Braking kills motor - The 1947 - Present Chevrolet & GMC Truck Message Board Network

smoke wagon · 10-13-2011, 06:31 PM

Hi, i have a 4" lifted 72 shortbed, front disc with hawk pads, power steering, 1 ton brake booster, 600cfm holley, 327 rebuilt not long ago, 33 12.50's. The engine runs good and pulls good vacuum however, when i do any kind of braking the motor will bog down. It will idle back up or if i use power steering by turning the wheels it will kill it as i slow. With the 1ton brake booster ill have plenty of assisted braking even when it dies. Any good braking and it dies. Also the ignition is new HEI and tuned petty good. The truck runs great but this braking and dieing problem has me wantin to yank my hair out. Any ideas would be cool. I have searched till blue in face but cant find anything. On a side note just about everything on truck is new.
Ryan
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Rifter_Chevy · 10-13-2011, 06:41 PM

Ive had a bad booster cause this before.

smoke wagon · 10-13-2011, 07:34 PM

The booster was bad and i replaced it. Now it juet dies and i still have assisted brakes for a bit. Also i checked no sign of vac leaks. I take it that even though it is a carborated motor with big tires i shouldnt be having this issue. The hawk pads worked great to pep up its stopping power along with the new master cylendar and 1ton booster i thought that the problem would be fixed. The sad part is that im sure this truck could stop fast if i needed to but any type of breakin aside from light breaking will kill it.

BLAZERMAN · 10-13-2011, 08:05 PM

Sounds like it may be a carb problem...maybe check the float level? I dont know much about Holleys but thats where I would move onto since you know your booster is good.

onebadbowtie · 10-13-2011, 09:52 PM

have you tried bumping your idle up a bit to see if that helps any? just a thought. the booster was bad on my truck and the idle was set while it was bad. i put a new booster on it and it started dieing when i braked hard. so i turned the idle up a bit ant haven't had any problems since

Tex_50613 · 10-13-2011, 10:18 PM

I've had this happen when a automatic trans wouldn't properly downshift before die to a extra load on the motor, beyond that I have no ideas

smoke wagon · 10-14-2011, 12:11 AM

The floats are set just below the sight hole and the idle is at 900rpm. I tried adding a little fuel at idle an it didnt help. Thanks for the replys ryan
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mstrav1973 · 10-15-2011, 12:13 AM

Can you post some pics? Carb and booster showing hoses. Check valve good on the booster?

Matt

*72lb4x4* · 10-15-2011, 12:28 AM

Can you disconnect the vac to the booster and test w/o danger due to the brakes not working that well?

What happens if you're stopped and press the brakes? Any change in engine speed?

What happens if you put your foot on the brake pedal and start the engine?

smoke wagon · 10-15-2011, 09:31 AM

The booster Check valve is new and works good. If i disconnect the booster then the truck will stop but i have to give it alot of pedal. I havnt tride this though with new booster. Also the booster is connected directly to the manifold, no leaks but maybe by connectin it like that allows it to suck to much vacuum and kills the motor. Im sure the reason its dieing is because when i use the brakes it replenishes its vac supply quickly by pulling it from the motor causing if to die. I could hook it up at the carb but thats were the pcv to the valve cover is hooked up which is also good, i just replaced it and tried taking it off to see if it made a differance. Ryan
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smoke wagon · 10-17-2011, 04:57 PM

This weekend i moved the booster vac line from the rear of the manifold to the side of the carb where holley says to and that helped. Then i raised the fuel level in the rear bowl and now it only dies under really hard breaking which i guess is normal? Its werd because i thought that the rear fuel bowl was only used under harder excelleration when the secondary butterflies open. Now when the motor bogs from braking the engine will lower a bit and then rev up to counter. Works for me. Ryan
Posted via Mobile Device

10-13-2011, 06:31 PM	#1
smoke wagon Registered User Join Date: Jan 2011 Location: missouri Posts: 5	Braking kills motor Hi, i have a 4" lifted 72 shortbed, front disc with hawk pads, power steering, 1 ton brake booster, 600cfm holley, 327 rebuilt not long ago, 33 12.50's. The engine runs good and pulls good vacuum however, when i do any kind of braking the motor will bog down. It will idle back up or if i use power steering by turning the wheels it will kill it as i slow. With the 1ton brake booster ill have plenty of assisted braking even when it dies. Any good braking and it dies. Also the ignition is new HEI and tuned petty good. The truck runs great but this braking and dieing problem has me wantin to yank my hair out. Any ideas would be cool. I have searched till blue in face but cant find anything. On a side note just about everything on truck is new. Ryan Posted via Mobile Device

10-13-2011, 06:41 PM	#2
Rifter_Chevy Registered User Join Date: Mar 2011 Location: Vancouver, Canada Posts: 107	Re: Braking kills motor Ive had a bad booster cause this before. __________________ 1984 3/4 Ton Reg cab Longbox 4x4, Carbed 350/Turbo 400 Trans/205 T-Case

