I'm about to give up on the vacuum brakes and get the power master back.No matter what I do I can't get the things to hold boost on the line like the pm did.Sometimes when I hit them while driving they feel ok for a second or so then get hard,I find myself giving more stopping distance.I'm afraid to drive it in traffic.I've bled them over and over,this is the second booster /master cylinder cause I thought the first one was bad and I've adjusted the rear 3 times to make sure.I don't know what else to do??!?!?!?
Can Not Get Vacuum Brakes To Hold Boost!!!!!
- Thread starter 2QWIK4U
- Start date
This pedal getting hard, ain't right. Are you sharing the booster vac source with something else?. How old is the brake fluid?. Did you flush the brake fluid, or just bleed it?. Are you sure the plunger is *right* in the proportioning valve?.
How much boost are you trying to launch at?.
And there is the off chance of getting a few used items in a row that are bad.
I'm getting vacuum from the pcv line,only place I saw to tap into.I completely flushed the fluid before the install.Trying to leave around 7-8psi,but it "pushes through the brakes",even trying to do a burnout.Never had this problem before the swap.
Enlighten me a little on the proportioning valve.I had to change it about 6 yrs ago (AC Delco) but can't remember much about it.
Thanks!!!
Enlighten me a little on the proportioning valve.I had to change it about 6 yrs ago (AC Delco) but can't remember much about it.
Thanks!!!
Red Regal T
Senior Member
- Joined
- May 24, 2001
What Bruce said is probably your problem. Some guys have a problem using the PCV line while most do not. I don't know why but seems to be the case. I think you will see a great difference once you install the TTA vacuum block.
65vette396
Accepting Donations 4 C16
- Joined
- Feb 11, 2002
Both the guys above me are correct. Change the vacuum source and you should have great brakes. Drew
2quik4u, I have the same problem as you. I have changed everything. I helped install a vacuum brakes on my cousins TR, and his brakes are worse than mine and he has the TA vacuum block for the brakes and even has a vacuum pump!!
So what I have learned is vacuum brakes on TR's suck!! just my 2cents.
So what I have learned is vacuum brakes on TR's suck!! just my 2cents.Vacuum works fine. I have it on mine. My dad has it on his. Most of my friends have it. It plain works well and has been super reliable.
If you are having problems then here are a few suggestions (some are redundant):
check proper function of the booster (make sure there is no loud hissing when the pedal is pressed while engine is running. If you hear a loud continuous hiss while holding the pedal, then you have a hole in the diaphram and the booster should be replaced as this will be the spot where you will loose vacuum)
check proper function of the check valve
check vacuum source
make sure you have more than 10 inches of vacuum available (cams with a lot of duration and/or over lap will kill the vacuum)
make sure you dont have a misfire or a cylinder down on compression or a huge vacuum leak some where else (such as the climate control, cruise control or any of the other vacuum sources)
It should also be noted that there are 2 different boosters fitted to G bodies.
One is a single diaphram (large diameter, shallow housing depth)
The other is a dual diaphragm (small diameter, thick housing)
I always use the dual diaphram. The TTA's had a dual diaphram as well that was mechanically identical to the G body unit.
Anytime someone has a problem with the pedal loosing assist I strongly question many of the above items since it should work flawlessly. The TTA came stock with it (as is common knowledge) and utilized all of the same critical parts that a Buick would have (cam, intake, etc).
Many guys dont like it when the tune/running condition of their engine is questioned, but those things play a big part in your vacuum readings. Parts integrity is also crucial. Not that G body boosters go bad that often as I have never lost one personally, but it is mechanical and is possible. The one on my car is used from a salvage yard and has been on there for almost 5 years now.
If you are having problems then here are a few suggestions (some are redundant):
check proper function of the booster (make sure there is no loud hissing when the pedal is pressed while engine is running. If you hear a loud continuous hiss while holding the pedal, then you have a hole in the diaphram and the booster should be replaced as this will be the spot where you will loose vacuum)
check proper function of the check valve
check vacuum source
make sure you have more than 10 inches of vacuum available (cams with a lot of duration and/or over lap will kill the vacuum)
make sure you dont have a misfire or a cylinder down on compression or a huge vacuum leak some where else (such as the climate control, cruise control or any of the other vacuum sources)
It should also be noted that there are 2 different boosters fitted to G bodies.
