Hydro Brake Part Number 85 Blazer

[Russtypickle]

Hi All, I've got an 85 Blazer with hydroboost power brakes. As it turns out I'm pretty sure the master cylinders inner seals are wearing out as it's starting to lose breaking power (completely) intermittently, I've bled the brakes and there's no leaks. My problem is that I can't find a part number for it. Has anyone had to order one and have a part number? My master cylinder does not have any casting numbers on it from what I can see. I've attached a couple photos. My Blazer used to be a diesel but was converted to a 350 by the previous owner, thus the hydro brakes.

 

[nvrenuf]

I don’t understand, why can’t you go to your preferred parts supplier’s website and look up a m/c?

 

[Russtypickle]

I don’t understand, why can’t you go to your preferred parts supplier’s website and look up a m/c?

I tried, one can't get the one they list and the other (online) couldn't confirm it was for hydro or vacuum assist.

 

[xm20k]

Power brakes are power brakes doesn't matter if hydro or vacuum. Order the one for your year, make, model with power brakes.

 

[Russtypickle]

Power brakes are power brakes doesn't matter if hydro or vacuum. Order the one for your year, make, model with power brakes.

You'd think so but you'd be wrong. From my understanding the throw and diameter of the piston is different.

 

[SquareRoot]

Power brakes are power brakes doesn't matter if hydro or vacuum. Order the one for your year, make, model with power brakes.

Wrong.

 

[SquareRoot]

You'd think so but you'd be wrong. From my understanding the throw and diameter of the piston is different.

Partially correct. I converted my 85 from vacuum to hydro. Donor was a diesel so I swapped the whole system. The diameter of the piston may be different as well as the length of the pushrod between the hydro and the m/c. Piston diameter is related to the brake system option. Your K5 would have the smaller diameter rear drums and corresponding brake drum cylinders. Rockauto usually has them.

 

[Turbo4whl]

I tried, one can't get the one they list and the other (online) couldn't confirm it was for hydro or vacuum assist.

Go to or call a GM dealer. They will have a part number. May be discontinued, but the number will help you locate what you need.

 

[Keith Seymore]

Since you graciously provided a photo of the "KH" broadcast code sticker I can tell you the corresponding part number is 25509416.

More importantly I can say it is the same as m/c as any diesel blazer or 1/2 ton dsl Suburban (JD5) or 3/4 ton 2 or 4wd pickup with JD6.


K

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[Keith Seymore]

In English that would be:

JD5
C/K10516 = 1/2 ton Blazer w dsl
C/K10703 = 1/2 ton SWB pu w dsl
C/K10903 = 1/2 ton LWB pu w dsl
C/K10906 = 1/2 burb w dsl

JD6
C/K20903 = 3/4 ton pu dsl

K

 

[Keith Seymore]

By the way - looks like it's the same for 84, 85, 86 and 87.

 

[Russtypickle]

Since you graciously provided a photo of the "KH" broadcast code sticker I can tell you the corresponding part number is 25509416.

More importantly I can say it is the same as m/c as any diesel blazer or 1/2 ton dsl Suburban (JD5) or 3/4 ton 2 or 4wd pickup with JD6.


K

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Brilliant, that's awesome, thanks Keith!

 

[Russtypickle]

Thanks again, part ordered, should be here Thursday!

By the way - looks like it's the same for 84, 85, 86 and

 

[xm20k]

1981, 1982, 1983, 1984 & 1985 Chevrolet Impala, Caprice and All Passenger Car with 350N Diesel Engine Except Export Models

1984 & 1985 Chevrolet Impala, Caprice and All Passenger Car with 305H Engine Except Export Models

1981 Chevrolet and GMC 10 Series (03) Pickup Truck with JD3 and JD5 Brake Options

1982 Chevrolet & GMC C/K 10 & 20 Series Trucks including Pickup, Suburban, Blazer and Cab Chassis with JD3, JD5 and JD6 Brake Options Except Export Models and is 1st Design but this replaces 1st & 2nd Design Cylinders 2nd design was part number 18008068 and was a Moraine Type Cylinder and was replaced by this Bendix unit for 1982

1983, 1984 & 1985 Chevrolet and GMC C/K 10 & 20 Series Truck including Pickup, Suburban and Cab Chassis with JD3, JD5 and JD6 Brake Options

1986, 1987, 1988 & 1989 Chevrolet and GMC R/V 10 & 20 Series Old Style Truck including Pickup, Suburban and Cab Chassis with JD5 and JD6 Brake Options

1990 & 1991 Chevrolet and GMC R/V 10 & 20 Series Old Style Truck including Pickup, Suburban and Cab Chassis with JD5 (Hydraulic Power Disc/Drum) Brake Option

GM part number is 25509416 in parts group 4.650.


Almost like they used the same pool of parts for their many different vehicles​

 

[Keith Seymore]

Almost like they used the same pool of parts for their many different vehicles​

Of course.

There is a finite library of parts to choose from. We would mix and match all the components on those charts until we got the pedal feel, travel, deceleration, durability and FMVSS compliance we were looking for.

K

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