vacuum brakes not holding any boost

[Timbuick]

I'm almost too ashamed to say...
60' was 2.2, et at 14.4 and terminal speed at 76mph.
Shockingalso, had a problem getting revs up to burn out, so i wonder what i happening there.
The guy that sold the car to me stated that it was time to fit a bigger turbo, that would need a better convertor.
Prior to today i ran small block Mopar and could launch at 2000rpm, so this `Buick has rather suprised me in the lack of launch. That said, its far quicker than the Mopar from a rolling start.

 

[TurboDave]

Another big issue I've noticed over the last 24 years, with difficulty holding boost on the foot brake has a LOT to do with heat in the rear drum/shoes. No matter what braking system you use, ANY heat built up back there (like what happens during a foot brake burnout) will absolutely KILL the rear brake clamping efficiency.
To answer an earlier question, a line lock will not help hold more boost on the line, that's not what it's for.
However it will help indirectly..... Set the line lock to do your burnout so that there's no braking applied to the rear wheels and no heat built up in the rear shoes. It only takes a little heat to kill their effectiveness!!!

And of course a too tight converter adds to the difficulty, but one of my first mods many years ago was the line lock, and after it's install I was able to build and hold 15# of boost on the stock converter.

Tons of line pressure and cold shoes!!

 

[TurboDave]

These "my vacuum brakes won't hold boost" threads always amaze me?

The stock brakes on a Regal are all the same no matter if they are vacuum, PM, Hydroboost or manual, difference is the manner in which they assist the leg muscles. The calipers, shoes, pads and cylinders are all the same, so they should ALL have the same holding power.

.

I'm thinking there's still a big difference in line pressures from system to system. Even a good vacuum system just can't hold the kind of boost a PM or HB system seems to be able to do.

There must be a reason that almost every modern day turbo charged vehicle produced uses a HB system or some modern darivative of it. I always have to chuckle at the old arguement drug out that "pontiac uses vacuum brakes, they must know something". Well, consider the fact that maybe, just maybe they didn't know best.

Oh well, just some thoughts.

I really don't have anything against vacuum brake change overs. It's a nice alternative to spening money on the PM. Me, I'll keep running my PM's until it gets too costly. So far, not bad. On two GN's I've replaced one accumulator on one, and two on the other, and one pressure switch on each, over the last 24 years.
Like any other piece/part/system on the car, regular maintenance keeps them working fine for years.

 

[Red Regal T]

I'm almost too ashamed to say...
60' was 2.2, et at 14.4 and terminal speed at 76mph.
Shockingalso, had a problem getting revs up to burn out, so i wonder what i happening there.
The guy that sold the car to me stated that it was time to fit a bigger turbo, that would need a better convertor.
Prior to today i ran small block Mopar and could launch at 2000rpm, so this `Buick has rather suprised me in the lack of launch. That said, its far quicker than the Mopar from a rolling start.

Nonsense! No reason at all to be ashamed of that time. Obviously your car is basically stock. If you're not using alcohol or race gas, this is a typical ET for a stock TR. I routinely get 2.2 60's with street tires. I don't even build boost on the line or want to. My tires would merely go up in smoke. But be encouraged. Practically any upgrade you do to your TR will show up as quicker ETs.

 

[Timbuick]

thanks for the input guys. I think what shocked me is that on the street the car is fast, way faster the my Mopar was and spins the tires in second gear.
I was using alky, but at only 16lbs of boost as it was my first ever run. Seemed sensible at the time and i had zero knock on slightly fat 02s of 796/803.

Meantime, i'll install a line lock and double check brake shoe adjustment before the next session.

 

[TurboDave]

Nonsense! No reason at all to be ashamed of that time. Obviously your car is basically stock. If you're not using alcohol or race gas, this is a typical ET for a stock TR. I routinely get 2.2 60's with street tires. I don't even build boost on the line or want to. My tires would merely go up in smoke. But be encouraged. Practically any upgrade you do to your TR will show up as quicker ETs.

You should have come to the TB.com nationals and watched the street tire class. You'd have seen some pretty impressive 60's times. I'm talking 1.8's and a few better.
We're talking REAL street radials.

I've had no problem with 1.8-1.9 60's on my Firestone Firehawks. Oh, and a good track prep doesn't hurt either.
Just takes the right technique. And 24 years of experience in the same car doesn't hurt.

 

[Red Regal T]

Oh, and a good track prep doesn't hurt either.

End of the story!

 

[Red Regal T]

thanks for the input guys. I think what shocked me is that on the street the car is fast, way faster the my Mopar was and spins the tires in second gear.
I was using alky, but at only 16lbs of boost as it was my first ever run. Seemed sensible at the time and i had zero knock on slightly fat 02s of 796/803.

Meantime, i'll install a line lock and double check brake shoe adjustment before the next session.

You'll work it out.

 

[1quick6]

I'm thinking there's still a big difference in line pressures from system to system. Even a good vacuum system just can't hold the kind of boost a PM or HB system seems to be able to do.

That's my understanding anyway. Hydroboost offers tremendous line pressure.

People sure seem to get their feathers ruffled with these brake threads. Most of the time, the point is that you have options.

 

[Timbuick]

actually track seemed fine and the car went straight and true. Just slow:redface:
i'll keep my vac brakes as 99% i'm on the street and they always pull up without drama.

Just thought of something else! My idle blms are still high (long story...), which would be a vac leak and make matters worse I suspect.

As for experience, another 23 years and i'll be good, if a little old:biggrin:

 

[Timbuick]

Quick update!!
Read my time slips wrong last night. My et was only 14.4, but speed was 101mph every time! So, get the 60' down and things should look a lot better!

 

[Red Regal T]

That prior mph was kind of confusing. I told you. Things are looking up already.

 

[1quick6]

Quick update!!
Read my time slips wrong last night. My et was only 14.4, but speed was 101mph every time! So, get the 60' down and things should look a lot better!

Heh. I was thinking I read your original post wrong. 101 is much better than 74 or whatever it was. Your car has definite potential! You already have 7 mph over a stocker even with your launch problems, so once you get your traction worked out and can hold a bit of boost for the launch, you will be wearing a permanent smile.

 

[Timbuick]

Thanks guys, reading the speed correctly certainly cheered me up:wink:

 

[JimP]

I have a vac set up, dual diaphragm booster, brakes work great under regular driving. Initially when trying to hold boost I couldn't hold any with the power master or the vacuum set up. I ditched the power master when without warning the light came on and I had to be able to squat 800 lbs to slow the car. That was the first and last time I was going to experience that.

Since converting to vacuum I have done the following, added a line lock, added the two large softer brake shoes as well as S-10 manual brake wheel cylinders. I was then able to hold between 5-8 lbs. I then changed the brake lines to stainless steel braided flex hoses, this greatly improved the pedal feel and increased the holding power. I have seen 15 lbs of boost in some cases with launches causing my radio to fly out of the dash.

I'd consider looking at the rubber flex hoses if they are still in place. It they are old they will expand which takes away from your holding power. I've also noticed that when I have done a burn out without the line lock I can't hold as much boost due to the heat in the rear brakes. It took several attempts at bleeding the system as well.

 

[Timbuick]

thanks Jim, I do have a set of larger calipers and braided hoses to go on the front brakes which should help.

 

[Red Regal T]

I have seen 15 lbs of boost in some cases with launches causing my radio to fly out of the dash.

.

HA-HA-HA :biggrin:

 

[84BuickGNYorkPA]

I have a vac set up, dual diaphragm booster, brakes work great under regular driving. Initially when trying to hold boost I couldn't hold any with the power master or the vacuum set up. I ditched the power master when without warning the light came on and I had to be able to squat 800 lbs to slow the car. That was the first and last time I was going to experience that.

Since converting to vacuum I have done the following, added a line lock, added the two large softer brake shoes as well as S-10 manual brake wheel cylinders. I was then able to hold between 5-8 lbs. I then changed the brake lines to stainless steel braided flex hoses, this greatly improved the pedal feel and increased the holding power. I have seen 15 lbs of boost in some cases with launches causing my radio to fly out of the dash.

I'd consider looking at the rubber flex hoses if they are still in place. It they are old they will expand which takes away from your holding power. I've also noticed that when I have done a burn out without the line lock I can't hold as much boost due to the heat in the rear brakes. It took several attempts at bleeding the system as well.

Wow, what a difference with the SS brake lines.... something else to add to the list of things to do....

Chuck