Interesting brake problem

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Malaysia
I have a rather interesting problem with my car's brakes. If I turn the steering to full lock, rev the engine then proceed to step on the brake pedal. The pedal sinks to the floor. All 3 conditions are needed to replicate this and has led to some hairy moments during 3 point turns. Anyone has any ideas?
 
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998
Location
Lexington, SC
What if you are at a stop light and keep the wheels straight and then rev the engine and depress the brakes, will the pedal go to the floor then? Try it for a while to see. If so, it means a bad master cyl. The only explanation for the 'turn full lock' is it has to do with power steering affecting the power brakes. If you do have power steering and brakes, check the vacuum hoses that run from the intake manifold to both the P/S and P/B. Are they cracked and leaking?
 

takax2040

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Doesn't happen when everything's straight. I have power steering and power brakes. But doesn't the power steering use a power steering pump driven off the engine?
 
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Kansas
 Originally Posted By: takax2040
I have a rather interesting problem with my car's brakes. If I turn the steering to full lock, rev the engine then proceed to step on the brake pedal. The pedal sinks to the floor. All 3 conditions are needed to replicate this and has led to some hairy moments during 3 point turns. Anyone has any ideas?
Make and model? Vacuum brakes or power steering hyraulically assisted brakes? (Me thinks the latter)
 
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25,045
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ON, Canada eh?
 Originally Posted By: takax2040
I have a rather interesting problem with my car's brakes. If I turn the steering to full lock, rev the engine then proceed to step on the brake pedal. The pedal sinks to the floor. All 3 conditions are needed to replicate this and has led to some hairy moments during 3 point turns. Anyone has any ideas?
It sounds like you have a collapsed brake hose. This can't be seen, and the hoses should be replaced. Make sure to bleed the system after replacement.
 

takax2040

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Malaysia
Hmm interesting. Why is it only happening at full lock. Could the wheel movement kinda trigger the collapse. If so then do I just replace those brake hoses at the wheels?
 
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snowblind in TX
It's obviously caused by something in the hydraulic boost system. When you have the wheel at full lock the spool valve jacks the pressures around and it is effecting the brake boost as well. Check around and see if this is "normal operation". You would be surprised at what is called "normal operation" by manufacturers. I don't think there is any problem with the actual brake system involving the brake fluid/lines.
 
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ME
Is there a big round drum shaped thing on the car firewall by where the brake lines all lead? If there is, you have vacuum power brakes. If alternatively you have hydraulic hose that coincides with your steering rack and or belt driven pump in some "Tee" you have hydroboost brakes. We need to know. I also suspect this latter option.
 

Kestas

Staff member
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The Motor City
 Originally Posted By: Kruse
Vacuum brakes or power steering hyraulically assisted brakes? (Me thinks the latter)
I've never seen hydraulically assisted brakes. You mean there are power brakes systems designed to share the same hydraulics with the power steering system? Who has it?
 
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Santa Barbara, CA
im gonna suspect hydroboost as well. my mustang did that and it was somewhat normal. although when that hydroboost system worked it was a lot better than any vacuum brakes, pedal was rock hard.
 
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ON, Canada eh?
 Originally Posted By: takax2040
Hmm interesting. Why is it only happening at full lock. Could the wheel movement kinda trigger the collapse. If so then do I just replace those brake hoses at the wheels?
Because it's stressing the hoses or relaxing the hoses in this position (depending on the vehicles setup).
 
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2,439
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snowblind in TX
 Originally Posted By: Kestas
I've never seen hydraulically assisted brakes. You mean there are power brakes systems designed to share the same hydraulics with the power steering system? Who has it?
Many GM trucks (3/4 ton and above) as well as every Regal Turbo had hydroboost. I retrofitted a hydroboost setup in my '69 Camaro as I had no room for a conventional vac booster and really pathetic idle vacuum as well.
 
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snowblind in TX
 Originally Posted By: bdcardinal
94-04 mustangs with 4.6 SOHC and DOHC as well as 00 Cobra R's have hydroboost. also any ford with a turbo diesel has hydroboost.
The sad part of that is I worked for so long in a Ford shop and never knew that. I never worked on brake systems, except to trouble shoot electrical/module/controller problems on them.
 
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Kansas
 Originally Posted By: Kestas
 Originally Posted By: Kruse
Vacuum brakes or power steering hyraulically assisted brakes? (Me thinks the latter)
I've never seen hydraulically assisted brakes. You mean there are power brakes systems designed to share the same hydraulics with the power steering system? Who has it?
As others have posted, a setup like this is common on diesel-engined cars because the intake manifold on a diesel has no vacuum. However, the chevette diesel has a little vacuum pump mounted behind the alternator just to generate some vacuum for the brake power booster. Pretty primitive. A few gasoline cars have used the hydraboost for various reasons, one is that some high performance gas cars have lower intake manifold vacuum.
 
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2,698
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Silicon Valley
 Originally Posted By: StevieC
 Originally Posted By: takax2040
Hmm interesting. Why is it only happening at full lock. Could the wheel movement kinda trigger the collapse. If so then do I just replace those brake hoses at the wheels?
Because it's stressing the hoses or relaxing the hoses in this position (depending on the vehicles setup).
Why does this permit the pedal to go to the floor?
 

takax2040

Thread starter
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19
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Malaysia
 Originally Posted By: Tosh
 Originally Posted By: StevieC
 Originally Posted By: takax2040
Hmm interesting. Why is it only happening at full lock. Could the wheel movement kinda trigger the collapse. If so then do I just replace those brake hoses at the wheels?
Because it's stressing the hoses or relaxing the hoses in this position (depending on the vehicles setup).
Why does this permit the pedal to go to the floor?
Not really sure but after replacing the master cylinder there seems to be nothing left to replace so I'm willing to try anything. Does the ABS have anything to do with it?
 
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2,260
Location
SD
 Originally Posted By: takax2040
 Originally Posted By: Tosh
 Originally Posted By: StevieC
 Originally Posted By: takax2040
Hmm interesting. Why is it only happening at full lock. Could the wheel movement kinda trigger the collapse. If so then do I just replace those brake hoses at the wheels?
Because it's stressing the hoses or relaxing the hoses in this position (depending on the vehicles setup).
Why does this permit the pedal to go to the floor?
Not really sure but after replacing the master cylinder there seems to be nothing left to replace so I'm willing to try anything. Does the ABS have anything to do with it?
I sure wouldn't suspect the ABS, and I don't see how a brake hose could cause it, either. I'm with the others: I bet you have a hydroboost-type system. Let us know.
 
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