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#1 |
Registered User
![]() Join Date: Dec 2006
Location: CA
Posts: 331
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Engine running rough after changing brake booster?
Hi guys,
I needed a new master cylinder, as it was leaking fluid very slowly out of the back by the booster. But after changing it out, the brake booster started leaking air badly, so I figured it was a coincedence, and I ended up changing that out with a brand new rebuilt unit. But now the engine is running like crap (within 10 minutes after installing the booster). It can't be a bad vacuum, though, as even when I plug the vacuum line going to the booster, there is no change. It's almost like I lost a cylinder, as it's shaking almost out of the truck. Does anyone have any ideas of anything where a booster could cause the engine to run rough? Thanks in advance... ![]() |
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#2 |
Old Skool Club
![]() Join Date: Jun 2001
Location: Benton, AR "The Heart of Arkansas"
Posts: 10,880
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Re: Engine running rough after changing brake booster?
What about the hose from the manifold to the booster? The check valve in the booster or in the hose from the manifold? Sounds too much like it is a vacuum leak to just dismiss it, to me.
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Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was. |
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#3 |
Registered User
![]() Join Date: Dec 2006
Location: CA
Posts: 331
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Re: Engine running rough after changing brake booster?
I'll try that as soon as I get off work in an hour or so. The hose is relatively new though, but maybe it got twisted or something. It also smelled kind of strange, almost like it was burning berry juice? Does brake fluid smell sweet when it burns, or just smell like burned engine oil? It didn't smell like coolant though.
I will also run a compression test just to be sure it isn't something else. |
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#4 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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Re: Engine running rough after changing brake booster?
check all the plug wires to make sure you didnt loosen one either on the plug or pull one off the dizzy while you were changing the booster and master cyl
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71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY |
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#5 |
Self-proclaimed LED man
Join Date: Nov 2003
Location: Harrisburg, Missouri
Posts: 1,021
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Re: Engine running rough after changing brake booster?
Sounds like you have a vacuum leak somewhere. That's the only affect to the engine that a power brake booster would have.
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My LED Website My Photobucket Album of LED's Ask me about hand-made custom L.E.D brake and reverse lights. <- LINK I also do LED: -Third Brake/Cargo -Brake (truck and burb) -Reverse (truck and burb) -67-68 Front Turn Signals -69-70 Front Turn Signals -71-72 Front Turn Signals -GMC Front Turn Signals I can also do custom lights for other vehicles....i did a set for a AMC Gremlin once ![]() Norwood Survivor |
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#6 |
Self-proclaimed LED man
Join Date: Nov 2003
Location: Harrisburg, Missouri
Posts: 1,021
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Re: Engine running rough after changing brake booster?
I've heard stories of the seals leaking. When the seal leaks the engine would suck brake fluid out of the resevior. Have you noticed it smoking or mysteriously dissapearing brake fluid??
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My LED Website My Photobucket Album of LED's Ask me about hand-made custom L.E.D brake and reverse lights. <- LINK I also do LED: -Third Brake/Cargo -Brake (truck and burb) -Reverse (truck and burb) -67-68 Front Turn Signals -69-70 Front Turn Signals -71-72 Front Turn Signals -GMC Front Turn Signals I can also do custom lights for other vehicles....i did a set for a AMC Gremlin once ![]() Norwood Survivor Last edited by 724x4a/cchevy; 10-16-2008 at 07:57 PM. |
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#7 |
Registered User
Join Date: Jul 2008
Location: brazil,Indiana
Posts: 8
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Re: Engine running rough after changing brake booster?
check your spark plug's #7 esspecially,if booster had a vacuum leak it may have fouled the plug.
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#8 |
Registered User
![]() Join Date: Dec 2006
Location: CA
Posts: 331
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Re: Engine running rough after changing brake booster?
well, that got my hopes up that last one. Welcome to the board by the way... The plug looked okay though. it was a little lighter than the number one plug, actually. I'm out of time for tonight, but this has to be something simple. The vacuum was registering only 13 or so, and I could have sworn it used to be more like 15 or 16. I'm not sure if it's due to my moving to a higher altitude. The carb idle is tuned okay, but does altitude (7,000 ft) cause a lower vacuum? The needle is bouncing a bit, too.
But tomorrow I'll pull all the plugs and do a quick pressure test just in case, and put in new plugs and check all the wires, etc. I did notice the vacuum advance wasn't working, so that's a small leak, but didn't change the overall vacuum when I plugged it. I'll let you all know what it was if I find it. Here's a pic of the truck. It's a 72 3/4 ton highlander. |
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#9 |
I'm a poor spectator
Join Date: Aug 2006
Location: San Antonio, Tx
Posts: 2,287
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Re: Engine running rough after changing brake booster?
15 or 16 is pretty low. 21 to 24 would be more like it especially on a stock motor.
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2006 Jeep Unlimited IMPACT ORANGE 1993 Chevy 2500 4x4 ExCab LWB 454/NV4500 Tow rig ![]() 1977 Ford F100 2x4 LWB 1st truck I owned, still have it!!! ![]() 1979 Ford F150 4x4 SWB Built Ford Tough!!! ![]() 1971 Chevy Blazer 350 / SM465 / NP205 UNDER CONSTRUCTION Soon to have a LQ4 6.0!!! |
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#10 |
Registered User
Join Date: Apr 2001
Location: DALLAS,TX
Posts: 21,977
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Re: Engine running rough after changing brake booster?
Your 'new' part could be bad. Swap it for another & see if the problem persists.
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67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... Cubic inches is like Indiana Jones with a cheap pistol. |
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#11 |
Registered User
Join Date: Oct 2008
Location: VA
Posts: 16
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Re: Engine running rough after changing brake booster?
