vacuum pump for brakes

[turbo buicks]

a friend of mine runs a separate vacuum pump in his GN with vacuum brakes to keep constant brake power. ive noticed if i boost to say 5 psi and slam on the brakes in an emergency stop the pedal gets stiff and the car barely stops. also i blew a vac. line off the MAP sensor the other day and the car only pulled 10 inches of vacuum (normal is around 17-20 inches on my car) and when i slammed on the brakes (testing new calipers, rotor, and wheel cylinders) the pedl got stiff 1/2 way down and the car rolled to a stop in about 2 seconds. after reconnecting the vacuum line it would lock up the brakes again. i only boosted to about 10 psi yesterday so at 20+ psi (when i get this thing running OK) i can imagine what it will do to the MAP line and i dont want half ass brakes at 100+ MPH. anyone know (links) where i can get a separate vacuum pump so i can have constant braking pressure and maybe be able to hold some boost at the line?

 

[Steve Wood]

I have never had problems unless the vacuum was down around 10 inches...then the same problem as a big cammed car.

I guess if everything was working properly, then one might be able to ride the brakes until the vacuum was exhausted. Never heard anyone with a TTA complain of the problem, tho.

I suspect the key is that the vacuum booster can not have a hole in one of the diaphrams, etc.

All that as it may, seems like GM used a vaccum assist pump on some of the Citations and small Cadillacs a few years ago. A search of the mailing list archives might give some more info.

A very expensive solution can be found at:

http://www.mpbrakes.com/MP8.HTM

 

[turbo buicks]

thanks steve. i tried slamming on the brakes in ym driveway at 15 inches of vacuum and they wouldnt lock up and the pedal got hard but i was only going about 2 mph. $390 for a product that would ensure braking safety is fine in my book. sucks when ya cant stop would a 204-214 speedpro cam cause a low vacuum (poor braking) condition?

 

[Roger]

I paid about $250 at Autozone for a citation booster.
I went back to PM & resolved my brake problems.
I have a never used Citation pump I'd like to get rid of.

 

[Steve Wood]

Having three cars with vacuum brakes for a number of years, I always suspect that something is wrong in the system somewhere when such problems are reported.

The factory had no problem with installing vacuum brakes on the TTAs and I kinda doubt they would do it if they thought there was a potential safety issue-altho, admittedly, they do some seemingly dumb things at times.

Once, when I had a 221 deg cam and relatively low vacuum (10-11"), I could force it to run out of vacuum.

With milder cams, I have never had the problem. With a properly working booster, checkvalve, etc., it should be hard to fall short of vacuum. Be sure the check valve is not allowing boost to blow into the booster.

Good brakes are mandantory so I hope you get it figured out.

 

[KWIKR 1]

I have the SP 204/214 and have the exact same problem . The front of my car stopped 1 ft off of the back of a tow truck last season .when trying to stop after a 80ft quick boost off of a stop light . I just recently purchased a vacuum resivoir can hoping it may help .

 

[turbo buicks]

thanks KWIKR 1, thats the kinda results im looking for. looks like i may need a vacuum pump after all. after boosting tho i found the pedal wont even go down barely any at all. is this what happened to you or did you wiat till it got back intop vacuum and then apply the brakes fully? also how much vacuum does your car pull at idle?

 

[KWIKR 1]

I would try the can first . My car did stop only after both feet and my body weight standing on the pedal . Felt like there was no "assist" to the brakes while it was happening . Very scary . Brakes were fine after it happened as I drove away at a lower speed . I notice it only happens when you do a quick blast/boost and then try a sudden stop . other then that they are fine driving around town or on the highway . it may have something to do with the larger exhaust duration for some reason . I'm going to try the vacuum can this season .and if that does not work I am going back to the PM . My wife drives the car and likes to boost it around a little and I'd hate for anything to happen . The only good thing about it . was the problem stopped her from driving the car last year . engine pulled 14-16 inches of vacuum .

