Engine Vacuum/Brake problem revisited
Thread Starter
Drifting
Joined: Apr 2000
Posts: 1,915
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From: Maurice, LA
Engine Vacuum/Brake problem revisited
I have been fighting a braking issue for awhile now. Motor is basically stock besides straight pipes with flowmaster 50's, no AIR pump and disconnected EGR valve, and cold air induction with a K&N filter. The problem is the worse when the weather is cold outside and so is the engine. When applying the brakes, it feels like I have no booster. I have done the following:
New master cylinder
Changed fluid/bled lines
New booster
New check valve
New vac line to booster
Verified that booster inline filter is not clogged or leaking
I am concerned that my motor may not be making enough vacuum at times. I have heard that 17 to 22 inches of Hg is good for brakes. I have not checked it with a guage yet. The engine seems to run fine and I have done a tune up and changed the oil recently. There are no visible vac leaks and it idles normally in closed loop.
When i apply the brakes when the motor is cold its hard as a brick. Seems to clear up a bit as the engine reaches opperating temp. When applying the brakes gently it is not as hard as applying them quickly.
If any of you gurus has any tips on verifying engine vacuum please help as this is a daily driver. I really appreciate the help. Thanks.
New master cylinder
Changed fluid/bled lines
New booster
New check valve
New vac line to booster
Verified that booster inline filter is not clogged or leaking
I am concerned that my motor may not be making enough vacuum at times. I have heard that 17 to 22 inches of Hg is good for brakes. I have not checked it with a guage yet. The engine seems to run fine and I have done a tune up and changed the oil recently. There are no visible vac leaks and it idles normally in closed loop.
When i apply the brakes when the motor is cold its hard as a brick. Seems to clear up a bit as the engine reaches opperating temp. When applying the brakes gently it is not as hard as applying them quickly.
If any of you gurus has any tips on verifying engine vacuum please help as this is a daily driver. I really appreciate the help. Thanks.
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Originally Posted by GiDvEtTe84
I have been fighting a braking issue for awhile now. Motor is basically stock besides straight pipes with flowmaster 50's, no AIR pump and disconnected EGR valve, and cold air induction with a K&N filter. The problem is the worse when the weather is cold outside and so is the engine. When applying the brakes, it feels like I have no booster. I have done the following:
New master cylinder
Changed fluid/bled lines
New booster
New check valve
New vac line to booster
Verified that booster inline filter is not clogged or leaking
I am concerned that my motor may not be making enough vacuum at times. I have heard that 17 to 22 inches of Hg is good for brakes. I have not checked it with a guage yet. The engine seems to run fine and I have done a tune up and changed the oil recently. There are no visible vac leaks and it idles normally in closed loop.
When i apply the brakes when the motor is cold its hard as a brick. Seems to clear up a bit as the engine reaches opperating temp. When applying the brakes gently it is not as hard as applying them quickly.
If any of you gurus has any tips on verifying engine vacuum please help as this is a daily driver. I really appreciate the help. Thanks.
New master cylinder
Changed fluid/bled lines
New booster
New check valve
New vac line to booster
Verified that booster inline filter is not clogged or leaking
I am concerned that my motor may not be making enough vacuum at times. I have heard that 17 to 22 inches of Hg is good for brakes. I have not checked it with a guage yet. The engine seems to run fine and I have done a tune up and changed the oil recently. There are no visible vac leaks and it idles normally in closed loop.
When i apply the brakes when the motor is cold its hard as a brick. Seems to clear up a bit as the engine reaches opperating temp. When applying the brakes gently it is not as hard as applying them quickly.
If any of you gurus has any tips on verifying engine vacuum please help as this is a daily driver. I really appreciate the help. Thanks.
Sounds like your brake booster may ge on the way out!
Hard pedal is generally the first sign
If you are satisfied that you have no vacuum leaks, then my vote would be for the booster!
seeya
Jack
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
I'd first put a vacuum gauge on the engine and see what it's pulling and if the reading is steady.
If low or flucuating, check all the vacuum hoses to make sure no port is unplugged and no hose is leaking.
Jake
If low or flucuating, check all the vacuum hoses to make sure no port is unplugged and no hose is leaking.
