Brake adjustment, with bias adjuster

I have a brake bias adjuster valve in the cockpit of my car. I'm guessing this is just a valve that, when open all the way, gives full pressure to the rear brakes (no bias), and as it is closed it starts to choke off some of that pressure to the rear, giving a bias to the front.

So please tell me if I am adjusting my brakes correctly. This is what I do:

1. open the bias valve all the way
2. adjust the front brakes until the pads just begin to rub, then back off 2 notches
3. depress the brake pedal until the front brakes lock and hold the pedal in that position with a clamp
4. Adjust the rear brakes until the pads just start to rub, then back off two notches.

My thinking is that I now have brakes that are naturally biased to the front, and full adjustability with the valve to create more bias to the front by closing off the rear brakes as needed.

Is this correct?

Bonus Question:

The last time I drove, under full braking, the front tires wobbled left and right pretty crazily. Is this normal or a sign of brakes out of adjustment, or something else? (hence question 1, "am I doing this right?")

Thanks for any help. First race is April fool's day and I don't want any surprises!

Paul

not sure how your brake bias is set up.. many cars are adjusting proportioning between the pushrods (not a valve). Do you have separate master cylinders for the front and rear? are there two pushrods connected to the brake pedal assembly?

the wobbly front tires sound like something else has too much play or is loose. usually within the steering components/linkages or suspension rod end joints (pull/push rod, tie rod, camber rod, etc). just lift the front end and try to individually wiggle the tires, checking for any unwanted play.

Quote:

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Originally Posted by mikey

Do you have separate master cylinders for the front and rear? are there two pushrods connected to the brake pedal assembly?

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yes and yes. The push rods are connected to the brake pedal, and there is an offset so that the front brakes get more force.

I also have this thing next to my left hip, with lines going to the rear brakes.

http://i.imgur.com/fSLkw24.jpg

I have assumed this is for fine tuning the bias but I really haven't messed with it much, just left it like the previous owner had it set. I did experiment with it a little on some low speed runs, but didn't notice anything, but it may be that I just don't know yet what I'm looking to notice.

Quote:

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Originally Posted by 2Dogs

yes and yes. The push rods are connected to the brake pedal, and there is an offset so that the front brakes get more force.

I also have this thing next to my left hip, with lines going to the rear brakes.

http://i.imgur.com/fSLkw24.jpg

I have assumed this is for fine tuning the bias but I really haven't messed with it much, just left it like the previous owner had it set. I did experiment with it a little on some low speed runs, but didn't notice anything, but it may be that I just don't know yet what I'm looking to notice.

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That is a valve to adjust pressure to the rear brakes. If it's a Wilwood there should be an arrow on the knob to tell you which way to turn it for less or more. Under braking as the nose dives and weight is transferred to the front, the rear brakes tend to lock up because there is less weight on them. The way I have mine set is that the fronts would lock up just before the rears do.

You go a lot faster without using brakes...

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Originally Posted by grapefarmeral

You go a lot faster without using brakes...

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So you're recommending I delete my brakes?

Paul
The shaking might be bad bushings in ft end or Shocks that can't control
the mass of the wheels.
Are you running the Challenge Cup Wheels?
Lots more weight so the shocks need to be really good to control things
I Use a Wilwood control like yours and never adjust it during Shoe adjustments.
Sherman

2Dog:

I can only make suggestions based on what I have done on my car and on customer cars.
Go back to square one. Open up your bias adjuster ( valve). Get the car up on jack stands. Adjust the front and rear brakes so that they do not turn, then back off until there is no drag. Usually takes about 5 clicks on the front and 7 on the rear on both adjusters from full lock. If there is a slight "tick" depress the pedal while the wheel is turning. Now get the wife, girlfriend, son, daughter or,... to sit in the car. Depress the pedal SLOWLY and steadily until you lock the front wheels. Hold the pedal and check the rear wheels .They should just be able to be turned ( with some force) . If the rears are locked and the fronts are either locked or not locked, then you have to adjust the distance of the fulcrum ( spherical bearing inside your brake set up) Moving the spherical closer to one or the other master will quicken the locking of that wheel. You can also fine tune with the rods that go into each master after setting the spherical bearing. Once you have the fronts locked and the rears turning you are very close to the correct bias.
I am also going to assume that you have not changed the WHEEL cylinders from 22mm front and 19 rear to something else.

