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Discussion Starter · #1 ·
I am massively confused on the part number for the 9C1 master cylinder. I have a 1995 9C1 and I want the larger 9C1 style MC. Could someone please tell me what the correct GM and/or AC-Delco part number is? (or any equivalent)

The B-Body parts fiche/CD has this to say (get ready to be confused....):

Above, GM #18030951 / AC-Delco #18M709 is listed 3 separate times.
For 96 Police it says 1 1/4" cylinder bore (this would be 31.75mm).
For 95 Police, it says 21mm (this would be .83").
For 95-96 Rear Disc it says 28.6mm and 40mm bore (converts to 1.125" & 1.575")

I am confused! How can the same part number have 3 different cylinder bore dimensions?


Also, the local AC-Delco parts warehouse guy wants to sell me AC-Delco #174-715, which he swears is correct for what I want. Below is all the parts CD has to say about AC-Delco #174-715. I don't know what the cylinder dimensions are for it.


If the correct 9C1 master cylinder is no longer available as a replacement part, then I'll go ahead and rebuild. The part number stamped on the bottom of the master cyl. body on the car now is GM 18012985. I don't know if this is original -- so I don't even know if this is the one I really want Wouldn't want to go to the trouble of rebuilding the smaller master cylinder.

Help!

-- Dan
'95 9C1
 
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Discussion Starter · #2 ·
Update.

I tore down the existing MC and measured the bores. Both are 1 1/4" (31.75mm).

I don't think this is the "larger 9C1 master cylinder". Is it?

If I want the "larger 9C1 MC" should I still be looking for one which has 28.6mm and 40mm bores?

I've read all the posts I can find on this and I'm still confused.

Anyone? Anyone?

-- Dan
'95 9C1
 
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Discussion Starter · #3 ·
OK. On further reading, it looks like the 1 1/4" for both bores is the 9C1 MC.

Impala SS's got the 1 1/8" (=1.125" = 28.6mm) bored MC. God knows what that 21mm deal is on the parts fiche / CD -- or why they all have the same part number UNLESS one MC cylinder now REPLACES all the varying dimensions that once existed.

So, looks like the 1 1/4" MC is what I have to find. Any way to tell the bore dimensions without pulling the thing apart? I'm going to take my existing MC body with me for external comparison. Not sure if that will tell me anything...

-- Dan
 
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Discussion Starter · #4 ·
Maybe if I just talk enough -- I'll figure it all out. Kind of like going to a psychiatrist...

Went to the AC-Delco parts warehouse today. Purchased AC-Delco #174-715 (GM #18029971) for $183 + tax. This is identical to the 1 1/4" bore MC cylinder I took off the 9C1. Didn't disassemble the new MC -- but they have the exact same 18012985 part # stamped on the bottom of the MC body. The 174-715 / 18029971 part # is for the whole kit, meaning: MC body, resevoir, cap, diaphragm, etc.

As for the AC-Delco 18M709 part #, the parts guy said that this is an AC-Delco aftermarket part, whereas the 174-715 / 18029971 is an OEM part.

-- Dan
'95 9C1
 
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Discussion Starter · #5 ·
Heh, even though nobody was replying to your post, rest assured somebody has found it useful. :)

I actually want to make a 94 Roadmaster have the brake feel that my 90 9C1 does. Do you know if I can just buy this master cylinder part and be done with it? Or will I have to change the brake booster as well.

Thanks!
Chris
90 9C1

Originally posted by Dan Mrvos:
Went to the AC-Delco parts warehouse today. Purchased AC-Delco #174-715 (GM #18029971) for $183 + tax. This is identical to the 1 1/4" bore MC cylinder I took off the 9C1. ...the whole kit, meaning: MC body, resevoir, cap, diaphragm, etc.

As for the AC-Delco 18M709 part #, the parts guy said that this is an AC-Delco aftermarket part, whereas the 174-715 / 18029971 is an OEM part.

 
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Discussion Starter · #6 ·
Dan,

Thanks for the research and information. There always seemed to be some confusion about the 9C1 master cyclinder and you cleared it up. :D

Regards,
John
 
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Discussion Starter · #7 ·
ok now i have a question... i have a 96 SS so what is the propper a/d delco and gm part numbers for me???
 
