New brake booster with a mind of its own

[WarWobble]

My brake booster stopped boosting and started hissing at my foot from behind the pedal whenever I applied the brakes, so I replaced it. I ordered a cheap one off Amazon from a relatively new manufacturer called "A-Premium." Why? Because I was very impressed with the quality and corrosion-resistance of their polished steel door handles, and thought they might also make a quality booster at a reasonable price.

When I removed the old booster I could clearly see a crack on the plastic part hidden behind the rubber boot and significant rust on the side that bolts to the firewall. There were no signs of a master cylinder leak. The master cylinder is about 8 years old and appears to be in good shape.

When I tried out the new booster, the brake pedal felt both mushy and powerful. I definitely had plenty of boost, and after driving for a while, it started to do something very strange: the pedal would sink down further than I was pressing it myself and sometimes wouldn't return untill I hooked my toe under it and pulled it back. I would go to apply 50% of my braking power, and the Jeep would appy 100% until I either pulled the pedal back or laid on the gas.

I swapped the old check valve back in and it made no difference. Both valves are good. The vacuum hose is free of obstructions or leaks.

I disconnected the vacuum line, capped off the manifold inlet, and have been stopping my 33s with pure unassisted leg-power ever since. With power assist disabled, the pedal is quite firm; every day is leg day now (at least for righty).

Did I buy the world's most outrageously defective brake booster, or could the problem be something else? My master cylinder is about 8 years old, rear wheel cylinders are about 9 years old, and the front calipers and all flexible hoses are from before my time with the vehicle.

Just a wacky booster, or could there be more to it?

 

[KennethS]

You have a faulty booster. I had similar symptoms with a replacement on my classic car. Send it back and get another one.

 

[aston4]

Scary. Send it back.

 

[DuckNut]

Stopping mine is a chore. Been researching using the power steering pump as the booster. But finding people who can tell you how much additional force is supplied is akin to finding an honest politician. Everything is great, so much better...ok, by how much. Please hold until you forget your original question.

 

[WarWobble]

Thanks. Sounds like an open-and-shut case. I've ordered a different booster.

 

[WarWobble]

I just installed a rebuilt booster from Advance Auto Parts. The pedal hasn't gotten stuck yet like with the last one, but it is still a very soft pedal.

I have plenty of braking power, the pedal is easy to press, and it doesn't apply itself and get stuck, so maybe I shouldn't complain... but I guess I'm not used to my pedal feeling like a puddle of mud.

 

[WarWobble]

I usually feather my brake pedal now when stopping, because I decelerate more suddenly than I intend to at first, then back it off, but then I'm not slowing fast enough. It's still difficult to control the pedal with precision, because it feels like there is a block of memory foam between the pedal and my foot... yet the pedal is so firm with the vacuum line disconnected.

 

[macleanflood]

All I can say is new parts are just pure crap these days.

Might need to try and source the part elsewhere.

I'd almost suggest finding a used Mopar in a junkyard.

I wonder if there is a rebuild kit for your original.

-Mac

 

[mrblaine]

Stopping mine is a chore. Been researching using the power steering pump as the booster. But finding people who can tell you how much additional force is supplied is akin to finding an honest politician. Everything is great, so much better...ok, by how much. Please hold until you forget your original question.

Standard TJ master and booster deliver anywhere from 1100 to 1400 psi into the calipers. Hydroboost with the same master delivers 2000-2400 psi. Those are numbers I measured myself. That said, no one tagged me in to answer, so there you go.

 

[mrblaine]

All I can say is new parts are just pure crap these days.

All the parts you just got from me are new, which ones are crap? Point them out and I'll keep replacing them until we get some that aren't crap.

 

[macleanflood]

All the parts you just got from me are new, which ones are crap? Point them out and I'll keep replacing them until we get some that aren't crap.

Except your off course! Cheap parts from the parts store vs. curated and carefully selected parts from the experts.

Any suggestions for the OP as to where to source a good booster?

Or do you think the issue lies elsewhere like the rod?

-Mac

 

[mrblaine]

Except your off course! Cheap parts from the parts store vs. curated and carefully selected parts from the experts.

Any suggestions for the OP as to where to source a good booster?

Or do you think the issue lies elsewhere like the rod?

-Mac

He needs to bleed the system first and make sure the squishy pedal isn't air in the system. After that, no idea where to get a good booster.

 

[DuckNut]

Standard TJ master and booster deliver anywhere from 1100 to 1400 psi into the calipers. Hydroboost with the same master delivers 2000-2400 psi. Those are numbers I measured myself. That said, no one tagged me in to answer, so there you go.

No worries. This is great info and thank you for the response. Fantastic!

Why can't these companies post that info! It seems like they are trying to sell their products without any proven data and it smells like snake oil.

This leads me to other questions.

There are 198 brake manufacturers and 197 of those claim to have invented sliced bread. Ours feels better. Ours can stop the space shuttle. Ours are quietest. Ours stops the shortest. Ad nauseum.

