OBS to NBS Master Cylinder Upgrade REPORT

[Gibson]

On the step bore OBS MC, the primary bore pushes high volume up to a certain pressure then transitions to the smaller secondary bore and begins to develop pressure at a more rapid rate.

I know this is an ancient thread,,, but, the purpose of the "step bore" MC is somewhat diff from above.
The step bore MC is made to supply "high volume/low pressure" to the rear drum brakes with the large bore piston.
The small piston supplies "low volume/high pressure" to the front discs.
The two pistons are separated by brake fluid, and their is no "transition of pressure" from low to high.
Each piston operates its respective circuit in an independent manner.
The "transition" type, or "quick take-up" MC, is used for the new "low drag" all disc systems, and it uses three pistons,, but is not like the "step bore" MCs on the older rigs.

 

[Supercharged111]

I know this is an ancient thread,,, but, the purpose of the "step bore" MC is not what is stated above.
The step bore MC is made to supply "high volume/low pressure" to the rear drum brakes with the large bore piston.
The small piston supplies "low volume/high pressure" to the front discs.
The two pistons are separated by brake fluid, and their is no "transition of pressure" from low to high.
Each piston operates its respective circuit in an independent manner.

I believe it creates a front heavy bias as the 8 luggers don't have this.

 

[dfarr67]

Is the NBS disk/disk MC output equal between front and rear, or is there a bias...if a bias which nipple is assigned front or rear?

 

[Supercharged111]

The NBS masters are single bore masters, no bias applied there. It's probably applied inside the ABS pump as this is how the Corvette did it starting in 97.

 

[dfarr67]

OK sounds good, in a previous life the '89 had the rwal removed and re plumbed with front nipple feeding front brakes, rear feeding rear. I've ordered a 2008 Express 2500 disk/disk MC so this is a non issue, it's feeding a '99 disk/disk proportioning valve.

 

[1998SSLT]

it fits in a parking structure!? LOL

my picture uploading is not working....

mine virtually looks exactly like that though. all I have is the junction block, and the abs/proportioning unit... no other hardware, just lines.
but the 1993 master cylinder looks pretty huge....
I just hate how it always feels like there is air in these brakes!!! driving or engine off you can pump the pedal and feel pressure build. it always feels low at the start.
im saving to do all this when convenient: the new master, pads, rotors, and check all line flares for cracks (last year the truck got all new rubber lines so those seem just fine)

I wonder I the calipers could be drawing in air...

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Have you tried this yet? Mine were as you described and I did this. It helped a lot.

 

[needlenose]

I have a 99 Suburban C1500 and my brake lines are different sizes. The front(from the m/c) is much larger than the rear(on the m/c).

I don't *think* this will be a problem since both holes have the same taper? The front will just sit further down on the taper before tightening? Has anyone else done this swap with these lines?

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[kennythewelder]

First off, your pics dont work. Yes, I have a 2002 Tahoe MC on my 97. It takes a brake line adaptor. You can get it at autozone. Its blp 22, or 23 I dont remember. There is a thread on here about the swap, and it gives you all the info you need. Here is a pic of mine installed . I did the swap a few years ago. Its been good for me. I havent had any issues with the swap .

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[kennythewelder]

My bad, the parts you need are on the very first post of this thread.

 

[needlenose]

My bad, the parts you need are on the very first post of this thread.

Sorry, it's just that I'm an idiot.

I actually ordered the the brass conversion fitting with the m/c. But the two line fittings looked the exact same(My eyes aren't what they used to be). I was just looking at the size of the line.

This thread explains it:

https://www.gmt400.com/threads/how-to-nbs-master-cylinder-swap-for-firm-brake-pedal.17998/

Thanks!