Hydroboost Brake Upgrade for the TJ

[Stu Olson]

I finished my Vanco Hydroboost install this past week and got the write-up done a bit ago. I am extremely pleased with the results.

Check it out at http://www.stu-offroad.com/hydroboost/hydroboost-1.htm

http://www.stu-offroad.com/hydroboost/hboost-11.jpg

[danno]

Stu, you mentioned in your write-up that "If one simply attached a bigger bore master cylinder to the stock vacuum booster, you would actually see a decrease in brake performance."

By decrease in brake performance do you mean that the brakes will not work as well for a given pedal pressure?

My problem (apparently a common one) is with volume. When I depress the brakes in a simulated emergency stop the brake pedal travels to the stops without being able to lock up the front brakes unless it is wet.

I had figured that a larger bore master cylinder would provide more volume to the brakes for a given movement of the brake pedal, but the effort required to press the brake pedal would go up a bit for the same or better braking performance.

Does this make sense given the amount of research you have done on braking recently?

[roger]

Danno,

I have the same understanding as you. For a given amount of pressure applied to the brake pedal, less hydraulic pressure is created because the larger bore results in less pressure per square inch being applied by the master cylinder piston.

If someone knows otherwise, please correct me.

-Roger

[danno]

Hmm, so if I were to go with a larger bore master cylinder with the same vacuum booster I could indeed increase the performance of my brakes...

only it would result in an increase in pedal pressure to do so...

that might be something I could live with.

[Stu Olson]

A larger bore master cylinder will push more fluid but at a lower pressure, given all other things equal.

This means your pedal will sit higher when you push...it won't go down towards the floor as far.

No, you will not see a brake performance increase if you keep the same booster and go with a larger bore master cylinder. Your current booster can only produce X amount of mechanical advantage. Since that X amount has not changed (it is a function of the booster)....and you are applying that same mechanical advantage to a larger bore cylinder, you will see less pressure at your wheels and so a drop in braking performance.

That is why I had to add the Hydroboost to my TJ when I went to a larger bore master cylinder. I see more fluid flow (bigger bore on master cylinder) at a higher pressure (beefier booster).

[XJ Un-Limited]

Wouldn't upgrading to a different booster be an option? Might require a bit of fab work, but something out of a bigger truck/car.. such as a 1/2 or 3/4 ton truck? Just wondering if it's possible........

[danno]

Thanks for clarifying this Stu. I wasn't aware that the pressure was limited by size and vacuum capacity of the booster. I had always assumed that stronger leg = more pressure, but it sounds like no matter how hard you press on the brake pedal, the system will always top out at a given pressure as a function of the MC bore and Booster size.

I had an Early Bronco before I got my Jeep and it was definitely the case of stronger leg = better braking with that vehicle.... Drums all around, no power assist.

[Stu Olson]

Wouldn't upgrading to a different booster be an option? Might require a bit of fab work, but something out of a bigger truck/car.. such as a 1/2 or 3/4 ton truck? Just wondering if it's possible........
Yes...that is what I did....upgraded to a different booster, a Hydroboost. The Hydroboost I installed is normally found in a 1 ton truck.

[XJ Un-Limited]

Heh, I didn't read the whole article. :p Just glanced it over. I suppose getting one out of a boneyard would still be possible. For those who don't want to spend the money or on a budget. Of course this wouldn't be a chore for just anyone.

[AZJeepdad]

Umm, WRONG. A larger bore master cylinder will give you more FORCE at the wheels with a lower pressure. More FORCE will equal greater braking performance. The basic hydraulic theory outlined by Pascal in the 1620's states that Force = pressure X area and Pressure = force / area. Apply this principle to the hydraulic system to improve performance. However you are correct about the vacuum booster providing a certian amount of assist force regardless. I've designed many braking systems, it's my job to know these things :)

Tom LaFrance

[JamesT]

Umm, WRONG. A larger bore master cylinder will give you more FORCE at the wheels with a lower pressure. More FORCE will equal greater braking performance. The basic hydraulic theory outlined by Pascal in the 1620's states that Force = pressure X area and Pressure = force / area. Apply this principle to the hydraulic system to improve performance. However you are correct about the vacuum booster providing a certian amount of assist force regardless. I've designed many braking systems, it's my job to know these things :)

Tom LaFrance

What u talking about Willis?
Who are you responding to Tom? I missed it.

[AZJeepdad]

A larger bore master cylinder will push more fluid but at a lower pressure, given all other things equal.

No, you will not see a brake performance increase if you keep the same booster and go with a larger bore master cylinder. Your current booster can only produce X amount of mechanical advantage. Since that X amount has not changed (it is a function of the booster)....and you are applying that same mechanical advantage to a larger bore cylinder, you will see less pressure at your wheels and so a drop in braking performance.



THIS part James :)

[Stu Olson]

Umm, WRONG. A larger bore master cylinder will give you more FORCE at the wheels with a lower pressure. More FORCE will equal greater braking performance. The basic hydraulic theory outlined by Pascal in the 1620's states that Force = pressure X area and Pressure = force / area. Apply this principle to the hydraulic system to improve performance. However you are correct about the vacuum booster providing a certian amount of assist force regardless. I've designed many braking systems, it's my job to know these things :)

Tom LaFrance
Hi Tom,

I am certainly no engineer, so maybe I have explained this incorrectly....but doing the actual work myself seems to indicate that I am correct.

We have measured TJ caliper pressure while changing only the master cylinder bore diameter and it supports what I initially said.

A stock TJ has approximately 1500 PSI front caliper pressure (it will vary from vehicle to vehicle but that is a fairly common number). The stock MC bore is 1" on a stock TJ master cylinder (at least it was when we measured it). We then installed a master cylinder with a 1 1/8" bore. We left everything else the same on that vehicle and we saw approximately 1200 PSI at the front caliper. Your brake pedal will feel higher and the MC stroke will be shorter than it was, but we didn't see an improvement in braking performance. With less pressure applied to the same sized caliper piston, there was less force acting on the front pads.

I've never designed a brake system and certainly never will. All I can go on is what we saw in the real world. :)

Where did I go wrong?

Edit: I came back to add a couple of comments and see if these made sense.

I have a 100 pound block of concrete.

I set the 100 block of concrete on a small block of steel that measures 1" on a side.

Am I correct in assuming that if I were to measure the force under the 1 square inch (surface area) block of steel, it would be 100 pounds per square inch?

If the above is true (and it seems it would be), and I were to increase the dimensions of the steel block so that there were 2 square inches of surface area on the bottom side, would my force then be equal to 200 pounds per square inch? ....ummmm.....no....not the way I see it.....I think it would be 50 pounds per square inch. Is this correct?

Now that same 50 PSI of pressure is applied via a tube to the caliper piston....where the surface area is still the same (we didn't change its dimensions). Half the pressure applied to the same surface area will yield half the force (force = pressure x area)

[AZJeepdad]

Stu,

The critical missing ingredient is amount of pedal travel (deflection) and amount of pressure applied by the user (foot).

Granted, you may have developed 1500psi with the OE master cyl, but what was the deflection? How far did the pedal travel to develop that pressure?
Granted, the replacement (larger) master developed 1200psi, but again, how much deflection?
If measuered, I bet you would have found that with the same amount of deflection, pressure would have been higher with the larger master.
1/8 of a difference is hardly enough to make much of a change I admit. Also, did you check and adjust the pusrod length when performing the experiment?

I did a similar upgrade on my CJ from a 7/8 bore to a 1 1/8 bore master, and I still have grease spots on my windshield where my face hit it from stopping so well :)

Regardless, the moral is, go hydroboost for the best stopping regardless of what sized master cylinder you decide to use.

[Linda]

Yes...that is what I did....upgraded to a different booster, a Hydroboost. The Hydroboost I installed is normally found in a 1 ton truck.

They were also used on '80s diesel Cadillacs and GMC station wagons. :D

[Stu Olson]

Stu,

The critical missing ingredient is amount of pedal travel (deflection) and amount of pressure applied by the user (foot).

Granted, you may have developed 1500psi with the OE master cyl, but what was the deflection? How far did the pedal travel to develop that pressure?
Granted, the replacement (larger) master developed 1200psi, but again, how much deflection?
If measuered, I bet you would have found that with the same amount of deflection, pressure would have been higher with the larger master.
1/8 of a difference is hardly enough to make much of a change I admit. Also, did you check and adjust the pusrod length when performing the experiment?

I did a similar upgrade on my CJ from a 7/8 bore to a 1 1/8 bore master, and I still have grease spots on my windshield where my face hit it from stopping so well :)

Regardless, the moral is, go hydroboost for the best stopping regardless of what sized master cylinder you decide to use.

I'm sorry for not mentioning the obvious...of course, pedal tavel, which directly relates to pressure applied to the master cylinder, would have to be the same for either setup....if it were not, the results would be completely meaningless. ( I thought I would have gotten a bit more credit on this point....wow, what a hard crowd to please). :)

Yes....the pedal was pushed, in both cases, until there was no more travel left. I honestly do not remember if we hit the floor or simply reached the physical limit of travel.

And yes, the push rod was adjusted to the correct length, by the factory and by the power brake system technician.

Tom, as I didn't get a response from you concerning my 100 pound block of concrete scenario, I made a quick trip over to the desk of one of the instructors that teaches hydraulics at the training center. Since he deals with this stuff during his classes, I felt he would certainly know the answer. He agreed that doubling the surface area of the block of steel will result in half of the pounds per square inch.

Likewise, when I asked him what would happen if I increased the bore in a master cylinder, he responded that the resultant line pressure (to the calipers) will decrease unless more input pressure is applied to the master cylinder (given that everything else in the system remains as it was).

So be it......I am totally satisfied with my findings and I still stand behind everything I have said.

One thing I've learned over the past 6 weeks of working on this brake project....the vast majority of people equate a high pedal with minimal travel to an improved braking system. I witnessed this on multiple occasions....and then once the line pressure gauge was installed, it was quite interesting to watch their expression when they found that there was 300 or 400 PSI less pressure than what they had been running with. Their response....."But the brakes feel better...they really do....I almost went through the windshield." Because of that, I was very glad I opted to record the actual results with tape measure and pressure gauge.

[danno]

Stu, so when does the "after" video come out? Need some help with it?

[Stu Olson]

As a matter of fact, I just might need a hand with the video.

I was planning on doing the last 60~0 MPH deceleration test this coming Saturday buy MikeW, my buddy to has been assisting me on this project, has out of town company and can not make it.

I sent another buddy an e-mail just this evening but have not heard back from him yet (no idea if he will be free on Saturday or not).

If you are interested in helping....I need someone to run my digital camcorder and help with the tape measure....let me know. I am going to drop the Wilwood prop valve in the TJ Saturday AM and also need someone to push the brake pedal for the final bleed.

Having a couple of guys over on Saturday would be great. Drop me an e-mail at stu@stu-offroad.com if you are interested.

[AZJeepdad]

Stu,

I AGREE with you regarding the pressure drop, however my main point is about FORCE.

My favorite example:

Applying a 10lb force on a 1in piston (master) will result in 5lbs of force in a 1/2in piston (caliper). It will move 2x as far

Applying a 10lb force on a 1in piston (master) will result in 10lbs of force in a 1in piston (caliper). It will move equal distance

Applying a 10lb force on a 1in piston (master) will result in 20lbs of force in a 2in piston (caliper). It will move 1/2 as much

Therefore it can be said (applying this theory), by increasing the master cylinder piston bore, you LOWER the pressure yet INCREASE that force. You need to press the pedal less distance to generate that force at the caliper.

Larger piston = less pressure + MORE FORCE

Force is what stops ya :)

[Stu Olson]

Hi Tom,

Your example is excellent except that we were talking about changing the master cylinder pistion size, not the caliper size. Let's use Pascal to find the correct answer....and since you want to use force, let's use his equation as it applies to force and area.