 

[6=8]

I agree with Steve... Something is not right.

If your car typically generates vacuum readings high enough for the brakes to work (say 16 in hg+), than I would think you need additional storage, not a pump. Pumps are for setups that cannot generate a high enough vacuum signal to begin with, as in radical cams (with more Overlap).

The vacuum system should be sealed well enough to provide strong brakes using reserve vacuum and not rely on a constantly high manifold vacuum signal to get the job done. If your running high boost pressures, consider clamping every vacuum line you have!

Master Power Brakes, which does offer a conversion kit for our turbo cars (About $500) as well as optional vacuum pumps, recommends running rather long vac lines to act as a reserve reservoir (Vacuum storage). Taking this line of thought a little further (and for piece of mind) I would think plumbing in a dedicated vacuum reservoir before the brake booster would be a nice inexpensive way to increase capacity of the braking system in 0 vacuum, boosted, or even slight vac leak conditions, as long as the check valve is moved ahead of the reservoir and that it seals 100%.

If you think about it, we already have a vacuum reservoir and check valve system in our cars for the ventilation system. If this system is working, even with the car shut down, you can get the vents to cycle at least once... Should be true for vacuum "Conversion" brakes as well!

But all of this is useless if your brake booster diaphragm or the check valve leaks. If you shut your car off in the driveway and wait a moment or two, you should still have at least one power assisted brake press. If not, I would suspect you either have a leak, or the check valve/grommet needs replacing.

Just to let the other members know: I have just converted with used components, and I can boost to 10psi and "Panic Stop", including locking up the wheels if I want, without issue. If you can't, something is wrong with the parts or the install, not the concept.

Vacuum brakes are reliable, and have proven this for years... they work in momentary 0 vacuum conditions (Panic stops) without issues. The big difference is that in non-boosted applications, the brakes will still work reasonably well in spite of small leaks. In our cars, it is just a bit more critical to seal these systems well and prevent boost from canceling out the vacuum stored in the brake booster.

I hope this helps a bit! If you still need a vacuum pump: http://mpbrakes.com/mp27.htm

 

[bruce]

When I bought my car I drove it 1,200 miles and once in town had the POS PM fail.

Said never again, will I risk that.

Installed a Vac system.
One day backing out the garage, engine faltered, and tapped the gas, which spooled the turbo. So wound up in reverse in boost with no brakes.

said never again, will I risk that.

Installed a Manual set-up. So now the only possible failure is loose of fluid, or M/C dieing. Also, much better pedal feel, thou, a slight increase in pedal effort. I feel alot safer not having to worry about an electrical or vac problem not allowing me to stop.
YMMV

 

[KWIKR 1]

I thought the same thing at first that something was wrong . But EVERYTHING was replaced in my system with top name parts . And I mean everything (except brake lines ), back to front of car . nothing came from the junk yard . and I went over it looking for any type of leak , but everything checked out . I even tried out 3 different brand new check valves .

The vacuum can comes with a check valve . I take that it gets piped to the vacuum block . then a seperate line goes from the can (brass fitting) to the check on the booster . is this the correct way to hook it up ? thanks.

 

[turbo buicks]

thanks bruce and 6=8, i have talked to a few with manual brakes and they recommened against them for a street car tho. bruce, how did you get into boost in your driveway in reverse? you must have floored it all the way. what turbo were you running? 6=8, do you have a link to the turbo cars brake conversion kit you spoke of?

 

[6=8]

Master Power Brakes

Hey I found it again! Here you go:

http://www.mpbrakes.com/BM8743.HTM

Interesting that it also states that it will work with the existing brake pedal...

This was my plan "B": If the used parts failed to work for me, I was planning on getting this system.

Probably needs 18" hg because of the pedal arm. I wonder if you can use this same setup at 16" hg with the correct vac brake arm? Humm.... Maybe something to ask them about.