Jake
Melting Slicks
Joined: May 2003
Posts: 2,076
Likes: 281
From: Dyersburg TN
While the pedal is hard, press on it, bring the RPMs up (you don't have to wake up the neighbors, just up the engine speed) then let off the gas. That should create lots of vacuum. If it is low vacuum, you should feel the pedal sink in with the high vacuum. If not, I would check the pedal linkage and calipers for something in a bind.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Where'd you buy the booster? I replaced the one on my Ford with a reman one that was bad, took it back to autozone, and got another bad one and put that one on. 
By then I was just sick of working on it. I left that crappy one in.
When they say "Limited Lifetime" warranty, they mean it!
By then I was just sick of working on it. I left that crappy one in. When they say "Limited Lifetime" warranty, they mean it!
Pro
Joined: Mar 1999
Posts: 678
Likes: 0
From: Oslo, Norway
Hi.
When I bought my 85 some 8 yrs ago I had never had an american car. The first trip was a very negative surprice with the brakes. I had a feel that I had to stand up pressing the pedal to get the wheels locked. The vacuum was fine the booster seemed to work. I heard that the brakes on these cars were crap and there was nothing to do with it. Well I took out the pads and they were glassed. I put in some semi metal pads and that made the brakes better but not good. Then after a couple of years I came over the EBS greenstuff pads. It was as I got new brakes. The brakes are now acceptable for daily driver as I compare them to european cars as I live in Norway. There is another advantage there s little brake dust. I have now modified the engine so I do not have so much vaccum 14inch.
The brakes are not good as they have only one piston and not a very large brake pad area. Strange that they made the brakes so bad on a performance car.
I love my vette, but this is something they could have done better.
When I bought my 85 some 8 yrs ago I had never had an american car. The first trip was a very negative surprice with the brakes. I had a feel that I had to stand up pressing the pedal to get the wheels locked. The vacuum was fine the booster seemed to work. I heard that the brakes on these cars were crap and there was nothing to do with it. Well I took out the pads and they were glassed. I put in some semi metal pads and that made the brakes better but not good. Then after a couple of years I came over the EBS greenstuff pads. It was as I got new brakes. The brakes are now acceptable for daily driver as I compare them to european cars as I live in Norway. There is another advantage there s little brake dust. I have now modified the engine so I do not have so much vaccum 14inch.
The brakes are not good as they have only one piston and not a very large brake pad area. Strange that they made the brakes so bad on a performance car.
I love my vette, but this is something they could have done better.
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Thread Starter
Drifting
Joined: Apr 2000
Posts: 1,915
Likes: 0
From: Maurice, LA
Ok i did some testing. It was 62 this morning. Unplugging the booster does make my idle go way up. I attached the gauge to that booster line before i started the engine for the first time today. It was pulling 14" and progressed as the engine warmed up. 19" in closed loop in running temp. Does this sound right? I havent checked for leaks yet. The needle is nice and steady and doesnt bounce.
I bought the booster at a local parts house, remanufactered. I also changed my pads and it gave me more pedal but the problem is still there. No codes either.
Another observation: My PVC valve is supposed to be a "T" type but it only has 1 elbow. The line going to the canister purge silenoid as indicated by my picture is diconnected and just hanging. I dont know how this would affect vacuum. All other lines seem to be fine. What do you guys think?
I bought the booster at a local parts house, remanufactered. I also changed my pads and it gave me more pedal but the problem is still there. No codes either.
Another observation: My PVC valve is supposed to be a "T" type but it only has 1 elbow. The line going to the canister purge silenoid as indicated by my picture is diconnected and just hanging. I dont know how this would affect vacuum. All other lines seem to be fine. What do you guys think?
Last edited by GiDvEtTe84; Nov 19, 2004 at 09:05 AM.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Originally Posted by GiDvEtTe84
Ok i did some testing. It was 62 this morning. Unplugging the booster does make my idle go way up. I attached the gauge to that booster line before i started the engine for the first time today. It was pulling 14" and progressed as the engine warmed up. 19" in closed loop in running temp. Does this sound right? I havent checked for leaks yet. The needle is nice and steady and doesnt bounce.
I bought the booster at a local parts house, remanufactered. I also changed my pads and it gave me more pedal but the problem is still there. No codes either.
Another observation: My PVC valve is supposed to be a "T" type but it only has 1 elbow. The line going to the canister purge silenoid as indicated by my picture is diconnected and just hanging. I dont know how this would affect vacuum. All other lines seem to be fine. What do you guys think?
I bought the booster at a local parts house, remanufactered. I also changed my pads and it gave me more pedal but the problem is still there. No codes either.
Another observation: My PVC valve is supposed to be a "T" type but it only has 1 elbow. The line going to the canister purge silenoid as indicated by my picture is diconnected and just hanging. I dont know how this would affect vacuum. All other lines seem to be fine. What do you guys think?
You need to plug or connect any vacuum hoses that you find not attached.
14" at start up is on the low side. I don't think a change of 5" in vacuum reading is a good sign; too wide a variation, 14 to 19.
Make all the hose connections and check to see what difference it makes.
Keep us posted.
Jake
Thread Starter
Drifting
Joined: Apr 2000
Posts: 1,915
Likes: 0
From: Maurice, LA
Just another note: I tested the vac @ 45 degrees and cold starting the engine. The effect was similar to that of my previous test. Idle is about 1500 rpm in open loop. 14" until warmed up. Is this normal? I thought more RPM should give you more vacuum. I realize that the IACs were open in closed loop as well. I have a small propane bottle that i will use to try to find leaks. I will let you guys know what i find.
Last edited by GiDvEtTe84; Nov 27, 2004 at 11:19 AM.
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Originally Posted by GiDvEtTe84
Just another note: I tested the vac @ 45 degrees and cold starting the engine. The effect was similar to that of my previous test. Idle is about 1500 rpm in open loop. 14" until warmed up. Is this normal? I thought more RPM should give you more vacuum. I realize that the IACs were open in closed loop as well. I have a small propane bottle that i will use to try to find leaks. I will let you guys know what i find.
At 14 in/hg your brakes should work OK. I have worked on cammed up cars using a comp 306 cam with less vacuum than what you have and their brakes work fine. If I were you I would remove that booster and have it checked at a reputable rebuilder or get an exchange from where you got it. I fought a problem just like yours in a 69 boss 302 mustang that the customer had me install a $3000 Baer brake system on. When I got it done, the car would hardly stop with me standing on the pedal, and the pedal was hard like a rock. I didn't relish the idea of pulling the booster because in a mustang it was a ROYAL PITA. I sent the booster to a company here in Portland called Brake Systems. They rebuild boosters there. I had them check it out and sure as heck thats what the problem was. This car had a 351 385Hp crate motor in it that had a healthy cam as well. Its idle vacuum was about 13 in/hg and once the booster was fixed the problem basically went away.
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
I agree 14" should be enough for the booster, but 14" at idle is low for a stock cam -- it should be at least 18".
Most stock cams I have seen can do about 20" at idle warmed up.
My performance cam can do 15" at idle.
Tom Piper
Most stock cams I have seen can do about 20" at idle warmed up.
My performance cam can do 15" at idle.
Tom Piper
Thread Starter
Drifting
Joined: Apr 2000
Posts: 1,915
Likes: 0
From: Maurice, LA
Thanks for the replies. Like I said, its wierd cause it starts off at 14 and gets to 19 when warmed up. I am gonna try to put a T in the booster line and check it with the booster connected.
Thread Starter
Drifting
Joined: Apr 2000
Posts: 1,915
Likes: 0
From: Maurice, LA
I talked to a local mechanic and he said to check the gaskets beneath the TBs, take em off and clean the passages, and make sure all the ports on the TB's and pulling vac. Makes sense?
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by GiDvEtTe84
What about a gasket that expands when the engine warms up? What about a defective IAC? (we have 2 of em)
The IACs are not the problem unless they are cracked or have bad gaskets and are leaking air. Even if that were the case, the idle speed would be outta sight. The same is true of the TB gasket(s). If you had vacuum leaks, the idle would go "way up" like it did when you pulled the vaciim hose off of the brake booster.
Your vacuum is fine, hot. You brakes aren't. It seems you're chasing side issue that isn't even the reason you posted, and that *I'M* not convinced is even a problem.
Focus.
RACE ON!!!
Thread Starter
Drifting
Joined: Apr 2000
Posts: 1,915
Likes: 0
From: Maurice, LA
For instance, it was in the upper 30's this morning. Let the car warm up. Still hard. Drove for 5 minutes, not hard anymore. I was going 60 mph and slammed the brakes really quick, they were hard. Again, from 60, let the accel go and pressed brakes slowly, they work fine.
Im pretty sure its a remanufactured booster, but i will check.
Im pretty sure its a remanufactured booster, but i will check.