P30 JB8 master cylinder substitutions?

[RickNC]

I replaced the original master cylinder (14066245) 18 months ago with a new Raybestos replacement since GM/Bendix/ACDelco no longer produces that part.

Like most every chassis related replacement part I have used so far that is not GM or ACDelco it hasn’t lasted very long. The master cylinder is leaking past the front seal. I wasn’t sure at first. It being mated to the Hydroboost it was also possible the hydroboost may have been leaking. I confirmed it by adding a ultraviolet tracer to the brake fluid last week and checking the entire brake system with a ultraviolet light after driving for an hour.

I researched some other part numbers and came up with another P30,JB8 spec,master cylinder GM#19176448 or AC Delco 18M230 which is still available new through GM or ACDelco.Same port threads, same part # for internals, casting looks the same. But the years don’t match up. I have only found one mention of interchange on a motorhome chassis which was on Amazon in a customer review. Not always a reliable source.

If anyone has done, read or heard of a master cylinder swap using the 18m230 master cylinder I would appreciate hearing about it.

[George Schweikle]

Have you tried this source? https://www.google.com/search?client...gm+parts+giant

Originally Posted by RickNC

I replaced the original master cylinder (14066245) 18 months ago with a new Raybestos replacement since GM/Bendix/ACDelco no longer produces that part.

Like most every chassis related replacement part I have used so far that is not GM or ACDelco it hasn’t lasted very long. The master cylinder is leaking past the front seal. I wasn’t sure at first. It being mated to the Hydroboost it was also possible the hydroboost may have been leaking. I confirmed it by adding a ultraviolet tracer to the brake fluid last week and checking the entire brake system with a ultraviolet light after driving for an hour.

I researched some other part numbers and came up with another P30,JB8 spec,master cylinder GM#19176448 or AC Delco 18M230 which is still available new through GM or ACDelco.Same port threads, same part # for internals, casting looks the same. But the years don’t match up. I have only found one mention of interchange on a motorhome chassis which was on Amazon in a customer review. Not always a reliable source.

If anyone has done, read or heard of a master cylinder swap using the 18m230 master cylinder I would appreciate hearing about it.

[RickNC]

Originally Posted by George Schweikle

Have you tried this source? https://www.google.com/search?client...gm+parts+giant

Thanks for the reply George. I use GMParts Giant all the time since it is one of the few that will recognize a P30 serial number. But I have to copy the part number and paste on www.wholesalegmpartsonline.com for a viewable parts fiche.

Since last night I have tracked down 2 NOS master cylinders on EBAY. GM ( actually Bendix) discontinued that part in 2012. That is quite a while for the seals and O rings to be air exposed.

The 18M230 is available on Amazon Prime so I ordered that this morning. If it doesn’t match up on the bench I can use the free return.

[Brob]

Be sure to post your results here when you find out if it works. I'm sure it will aid someone else in the future.

[RickNC]

Originally Posted by Brob

Be sure to post your results here when you find out if it works. I'm sure it will aid someone else in the future.

Will do [emoji106]

[RickNC]

The new AC Delco mastercylinder came last night and I pulled the old one this morning. Here are side by side pics. Every dimension is exactly the same except for a .015 difference in the Primary output port id (first image).There are no residual valves on either master cylinder. The GM casting is a bit thinner in the reservoir area and the bail is thicker.

The caps are the same. Note that old cap has been modified to accept a remote reservoir.

Let me know if you think I’m missing something. other wise I will glue the cap on tonight and install tomorrow.

[twinboat]

Can't measure the picture, is the cylinder diameter the same ?

[RickNC]

Originally Posted by twinboat

Can't measure the picture, is the cylinder diameter the same ?

Same diameter 1-5/16”. I also cross referenced the Primary and secondary piston and spring assemblies for both, they have the same part numbers.

[RickNC]

Installed, bled and test drove the RV yesterday. Everything is working as it should. Pedal effort and travel feels the same to me, Wife drove it and says it feels like less pedal effort to her. No more leaks ....So Success!

Interesting side note, I also had discussed this in a Facebook group. One of the members there is a retired engineer who worked 20 years for Delphi which is the primary source of automotive components for GM before he retired in 2008. He told me this morning that the slightly larger port inside diameter on the primary was likely the difference in part numbers. He said while the larger port would make almost no difference on my application, It would improve initial response on a larger caliper bore by allowing more fluid to pass through the primary port for the same effort.

[Boom Sounds]

I am having the same dilemma on my 91 Airstream P30. I have used an 18M230 for a few years, but it has now failed which seems a common fault on the rebuilt units. I also came across this one, https://www.carid.com/cardone/brake-...n-13-1982.html, but haven't tried it yet. Deets as follows:

Chevrolet
MY83-83 - C30 Custom, Scottsdale, Silverado with "1925" Stamped Master Cylinder; with Hydroboost; Supplied w/Reservoir
MY84-84 - C30 Custom, Scottsdale, Silverado with Hydroboost; Supplied w/Reservoir
MY85-86 - K30 Custom, Scottsdale, Silverado with "1925" Stamped Master Cylinder; Supplied w/Reservoir
MY93-93 - P30 with Brake Code JB8; with Forward Control Chassis Cab; GM Brake Codes are on the "Service Parts Identification" sticker. without Cab; Supplied w/Reservoir; Front Brake Type: Disc; Rear Brake Type: Drum
with Brake Code JD7; with Forward Control Chassis Cab; GM Brake Codes are on the "Service Parts Identification" sticker. without Cab; Supplied w/Reservoir; Front Brake Type: Disc; Rear Brake Type: Drum
with Motorhome Chassis; without Cab; Supplied w/Reservoir; Front Brake Type: Disc; Rear Brake Type: Drum
MY87-90 - P30 Base, Step-Van with Hydroboost; with Brake Code JB8; with Forward Control Chassis Cab; GM Brake Codes are on the "Service Parts Identification" sticker. Supplied w/Reservoir; Front Brake Type: Disc; Rear Brake Type: Drum
MY84-89 - P30 Base, Step-Van with Hydroboost; with Brake Code JB8; with Motorhome Chassis; GM Brake Codes are on the "Service Parts Identification" sticker. Supplied w/Reservoir; Front Brake Type: Disc; Rear Brake Type: Drum
MY88-88 - R30 Cheyenne, Custom Deluxe, Scottsdale, Silverado with Hydroboost; Supplied w/Reservoir
MY91-91 - R3500 Cheyenne, Silverado with Hydroboost; Supplied w/Reservoir
MY87-88 - V30 Cheyenne, Custom Deluxe, Scottsdale, Silverado with Hydroboost; Supplied w/Reservoir
MY90-91 - V3500 Cheyenne, Scottsdale, Silverado with Hydroboost; Supplied w/Reservoir
GMC
MY85-85 - C3500 Base, High Sierra, Sierra Classic with Hydroboost; Supplied w/Reservoir
MY84-85 - K3500 Base, High Sierra, Sierra Classic with "1925" Stamped Master Cylinder; Supplied w/Reservoir
MY94-96 - P3500 with Forward Control Chassis Cab; without Cab; Supplied w/Reservoir; Front Brake Type: Disc; Rear Brake Type: Drum
MY92-92 - P3500 with Hydroboost; with Brake Code JB8; with Forward Control Chassis Cab; GM Brake Codes are on the "Service Parts Identification" sticker. Supplied w/Reservoir; Front Brake Type: Disc; Rear Brake Type: Drum
MY85-91 - P3500 Base, Value Van with Hydroboost; with Brake Code JB8; with Forward Control Chassis Cab; GM Brake Codes are on the "Service Parts Identification" sticker. Supplied w/Reservoir; Front Brake Type: Disc; Rear Brake Type: Drum
with Hydroboost; with Brake Code JB8; with Motorhome Chassis; GM Brake Codes are on the "Service Parts Identification" sticker. Supplied w/Reservoir; Front Brake Type: Disc; Rear Brake Type: Drum
MY89-89 - P3500 Base, Value Van with Hydroboost; with Brake Code JB8; with Motorhome Chassis; GM Brake Codes are on the "Service Parts Identification" sticker. Supplied w/Reservoir; Front Brake Type: Disc; Rear Brake Type: Drum
MY93-93 - P3500 with Motorhome Chassis; without Cab; Supplied w/Reservoir; Front Brake Type: Disc; Rear Brake Type: Drum
MY87-91 - V3500 Base, High Sierra, Sierra Classic, SLE with Hydroboost; Supplied w/Reservoir

[RickNC]

Originally Posted by Boom Sounds

I am having the same dilemma on my 91 Airstream P30. I have used an 18M230 for a few years, but it has now failed which seems a common fault on the rebuilt units. I also came across this one, https://www.carid.com/cardone/brake-...n-13-1982.html........

The 13-1982 is a good number I looked at that one before buying the ACDelco part. I tend to have better luck with the ACDelco parts. Personally I have never had a rebuilt MC cylinder or clutch master cylinder that ever lasted more than a year or two. That is why I always buy new.

[Boom Sounds]

Originally Posted by RickNC

The 13-1982 is a good number I looked at that one before buying the ACDelco part. I tend to have better luck with the ACDelco parts. Personally I have never had a rebuilt MC cylinder or clutch master cylinder that ever lasted more than a year or two. That is why I always buy new.

Hi Rick - is your 18M230 still running fine? I am about to install another one in my 1991 250 454 on a P30 chassis. Brake code JB8 on 16" wheels.

The Cardone is an interesting one. I actually found the old Bendix unit which was swapped in about 2008. It might have been original. When I cross referenced the casting number, it chucked up the Cardone one as a replacement.

I've found the CARID website very good at filtering out to the correct units. It allows the user to differentiate between JB7 and JB8, Van, stripped chassis and Motorhome chassis.
https://www.carid.com/service-type/b...placement.html

I usually hang out on the Airstream Forum. 454 P30 chassis owners can find lots of interesting stuff there.

[RickNC]

Originally Posted by Boom Sounds

Hi Rick - is your 18M230 still running fine? I am about to install another one in my 1991 250 454 on a P30 chassis. Brake code JB8 on 16" wheels.



The Cardone is an interesting one. I actually found the old Bendix unit which was swapped in about 2008. It might have been original. When I cross referenced the casting number, it chucked up the Cardone one as a replacement.



I've found the CARID website very good at filtering out to the correct units. It allows the user to differentiate between JB7 and JB8, Van, stripped chassis and Motorhome chassis.

https://www.carid.com/service-type/b...placement.html



I usually hang out on the Airstream Forum. 454 P30 chassis owners can find lots of interesting stuff there.

Mine is new with about 850 miles since install. I also have JB8 brakes with the rear drums and 16” wheels.
I bought my MC through Amazon $45.

[udid]

One of the issues with rebuilt units is how long they sit on the shelf after having been rebuilt. They sit with no fluid in them.


This is one of those items that should only be rebuilt once ordered.