Master Cylinder Overhault/Swap

[denpo]

It looked odd, so I checked and that MC only has a bore of 24 mm or 0.94 inches.
OEM sizes are 1" for manual and 1.125" for boosted.
I haven't used a 1" MC on a Hydroboost, just bigger ones, so I don't know if that will result in a lower than normal pedal or not. I'm sure the end hydraulic pressure would be fine with the HB.
Considering all the added BS with the fittings, I would choose another. One other downside is the bubble flare, ISO or SAE both have a limited lifetime.

Here are a couple of alum masters that use the SAE double flare. The 1/2"-20 and 9/16"-18 flare nuts are reuseable from your old lines (as may be your complete lines) and are common to all GM of that era. Most parts stores have them.

Same bore as the OEM power master:
1990 Chevrolet Truck K2500 3/4 Ton 4WD - Pickup
Brake Master Cylinder Bore Size : 1.125"
Brake Master Cylinder Line Thread Size : 1/2"-20, 9/16"-18

Whopping Bore
2005 Chevrolet Truck Silverado 2500HD 3/4 Ton
Brake Master Cylinder Bore Size : 37 mm (1.46 inch) :amazed:
Brake Master Cylinder Line Thread Size : 2 x 1/2"-20 (double flare)

A couple months ago, in an attempt to lessen the softness of the stock pedal and increase the pedal height, I tried a number of master cylinder combinations. It involved making a new pushrod for the common newer short mc pistons and making several sets of MC to combo valve lines. I used all rebuilt cylinders because of price and probably still spent 75 bucks in fluid alone.
I didn't try the NMC P2903 (got sick of bleeding brakes etc), but I would say that combined with the HB, it would be the ultimate for a combination of maximum hydraulic pressure and high pedal. With a regular vacuum booster, it should provide a fairly stiff high pedal, like modern power brakes, if not more firm.

I ended up being satisfied with a 1-1/4" master and it's really hard to tell from stock in appearance, but it is cast iron.

Damn damn damn, somebody hit me please, how did I miss this post, and spent so much time trying to get past the downside.
Ok, let's get back to the scrapyard.

 

[mrvette]

It looked odd, so I checked and that MC only has a bore of 24 mm or 0.94 inches.
OEM sizes are 1" for manual and 1.125" for boosted.
I haven't used a 1" MC on a Hydroboost, just bigger ones, so I don't know if that will result in a lower than normal pedal or not. I'm sure the end hydraulic pressure would be fine with the HB.
Considering all the added BS with the fittings, I would choose another. One other downside is the bubble flare, ISO or SAE both have a limited lifetime.

Here are a couple of alum masters that use the SAE double flare. The 1/2"-20 and 9/16"-18 flare nuts are reuseable from your old lines (as may be your complete lines) and are common to all GM of that era. Most parts stores have them.

Same bore as the OEM power master:
1990 Chevrolet Truck K2500 3/4 Ton 4WD - Pickup
Brake Master Cylinder Bore Size : 1.125"
Brake Master Cylinder Line Thread Size : 1/2"-20, 9/16"-18

Whopping Bore
2005 Chevrolet Truck Silverado 2500HD 3/4 Ton
Brake Master Cylinder Bore Size : 37 mm (1.46 inch) :amazed:
Brake Master Cylinder Line Thread Size : 2 x 1/2"-20 (double flare)

A couple months ago, in an attempt to lessen the softness of the stock pedal and increase the pedal height, I tried a number of master cylinder combinations. It involved making a new pushrod for the common newer short mc pistons and making several sets of MC to combo valve lines. I used all rebuilt cylinders because of price and probably still spent 75 bucks in fluid alone.
I didn't try the NMC P2903 (got sick of bleeding brakes etc), but I would say that combined with the HB, it would be the ultimate for a combination of maximum hydraulic pressure and high pedal. With a regular vacuum booster, it should provide a fairly stiff high pedal, like modern power brakes, if not more firm.

