Master Cylinder Cap Gasket - The 1947 - Present Chevrolet & GMC Truck Message Board Network

macblazer · 04-29-2015, 04:36 PM

Anyone have any clue where the heck you can find a replacement gasket for the master cylinder cap?

I've got a 1971 Chevy C20 Longbed and I'm having a royal pain of a time finding one that will match.

WarMonger · 04-29-2015, 05:54 PM

Do you have a pic of what you need? I just replaced my Master cylinder and I have my old one. Nothing wrong with the gasket or top cover.

macblazer · 04-29-2015, 07:58 PM

Quote:

Originally Posted by WarMonger

Do you have a pic of what you need? I just replaced my Master cylinder and I have my old one. Nothing wrong with the gasket or top cover.

See the pictures attached

macblazer · 04-29-2015, 07:59 PM

Quote:

Originally Posted by macblazer

See the pictures attached

Basically the rubber gasket seems to be worn out and doesn't seal tight anymore so fluid leaks out from time to time. I've tried a bunch of different places and have yet to find a place that sells just the gasket. Don't really want to replace the entire master cylinder just because of a bad cap gasket.

**johnmiller66** · 04-29-2015, 08:03 PM

If you find one please post where you got it. I just put a new booster and master cylinder on mine. It leaks like crazy out the cap. The top of the master is beat to hell and won't seal properly. I don't really want to change out the master but I might have to. I should of looked over the Oreilys crap before I installed it.

macblazer · 04-29-2015, 08:20 PM

Quote:

Originally Posted by johnmiller66

If you find one please post where you got it. I just put a new booster and master cylinder on mine. It leaks like crazy out the cap. The top of the master is beat to hell and won't seal properly. I don't really want to change out the master but I might have to. I should of looked over the Oreilys crap before I installed it.

Yeah if I can't find a replacement gasket I might just have to replace the master cylinder as well.

Didn't have this problem with my 72 because with that one I had the entire brake system replaced except for the lines back when I got it. So I guess I didn't realize finding this rubber gasket would be this much of a pain in the ass.

Aruba1 · 04-29-2015, 08:55 PM

Can you post a picture of the master cylinder itself? From the upper picture it seems like what you have is a C10 master cylinder. Maybe that is your problem but I believe (someone correct me) that the caps are the same. Here are some pics of C10 vs C20 MC. http://67-72chevytrucks.com/vboard/s...d.php?t=666291

macblazer · 04-29-2015, 08:57 PM

Quote:

Originally Posted by Aruba1

Can you post a picture of the master cylinder itself? From the upper picture it seems like what you have is a C10 master cylinder. Maybe that is your problem but I believe (someone correct me) that the caps are the same. Here are some pics of C10 vs C20 MC. http://67-72chevytrucks.com/vboard/s...d.php?t=666291

Maybe....I can actually check that. I have a 1972 C10 in the driveway right in front of this 71 C20.

Andy4639 · 04-29-2015, 09:14 PM

They advertise it. I would try talking to some one else about it.
Just for reference I was going by the picture posted.
The C/20 maybe different.

http://www.dormanproducts.com/c-504-...r-gaskets.aspx

Shell · 04-29-2015, 09:26 PM

The P/N I posted is for the C10

macblazer · 04-29-2015, 09:38 PM

Quote:

Originally Posted by Shell

The P/N I posted is for the C10

I'll check the master cylinder on my 72 C10 tomorrow and see if it matches the one on the 71 C20. If so I'll just order the C10 one posted above. Thanks for all the ideas guys!

This truck was sitting for probably 6-9 months when I bought it so I've been replacing a lot of rubber parts and such to take care of minor leaks here and there.

Shell · 04-29-2015, 08:57 PM

Dorman p/n 42071. NAPA or any of the parts should be able to get them.

EARNHARDT#3 · 04-29-2015, 10:01 PM

http://pages.ebay.com/link/?nav=item...d=111175679004

Aruba1 · 05-01-2015, 10:35 PM

Any update?

macblazer · 05-01-2015, 11:17 PM

Ordered one and waiting for it to show up. So we'll see when it arrives.

**johnmiller66** · 05-02-2015, 09:27 AM

Hears a pic of my master cylinder and the new gasket advance auto ordered for me. It's about an inch to small in length and about a half an inch to narrow.

**johnmiller66** · 05-02-2015, 09:27 AM

Master

macblazer · 05-02-2015, 11:45 AM

Quote:

Originally Posted by johnmiller66

Master

Looks like about the same one I have.

RichardJ · 05-02-2015, 01:09 PM

If the cap is bent, you should probably replace it, even if it's just one from a wrecking yard. The problem isn't so much as it leaking fluid, the problem is in allow any air to enter. Humidity in the air is easily absorbed by brake fluid, contaminating the fluid and causing corrosion.

macblazer · 05-02-2015, 02:59 PM

Ordered this one:

Description SKU
MOTORMITE BRAKE MASTER CYLINDER CAP GASKET 42071 MM42071.1764

Ordered it from carpartkings.com and it looks like it might be a fraction of an inch smaller on the sides, but still looks like it fits in all the areas it needs to. I sprayed down the master cylinder down with brake cleaner so we'll see if we get any more leaks, but so far so good. I think it was about $9.00 with shipping and everything.

EARNHARDT#3 · 05-02-2015, 07:27 PM

Quote:

Originally Posted by macblazer

Ordered this one:

Description SKU
MOTORMITE BRAKE MASTER CYLINDER CAP GASKET 42071 MM42071.1764

Ordered it from carpartkings.com and it looks like it might be a fraction of an inch smaller on the sides, but still looks like it fits in all the areas it needs to. I sprayed down the master cylinder down with brake cleaner so we'll see if we get any more leaks, but so far so good. I think it was about $9.00 with shipping and everything.

That's the exact one I posted above for you. If you look the ebay seller is carpartkings.

MagmaJct · 05-03-2015, 02:08 PM

I recently had to replace mine. This diaphragm prevents moisture in the air from contaminating the fluid. It allows for a partial vacuum that may occur as the fluid is "consumed". (A small amount of fluid always leaks past the seals in the calipers and wheel cylinders and must be made up.)

I got mine from O'Reilly's, but I had to go to a hub store. I tried to look it up on their site so I can just paste the link here. But their stupid site wants me to enter the specifics of my vehicle. When I did that, it "found nothing". I know they have it, but I doubt it's in their database for working with our trucks.

Regards,
Mike

70's luvr · 04-19-2016, 09:11 AM

I bought a replacement and just stacked it on top of original. Obviously harder to lock cap down but no more leaks.

mike16 · 04-19-2016, 05:45 PM

Yea. I was going to mention doorman and the Help rack at any local parts store.

also the lids with rubber, I think, are also available from corvette parts vendors too. Usually correct and good quality but being a corvette part you pay for that certainty that its correct and good.

Dave K. · 04-19-2016, 06:57 PM

I had a similar problem with a rebuilt master I bought. Found that the spring clamp just wasn't strong enough and replaced with the old one and no more leaks...

04-29-2015, 04:36 PM	#1
macblazer Registered User Join Date: Jul 2008 Location: Austin, Tx Posts: 23	Master Cylinder Cap Gasket Anyone have any clue where the heck you can find a replacement gasket for the master cylinder cap? I've got a 1971 Chevy C20 Longbed and I'm having a royal pain of a time finding one that will match.

04-29-2015, 05:54 PM	#2
WarMonger Registered User Join Date: Jan 2015 Location: Ventura, CA Posts: 818	Re: Master Cylinder Cap Gasket Do you have a pic of what you need? I just replaced my Master cylinder and I have my old one. Nothing wrong with the gasket or top cover. __________________ ..................... ____ .........________//__{\_____ ,,,,,,,/__(O)___//___/__(O)_/ 1970 C20 -_--_--_- ______ _--_--_- /___\|__\____ -_--_-_ \|_(0)\|__\|_(0)] 1972 K5

04-29-2015, 08:03 PM	#5
johnmiller66 Active Member Join Date: Mar 2014 Location: Wichita Kansas Posts: 100	Re: Master Cylinder Cap Gasket If you find one please post where you got it. I just put a new booster and master cylinder on mine. It leaks like crazy out the cap. The top of the master is beat to hell and won't seal properly. I don't really want to change out the master but I might have to. I should of looked over the Oreilys crap before I installed it.

04-29-2015, 08:55 PM	#7
Aruba1 Registered User Join Date: Apr 2014 Location: Birmingham, AL Posts: 560	Re: Master Cylinder Cap Gasket Can you post a picture of the master cylinder itself? From the upper picture it seems like what you have is a C10 master cylinder. Maybe that is your problem but I believe (someone correct me) that the caps are the same. Here are some pics of C10 vs C20 MC. http://67-72chevytrucks.com/vboard/s...d.php?t=666291

04-29-2015, 09:14 PM	#9
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Re: Master Cylinder Cap Gasket They advertise it. I would try talking to some one else about it. Just for reference I was going by the picture posted. The C/20 maybe different. http://www.dormanproducts.com/c-504-...r-gaskets.aspx __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

04-29-2015, 09:26 PM	#10
Shell Registered User Join Date: Apr 2015 Location: Brandon Ms Posts: 23	Re: Master Cylinder Cap Gasket The P/N I posted is for the C10 __________________ It's not how much you put in it, it's how much you get out of it!! 68 Chevy C10

