Master Cylinder Options

[augr]

Looks like my master cylinder needs to be replaced so I am wondering if anyone has used one of the larger bore models?

I've been reading that the larger bore enhances braking power by increasing line pressure and supposedly stops better and gives you a more firm brake pedal. But I haven't read anything about someone actually using it.... mostly speculation it seems and hearsay on the negative effects.

Has anyone gone the larger bore route and did you notice any difference in braking power? Any negative effects like leaking calipers due to more pressure? I've never had any issues and I've installed modern master cylinders and brake boosters on 4 wheel drum brake vans from the 60's without those options from factory.

Found this one that is pretty big comparatively.... RAYBESTOS Part # MC390542 Professional Grade; Bore Size=37mm Number of Ports=2 and it's just shy of $85 compared to the ACDELCO which is at $260. That's a huge difference!

I know cheap parts aren't always a good solution but it's not like Raybestos doesn't have brand equity.

What do you guys think?

Forgot to mention... 2001 Tahoe 2x4 w/5.3L

Cheers!

[j cAT]

Originally Posted by augr

Looks like my master cylinder needs to be replaced so I am wondering if anyone has used one of the larger bore models?

I've been reading that the larger bore enhances braking power by increasing line pressure and supposedly stops better and gives you a more firm brake pedal. But I haven't read anything about someone actually using it.... mostly speculation it seems and hearsay on the negative effects.

Has anyone gone the larger bore route and did you notice any difference in braking power? Any negative effects like leaking calipers due to more pressure? I've never had any issues and I've installed modern master cylinders and brake boosters on 4 wheel drum brake vans from the 60's without those options from factory.

Found this one that is pretty big comparatively.... RAYBESTOS Part # MC390542 Professional Grade; Bore Size=37mm Number of Ports=2 and it's just shy of $85 compared to the ACDELCO which is at $260. That's a huge difference!

I know cheap parts aren't always a good solution but it's not like Raybestos doesn't have brand equity.

What do you guys think?

Forgot to mention... 2001 Tahoe 2x4 w/5.3L

Cheers!

what is wrong / defective with the master cyl. ?

pedal to the floor is usually the brake lines leaking /rusted. don't take much of a leak for this to occur.

sometimes its the abs valve unit.

with 4 wheel disc brakes in the tahoe you should not need a larger master cyl. the abs might come on more often with the greater pressures when you brake.

[augr]

Thanks for the reply jcat. The abs is what my fear was with the larger bore. I agree it might cause problems.

What's happening is when I press down hard on the pedal (engine on), it slowly floors. If I don't press down hard, it doesn't. Since the Master Cylinder reservoir looks like it has a lot of crud/sludge and just looks dingy in general, I imagine the seals are pretty worn by now. Replacing the unit is cheaper than a rebuild kit. The Tahoe has almost 200,000 miles on it and the brake components with the exception of pads have never been replaced. It's a California desert car so I have no rust issues.

Now I see there are $80 and $250 master cylinders. Everyone keeps saying go with the best but I don't know if those same people have gone cheap and have any real world experience as such. It's easy to fork out $250 and assume it's the best but is it really?

[j cAT]

Originally Posted by augr

Thanks for the reply jcat. The abs is what my fear was with the larger bore. I agree it might cause problems.

What's happening is when I press down hard on the pedal (engine on), it slowly floors. If I don't press down hard, it doesn't. Since the Master Cylinder reservoir looks like it has a lot of crud/sludge and just looks dingy in general, I imagine the seals are pretty worn by now. Replacing the unit is cheaper than a rebuild kit. The Tahoe has almost 200,000 miles on it and the brake components with the exception of pads have never been replaced. It's a California desert car so I have no rust issues.

Now I see there are $80 and $250 master cylinders. Everyone keeps saying go with the best but I don't know if those same people have gone cheap and have any real world experience as such. It's easy to fork out $250 and assume it's the best but is it really?

I bet the problem with the brakes not working good is the fact that the fluid is old. before replacing the master cylinder get the vehicle brake fluid flushed out if it looks bad. check for leaks then replace the master cylinder. contaminated fluid does not compress very good.

if the pedal still goes to the floor slowly after this work then this may be the abs valves. some have created the condition for the abs to come on to try and fix this some have had success..when the valves are worked they sometimes seat better.

[augr]

My bad I neglected to mention that I did the fluid when I did the pads about a year ago.

I have the ABS currently out of the car waiting for the EBCM to come back from repairs. Might be a good time to replace those valves but they look pressed in. I don't suppose there's a rebuild service out there? They're $650! I'm referring to the hydraulic unit. Are you refering to the modulator valve or the valves on the hydraulic unit?

[j cAT]

Originally Posted by augr

My bad I neglected to mention that I did the fluid when I did the pads about a year ago.

I have the ABS currently out of the car waiting for the EBCM to come back from repairs. Might be a good time to replace those valves but they look pressed in. I don't suppose there's a rebuild service out there? They're $650! I'm referring to the hydraulic unit. Are you refering to the modulator valve or the valves on the hydraulic unit?

the electronic portion of the ABS can be repaired. the hydro section is not repairable. even the dealership does not repair it.

cylcing the ABS and or while bleeding cylcling the ABS might work. with the brake fluid being flushed out just check for leaks again . could be at the caliper pistons or if you have rear drums the brake cyl.

check along the driver side the lines running to the rear brake units.

trying a scrap yard ABS would be the cheaper way to go ..these ABS units are very expensive.

wheneven I replace pads on a vehicle with an abs unit I open the bleed screw then push back caliper pistons. the cal pistons are loaded with debris that will screw up the ABS valves.

[augr]

So I decided to go with the larger bore master cylinder (37mm). The more I thought about it, the less it made sense that I would get lockup on an ABS system from more pressure since ABS is designed to stop lockups.

I am very pleased with the result. The larger bore raised the pedal, made it slightly harder and seems to do a better job of getting the car stopped with less pressure. I get absolutely no lockup on a hard brake and it stops shorter as now it feels like all 4 wheels are adding to the braking power. I tried locking up several times at 30mph, 50mph, 65mph and it just stopped straight and really quickly with full steering control.

My rear disks seem to work better too as I also get less nose dive but that could be due to the old one malfunctioning.

Anyway for those interested, in my opinion, a larger bore master cylinder is a good upgrade if you're in the market for one.

I picked up a brand new NAMCCO brand master cylinder on ebay for $50 shipped.

A special thanks to j_cat for the tips and advice!

[j cAT]

Originally Posted by augr

So I decided to go with the larger bore master cylinder (37mm). The more I thought about it, the less it made sense that I would get lockup on an ABS system from more pressure since ABS is designed to stop lockups.

I am very pleased with the result. The larger bore raised the pedal, made it slightly harder and seems to do a better job of getting the car stopped with less pressure. I get absolutely no lockup on a hard brake and it stops shorter as now it feels like all 4 wheels are adding to the braking power. I tried locking up several times at 30mph, 50mph, 65mph and it just stopped straight and really quickly with full steering control.

My rear disks seem to work better too as I also get less nose dive but that could be due to the old one malfunctioning.

Anyway for those interested, in my opinion, a larger bore master cylinder is a good upgrade if you're in the market for one.

I picked up a brand new NAMCCO brand master cylinder on ebay for $50 shipped.

A special thanks to j_cat for the tips and advice!

Thanks for the result of your modification . also the cost and supplier info. I know that the brake pedal effort on these vehicles is higher than most other vehicles. having to use less force to get the desired braking effort is a nice modification. I'm sure other members will find this quite useful.. good luck..