Replacement Brake Master Cylinder - Best Option?

[Hackyman]

Replacing front and rear brakes with a Black Magic Brakes 16" big brake kit, as well as replacing the back calipers. I am considering replacing the master cylinder at the same time. Jeep has 155k miles and I assume the master is original. Two questions:

1. Is this stupid?
2. What is the best option for parts that are available?

 

[MichaelGH]

I would wait and see how it acts after all the brake work is completed.

As long as you aren’t already experiencing issues with the booster.

I am running an SKP booster from RockAuto. Not my first choice, but it seems to be alright.

 

[TheBoogieman]

Replacing front and rear brakes with a Black Magic Brakes 16" big brake kit, as well as replacing the back calipers. I am considering replacing the master cylinder at the same time. Jeep has 155k miles and I assume the master is original. Two questions:

1. Is this stupid?
2. What is the best option for parts that are available?

The guy that sells you the BMBs could answer that question for you. No need for others' opinions.

 

[Hackyman]

Yes, but I figured it I would not bother him with every decision I ever make.

 

[mrblaine]

Replacing front and rear brakes with a Black Magic Brakes 16" big brake kit, as well as replacing the back calipers. I am considering replacing the master cylinder at the same time. Jeep has 155k miles and I assume the master is original. Two questions:

1. Is this stupid?
2. What is the best option for parts that are available?

I would wait and see how it acts after all the brake work is completed.

As long as you aren’t already experiencing issues with the booster.

I am running an SKP booster from RockAuto. Not my first choice, but it seems to be alright.

That

Yes, but I figured it I would not bother him with every decision I ever make.

Best option is probably a crap shoot. We've had great success with the Dorman master in the Super 16 and 17" brake kits. I've used a few of the Dorman brand for stock replacements with a few failures. We used Centric for the JK kits, zero failures. Use the Centric TJ version for Super 16 and 17", 50% failure rate.

We have had similar sporadic results with a few others trying to find something dependable.

I'd make the stock last as long as possible.

 

[macleanflood]

I'm getting close to installing my iBooster.

I need to stop breaking things long enough to start braking things.

-Mac

 

[Rickstar321]

After bouncing my TJ down the last bit of a very steep decline denting every skid plate I had due to brake fade I decided to do the WJ knuckle swap. Which includes larger 2 caliper brakes, and while I was in there I did this master cylinder swap.

(but I'm also the crazy guy that installed Gladiator control arms in his TJ... so take this with a grain of salt... lol)

I've been running it 2 years with no issues and it stops on a dime. No more brake fade.

2000 Dodge Ram Van Master Cylinder Swap

 

[mrblaine]

After bouncing my TJ down the last bit of a very steep decline denting every skid plate I had due to brake fade I decided to do the WJ knuckle swap. Which includes larger 2 caliper brakes, and while I was in there I did this master cylinder swap.

(but I'm also the crazy guy that installed Gladiator control arms in his TJ... so take this with a grain of salt... lol)

I've been running it 2 years with no issues and it stops on a dime. No more brake fade.

2000 Dodge Ram Van Master Cylinder Swap

View attachment 637731

No, it does not stop on a dime unless you have Hulk thighs. The WJ calipers have nearly the exact same piston area as the stock caliper so the only thing you have done with your 1.25" bore Ram Van 3500 master is decrease the pressure into the calipers by 50% since that is the exact difference in bore piston area between it and the stock 1" bore master. That's how it works, that's how hydraulics work, and the guy whose video you watched, did you no favors whatsoever.

A little math for you. Stock caliper has a 66mm piston which is 5.30 square inches of area. WJ has dual 48mm pistons which is 2.80 per for a total of 5.60 square inches. Minor difference of no consequence.

Stock master is 1" bore diameter, the 1.25" bore is 50% larger in piston area which REDUCES the pressure into the calipers with the same leg effort by 50%. You have a high hard pedal that fools you into thinking you've done something good instead of listening to some retard who made a video talking about fucking "secrets". You wanna see an actual improvement, put the stock master back on and amaze yourself with what simple math can do.

 

[ColoJeep]

No, it does not stop on a dime unless you have Hulk thighs. The WJ calipers have nearly the exact same piston area as the stock caliper so the only thing you have done with your 1.25" bore Ram Van 3500 master is decrease the pressure into the calipers by 50% since that is the exact difference in bore piston area between it and the stock 1" bore master. That's how it works, that's how hydraulics work, and the guy whose video you watched, did you no favors whatsoever.

A little math for you. Stock caliper has a 66mm piston which is 5.30 square inches of area. WJ has dual 48mm pistons which is 2.80 per for a total of 5.60 square inches. Minor difference of no consequence.