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Discussion Starter · #8 ·
cdt9c1 and mess21,
Sorry but I don't know the answers to your questions. I hope someone else on the forum will.

What I did learn through this experience AND from this thread: http://impalassforum.com/noncgi/ultimatebb.php?ubb=get_topic;f=23;t=001494#000000

... is that the b-body parts fiche/CD has a lot of mistakes. Errors creep in between GM and the outsourced company that does the publishing of the parts books.

I guess the only real solution when you run across stuff that doesn't make sense is to talk to a knowledgeable person on this forum -- or a local GM or AC Delco parts man who you trust.

-- Dan
 
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Discussion Starter · #9 ·
Dan,

What is even more interesting is that looking at the AC Delco parts info, the Caprice in several iterations, including with rear discs, uses the same M/C as the Impala SS--ACD #174-715.

The 18M709 ACD Durastop (non-OEM) M/C is the only part that actually is listed as having a 1.25" bore, but ACD also says it is other sizes, too, depending on application, and reads exactly the same as for the Impala SS. And this is direct from the ACD website. (this info may look like crap as it displays here)

1996 CHEVROLET CAPRICE CLASSIC V8 5.7L 350cid GAS FI N Engine VIN = P
Qty
Req Qty
ACDelco Part# Description

BRAKE/WHEEL HUB / MASTER CYLINDER

01 174-715
CYLINDER,BRK MAS
With RPO ANTILOCK DISC BRK(JL9) 4 DOORS


01 174-715
CYLINDER,BRK MAS
With RPO ANTILOCK DISC/DRUM BRK(JM4) ^ SEO TAXI CAB(9C6)


01 174-724
CYLINDER,BRK MAS
With RPO ANTILOCK DISC/DRUM BRK(JM4) Without RPO SEO PUBLIC SERVICE VEH(1A2) ^ SEO TAXI CAB(9C6)


AR 18M708
CYLINDER,BRK MAS DURASTOP
40 & 28.6MM CYLINDER BORE)(RR DRUM BRAKES)(W/PB Without RPO SEO POLICE CAR(9C1) ^ SEO TAXI CAB(9C6)


AR 18M709
CYLINDER,BRK MAS DURASTOP
REAR DISC BRAKES 28.6 & 40MM CYLINDER BORE


AR 18M709
CYLINDER,BRK MAS DURASTOP
With RPO SEO POLICE CAR(9C1) ^ SEO TAXI CAB(9C6) 1 1/4 CYLINDER BORE)(RR DRUM BRAKES OR 4 WHL DISC BRAKES)(W/PB


1996 CHEVROLET IMPALA SS V8 5.7L 350cid GAS FI N Engine VIN = P
Qty
Req Qty
ACDelco Part# Description

BRAKE/WHEEL HUB / MASTER CYLINDER

01 174-715
CYLINDER,BRK MAS
With RPO ANTILOCK DISC BRK(JL9)

Further confusion, from the 1994 models--same info listed for both Caprice and Impala SS:

1994 CHEVROLET CAPRICE CLASSIC V8 5.7L 350cid GAS FI N Engine VIN = P
Qty Req Qty ACDelco Part# Description
BRAKE/WHEEL HUB / MASTER CYLINDER
01 174-715 CYLINDER,BRK MAS
With RPO ANTILOCK DISC BRK(JL9) 4 DOORS
01 174-715 CYLINDER,BRK MAS
With RPO ANTILOCK DISC/DRUM BRK(JM4) ^ SEO TAXI CAB(9C6)
AR 18M641 CYLINDER,BRK MAS DURASTOP
REAR DISC BRAKES)(WITH POWER BRAKES 1 1/4 CYLINDER BORE 4 DOORS
AR 18M641 CYLINDER,BRK MAS DURASTOP
1 1/4 CYLINDER BORE)(RR DRUM BRKS)(W/PB
AR 18M683 CYLINDER,BRK MAS DURASTOP
28.6 & 40MM CYLINDER BORE)(RR DRUM BRAKES)(W/PB
 
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