One is a single diaphram (large diameter, shallow housing depth)
The other is a dual diaphragm (small diameter, thick housing)
I always use the dual diaphram. The TTA's had a dual diaphram as well that was mechanically identical to the G body unit.
Anytime someone has a problem with the pedal loosing assist I strongly question many of the above items since it should work flawlessly. The TTA came stock with it (as is common knowledge) and utilized all of the same critical parts that a Buick would have (cam, intake, etc).
Many guys dont like it when the tune/running condition of their engine is questioned, but those things play a big part in your vacuum readings. Parts integrity is also crucial. Not that G body boosters go bad that often as I have never lost one personally, but it is mechanical and is possible. The one on my car is used from a salvage yard and has been on there for almost 5 years now.
Red Regal T
Senior Member
- Joined
- May 24, 2001
TR, or any other kind of car, vacuum brakes work the same and it's just bad information to say vacuum brakes aren't good. If yours are not, there is something wrong with your particular setup. There just is no downside to vacuum brakes.
I still I have the stock power master brake unit on mine. I was about to convert to vacuum brakes but decided to rebuild the master cylinder and add the ron custom max boost brake module. Since I have done this the car brakes extremly well and I could hold more boost than I ever did. The way the ron custom brake module works is that when it is engaged by a momentary switch it bybasses the stock brake proportion valve and sends alot more pressure to the rear brakes which makes it alot easier to create boost off the line. I have done my best 60ft (1.52) at 9 lbs of boost, but I am sure that I could hold up to 12 lbs or even more but still haven't tried it. The only thing I know is that this brake module works well for me.
3.8VSIX How much mileage did your car have before changing your valve springs. Did you see any performance gain after changing your valve springs.
86 Grand National t-top (59000km)
stock long block,stock suspension, red stripe convertor, te44, smc alk injection, 24lbs boost, 94 octane, hooker cat back with dyno max ultra flow muffers, tomco 30lbs injectors, dynotech stage 4 street chip, thdp, mease 24 row IC, MT drag radials (275/50/15) 3800lbs race weight.
best ET
60FT=1.52
1/8= 7.38
I/4= 11.74
MPH=113
BEST MPH= 114
3.8VSIX How much mileage did your car have before changing your valve springs. Did you see any performance gain after changing your valve springs.
86 Grand National t-top (59000km)
stock long block,stock suspension, red stripe convertor, te44, smc alk injection, 24lbs boost, 94 octane, hooker cat back with dyno max ultra flow muffers, tomco 30lbs injectors, dynotech stage 4 street chip, thdp, mease 24 row IC, MT drag radials (275/50/15) 3800lbs race weight.
best ET
60FT=1.52
1/8= 7.38
I/4= 11.74
MPH=113
BEST MPH= 114
Since the topic of proportioning valves has been mentioned. I'd suggest folks read this.
The TRs use combination valves. The combination valve includes a proportioning valve, metering, and pressure differential switch.
Most if not all proportioning valves, don't in the true sense of the word. They do have a huge effect on the knee-over point, as explained in the following.
http://www.stoptech.com/whitepapers/proportioning_valves.htm
The TRs use combination valves. The combination valve includes a proportioning valve, metering, and pressure differential switch.
Most if not all proportioning valves, don't in the true sense of the word. They do have a huge effect on the knee-over point, as explained in the following.
http://www.stoptech.com/whitepapers/proportioning_valves.htm
What kind/part number check valve do use? I have gotten my vacuum source from the pcv valve as per the directions for the conversion from gnttype.org and from Red Regal T and used 3/8 fuel line. Advance Auto only had two check valves and they were both way to small. Which direction does the valve go?
Red Regal T
Senior Member
- Joined
- May 24, 2001
The check valve you need is the one included with the brake kit. It is the ivory colored part plugged into the vacuum canister next to where the master cylinder is located. You don't need an additional check valve.
Another thing I didnt see mentioned here was revving up the engine a little in nuetral, then putting it in gear and trying to build boost. If I dont rev mine up a little then I can only build about 2#s, if I rev it up to build up the vaccum a little, I can get 5 pretty easy. This is on street radials.