You should have 15-16 at idle. You will only have 20+ under decel while in gear. If the engine was fine before the booster change, there's no reason to do compression or leak down test. Look at vacuum system one more time. 724 is right about the booster seals possibly leaking and sucking fluid. Have you ruled this out?
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#12 |
Registered User
![]() Join Date: Sep 2007
Location: Fairdale, Kentucky
Posts: 561
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Re: Engine running rough after changing brake booster?
Sounds like a bad booster. Plug all the ports. If it idles then replace lines one at a time. You might find one internaly colapsing or a hole that you might not see. Also if you ported in the bottom of the carb check to make sure you didn't move the carb of loosen up the fitting, and check carb base nuts. Of course you can check this with some carb cleaner or WD40 at the carb base. Good luck
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#13 |
Senior Member
![]() Join Date: Apr 2008
Location: Franklinton NC
Posts: 1,309
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Re: Engine running rough after changing brake booster?
A bouncing needle on a vacuum gauge is usually a sign of a sticking or bad valve.A compression test is in order.
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#14 |
Registered User
Join Date: Oct 2005
Location: Metro Vancouver
Posts: 444
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That is a beautiful highlander seat,
any details where you got it recovered.
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1972 Chevy C10 Custom Deluxe Highlander 1972 Chevy C10 Custom Deluxe Medium Green |
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#15 |
Firefighter
Join Date: Feb 2001
Location: Yellville, Ar, USA
Posts: 1,943
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Bouncing needle usually is valve related, like a broken spring, mine did this.
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'72 Chevy SWB 350 Auto '67 GMC LWB 350 4 speed '70 Chevy 4x4 Stepside 350 Auto Yellville, Ar. USA ![]() ![]() Last edited by BLACK AND BLUE 67-72; 10-17-2008 at 11:36 AM. |
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#16 |
Registered User
Join Date: Apr 2006
Location: East Sooke B.C. Canada
Posts: 543
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Re: Engine running rough after changing brake booster?
If it ran fine before changing the booster, and with the new one runs bad. I would suspect that the idle mixture was richened up to compensate for the old leaking booster.
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#17 |
Registered User
![]() Join Date: Dec 2006
Location: CA
Posts: 331
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Re: Engine running rough after changing brake booster?
Okay guys, I've got an update and it aint pretty. cylinder #4 has given me its all, but she's no longer holding any compression. Well, 30 lbs, actually. It was nice while it lasted...
![]() So that was one heck of a coincedence, but the brakes had nothing to do with it. On a related note, when I held the shop air to the cylinder at top dead center, air was rushing out the exhaust, so it must be a stuck or bent exhaust valve. I'm not sure it's worth just getting this one valve fixed, or replacing the whole engine. I only was told it was about 3 or 4 years old and was a full rebuild. It's a '78 400 c.i. small block with solid lifters. And a bad valve. The head number is 3947041 with a date of C18 70, and a stamp of GM 13. Oh yeah, all other cylinders were exactly 160psi stone cold. Any recommendations? |
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#18 |
Hand Crafted C-10
![]() Join Date: Aug 2006
Location: Burien, WA
Posts: 5,180
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Re: Engine running rough after changing brake booster?
I'd pull the head and get it to a machine shop. If you need the truck now, slap on a used head until the repair is made. WAY easier (and cheaper) than replacing an engine.
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#19 | |
Old Skool Club
![]() Join Date: Jun 2001
Location: Benton, AR "The Heart of Arkansas"
Posts: 10,880
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Re: Engine running rough after changing brake booster?
Quote:
So, you know my opinion is to just get the one fixed that is bad, and drive it. These are tough economic times, you know......
__________________
Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was. |
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#20 |
Firefighter
Join Date: Feb 2001
Location: Yellville, Ar, USA
Posts: 1,943
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Pull your valve cover and check your springs, make sure one isn't broken!!!! I had the exact same problem with mine, I thought i had a bad valve and was starting to pull the head and when I pulled the valve cover I saw the broken spring....
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'72 Chevy SWB 350 Auto '67 GMC LWB 350 4 speed '70 Chevy 4x4 Stepside 350 Auto Yellville, Ar. USA ![]() ![]() |
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#21 |
Registered User
![]() Join Date: Dec 2006
Location: CA
Posts: 331
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Re: Engine running rough after changing brake booster?
I'm with Chev lo Ray. these are rough times. I got the head off today, and the one valve is visibly sunk down in the head. I'm off to the Machine shop Monday morning to just fix this one valve. the springs looked good, and the cylinders had a small ridge that was more visible than actually worn. Plus the other cylinders had good compression. I checked the valve lift and it was the same as the others.
So hopefully it won't be too costly at the machine shop. Thanks to everybody for your advice. ![]() |
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#22 |
Registered User
![]() Join Date: Sep 2007
Location: Fairdale, Kentucky
Posts: 561
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Re: Engine running rough after changing brake booster?
pull off the valne cover and back the exhaust rocker nut a few turns to the left (lefty loosey) and do a compression check.. see if you can buy some time.. if the valve was set a bit on the tight side you might have enough spring to get it to seal for a bit longer... just a thought...
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#23 |
Registered User
Join Date: Oct 2008
Location: VA
Posts: 16
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Re: Engine running rough after changing brake booster?
Glad you could find the problem quickly. Hopefully you get out of the machine shop for a couple hundred bucks.
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#24 |
Registered User
Join Date: May 2008
Location: Alta Loma, Ca.
Posts: 930
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Re: Engine running rough after changing brake booster?
Should be less than that! I just had my heads redone and they replaced 4 valves, all new seals valves regound. $300.00 including the gasket set (Felpro)
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