Pascals theory says:

(Force1 divided by Force2) = (Area1 divided by Area2)

So that we are comparing apples to apples here, Force1 and Area1 apply to the master cylinder piston and Force2 and Area2 apply to the caliper piston.

In your 2nd example, where both pistons were equal sized, the pressure applied to the caliper piston certainly equals the pressure applied to the master. I agree totally. If we plug those numbers into the above formula, we get:

(10 pounds divided by 10 pounds) = (1 sq. in. divided by 1 sq. in.)

Pascal's theory proves that the 10 pounds applied to the 1" master cylinder piston is felt equally in all directions and on all surfaces it pushes on.....so yes, we certainly do get 10 pounds of pressure applied to the 1" caliper piston...so we see 10 PSI.

Now....lets double the area of the master cylinder piston and run your numbers the numbers through the above formula:

(10 divided by Force2) = (2 sq. in. divided by 1 sq. in)

(10 / x) = ( 2 / 1)

To keep our equation balanced, Force2 now equals 5 pounds.

As you can see, by doubling the surface area of the master cylinder piston and maintaining the same 10 pounds (that would be your foot on the brake pedal pushing with the same pressure, regardless of piston diameter), we end up with half the force we had before.

I will not argue that force is what stops the vehicle....but I won't buy into the theory that half the force at the caliper will make the vehicle stop in a shorter distance.

[Linda]

Stu,

I picked this up from the 4BT forum. I don't know if this is the pump that came with the kit you used. If it was then Vanco (the company that sells the conversion kit) did it right the first time.

"The power steering pump on the Cummins 4BT is NAPA part number 20-8709. It is for the P series chevy vans and trucks with hydroboost. According to Saginaw, it has the highest volume and pressure of all the medium duty pumps they produce. It is a bolt on with no modifications other than presseing off the old gear and pressing on to the new pump." FYI. Power steering pumps on the Cummins B-series engines are gear driven.

[JamesT]

Stu,

I just got finished with the rough installation of the Vanco system for my CJ.
All 4 high pressure hose ends that mate to Vanco's adapters leak. The adapters I am talking about are the bent tubing with flares on the ends. What a mess.
In addition, one of the adapters is too long and it hits the hood.
Further, while it works, the long high pressure hose could have been 2"-3" longer and it would have made life easier.

Other than that....

Sorry for taking your thread OT.

[Linda]

James,

Check out Granberry Supply. They deal in hydraulic lines and fittings. I am sure they have the parts you need. http://www.granberry.com/contactus.asp

There is also a low rider/show car supplier in Laveen or Awhatukee (S Phx) that makes custom braided steel hyrdaulic lines. Unfortunately I don't know their name. They were mentioned in a 4x4 magazine a few years back. Maybe someone in the VJC knows who I am talking about.

[Stu Olson]

James,

Sorry to hear about your leak issue. Give Vanco a call (I assume you already have) and let them know. I'm quite sure that the fittings required for a CJ are different than those used on the TJ (would make sense). I'd confident that Van does not make the hoses nor machine the adpaters. I've visited his shop and didn't see the equipment for that.

[JamesT]

I will call them on Monday. By the time I figured out the problems on Friday it was too late. I sent an email.

This ended up being one of those jobs that seemed easy enough (considering I read the instructions twice before doing the install) and is being a PITA.
On top of this, the water pump started peeing and I think the altenator took a dump. Still fighting submersing problems. lol

[JamesT]

Well I talked to Vanco today. They apologized profusly.
It seems they started making their own adapters and hoses, just before I got my kit shipped to me and they have had some issues (they didn't know about the issues until people started calling in with problems). They shiped me the parts to fix the problems today.

On another good note, when I was putting the Jeep back on the trailer last night, to get ready for the week, the brake pedal felt so good. Without bleeding the system, the pedal only moved about 1.5" total, before it was close to 4".