04-29-2015, 08:57 PM	#12
Shell Registered User Join Date: Apr 2015 Location: Brandon Ms Posts: 23	Re: Master Cylinder Cap Gasket Dorman p/n 42071. NAPA or any of the parts should be able to get them. __________________ It's not how much you put in it, it's how much you get out of it!! 68 Chevy C10

04-29-2015, 10:01 PM	#13
EARNHARDT#3 Registered User Join Date: May 2014 Location: PA Posts: 1,417	Re: Master Cylinder Cap Gasket http://pages.ebay.com/link/?nav=item...d=111175679004 __________________ 1967 C10, LWB, 250, Powerglide, PS, PB, 3/4 STATIC DROP

05-01-2015, 10:35 PM	#14
Aruba1 Registered User Join Date: Apr 2014 Location: Birmingham, AL Posts: 560	Re: Master Cylinder Cap Gasket Any update?

05-01-2015, 11:17 PM	#15
macblazer Registered User Join Date: Jul 2008 Location: Austin, Tx Posts: 23	Re: Master Cylinder Cap Gasket Ordered one and waiting for it to show up. So we'll see when it arrives.

05-02-2015, 09:27 AM	#16
johnmiller66 Active Member Join Date: Mar 2014 Location: Wichita Kansas Posts: 100	Re: Master Cylinder Cap Gasket Hears a pic of my master cylinder and the new gasket advance auto ordered for me. It's about an inch to small in length and about a half an inch to narrow. Attached Images

05-02-2015, 09:27 AM	#17
johnmiller66 Active Member Join Date: Mar 2014 Location: Wichita Kansas Posts: 100	Re: Master Cylinder Cap Gasket Master Attached Images

05-02-2015, 01:09 PM	#19
RichardJ Registered User Join Date: Apr 2010 Location: So Cal Posts: 1,460	Re: Master Cylinder Cap Gasket If the cap is bent, you should probably replace it, even if it's just one from a wrecking yard. The problem isn't so much as it leaking fluid, the problem is in allow any air to enter. Humidity in the air is easily absorbed by brake fluid, contaminating the fluid and causing corrosion. __________________ '67 GMC 2500, 292, 4spd, AC

05-02-2015, 02:59 PM	#20
macblazer Registered User Join Date: Jul 2008 Location: Austin, Tx Posts: 23	Re: Master Cylinder Cap Gasket Ordered this one: Description SKU MOTORMITE BRAKE MASTER CYLINDER CAP GASKET 42071 MM42071.1764 Ordered it from carpartkings.com and it looks like it might be a fraction of an inch smaller on the sides, but still looks like it fits in all the areas it needs to. I sprayed down the master cylinder down with brake cleaner so we'll see if we get any more leaks, but so far so good. I think it was about $9.00 with shipping and everything.

05-03-2015, 02:08 PM	#22
MagmaJct Registered User Join Date: May 2008 Location: Mesa, AZ Posts: 281	Re: Master Cylinder Cap Gasket I recently had to replace mine. This diaphragm prevents moisture in the air from contaminating the fluid. It allows for a partial vacuum that may occur as the fluid is "consumed". (A small amount of fluid always leaks past the seals in the calipers and wheel cylinders and must be made up.) I got mine from O'Reilly's, but I had to go to a hub store. I tried to look it up on their site so I can just paste the link here. But their stupid site wants me to enter the specifics of my vehicle. When I did that, it "found nothing". I know they have it, but I doubt it's in their database for working with our trucks. Regards, Mike __________________ I own 3 classic vehicles. 1971 LWB C10 Deluxe. 1974 VW Super Beetle. 1971 VW Fastback. The C10 and the Super Beetle run, the Fastback is just not there yet! Please visit my Super Beetle and Fastback profile on TheSamba.



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04-19-2016, 09:11 AM	#23
70's luvr Registered User Join Date: Nov 2013 Location: Spring Hill,Fl Posts: 223	Re: Master Cylinder Cap Gasket I bought a replacement and just stacked it on top of original. Obviously harder to lock cap down but no more leaks.

04-19-2016, 05:45 PM	#24
mike16 Registered User Join Date: Dec 2009 Location: bisbee, arizona Posts: 1,529	Re: Master Cylinder Cap Gasket Yea. I was going to mention doorman and the Help rack at any local parts store. also the lids with rubber, I think, are also available from corvette parts vendors too. Usually correct and good quality but being a corvette part you pay for that certainty that its correct and good.

04-19-2016, 06:57 PM	#25
Dave K. Registered User Join Date: Jul 2009 Location: Milwaukee, WI Posts: 575	Re: Master Cylinder Cap Gasket I had a similar problem with a rebuilt master I bought. Found that the spring clamp just wasn't strong enough and replaced with the old one and no more leaks...

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