I ended up being satisfied with a 1-1/4" master and it's really hard to tell from stock in appearance, but it is cast iron.

Damn damn damn, somebody hit me please, how did I miss this post, and spent so much time trying to get past the downside.
Ok, let's get back to the scrapyard.

Before my HB conversion, I went to a truck m/cyl 1 5/16 bore I think, that gave me a much better pedal with the old booster, but still too soft,....went to HB without touching any of the brake lines....and it was WAY too sensitive, went to a stock size bore aluminum unit from Pirate Jack racing...and it's perfect....

 

[denpo]

went to a stock size bore aluminum unit from Pirate Jack racing...and it's perfect....

By stock, you mean 1'' or 1''1/4?

 

[mrvette]

went to a stock size bore aluminum unit from Pirate Jack racing...and it's perfect....

By stock, you mean 1'' or 1''1/4?

I forget the size, now....it was for the power brakes, supposedly....

but for the VAC booster....

 

[denpo]

went to a stock size bore aluminum unit from Pirate Jack racing...and it's perfect....

By stock, you mean 1'' or 1''1/4?

I forget the size, now....it was for the power brakes, supposedly....

but for the VAC booster....

So it is 1'' 1/4
Thanks Gene.:thumbs:

 

[010752]

went to a stock size bore aluminum unit from Pirate Jack racing...and it's perfect....

By stock, you mean 1'' or 1''1/4?

I forget the size, now....it was for the power brakes, supposedly....

but for the VAC booster....

So it is 1'' 1/4
Thanks Gene.:thumbs:

From previous post

It looked odd, so I checked and that MC only has a bore of 24 mm or 0.94 inches.....
OEM sizes are 1" for manual and 1.125" for boosted.

 

[denpo]

went to a stock size bore aluminum unit from Pirate Jack racing...and it's perfect....

By stock, you mean 1'' or 1''1/4?

I forget the size, now....it was for the power brakes, supposedly....

but for the VAC booster....

So it is 1'' 1/4
Thanks Gene.:thumbs:

From previous post

It looked odd, so I checked and that MC only has a bore of 24 mm or 0.94 inches.....
OEM sizes are 1" for manual and 1.125" for boosted.

Ooops, sorry. Look like I can help forgetting your post.

 

[mrvette]

By stock, you mean 1'' or 1''1/4?

I forget the size, now....it was for the power brakes, supposedly....

but for the VAC booster....

So it is 1'' 1/4
Thanks Gene.:thumbs:

From previous post

It looked odd, so I checked and that MC only has a bore of 24 mm or 0.94 inches.....
OEM sizes are 1" for manual and 1.125" for boosted.

Ooops, sorry. Look like I can help forgetting your post.

Sorry I can't remember to forget shit forever...but methinks Noonie is right....1.125 'feels' correct....

:clobbered::gurney:

 

[denpo]

I forget the size, now....it was for the power brakes, supposedly....

but for the VAC booster....

So it is 1'' 1/4
Thanks Gene.:thumbs:

From previous post

It looked odd, so I checked and that MC only has a bore of 24 mm or 0.94 inches.....
OEM sizes are 1" for manual and 1.125" for boosted.

Ooops, sorry. Look like I can help forgetting your post.

Sorry I can't remember to forget shit forever...but methinks Noonie is right....1.125 'feels' correct....

:clobbered::gurney:

Of course that's what I was implying, it's 1"1/8 and not 1"1/4 for a stock vacuum assisted brake.

 

[mrvette]

So it is 1'' 1/4
Thanks Gene.:thumbs:

From previous post

It looked odd, so I checked and that MC only has a bore of 24 mm or 0.94 inches.....
OEM sizes are 1" for manual and 1.125" for boosted.

Ooops, sorry. Look like I can help forgetting your post.

Sorry I can't remember to forget shit forever...but methinks Noonie is right....1.125 'feels' correct....

:clobbered::gurney:

Of course that's what I was implying, it's 1"1/8 and not 1"1/4 for a stock vacuum assisted brake.

:drink::banghead::ill: