Chevy Master Cylinder upgrade

[V8path]

 

MC's are Marked! for Pathy and z32 etc... Some are valved for rear drum and others are valved for rear disc. Size code below.

BM33 = 13/16

BM38 = 7/8

BM44 = 15/16

BM50 = 1"

BM57 = 1 1/16

Both my trucks say BM50 but my 89 was originally a BM44.

 

 

 

 

Thanks for the additional info. I had upgraded to the BM57 few years back but with the leak in the booster I'm thinking about upgrading the whole system, starting with a new booster and MC. Been doing some research on going to a hydro boost and a MC from a 3/4 T pickup given the extra weight/rolling mass of 35" tires and the HP from a V8.

 

I've already the D52 OEM calipers in the front and Nissan OEM discs in the rear, and looking to upgrade to the Wilwood D52 dual pistons for the front, and D154 for the rear.

 

Just wondering if anyone here has much detailed experienced with Hydro Boost, be it GM or other's. Kingman looks to have a bad experience and is 100% turned off with the GM versions of the Hydro boost?

[Kingman]

They are a constant problem, weekly we have them in the shop with leaks (bad seals in the MC) and generally awful brake pedal feel although not using the Kelsey-Hayes ABS system could help it a lot. Have never been a fan...

 

The only problems we've had with Ford's rendition is the swivel line from the power steering reservoir blowing off the MC. It's messy and you lose all pressure for power steering and braking almost instantly. They make beefed up lines for this.

[V8path]

They are a constant problem, weekly we have them in the shop with leaks (bad seals in the MC) and generally awful brake pedal feel although not using the Kelsey-Hayes ABS system could help it a lot. Have never been a fan...

 

The only problems we've had with Ford's rendition is the swivel line from the power steering reservoir blowing off the MC. It's messy and you lose all pressure for power steering and braking almost instantly. They make beefed up lines for this.

 

Is the brake pedal feel a result of the MC issue, and its not the hydro boost itself? If that is the case, wouldn't that be fixed with a better MC from a different vehicle that fits whatever hydro boost being used?

 

For a custom set up, I could use a reliable MC from a GM/Chev 3/4 Ton (I haven't read or found anything saying they're been issues with the GM MC's, and the appropriate hydro boost that it could be mated to, as the way to go?

 

I have to change the brake booster anyways, so am thinking this would be the time to upgrade/swap over to a hydro boost. I was originally thinking of a GM brake booster, but there's limited space as it is, especially as I have the longer coilover shock hoops that extend into through the wheel well.

[Kingman]

To be honest, its the system its self that makes it feel mushy, though not as bad as the older trucks. Anything hydro boost from GM has come in leaking out of the MC. 1/2 and 3/4 ton trucks or vans alike.

 

In all reality the power is definitely there and it's a viable option... I just can't stand how they operate.

[V8path]

Well so far I cut the little bullet nub off the brake booster shaft adjustment screw. Shimmed the MC out a bit, machined the holes a bit to get them to fit the studs, removed material off the mounting ears themselves, BLED THE MC, found adapters to go from 1/2"-10mm, bypassed the abs block and bled the entire system

 

Hey new4x4r, what did you use for a brake booster? You mention using a MC from 1979 Blazer - is that a pretty close fit?

[V8path]

To be honest, its the system its self that makes it feel mushy, though not as bad as the older trucks. Anything hydro boost from GM has come in leaking out of the MC. 1/2 and 3/4 ton trucks or vans alike.

 

In all reality the power is definitely there and it's a viable option... I just can't stand how they operate.

 

I was looking at the hydro boost system from a 2005 Tahoe. Have you much experience with that particular model?

 

It looks like new4x4r had pretty good results with the 79 Blazer MC, so maybe I'll have to find a MC that will bolt up to the Tahoe system.

 

I'm not set on any particular system other than the goal is to find a good system, or combination of interchangeable parts that is fairly easy to service and find parts if needed. Going GM is usually good when it comes to interchangeable and availability of parts, and a lot cheaper than Nissan OEM.

[Kingman]

Tahoe in particular, not on the hydro boost end no. I did do brakes all around on a Denali yesterday. It stopped fine but I still hated the pedal feel.

 

I'm not entirely sure why GM even uses the system on gasoline vehicles in the first place. There are so many others of the same size, different makes, that stop great with standard vacuum systems and less complication. Oh... the '07+ 1/2 ton GM trucks use a standard vacuum system as well, what gives?

[V8path]

Tahoe in particular, not on the hydro boost end no. I did do brakes all around on a Denali yesterday. It stopped fine but I still hated the pedal feel.

 

I'm not entirely sure why GM even uses the system on gasoline vehicles in the first place. There are so many others of the same size, different makes, that stop great with standard vacuum systems and less complication. Oh... the '07+ 1/2 ton GM trucks use a standard vacuum system as well, what gives?

 

So far, most of what I read is like anything. If a good system isn't set up right, or there's a weak link in the system, it won;t work right.

 

There's good availability and pricing for GM units in the mid 2,000's year range (Tahoe, Yukon, Silverado etc.) so if the hydro boost is not the problem area, what's your guess on what it is? The MC? If that's the case, I would look at a upgrade with a compatible MC from another vehicle. That shouldn't be that hard to find?

[MY1PATH]

What about upgrading boosters? Is there a larger booster out there that might fit? If you were running all stock components This would improve your powered assist and thus stopping power without having to match MC size to caliper volume and either going too big MC (hard pedal weak brakes) or too small MC (soft pedal too long stroke before brakes engage)

[V8path]

What about upgrading boosters? Is there a larger booster out there that might fit? If you were running all stock components This would improve your powered assist and thus stopping power without having to match MC size to caliper volume and either going too big MC (hard pedal weak brakes) or too small MC (soft pedal too long stroke before brakes engage)

 

That's always an option, but there's limited space so maybe going to a same diameter or slightly smaller diameter dual diaphragm diameter booster

 

It really comes down to personal preference (work required and $) and have a combination of components that work well together.

 

As for the MC, if I recall correctly, the Pathfinder OEM MC is 15/16" or 1". I went to the D52 GM 3/4 T calipers for the front, and have the OEM Nissan rear discs. So, I'm thinking a 1 1/8 MC is likely a good choice?

[MY1PATH]

15/16 to 1990
1" after 1990
both my trucks are running the 1" but my 89 does not stop as quick so (all other things being equal) I suspect its running a weaker booster than my 93.

[MY1PATH]

Also, most dual diaphragms are smaller diameter but obviously thicker.
Keeping it Nissan, I don't know what a Z32 booster looks like but I believe they were dual diaphragm... The TT also had a clutch booster to keep the left foot light when running a heavy clutch.

[V8path]

Also, most dual diaphragms are smaller diameter but obviously thicker.

Keeping it Nissan, I don't know what a Z32 booster looks like but I believe they were dual diaphragm... The TT also had a clutch booster to keep the left foot light when running a heavy clutch.

 

There are a few articles re going to a MC from a Turbo 300ZX (90-91 I think are the years). They have dual front ports on the opposite side, are 1 1/8", and are direct bolt on's to the Pathfinder OEM booster.

 

If keeping it Nissan is the goal, a Nissan dual diaphragm is the way to go, but given I've already gone to GM V8 power plant, trans, Dana 44 front, with planned upgrades for a 241 doubler and NP205 (DSD from a Ford) my goal is getting the best bang for the buck, and being able to have good/easy access to replacement parts if needed.

 

From Kingman's feedback, its not the hydro boost unit itself that's the issue, its the leaking MC's. Also, the pedal feel issue might be power steering pump or fluid flow issues. The way to go would be to look at a better/bigger MC (especially if running 35" tires) and looking at either a better quality power steering pump, or upgrade the system with a oil cooler, filter, etc. With the V8, 3/16 wall rectangular tube bumpers, 35" tires, the OEM brake system was likely never designed to stop a Pathfinder that is likely 700 - 800 lbs heavier, and needs to be able to stop if after launching it with 350 plus HP

 

Performance has a price, and high performance needs "know how" - everything from bolt on, to custom fab/modification.

