Panic Stop - Great Scott what just happened!

Do you know when the rear wheel cylinders were last replaced? Have you noticed any brake fluid dripping from a drum? Maybe pull the drums off and check that the shoes on both sides are dry? How old are the front calipers? Do you know when the brake fluid was last changed?

ALB posted:

Do you know when the rear wheel cylinders were last replaced? Have you noticed any brake fluid dripping from a drum? Maybe pull the drums off and check that the shoes on both sides are dry? How old are the front calipers? Do you know when the brake fluid was last changed?

Al,

The car is less than two years old and has been driven less than 2800 miles.  The brakes are not leaking and the new tires were installed less than 200 miles ago. 

Maybe the brakes on 1 rear wheel need to be adjusted?

I would get a trusted car guy friend and take a quick trip to a long stretch of empty road or a vacant t parking lot for some brake testing. Have your friend record or watch your wheels as you get up to speed and do a controlled "panic stop". Do this several times while he watches each side of the car. It sounds like the rears are locking up and the fronts aren't engaging enough. And as Al said one rear side, the side that tried to pass, is engaging with more force than the other.

You'll get a much better idea of what's happening which will give you a better diagnosis and a better plan for fixing the problem. We've had some on here with similar brake problems and one had an issue with one brake engaging too much and another with one brake that was sticking and not engaging at all. You'll need to figure out which problem you have.

With only 2,800 miles on the clock you haven't even gotten it "sorted out". There was no road testing done when the car was finished so now you're the one left to get all of these persnickety little safety issues, like properly working brakes, figured out.

Be careful but get it done.

I'm not saying it isn't the brakes as it might be. There might be a small leak in one wheel cylinder leaking just a touch of brake fluid on a drum, that would do it for sure. And you wouldn't see it outside the drum necessarily.

I'd also have an alignment done, if one rear wheel or both are toed out that would definitely cause this. You want zero rear toe or very slight toe-in. If your steering wheel was anything but perfectly straight ahead that could cause this also.

No proportioning valve ?

You'll have to remove the rear drums to find issue.  It could be slight fluid leak (brake cyl or axle seal), mis-adjusted shoes, glazed drum/shoes, loose shoe connector, etc.  I assume VS replaces all the rubber brake lines - but I still prefer the stainless steel braid covered lines as they don't balloon when under pressure (or fail by compressing and squeezing off fluid).  If you haven't driven it much this year the rotors and drums will get a slight rust coating which will wear off after a bit of driving.

I'm actually surprised the front discs did lock up first.  Although with such low weight there it wouldn't have been a handling issue.

WOLFGANG posted:

You'll have to remove the rear drums to find issue.  It could be slight fluid leak (brake cyl or axle seal), mis-adjusted shoes, glazed drum/shoes, loose shoe connector, etc.  I assume VS replaces all the rubber brake lines - but I still prefer the stainless steel braid covered lines as they don't balloon when under pressure (or fail by compressing and squeezing off fluid).  If you haven't driven it much this year the rotors and drums will get a slight rust coating which will wear off after a bit of driving.

I'm actually surprised the front discs did lock up first.  Although with such low weight there it wouldn't have been a handling issue.

He said the rears locked up but he didn't say anything about the fronts locking up or even engaging.

I had just the opposite.  My fronts locked and the rears did not.  We know how that turned out.

Lane that was a real tragedy for you and your car.... 

I find, the fronts lock up quite easily, especially on a bumpy road when you try to stop quickly.   I am not sure how that could be fixed when you consider the limited amount of weigh these cars have and the great rear weigh bias that is a pendulum waiting to swing forward given the chance. 

Pretty important on these cars to buy a very soft tire compound, sport rated, to give you the maximum amount of grip in a bad situation. 

I meant to type surpized the front didN'T lock up - defective mind control of keyboard

IaM-Ray posted:

 I find, the fronts lock up quite easily, especially on a bumpy road when you try to stop quickly.   I am not sure how that could be fixed when you consider the limited amount of weigh these cars have and the great rear weigh bias that is a pendulum waiting to swing forward given the chance. 

What size tire do you have on it? What rear brakes does the car have on it? Throw 40 or 50 lbs. in the frunk and then see how it reacts. 

The front brakes (factory Karrman Ghia discs, 4 1/2" rims with 135's- evil little pieces of rubber!) on my Cal Look Beetle would lock up if I wasn't careful; with wet or dusty pavement it was even worse. Increased braking power in the back helped balance it out. Al 

Seems to me that it might have been one of the fronts that locked up.  If your fronts were not locked and it was just the rears that were locked, it seems like that would just cause you to drag the rear end, not make it come around.

If the fronts lock, it will "push" and not turn, if the rears lock it will swap ends. You may have air in the lines or the master cylinder may be bad. I would bleed the brakes, and try a slow speed, 15-20mph panic stop on the dirt to see which wheels lock up. Ideally all of them should lock up at the same time. I have AC Industries  5 lug disks on the front and I can lock the fronts up at will. I'm guessing your master cylinder is not up to the task.  Also, wheel alignment and rear brake adjustment can steer you where you don't want to go in a panic stop!

aircooled posted:

No proportioning valve ?

This^ There are only a couple of things (all mentioned) that can cause this. You just need to get to the bottom of it and fix it.

I had a similar issue and discovered the previous owner had the master plumbed wrong (left to right instead of front to back) and was a near disaster when I discovered it.

I had the rear lock up on me once and did a full 180

OK, if you say so.  It just doesn't seem logical to me. Front wheels still spinning and rear wheels just dragging.  Can someone explain the physics of that? 

I've taking the car to a company here in Charlotte that specializes in foreign cars of all makes, models and from all eras. 

Have also sent them a photo copy of all the ideas those members of this forum have been so kind to give as to what they think the problem might be. 

If any one else is willing, I would be very grateful if you too will post your idea as to what you thing the problem might be which I will also forward to them.

Kind regards to everyone for your help,

Cliff

I think there is always an issue with one side or another pulling and the pendulum starts

but I agree the momentum vector should point forward 

in the winter here on a fwd golf you can with a slight turn left, pull the handbrake and turn left on a dime 

Scated the daylites out if me ... just saying 

ALB posted:

IaM-Ray posted:

 I find, the fronts lock up quite easily, especially on a bumpy road when you try to stop quickly.   I am not sure how that could be fixed when you consider the limited amount of weigh these cars have and the great rear weigh bias that is a pendulum waiting to swing forward given the chance. 

What size tire do you have on it? What rear brakes does the car have on it? Throw 40 or 50 lbs. in the frunk and then see how it reacts. 

The front brakes (factory Karrman Ghia discs, 4 1/2" rims with 135's- evil little pieces of rubber!) on my Cal Look Beetle would lock up if I wasn't careful; with wet or dusty pavement it was even worse. Increased braking power in the back helped balance it out. Al 

911 front end with vented disks essentially 944 equivalent style rear disks forgot the exact model

don't have the specs on the tires but 6 inch front 7 inch rears

weigh is good 

Cliff---man, I hate what happened to you in your car.  I am just about the last person here who can explain what caused the rear brakes to lock up  which I believe is what happened.  When I had rear drums before upgrading to disc I had a panic stop on I-40 heading East and the brakes didn't lock up but I was trying to manage a wild "Mr Toad" ride with the car not wanting to stop straight ahead.  Damned scary too.  I haven't had what I'd call hard braking since but think the disces will perform better based on how they stop in fairly aggressive driving.   I'll bet Carey at Beck would be able to provide a reason for your  experience.  I think a nice Beck owner like Lane could ask about this and have some light shed on this.  Have you Googled "Drum brakes locking in panic stop"?  

I hope you get to the bottom of this issue and whatever you find out, I'd recommend swapping the drums for discs.  CSP if you want the best and SoCal if you like, which is sorta what I have after the CB Performance ones didn't perform well for me.  I swapped out just the wheels.

Good luck, Cliff.

Cliff,  I know your intentions are noble, but don't be surprised if your "pointers and suggestions" to an experienced shop from your internet friends are met with less than an enthusiastic response.  Some shops are open to suggestions, some become belligerent, as in "If your internet friends are so smart, let them fix it.  I fix these things for a living."

I'm still mystified as to why the rear end would come around.  Would the same thing happen if you just pulled up on the e-brake and locked up the rear wheels?

Cliff Presley - Charlotte, NC posted:

 

I've taking the car to a company here in Charlotte that specializes in foreign cars of all makes, models and from all eras. 

         

Have also sent them a photo copy of all the ideas those members of this forum have been so kind to give as to what they think the problem might be. 

If any one else is willing, I would be very grateful if you too will post your idea as to what you thing the problem might be which I will also forward to them.

Kind regards to everyone for your help,

Cliff

 

Cliff....stop doing it to them, Man. Any decent shop ( and this looks like a real decent one ) will go over your brakes from front to back and left to right and make everything right before they send you home. Brakes are brakes and they've seen all that you've got before.

Sending them suggestions will possibly irritate them or possibly make them laugh if you're lucky. If the earlier of the two, at the very least they should charge you extra to take the time to read all the advice from these helpful and well intended spectators. 

Troy Sloan posted:

I'm still mystified as to why the rear end would come around.  Would the same thing happen if you just pulled up on the e-brake and locked up the rear wheels?

Yes it actually does, Maybe not a drastic kick out like Cliff had (I suspect some front braking could magnify it) Go try it sometime in a safe space. I think everyone should go out and drive these cars recklessly in a safe vacant lot, learn your car.

Troy Sloan posted:

I'm still mystified as to why the rear end would come around.  Would the same thing happen if you just pulled up on the e-brake and locked up the rear wheels?

Lift-off oversteer is where you do something to the car, such as, take your foot off the throttle, or brake, or change down a gear which puts more weight over the front of the car, and reduces the weight over the back of the car. The balance of the vehicle is upset and there is a weight transfer forward which increases the weight over the front axle. That means less grip on the rear tires, causing a skid. This type of oversteer is much more pronounced in rear-engine and mid-engine cars because the engine can act like a pendulum.

When Cliff took his foot off the accelerator the forward weight transfer shifted the weight to the front of the car, the front brakes may have activated which slowed the turning speed of the front wheels, the rear wheels locked up and lateral grip is severely reduced due to the lockup, and the car spins out or begins to drift. Any amount of steering input would also increase and/or exaggerate the amount of oversteer as well which in turn will cause the rear to overtake the front.

It typically happens while entering a turn but it can happen while going straight.

As an EVOC instructor this is the best I could come up with to explain it.

^

Robert M posted:

Troy Sloan posted:

I'm still mystified as to why the rear end would come around.  Would the same thing happen if you just pulled up on the e-brake and locked up the rear wheels?

When Cliff took his foot off the accelerator the forward weight transfer shifted the weight to the front of the car, the front brakes may have activated which slowed the turning speed of the front wheels, the rear wheels locked up and lateral grip is severely reduced due to the lockup, and the car spins out or begins to drift. Any amount of steering input would also increase and/or exaggerate the amount of oversteer as well which in turn will cause the rear to overtake the front.

It typically happens while entering a turn but it can happen while going straight.

As an EVOC instructor this is the best I could come up with to explain it.

Good explanation. With the exception of locking the rears this is how I set the kart in a turn or get it into a drift around a corner.

This makes a little more sense to me, because it involves some braking of the front wheels and/or being in a turn.  If a car is traveling in a straight line with no front braking and the rear brakes locked,  the rear would not come around and it would just come to a stop.... Correct? 

A quick check would be jack up each corner and have someone apply the brake petal.  Fully depressed the tire should be locked up.  Years ago NJ DMV State Inspection stations would get into you car - accelerate and brake, the pad they braked on measured if their was any brake pull.

Troy Sloan posted:

This makes a little more sense to me, because it involves some braking of the front wheels and/or being in a turn.  If a car is traveling in a straight line with no front braking and the rear brakes locked,  the rear would not come around and it would just come to a stop.... Correct? 

Variations in alignment, steering, suspension, and road contours means you are never in a "straight" line.

Heavy braking with the front wheels creates a force vector pushing backwards through the car opposing the forward momentum of the car. Weight transfer under braking, plus rear brakes locked up, means the rear end has virtually no traction. This means the rear end can move freely and is only constrained by the fact it's connected to the front of the car. As this prevents the rear from moving forward and backward, the only direction it can move is side-to-side. If the vector of the braking force is not perfectly in line with the center of mass of the rear end, it will cause a rotation of the whole car.

How about an analogy. Try to balance a pencil on your fingertip. Gravity pulling the pencil down is the forward momentum of the car. Your finger holding it up is the braking force from the front wheels. The top of the pencil is the rear of the car with no traction so there's nothing preventing it from moving side-to-side. If you don't move your finger to correct the balance, what happens? The "rear" of the pencil rotates to one side, falls, and "overtakes" the front. AKA, your "car" has spun out.

When you try to simulate this with just the emergency brake, generally you are not also pressing the brake pedal. Which means there is no force from the front wheels pushing back through the car. This is the equivalent of gripping the top of the pencil while letting the tip dangle freely. Without steering input, it'll tend to stay in a straight line.