Stock master is 1" bore diameter, the 1.25" bore is 50% larger in piston area which REDUCES the pressure into the calipers with the same leg effort by 50%. You have a high hard pedal that fools you into thinking you've done something good instead of listening to some retard who made a video talking about fucking "secrets". You wanna see an actual improvement, put the stock master back on and amaze yourself with what simple math can do.

Thanks for bringing the facts to the conversation !

 

[mrblaine]

Thanks for bringing the facts to the conversation !

Facts don't matter when you have a spiffy video sharing "TJ Secrets".

 

[ColoJeep]

Facts don't matter when you have a spiffy video sharing "TJ Secrets".

This mind set is how we ended up with a " community organizer " as president at a point in time . I'm good with hydraulic facts when it comes to brakes. Thanks.

 

[mrblaine]

This mind set is how we ended up with a " community organizer " as president at a point in time . I'm good with hydraulic facts when it comes to brakes. Thanks.

After more digging around than I care to admit, I found this chart which tells you exactly what I've been saying for the last 20 years trying to combat this ignorance. Ignore that we don't often see 14mm master cylinder bore sizes and just study the math and the reduction in pressure as the bore size increases. Their math is slightly off somehow though. You should be able to multiply the area increase percentage by the higher pressure of the smaller piston and get right at the new lower pressure. Interestingly, it does show the stark reality of just a basic doubling of the master size. Going from about a 9/16" bore master to a 1" bore master drops the line pressure from 1047 to 318.

 

[MikeE024]

Thanks for the explanation, @mrblaine.

For those skeptical minds, Wallace Racing's line pressure calculator also agrees that a MC with a 1.25" bore makes less line pressure than a MC with a 1.00" bore (when applying the same pedal force and with the same pedal ratio).

Source (third calculator on the page)

Note: Motion Raceworks calculator agrees as well.

 

[Rickstar321]

Thanks for the explanation, @mrblaine.

For those skeptical minds, Wallace Racing's line pressure calculator also agrees that a MC with a 1.25" bore makes less line pressure than a MC with a 1.00" bore (when applying the same pedal force and with the same pedal ratio).

View attachment 637810

View attachment 637811

Source (third calculator on the page)

Note: Motion Raceworks calculator agrees as well.

Welp I'm always learning , every day! (My ego is pretty bomb proof) Reading through all this it definitely makes sense. My misunderstanding was thinking that if you push 1-1/2 oz vs 1 oz of fluid into a smaller area (just for example) it would increase the pressure but I see that is incorrect.

I tried to edit my earlier post to correct it but it's not allowing me that option now.

Bottom line is I'll plan on going back to the OEM size. I'll be sure to come back and report the difference.

I guess the 1" larger rotor and small change in piston size was enough to get me past the brake fade and give me enough stopping power to convince me it was a legit upgrade... OR maybe replacing all the fluid made the real change... either way... Lessons learned!

I'm more interested in learning how to be a better Jeeper than fluffing up my ego .

Thanks again!

 

[mrblaine]

Thanks for the explanation, @mrblaine.

For those skeptical minds, Wallace Racing's line pressure calculator also agrees that a MC with a 1.25" bore makes less line pressure than a MC with a 1.00" bore (when applying the same pedal force and with the same pedal ratio).

View attachment 637810

View attachment 637811

Source (third calculator on the page)

Note: Motion Raceworks calculator agrees as well.

There is something wrong with the one from Wallace. There is no way a 50% increase in piston area only reduces the line pressure by 60 psi.

 

[ColoJeep]

There is something wrong with the one from Wallace. There is no way a 50% increase in piston area only reduces the line pressure by 60 psi.

I was wondering about their chart , it seems unclear if they are showing true piston area or piston diameter 1" vs. 1.25"

 

[mrblaine]

Welp I'm always learning , every day! (My ego is pretty bomb proof) Reading through all this it definitely makes sense. My misunderstanding was thinking that if you push 1-1/2 oz vs 1 oz of fluid into a smaller area (just for example) it would increase the pressure but I see that is incorrect.

I tried to edit my earlier post to correct it but it's not allowing me that option now.

Bottom line is I'll plan on going back to the OEM size. I'll be sure to come back and report the difference.

I guess the 1" larger rotor and small change in piston size was enough to get me past the brake fade and give me enough stopping power to convince me it was a legit upgrade... OR maybe replacing all the fluid made the real change... either way... Lessons learned!

I'm more interested in learning how to be a better Jeeper than fluffing up my ego .

Thanks again!

The resistance to brake fade is likely due to a superior caliper design, a larger rotor, and lower pressure output from the master. The WJ caliper is a much better caliper than the stock TJ caliper which is pretty terrible. The pad design is also better. The TJ 477 pad is way too long for the piston so it winds up flexing in the center and not applying the friction layer evenly across the face of the rotor. The WJ pad is short and has 2 pistons clamping it to the rotor so it works a fair bit better.