 

This is a hobby or for some, an obsession for others, and any and all productive information is the purpose of these forums. It helps us customize our rides (for some, "our builds") which is the whole purpose of this community.

[MY1PATH]

For information sake:

I just did some FSM searching. The pedal assist ratio of WD21 boosters goes from 5x to 8x. (8x being the newer stronger model, Hard to find in the fsm)

WD21 boosters were 9" primary and 8" secondary dual diaphragm but the late 2002 Xterra is a 9" and 9" dual diaphragm... I am personally going to do some more research into this and may even try it if it fits.

Edited July 8, 2015 by MY1PATH

[V8path]

To be honest, its the system its self that makes it feel mushy, though not as bad as the older trucks. Anything hydro boost from GM has come in leaking out of the MC. 1/2 and 3/4 ton trucks or vans alike.

 

In all reality the power is definitely there and it's a viable option... I just can't stand how they operate.

 

Hey Kingman, is there a MC that you suggest would be a upgrade to the GM ones that come in leaking? Given its a GM hydro boost, and if that's not the main issue and its the MC, there should be something from another model that is a interchangeable bolt on? Most of the after market MC's I see are 3 3/16" inch spacing between the 2 mounting holes.

 

From what I've read so far, having a power steering pump that puts out between 1,200 to 1,500 psi is ideal, and going to a 1 1/8" bore MC, along with a portioning valve is the way to go.

[V8path]

 

Hey Kingman, is there a MC that you suggest would be a upgrade to the GM ones that come in leaking? Given its a GM hydro boost, and if that's not the main issue and its the MC, there should be something from another model that is a interchangeable bolt on? Most of the after market MC's I see are 3 3/16" inch spacing between the 2 mounting holes.

 

From what I've read so far, having a power steering pump that puts out between 1,200 to 1,500 psi is ideal, and going to a 1 1/8" bore MC, along with a portioning valve is the way to go.

 

After a little more research, and talking to a couple guys that upgraded their Tahoe MC to a Chev 3/4T MC (NBS version), they're much happier with the braking feel and performance.

 

The other upgrade is the power steering pump volumes and PSI. Volume should be at 3 - 3.5 GPM and PSI ideally at 1,500. With the better MC, which is essential if going to bigger calipers or converting read drums to discs, make sure the power steering pump is putting out the flow and PSI needed, otherwise this will end up being a lot of work for no performance gains

[MY1PATH]

For information sake:

 

I just did some FSM searching. The pedal assist ratio of WD21 boosters goes from 5x to 8x. (8x being the newer stronger model, Hard to find in the fsm)

 

WD21 boosters were 9" primary and 8" secondary dual diaphragm but the late 2002 Xterra is a 9" and 9" dual diaphragm... I am personally going to do some more research into this and may even try it if it fits.

Xterra booster showed up yesterday. I might give it a shot this weekend.

[V8path]

Bled the MC to no avail. Tried to bleed the lines... Still nothing. Bypassed the abs block dealy and BAM more brakes then I know what to do with!

 

Hey new4x4r do you have pics and the MC part numbers you used, and how you plumbed the new MC?

 

Most of the GM MC's come with a large reservoir and small reservoir which (logic) would mean the larger reservoir should be for the larger front calipers, and the smaller reservoir for the smaller rear calipers.

 

But the listings I found show the smaller reservoir with a larger port size (9/16-18), and the larger reservoir with a smaller port size (1/2-20). Most manufacturer's listing show the larger port (9/16) as the primary port (but that is the smaller reservoir), and the smaller port (1/2) as the secondary port (larger reservoir).

 

Anyone able to sort out the confusion?