power brake booster issues.

jerry S · Dec 12, 2005

I have a MPBrakes power brake set up that includes an electric vacuum pump, 9 inch booster, and a dual bowl MC with 1 1/8 inch bore. My pedal is harder than hell and my brakes are actually worse than before the installation of the booster. I checked an I am pulling 21 inches of vacuum with the vac. pump. The shop that did the install says that the problem is that I have 4 wheel disks with 4 piston calipers each and that the MC is not properly sized for the disks. MPBrakes says that the size of the MC is fine. Could it be that the booster is itself bad? If so, how do you test for a bad booster?

Edbert · Dec 12, 2005

Generally if the booster holds the vacuum it is good. I do not know how they determine which booster fits a particular application but MCs are sized according to the volume of fluid required by each caliper. More volume required by bigger brakes/calipers/pistons means you need to move more fluid with the same pedal push, this will require more effort as a simple matter of physics.

LMan · Dec 12, 2005

jerry S said:
how do you test for a bad booster?

While your engine is at idle, pull the vac hose off the booster, and see if your engine suddenly sounds like it got a big ole vacuum leak.

Edbert · Dec 12, 2005

LMan said:
While your engine is at idle, pull the vac hose off the booster, and see if your engine suddenly sounds like it got a big ole vacuum leak.

Shouldn't make much (if any) difference for an electric vacuum pump though.

LMan · Dec 12, 2005

Edbert said:
Shouldn't make much (if any) difference for an electric vacuum pump though.

*zing!* Sorry, blew past that part.......prolly because I don't compute 'electric vac pumps' on brakes..sounds spendy!

jerry S · Dec 12, 2005

Here is the low down

the electric vacuum pump was disconnected from the booster and tested for vacuum. It pulled only 14 inches of vaccum at idle which means it ain't pulling its weight. It is supposed to kick in at 17 inches and pull 20-21 inches at idle until the motor pulls its own at higher rpm. For example, my manifold makes 30 inches of vacuum at 4500 rpm. The electric vacuum pump would be shut off here but turn itself back on when vacuum falls to 17 inches. the vacuum pump would keep vacuum at 20-21 inches until the engine gets to that point on its own. I have to rule out the alternator as a potential problem because I am also running an electric water pump, electric fuel pump, and electric fan in additon to the electric vacuum pump. Maybe the alt is overloaded at idle with all the accessories.

mxsman · Dec 26, 2005

I have an electric vacuum pump on mine also and I do not have the engine vacuum tied into it. Connect the electric pump straight to the booster and check it again. Should give you the 21 lbs; vacuum pump doesn't have enough volume to get 21 lbs through the engine.

jerry S · Dec 26, 2005

mxsman said:
I have an electric vacuum pump on mine also and I do not have the engine vacuum tied into it. Connect the electric pump straight to the booster and check it again. Should give you the 21 lbs; vacuum pump doesn't have enough volume to get 21 lbs through the engine.

I should be getting 21 inches whether the pump is hooked up to to the booster or not. The test for whether the pump or the booster is bad is to first disconnect the pump from the booster and test the vacuum. If the pump pulls 21 inches while disconnected (which it does not, btw), then the pump is fine. If your pump is fine and then connected to the booster, if you are not pulling 21 inches, then you have a leak in the booster, which means a bad booster. I tested just the pump and it only pulls 14-15 inches. Also, there is a switch connected to the pump that shuts itself off when you get to 18 inches. The pump never shuts off, even when the manifold was pulling 31 inches of vacuum. Ergo, the pump and the switch are both defective.

thehueypilot · Dec 26, 2005

Maybe you should ditch the fancy gizmos and run it the way the factory did back in 1969? I have power, four wheel disc brakes and the engine idles at about 12 -14 inches and they work fine.

jerry S · Dec 26, 2005

thehueypilot said:
Maybe you should ditch the fancy gizmos and run it the way the factory did back in 1969? I have power, four wheel disc brakes and the engine idles at about 12 -14 inches and they work fine.

I spent close to $400 on the damn thing and it isn't returnable for a refund. Since it is a sunk investment, I am determined to make it work. I am returning it for a new one. You see, I have a pretty heft cam which means I am not even close to having enough vacuum to run the booster at lower rpms. At higher rpm, the brakes work fine. At lower rpms, braking is a hair-raising experience, only for the brave and reckless. I almost rear-ended some guy when coasting to a halt. I almost had a heart attack. I was having visions of $10,000 in damage as I stood on the pedal with two feet.

fvike · Dec 27, 2005

So you don't produce enough vacuum.... And with that cam of yours, perhaps vacuum assisted brakes ain't the best option. Perhaps you need to spend even more money at http://www.hydratechbraking.com/. (Word of wisdom: If the sh1t don't work, spend more money on it! )
This will give you power brakes assisted by the PS pump. Costs $595.
Question is, if you are using the stock PS pump, will your TCP R&P suffer ?