The terrible thing about your video buddy is all of this info can be found on the internet in pretty short order. The factory knows far more about how to design this stuff than we do. All you have to do is look up the master cylinder bore size in the WJ and you will discover that it is the same 1" bore that the TJ has. A few underhood shots in an image search reveals they are both running very similar dual diaphragm boosters.

Hopefully you used the far better Akebono calipers and not the terrible Teves. If it helps at all, I was doing the WJ conversion when the WJ was just being switched from Teves to Akebono due to the factory caliper recall and buying the knuckles and calipers new from the dealer because the aftermarket hadn't started supplying them yet.

All that said, I'm impressed that you are willing to learn. That is far better than the gent who told me I should be dead because I challenged his belief that your TJ will overheat if you remove the thermostat.

 

[mrblaine]

I was wondering about their chart , it seems unclear if they are showing true piston area or piston diameter 1" vs. 1.25"

Our knowledge base is doomed. AI is taking over and compiling "facts" based on various assertions with little basis in truth. When I started looking for this info many years ago, I found site after site that explained very clearly with high clarity that the nature of hydraulic pressure is inversely related and the increase in master size will decrease the output pressure for a given input (leg force) by the exact percentage of the increase in area. It was simple and easy to understand.

Now that AI is involved, very difficult to find and several have stated that the smaller piston will firm up the pedal which is very incorrect.

Several of the older examples used a hydraulic floor jack as an example and show if you increased the area of the piston the handle was pushing down against, the jack would rise faster/further for each handle pump but would not do it with as much force.

 

[Rickstar321]

The resistance to brake fade is likely due to a superior caliper design, a larger rotor, and lower pressure output from the master. The WJ caliper is a much better caliper than the stock TJ caliper which is pretty terrible. The pad design is also better. The TJ 477 pad is way too long for the piston so it winds up flexing in the center and not applying the friction layer evenly across the face of the rotor. The WJ pad is short and has 2 pistons clamping it to the rotor so it works a fair bit better.

The terrible thing about your video buddy is all of this info can be found on the internet in pretty short order. The factory knows far more about how to design this stuff than we do. All you have to do is look up the master cylinder bore size in the WJ and you will discover that it is the same 1" bore that the TJ has. A few underhood shots in an image search reveals they are both running very similar dual diaphragm boosters.

Hopefully you used the far better Akebono calipers and not the terrible Teves. If it helps at all, I was doing the WJ conversion when the WJ was just being switched from Teves to Akebono due to the factory caliper recall and buying the knuckles and calipers new from the dealer because the aftermarket hadn't started supplying them yet.

All that said, I'm impressed that you are willing to learn. That is far better than the gent who told me I should be dead because I challenged his belief that your TJ will overheat if you remove the thermostat.

Yup new Akebono rotors and calipers (Oreillys), drilled at a machine shop... The knuckles I got are from a local "you pull it" yard (I wanted OEM), Also had them reamed for the above the knuckle GM 1 ton steering ends. (I got from Parts Mike), I custom made all my own DOM steering / Track bar.

I also swapped out the Dana 30/35 for TJ Rubi 44's at the same time... so there was a lot of changes happening back then. Got it all finished the weekend before a two week North East Arkansas to AZ / UT wheeling trip and back a year and a half ago and I still haven't put a stabilizer on it... hasn't needed one. AZ and UT really stress tested the brake system.

 

[mrblaine]

Yup new Akebono rotors and calipers (Oreillys), drilled at a machine shop... The knuckles I got are from a local "you pull it" yard (I wanted OEM), Also had them reamed for the above the knuckle GM 1 ton steering ends. (I got from Parts Mike), I custom made all my own DOM steering / Track bar.

I also swapped out the Dana 30/35 for TJ Rubi 44's at the same time... so there was a lot of changes happening back then. Got it all finished the weekend before a two week North East Arkansas to AZ / UT wheeling trip and back a year and a half ago and I still haven't put a stabilizer on it... hasn't needed one. AZ and UT really stress tested the brake system.

I've never been a fan of that method. I always preferred to use the Sport Trac rotor as an off the shelf part in case something happens that requires a quick local replacement. I've seen too many damaged rotors that needing a machine shop to get going again is not a great way to do things. Also not a fan of grinding on the knuckles to dial in the saddle spacing. I preferred to make my own unit bearing spacers, weld them on and then have the excess machined off to both put the saddle where it goes centered on the rotor and to get rid of the warped face the welding creates.

If you think you haven't needed a stabilizer, then you are probably assuming it is doing something other than buffering the impacts the tires impart to the steering bits.

I'm familiar with Parts Mike, been doing business with them for quite awhile now.