Troy Sloan posted:

I'm still mystified as to why the rear end would come around.  Would the same thing happen if you just pulled up on the e-brake and locked up the rear wheels?

Yes!    Back in the mid 80's I drove a Dodge Shelby Charger with a std transmission.   One of my favorite maneuvers was doing a 180, then peeling out in the opposite direction:    While going about 20Mph...  Cluth in, stick into first, trurn wheel slightly, engage parking break...  After 180, let off parking break, and pop the clutch to start burnout and fishtail on the other end.   So much fun!

Correct me if I'm wrong, because it's a little hazy, but it looks like you're saying that the rear end coming around is not just due to the rear wheels being locked up, it's due to front braking, steering input, road conditions, etc.. I understand that all of those things are always present when driving a car and everyone needs to be aware of that, but the cause of the rear end coming around is not simply due to the rear wheels being locked up.

I wish I could do as Bill suggested in a vacant parking lot and do an e-brake rear wheel lock up at speed to see what would happen.

sherco_chris posted:

If the fronts lock, it will "push" and not turn, if the rears lock it will swap ends. You may have air in the lines or the master cylinder may be bad. I would bleed the brakes, and try a slow speed, 15-20mph panic stop on the dirt to see which wheels lock up. Ideally all of them should lock up at the same time. I have AC Industries  5 lug disks on the front and I can lock the fronts up at will. I'm guessing your master cylinder is not up to the task.  Also, wheel alignment and rear brake adjustment can steer you where you don't want to go in a panic stop!

I think this is the post that has me wondering. He says "If the fronts lock, it will "push" and not turn," I agree with that, but I also think that could very well cause the rear end to come around even more likely than if just the rears were locked up.

Front wheels sliding, rears rolling - understeer. Relatively easy to control.

Rear wheels sliding, fronts rolling - oversteer. Much harder to control, especially in a car with heavy rear weight bias.

The physics (nicely explained by Justin) may be hard to visualize, but once the rear is sliding, it won't be long before the rear wheels are no longer lined up perfectly with the fronts. When that happens, the forces at work push the back more sideways the further out of line the back swings.

My car (and almost every other Speedster I've heard about) locks the fronts way before the rears. And the brakes on most modern cars are purposely proportioned to do the same because, again, understeer is easier for the average driver to control.

If the rears are locking first, it's nothing to fool around with and should be checked out by someone who knows VW brakes.

Troy Sloan posted:

sherco_chris posted:

If the fronts lock, it will "push" and not turn, if the rears lock it will swap ends. You may have air in the lines or the master cylinder may be bad. I would bleed the brakes, and try a slow speed, 15-20mph panic stop on the dirt to see which wheels lock up. Ideally all of them should lock up at the same time. I have AC Industries  5 lug disks on the front and I can lock the fronts up at will. I'm guessing your master cylinder is not up to the task.  Also, wheel alignment and rear brake adjustment can steer you where you don't want to go in a panic stop!

I think this is the post that has me wondering. He says "If the fronts lock, it will "push" and not turn," I agree with that, but I also think that could very well cause the rear end to come around even more likely than if just the rears were locked up.

Fronts active, rear active: car follows front wheels' steering.

Fronts active, rear locked: car follows front wheels' steering initially, rear end really wants to swing around front, car spins.

Fronts active, no rear brakes: car follows front wheels' steering.

Fronts locked, rear active: car continues straight regardless of steering, drag from rear wheels continuously pulls the car straight so it doesn't spin.

Fronts locked, rears locked: car continues straight regardless of steering, car will rotate unpredictably depending on differences in drag at all 4 wheels.

Fronts locked, no rear brakes: car continues straight regardless of steering at first, but drag imbalance from the front wheels can cause the car to rotate and alter the direction of travel or possibly spin.

No front brakes, rear active: car follows front wheels' steering.

No front brakes, rear locked: car follows front wheels' steering. Rear drag wants to pull the car straight, but steering input can make rear swing out due to low friction.

No front brakes, no rear brakes: downshift and pray

justinh posted:

No front brakes, no rear brakes: downshift and pray

Makes me think of an obscure Harry Chapin song about a truckload of bananas heading down the hill into Scranton, PA....  "ain't it funny how he named the only person who could save him now?"

Mitch and Justin, nicely explained.

Troy, a locked wheel has less traction than a rolling wheel under braking. I think that explains it right there.