' deal - I got a 9C1 wiper arm w/ the air deflector. It only cost me $200.

What? You say I got ripped off? Well what if I told you they threw in a stock 9C1 dual exhaust (cat-back), tranny support, and a complete rear end (posi w/ discs - not sure of the ratio, but hey, for $200 who cares)? :D

I've had a set of stock Impala SS manifolds (which should bolt right up to my 305 heads) and cats sitting around for a while now. I understand that I'll have to fool with the frame some to get the support to fit correctly.

Anyway, here are my questions: I've read here in the past that there is another piece that I will need to mate the support to the tranny. What is it & does anyone have the part number? (Yes I know, I should do a search through past posts but my dial-up is soooooooo slooooowwwww.)

Also, for those of you who have converted from rear drums to discs - what should I be prepared for? Any brake lines/hoses that I need to have on hand? And will I be able to bleed the brakes properly after making a whole rear end swap (I'll most likely be doing this by myself) or would I be better off paying a shop to make the switch?

TIA
 
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Discussion Starter #2
I believe the other tranny part you need Jay is the tailshaft from a 94-96 car.
 
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Discussion Starter #3
<BLOCKQUOTE>quote:</font><HR>Originally posted by FakeSS:
... Also, for those of you who have converted from rear drums to discs - what should I be prepared for? Any brake lines/hoses that I need to have on hand? And will I be able to bleed the brakes properly after making a whole rear end swap (I'll most likely be doing this by myself) or would I be better off paying a shop to make the switch?
TIA
<HR></BLOCKQUOTE>

Get a 94-96 proportioning valve AND 94-96 9C1 master cylinder.

The rear discs require more fluid volume to operate the caliper pistons to full travel than rear drums, so you need the 9C1 master cylinder. Actually the Impala SS one should work too but I think the 94-96 9C1 master cylinder (from memory) has a larger piston diam so the brake feel is harder. Cops must like it harder... <g>

The proportioning valve, OTOH, can be from ANY 94-96 B platform car. You *will* be doing the proportioning mod to it (described on the IGBA website), so you will have the full rear brake capability.

I don't know about the emergency brake cable. The SS/9C1 rear end uses a drum-in-rotor-hat ebrake, that is cable actuated. The 93 and prior cars use the std rear drums themselves (or at least one shoe) as the ebrake, but I don't know if the cable connection is the same or not. So you might have to go with the 94-96 SS/9C1 ebrake cable; I don't know if it is different from the 94-96 rear drum cars or not. Dal could probably tell you by comparing p/ns. HTH. - Ken
 
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Discussion Starter #4
Ken, is the drum in hat e-brake setup the reason that the rear brakes squeak so badly if you try to engage the e-brake while moving? (I tried to see how long it would take to stop the car with it if my brakes went out, lets just say the E-brake is only useful for holding the car off of the tranny when its in park on a slanted surface).
 
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Discussion Starter #6
Jay, the parking brake cable is different, but the brake lines are not. You should not have any trouble doing the swap by yourself. For the crossmember, you may not need the tailshaft itself, maybe only the trans mount. I am not sure on this, as I cannot remember exactly what my 91's tailshaft and mount looked like. Take a look at where your mount is before you buy a tailshaft assembly.

Axle ratio will be either a 3.08 or a 3.23. Easy to check by watching how many times the pinion rotates for 1 rotation of the axle shaft. Or, look for the stamping on the axle.

2LW : 3.08 open
2LX : 3.08 posi

2LY : 3.23 open
2LZ : 3.23 posi
 
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Discussion Starter #7
<BLOCKQUOTE>quote:</font><HR>Originally posted by Mike454SS:
Ken, is the drum in hat e-brake setup the reason that the rear brakes squeak so badly if you try to engage the e-brake while moving? ....<HR></BLOCKQUOTE>

I don't know for sure, but from what you described, I'd say yes.

The emergency (rear drum) brake that sits within the hat of the rear rotor is TINY, and it doesn't get used much. The squeaky sound was probably from rust and brake lining abrasion. - Ken '94 9C1
 
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Discussion Starter #8
For Ken Rolt--

Regarding the reason for the larger master cylinder on the 94-96 9C1 (1.25 on 9C1 vs 1.125 on Impala SS), I'm inclined to believe that the reason has nothing to do with the rear disc brakes, since they are the same on both vehicles.

It does, I believe, have to do with the greater piston travel on the front calipers, since the 9C1 uses a thicker pad, and the fluid displacement requirements at the point the 9C1 front pads (D614A) have worn to the same point that Impala pads (D614) would be screaming "replace me", the larger M/C would still have enough fluid-moving capability to finish off the extra .090" of pad on the 9C1 and keep the pedal within a reasonable (off the floor) travel range.

I do agree that a 1.25" M/C will (or SHOULD) give a firmer pedal on an Impala, but I don't think the police car engineers at GM were looking for a firmer pedal on the 9C1. I could be wrong, I will admit.

Let the discussion continue--show me how I'm wrong, Ken!
 