If every car insurance company can save 15% over everyone else why are rates higher than a $1? Is there any data out there that shows which brakes stop shortest? Which ones are dirty as hell? Clean as a whistle?

You know, some science based tests that are not sponsored or opinion, just science based that you know of?

Appreciate you mrblaine.

 

[mrblaine]

No worries. This is great info and thank you for the response. Fantastic!

Why can't these companies post that info! It seems like they are trying to sell their products without any proven data and it smells like snake oil.

This leads me to other questions.

There are 198 brake manufacturers and 197 of those claim to have invented sliced bread. Ours feels better. Ours can stop the space shuttle. Ours are quietest. Ours stops the shortest. Ad nauseum.

If every car insurance company can save 15% over everyone else why are rates higher than a $1? Is there any data out there that shows which brakes stop shortest? Which ones are dirty as hell? Clean as a whistle?

You know, some science based tests that are not sponsored or opinion, just science based that you know of?

Appreciate you mrblaine.

At the risk of pissing off certain unnamed individuals whom can't handle the truth, here is the problem with trying to publish or attest to any specific distances. It isn't repeatable, every aspect of environmental conditions has to be duplicated exactly to achieve the same result. If the customer can't achieve the same result, then that opens you up to some level of liability or at least the notion that you are being somewhat dishonest.

You need the same ambient temp, same tires, same road friction, same humidity level, etc. Each change in one or more of those factors alters the distance. Each stop alters the one after it.

We worked our asses off trying to figure out a way to compare distances. We had some really solid testers who knew what they are doing. At best, they could not get stops back to back within 20 feet of each other and that is not taking into account reaction times. The first stop is always the longest unless you continue into hot fade then those are longer. If you publish the best of the stops and then someone rear ends someone else and finds a way to prove that they started well inside your published distances and therefore should have been able to avoid the accident, now what? At best, it is a conversation that no one wants to have, at worst, that conversation involves attorneys.

As for clean and dirty, it all boils down to color. If the dust shows up, it is dirty, if it doesn't, it is clean. But, anyone concerned about the color isn't looking to solve their braking problem. Note that I said shows up. That's because the only way it doesn't show up is due to them never wearing out because wear is what produces both the dust from the pad and dust from the rotor. They all wear out so they all produce dust, the only thing that matters is what color the dust is.

 

[KennethS]

Which ones are dirty as hell? Clean as a whistle?

Just going by what I have read on many car forums, the pads that generate dust are reported to grip better and the “clean” pads don’t grip as well. This is just information posted by users on car forums and as such may not be 100% scientifically accurate.

 

[DuckNut]

At the risk of pissing off certain unnamed individuals whom can't handle the truth, here is the problem with trying to publish or attest to any specific distances. It isn't repeatable, every aspect of environmental conditions has to be duplicated exactly to achieve the same result. If the customer can't achieve the same result, then that opens you up to some level of liability or at least the notion that you are being somewhat dishonest.

You need the same ambient temp, same tires, same road friction, same humidity level, etc. Each change in one or more of those factors alters the distance. Each stop alters the one after it.

We worked our asses off trying to figure out a way to compare distances. We had some really solid testers who knew what they are doing. At best, they could not get stops back to back within 20 feet of each other and that is not taking into account reaction times. The first stop is always the longest unless you continue into hot fade then those are longer. If you publish the best of the stops and then someone rear ends someone else and finds a way to prove that they started well inside your published distances and therefore should have been able to avoid the accident, now what? At best, it is a conversation that no one wants to have, at worst, that conversation involves attorneys.

As for clean and dirty, it all boils down to color. If the dust shows up, it is dirty, if it doesn't, it is clean. But, anyone concerned about the color isn't looking to solve their braking problem. Note that I said shows up. That's because the only way it doesn't show up is due to them never wearing out because wear is what produces both the dust from the pad and dust from the rotor. They all wear out so they all produce dust, the only thing that matters is what color the dust is.

Thank you for the reply. Very insightful. I would have figured someone would have made a machine like a dyno to do tests. But that takes a pile of money and trying to get people to voluntarily pay to have their products tested, this sort of information will never be published for people to discover.

Thanks again and keep up the good work. I'm watching Mac's ibooster thread. Makes a lot of sense.

 

[WarWobble]

He needs to bleed the system first and make sure the squishy pedal isn't air in the system. After that, no idea where to get a good booster.

I should have the opportunity to try bleeding my brakes this weekend.

 

[Rickyd]

Standard TJ master and booster deliver anywhere from 1100 to 1400 psi into the calipers. Hydroboost with the same master delivers 2000-2400 psi. Those are numbers I measured myself. That said, no one tagged me in to answer, so there you go.

Don't tj brakes distort and bend with the pressure hydroboost generates?

 

[mrblaine]

Don't tj brakes distort and bend with the pressure hydroboost generates?

Don't you have an interior to critique somewhere?

 

[Rickyd]

Don't you have an interior to critique somewhere?

Don't put that foolishness on me for calling it out