10-13-2011, 07:34 PM	#3
smoke wagon Registered User Join Date: Jan 2011 Location: missouri Posts: 5	Re: Braking kills motor The booster was bad and i replaced it. Now it juet dies and i still have assisted brakes for a bit. Also i checked no sign of vac leaks. I take it that even though it is a carborated motor with big tires i shouldnt be having this issue. The hawk pads worked great to pep up its stopping power along with the new master cylendar and 1ton booster i thought that the problem would be fixed. The sad part is that im sure this truck could stop fast if i needed to but any type of breakin aside from light breaking will kill it. Last edited by smoke wagon; 10-13-2011 at 07:39 PM.

10-13-2011, 08:05 PM	#4
BLAZERMAN Currently Blazerless Join Date: Apr 2000 Location: St. Joseph Mo. Posts: 4,826	Re: Braking kills motor Sounds like it may be a carb problem...maybe check the float level? I dont know much about Holleys but thats where I would move onto since you know your booster is good. __________________ 1972 C/30 133" W.B. C&C 1970 GMC 3500 157" W.B. single wheel C&C

10-13-2011, 09:52 PM	#5
onebadbowtie Registered User Join Date: Feb 2010 Location: Parsons, KS Posts: 357	Re: Braking kills motor have you tried bumping your idle up a bit to see if that helps any? just a thought. the booster was bad on my truck and the idle was set while it was bad. i put a new booster on it and it started dieing when i braked hard. so i turned the idle up a bit ant haven't had any problems since __________________ James 94' Chevy K1500 Extended Cab 4x4 5.7 72' Chevy LWB K10, 350, SM465, NP205 Project "Daily Driver"

10-13-2011, 10:18 PM	#6
Tex_50613 Redneck Customs Bumpers, IA Join Date: Nov 2009 Location: Waterloo, IA Posts: 503	Re: Braking kills motor I've had this happen when a automatic trans wouldn't properly downshift before die to a extra load on the motor, beyond that I have no ideas __________________ Overkill is under rated, Redneck Customs Truck Club Hudson, IA "Clifford" 83 Chevy K20 4x4, Mudder 7" lift rolling 44's "Basterd Child" 86 Chevy K30 4x4 crue cab Dule, 7.3l international WIP '00 ex-cab Silverado 4x4 DD I hate red trucks but you can't tell by looking at what I own

10-14-2011, 12:11 AM	#7
smoke wagon Registered User Join Date: Jan 2011 Location: missouri Posts: 5	Re: Braking kills motor The floats are set just below the sight hole and the idle is at 900rpm. I tried adding a little fuel at idle an it didnt help. Thanks for the replys ryan Posted via Mobile Device

10-15-2011, 12:13 AM	#8
mstrav1973 Registered User Join Date: Oct 2008 Location: Meridian, Idaho Posts: 321	Re: Braking kills motor Can you post some pics? Carb and booster showing hoses. Check valve good on the booster? Matt __________________ 72 chevy k-10, swb, auto, 35's, rally's, posi, 4" lift, 2.5" old style 40 series flows with headers and crossover pipe and some other stuff!!

10-15-2011, 12:28 AM	#9
72lb4x4 Account Suspended Join Date: Jul 2006 Location: DFW Posts: 1,427	Re: Braking kills motor Can you disconnect the vac to the booster and test w/o danger due to the brakes not working that well? What happens if you're stopped and press the brakes? Any change in engine speed? What happens if you put your foot on the brake pedal and start the engine?

10-15-2011, 09:31 AM	#10
smoke wagon Registered User Join Date: Jan 2011 Location: missouri Posts: 5	Re: Braking kills motor The booster Check valve is new and works good. If i disconnect the booster then the truck will stop but i have to give it alot of pedal. I havnt tride this though with new booster. Also the booster is connected directly to the manifold, no leaks but maybe by connectin it like that allows it to suck to much vacuum and kills the motor. Im sure the reason its dieing is because when i use the brakes it replenishes its vac supply quickly by pulling it from the motor causing if to die. I could hook it up at the carb but thats were the pcv to the valve cover is hooked up which is also good, i just replaced it and tried taking it off to see if it made a differance. Ryan Posted via Mobile Device

10-17-2011, 04:57 PM	#11
smoke wagon Registered User Join Date: Jan 2011 Location: missouri Posts: 5	Re: Braking kills motor This weekend i moved the booster vac line from the rear of the manifold to the side of the carb where holley says to and that helped. Then i raised the fuel level in the rear bowl and now it only dies under really hard breaking which i guess is normal? Its werd because i thought that the rear fuel bowl was only used under harder excelleration when the secondary butterflies open. Now when the motor bogs from braking the engine will lower a bit and then rev up to counter. Works for me. Ryan Posted via Mobile Device



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