I also recommend getting the vapor trap... Helps keep those fumes out of the booster. A found one hanging on a rack at NAPA and installed it.

I bet that if you asked, these guys would know about vacuum can installs too!

KWIKR 1: Damn! Sounds like a lot of work, man! Sorry to hear about that... You're probably thinking: That A-hole got away with used parts, and I spent all this cash? But, "New" parts can be bad. Happens to me all the time. Where they remanufactured units? Maybe the boosters seal better as time goes on? Would be interesting to connect a vac gauge up between the check valve and booster for a leak test to see WTF is going on...

What you propose sounds right on the plumbing. You might want to contact MP Brakes (Links above) and see what they say about dbl check valves. I had a 30 year old booster rebuilt by MP (for a 69 Charger)... good folks, helpful, high quality work.

 

[KWIKR 1]

I'll report back this season if the can does the trick . .

 

[captrob]

Hey Bruce...

What is the application for the manual master cylinder? I'd like to try one out.
Thanks, CaptRob

 

[nboeck]

So before I buy and electric vacuum pump for my vacuum brakes, is this a better choice than switching back to powermaster brakes? The few mechanics I spoke to both recommended switching back and getting rid of vacuum...

 

[TurboBuickSix]

Powermaster

I personally have had A/G-bodies with vac brakes for the last 10 years or better and all stopped about the same when working properly.First time I got in the GN and used the PM brakes I was amazed and the braking power(almost put myself thru the window).Say what you will,but all systems working top notch including the hydroboost the PM stops the car the best from my hundreds of thousands of miles experience with these cars.Do the TTA's have disc brakes in the rear? Same size up front? Maybe that is why they would not need the might of the PM assist?? If and when my PM fails I will bite the bullet and get it working again regardless of cost.

BTW,I had this EXACT problem you and Bruce have described with my 84 T with Vac brakes that I converted to get rid of the leaking Hydroboost sys.Had to rev in neutral to get enough vac for spooling.Everything new,no problems,Postons 107 degree cam.Beware of certain folks pushing conversion kits on you to line their wallets,they don't care if you can't build boost at the line.

 

[nboeck]

Re: Powermaster

So if I have the current vacuum set-up and need to fix it you'd recommend going back to powermaster over getting the add-on to increase the vacuum? I'm not racing, just for daily street driving...

Originally posted by TurboBuickSix
I personally have had A/G-bodies with vac brakes for the last 10 years or better and all stopped about the same when working properly.First time I got in the GN and used the PM brakes I was amazed and the braking power(almost put myself thru the window).Say what you will,but all systems working top notch including the hydroboost the PM stops the car the best from my hundreds of thousands of miles experience with these cars.Do the TTA's have disc brakes in the rear? Same size up front? Maybe that is why they would not need the might of the PM assist?? If and when my PM fails I will bite the bullet and get it working again regardless of cost.

BTW,I had this EXACT problem you and Bruce have described with my 84 T with Vac brakes that I converted to get rid of the leaking Hydroboost sys.Had to rev in neutral to get enough vac for spooling.Everything new,no problems,Postons 107 degree cam.Beware of certain folks pushing conversion kits on you to line their wallets,they don't care if you can't build boost at the line.

 

[TurboBuickSix]

If your not racing then Vacuum is fine,I would go with the reserve can as already suggested.

 

[nboeck]

And with the vacuum pump add-on I shouldn't have problems say, going down a NYC street flooring it at around 60mph and then having to suddenly stop? This is basically what happened to me with 4 other people in the car last weekend...Not safe driving but I guess I'm used to a car that has working brakes. and wouldn't be a problem...just want to be as clear as possible before I do the work and find out it's not good enough..willing to spend extra for something different if it keeps me alive! Thanks.

Originally posted by TurboBuickSix
If your not racing then Vacuum is fine,I would go with the reserve can as already suggested.