BTW, in Popular Hot Rodding Magazine, jan 2006, there is an article about breaking systems. Here is a quote; "Genarally speaking, if the master cylinder bore is too large, the driver will feel a very hard feel with minimal pedal travel, and will have a difficult time genrating the necessary pressure to effectivly operate the brake system."

I thougth I should relay the info, since that is what you said your pedal feels like.

jerry S · Dec 27, 2005

fvike said:
So you don't produce enough vacuum.... And with that cam of yours, perhaps vacuum assisted brakes ain't the best option. Perhaps you need to spend even more money at http://www.hydratechbraking.com/. (Word of wisdom: If the sh1t don't work, spend more money on it! )

No way baby, I have spent all the money on these brakes I ever will.

fvike said:
This will give you power brakes assisted by the PS pump. Costs $595. Question is, if you are using the stock PS pump, will your TCP R&P suffer ?

I already have $395 invested in the electric vacuum pump which does the same thing as the PS pump assist. When the vacuum drops below 17 inches, the electric pump comes on and pulls 21 inches of vacuum until the manifold pulls vacuum in excess of 18 inches. then the pump shuts off. The brakes work just fine when I am in my power band. It is only when I am coasting at idle that things get frightening. That is what the electric pump is for. Mine just isn't working, that's all.

When building my engine, I could have gone with a moroso vacuum pump that would have boosted engine vacuum in general but I got talked into the electric vacuum pump by the guy who sold me the kit. I made my choice and I will live with it. As for the R&P, I have a manual rack so that is not an issue.

fvike said:
BTW, in Popular Hot Rodding Magazine, jan 2006, there is an article about breaking systems. Here is a quote; "Genarally speaking, if the master cylinder bore is too large, the driver will feel a very hard feel with minimal pedal travel, and will have a difficult time genrating the necessary pressure to effectivly operate the brake system."

I have 4 piston disks front and rear with 13 inch rotors. The 1 & 1/8 inch bore MC is just perfect for this application. A 1" would have given me too soft a pedal. My brakes work better than advertised when I stomp on them at higer rpm.

gsxrken · Mar 27, 2006

JerryS, any update on the vacuum pump issue? Can these pumps really pull 21 and yours was just bad?
Looking at the same "low-vac thus bad-pedal" you were when you bought the electric pump.

jerry S · Mar 27, 2006

gsxrken said:
JerryS, any update on the vacuum pump issue? Can these pumps really pull 21 and yours was just bad?
Looking at the same "low-vac thus bad-pedal" you were when you bought the electric pump.

either the pump or the switch was bad. I returned both for a new one only I have not installed it yet. MPBrakes thinks it could have been the switch because the pump was supposed to shut itself off when the engine manifold was pulling enough vacuum to run the booster only the pump never shut off. To be safe, I returned both. When I get it installed and running, I will report back.

I have been busy with skiing in the Alps and what not this past winter and with lots of snow and salt on the road, my car wasn't going to set one foot outside the garage anyway.

SoCalCruising · Mar 27, 2006

Are you still near Almere? Do the salt the roads there?

jerry S · Mar 27, 2006

SoCalCruising said:
Are you still near Almere? Do the salt the roads there?

I am so much "near" Almere as I am right in it. To answer your question, yes, they salt the roads, the bike paths, everything. We got a lot of snow this year, more than normal. Where I really got killed was during my ski trips. We got stuck in Switzerland in a blizzard that added 11 hours to our trip. 2.5 feet of snow in a matter of hours and 100 mph winds are not conducive to an easy trip. It was no better at the mountain either with 3 days being un-skiable due to blizzard conditions. I could not see past the tips of my skis.

But now, Spring has sprung. I am headed to Bitburg, Germany for the drag racing and will do some cruising here in the NL Saturday nights with the Cruise Brothers. http://www.cruisebrothers.nl/

SoCalCruising · Mar 27, 2006

Glad things are easing - weather-wise. Cruisebrothers? What a great name! My daughter is in Belfort, France (near Basel) teaching English at the Lycee there. She is complaining bitterly about the cold weather. She told us about the storm you mentioned. She comes back to SoCal in May - just when the weather will be getting nice there (it's almost always nice here). I used to work for Philips and made a number of trips to Eindhoven, but never stayed in the Amsterdam area. Your English is American. Are you an expat?

jerry S · Mar 27, 2006

SoCalCruising said:
Glad things are easing - weather-wise. Cruisebrothers? What a great name! My daughter is in Belfort, France (near Basel) teaching English at the Lycee there. She is complaining bitterly about the cold weather. She told us about the storm you mentioned. She comes back to SoCal in May - just when the weather will be getting nice there (it's almost always nice here). I used to work for Philips and made a number of trips to Eindhoven, but never stayed in the Amsterdam area. Your English is American. Are you an expat?

I am indeed an American. Our short-term expat deal is looking more and more like permanent exile. If it weren't for the Mustang, being able to ski the alps every year, and my being able to shoot and hunt here, I would have gone crazy years ago and moved back, with or without the missus. Thank God for the Mach 1, the guns, and the alps!

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