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Discussion Starter #9
<BLOCKQUOTE>quote:</font><HR>Originally posted by Navy Lifer:
... Let the discussion continue--show me how I'm wrong, Ken!<HR></BLOCKQUOTE>

Hell no. I think you ARE right.
 
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Discussion Starter #10
Navy Lifer then wrote to me offline and it adds to the further discussion so I'm posting it here:

<BLOCKQUOTE>quote:</font><HR> I've checked--93 9C1 (master cylinder diam) is 1.125", which I believe lends further support to myscenario. The only connection to the 94-96 cars is that the 93 car used the D614 pad, also on 94-96 Impala (RPO JB9). <HR></BLOCKQUOTE>

Then I'd say your idea, needing more MC swept volume to feed the longer throw 9C1 front discs is the correct ones.

Actually, I had written

<BLOCKQUOTE>quote:</font><HR> The rear [9C1] discs require more fluid volume to operate the caliper pistons to full travel than rear drums, so you need the 9C1 master cylinder.<HR></BLOCKQUOTE>

and that's still true. In addition to that, the front 9C1 calipers also demand more fluid because of the longer throw pads (as you reminded me), so I'll say it was for BOTH reasons.

To go any further with this, we'd have to compare the fluid demands for the disc/drum Caprice front calipers and rear drum wheel cylinders, and then compare the swept total volume at the wheels (from min wear to max wear) and as theroetically provided by the MC, against the WX3 with disc/disc and against the 9C1 with disc/disc.

That would be a neat exercise is sanity checking the work of the GM brake engineer(s).

Now if YOU want to look these up, by all means go ahead. <vbg> - Ken
 
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Discussion Starter #11
No need to pursue further.

The original post you made only contained an implicit reference to the rear discs as being [9C1] when in fact they are the same for the [WX3]--ie. Impala SS. Both are RPO J(*)9/JL9 combinations, and rear calipers are the same P/N.

I agree (with Ken) that the combination of larger calipers (NOT rotors, however) with rear discs--found ONLY on the 9C1--is the reason for the 1.25" M/C. In 1993, in Jay's case, the front calipers are the same as the 94-96 Impala, thus it should NOT be necessary to use the 1.25" M/C in his application.
 
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Discussion Starter #12
Wow, it's like I'm back in a mechanical engineering class (didn't stick with M.E.- went electrical instead). I'm finding this discussion very intersting.

It would seem that it all boils down to this:

Do the 9C1 rear discs require more volume (ie - a larger mc) than the 93 rear drums? How many pistons does each rear disc caliper have? I can see where, as Ken says, they may need additional volume - especially if they are two-piston calipers.

Thanks for all the input, guys! :D
 
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Discussion Starter #13
Jay,

The rear calipers are single piston. They probably do require a larger fluid volume, but not enough to go beyond the ability of the 1.125" master cylinder to handle in your application.

The "bottom line" is that if you install rear disc brakes (from Impala of 9C1), the master cylinder does not need to be changed, since you are effectively duplicating the Impala SS setup, which uses the same size master cylinder as your vehicle.

What has NOT been talked about to this point is the power booster used on the disc/drum vehicles compared to that used on the disc/disc vehicles. I'll admit I need to do some research here, but they are different, and the disc/disc boosters are more "powerful", I think. Considering that rear drum brakes are "self-energizing", less force input is ultimately required in the hydraulics to activate the drum brakes than what is needed to activate the rear disc brakes.

So, even though you don't really need to change the M/C, you might need to do something with the booster. If you DO decide to use the 1.25" 9C1 master cylinder, I think you will find the pedal force needed to stop the car much greater if you DON'T change the booster, too.

Waiting for Ken's comments :)
 
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Discussion Starter #14
Just to throw in my unscientific .02 here. I swapped out the rear in my 92 with a 3.23 disc rear and didn't change out the MC and the pedal feels fine. In fact it seemed to stop quicker but that's just SOTP with no data to back it up. I was able to hook up the emergency brake cable with no problems and the only minor snag I ran into is that the ABS lead is significantly longer on the disc rear than the drum one. Just tied it out of the way with zip ties, bled the whole thing and away I went. Total install time with two guys and many floor jacks and stands was about three hours. Didn't even take off the sway bars. And wait till you see the weight diff between the two rears. You'll die when you pick up the drum rear. <g>

Alex Melero
 
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Discussion Starter #15
hey Alex, would you care to expand a little bit regarding the rear end installation? Where did you get the info to install it, etc. Since my axle is leaking differential fluid into my drums, I'm looking at changing the whole rear end. Btw, how much did you pay for the rearend? thanks
 
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I really didn't go by any guide. We jacked up my 92 9c1 and a 94 L99 9c1 side by side. Took off the driveshafts and shocks and unbolted the control arms from where they bolted onto the axle. Swapped them around and reattached everything. My diff was leaking oil too. I got rid of it just in time. I paid $120 and had to give the guy I bought it from my old rear end. He installed it on his and we both drove away happy.
 
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