Intermittent power brakes? Help? - PowerStrokeNation : Ford Powerstroke Diesel Forum
 
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post #1 of 9 (permalink) Old 05-14-2011, 09:02 PM Thread Starter
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Intermittent power brakes? Help?

Just bought a 97 F250 extended cab for $1000 this morning

It has one small problem. The power brakes are intermittent. After a few pumps, you lose them. Drive for a bit, and they come back. If you sit at idle, it doesn't come back

My first thought was vacuum pump. But, if there is an issue with it, would it illuminate the dash light? The brake light on the dash comes on when there is an issue...and goes out when it's working?

Thanks for the help
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post #2 of 9 (permalink) Old 05-15-2011, 02:17 AM
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Re: Intermittent power brakes? Help?

I had a similar problem a year ago; brakes worked fine at rpm over 1200, but really squirelly at idle and no light ever. Two shops couldn't diagnose it and I finally replaced the vac pump - problem solved! Enjoy your OBS!
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post #3 of 9 (permalink) Old 05-15-2011, 03:36 AM Thread Starter
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Re: Intermittent power brakes? Help?

I put a vacuum guage directly on the pump, and then directly before the booster.

Off the pump, the guage bounced around at idle from 14 to 22 inch lbs....when the rpm's were raised it leveled off around 22.

At the booster, it was a solid 22 inch lbs the whole time.

thinking it is a booster, so ordered a new one today
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post #4 of 9 (permalink) Old 05-15-2011, 08:02 PM
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Re: Intermittent power brakes? Help?

dont bother with the booster. change out the vaccum pump. had the same issue and as soon as i replaced the pump brakes worked fine.

96 cclb f350.
idm mod,
gauges-boost/pyro/trans temp
afe stage 2 intake
dp to 4" straight pipe
studs, springs, pushrods
srp1
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238/100
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post #5 of 9 (permalink) Old 05-15-2011, 11:17 PM Thread Starter
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Re: Intermittent power brakes? Help?

Quote:
Originally Posted by biggreen96 View Post
dont bother with the booster. change out the vaccum pump. had the same issue and as soon as i replaced the pump brakes worked fine.
Did you check the vacuum at the pump?
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post #6 of 9 (permalink) Old 05-16-2011, 03:29 AM
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Re: Intermittent power brakes? Help?

no i used the finger test and the hose had very little suction and would not hold onto my finger. all the symptoms you described are what i experienced and as soon as i replaced the pump all issues went away

96 cclb f350.
idm mod,
gauges-boost/pyro/trans temp
afe stage 2 intake
dp to 4" straight pipe
studs, springs, pushrods
srp1
intercooler
electric fuel convertion
238/100
dp-tuner f6
T-4 mount and s470.
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post #7 of 9 (permalink) Old 05-16-2011, 03:49 AM
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Re: Intermittent power brakes? Help?

Thats the VP. No light that would come on either. Its an easy change just do it before it does decide to let go. 65+ on backroads, or highway is no fun when you lose brakes and power steering. Id be very surprised if it was anything else.

1997 F350 7.3 Powerstroke, 4x4, 135,400 miles, 4 1/2" up front 2" out back, 35" Kuhmo M/T's, 3" dp, 4" with no cat, K&N, Triple Auto Meter Gauges, IDM Mod, rebuilt E4OD, Beans Tunes
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post #8 of 9 (permalink) Old 05-18-2011, 03:51 AM Thread Starter
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Re: Intermittent power brakes? Help?

So...here is the update, and I am still confused as all get out.

Replaced the booster the other night. Same problem. Brakes got hard after a few applications.

Put the old booster in, changed the vacuum pump. Same problem.

THEN to top it off, the truck just died while cranking over tonight. Nothing, no dash lights, no crank, no nothing. Batteries are both charged, checked them both. I am going to check for bad grounds on the block tomorrow.

I can see why this is a $1000 truck. Still happy though
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post #9 of 9 (permalink) Old 05-18-2011, 09:30 PM
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Re: Intermittent power brakes? Help?

Straight from Ford manual
1. Check hydraulic brake system for leaks or insufficient fluid. With transmission in NEUTRAL, stop engine and apply parking brake control.
2. Apply brake pedal several times to exhaust all vacuum in the system.
3. Apply brake pedal and hold it in the applied position. Start engine. If vacuum system is operating, brake pedal will tend to move downward under constant foot pressure. If no motion is felt, the power brake booster system is not functioning.

Also thought might give you help

1. Remove vacuum booster hose from power brake booster and check valve connection. Manifold vacuum should be available at the check valve end of the vacuum booster hose with engine at idle speed and transmission in NEUTRAL. If manifold vacuum is available to the power brake booster, connect vacuum booster hose to power brake booster and repeat Steps 2 and 3 above. If no downward movement of brake pedal is felt, replace power brake booster.
2. Operate engine a minimum of 10 seconds at fast idle. Stop engine, and let vehicle stand for 10 minutes. Apply brake pedal with approximately 89 N (20 lb) of force. Brake pedal feel should be the same as that noted with engine operating. If brake pedal feels hard (no power assist), replace check valve and retest. If brake pedal feels spongy, bleed hydraulic system to remove air.



I would check the belt for glazing

97' F-350 7.3 5 speed, 160cc Rosewoods, 315/75r16s 16x10 MT fakelocks
96' F-350 7.5 5 speed, cali truck, 315/75r16s on Alcoas
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