As for the wheels flopping ( wobbling) I am guessing that you mean they seem to be trying to move toe out and toe in very quickly. Assuming that nothing is loose ( link pin not adjusted correctly, inner or outer bushing in the beam not in place) then I would say that you have a car that is going through drastic bump steer where the tires are trying to toe in and toe out. At lower speed this goes away???? Check to see how much toe change you have with you in the car, tie rods level and someone stepping on the front end and then lifting the beam. See if the tires are moving in and out a noticeable amount. A bump steer gauge can be made quite easily to measure this also.

Questions? I'm always happy to respond.
Dietmar
Quixote Racing
619 561 7774

1) Note: the the hydraulic bias adjuster functions by removing pressure (force) from the rear brake channel in this case. This is typically not the best way to operate a FV brake system because of the compromise being made between pedal travel and brake force generation. You should conserve the force at all times.

2) Almost any wear/play in any of the front suspension can cause vibration during braking. Just because you are racing with an antique piece of junk for a front suspension does not mean you can maintain it as a piece of junk.

Brian

I got my initial brake adjustment advice from Chandler, and based on what I have read his advice is sound. Dietmar's and Sherman's advice is consistent with Chandler's. I removed the worn brake shoes today and replaced them with new. So I adjusted the brakes according to their advice. I'm ignoring the bias valve for now. I still need to do some fine adjustments as the left side locks up before the right (I'm such a rookie!), but still, it felt a lot better just running through the neighborhood streets. New shoes were the ticket.

The left side brakes were worn down to 1mm, and the right side was still pretty beefy. I put new shoes on both sides. I'm curious as to why the left side was worn so much more.

As for the wobble, I checked for play and looseness and everything seems pretty snug except the steering box, and that play seems to be in the linkage. Holy cow, there are three universal joints in the steering column. The feel from steering wheel to tire is so sloppy. I'm guessing the wobble was from poor brake adjustment.

In general' I'm not used to this old technology. The biggest problem I'm facing is trying to understand what is normal for 1965 auto tech versus the 90's tech I'm used to. I have a Miata, and I'm pretty versed on what's normal and what's not. With the Vee, I can't tell what's normal and what's worn. Hell, it all seems worn! I'm not complaining. It just takes getting used to. :D

Don't forget the drums.

Disc brakes are more modern, but the principles are the same. You need good friction material pressing on a properly machined surface.

Look at the drums and watch for glazed, overheated or out of round surface. If you have to back off more than 4 or 5 notches (average - your mileage may vary) to eliminate drag, than you might have out of round drums. You then have to find someone who can run drums and just take as little as possible to get back in round. In the "old" days - most shops would start with a .010 rough cut and another finish cut. Do that and you will be throwing away good drums often.

Drums can also become tapered. See cutting drums above. Discs are better as they tolerate bad maintenance, right until metal to metal....

Hitting drums with sandpaper and brake clean each race never seems to hurt, if you have the time.

Lastly, make sure the adjuster spring stops are working. If not the shoes will work out of adjustment faster.

ChrisZ

The uncontrollable wobble in the front is usually called 'tramping'. It shakes the car pretty violently under some conditions - even when everything is "fine". This is a characteristic of the beetle front end although I don't know exactly WHY it is. The best fix for it is to add a steering damper back to it as that is how VW fixed it (it's STOCK on the beetle). It is a shock that connects between the pitman arm (or a location on one of the tie rods) and some solid part of the vehicle. The original beam has a mounting point for one end of the damper, but it is pretty much always removed when going into a vee. The problem installing one in a vee is finding a place to mount the solid end. Fortunately, there is no requirement for it to be 'in line', so you can work with a pretty high angle. This is how I did it in my old car...http://wedgeracing.com/frame/100_1634.JPG (the shock is the red thing). In my new car, the solid end is mounted further rearward at a higher angle and still works just fine. In some instances, you can get away without the damper, but most of the time it will cause problems somewhere down the line.

Another possible issue is the bushing that controls the inner end of the torsion arms (turkey legs). Unfortunately, it is almost impossible to determine if that is the problem without removing the spindles, pulling the arms out and removing the spring pack. With the spring pack out, it will be obvious when you slide the arm into the beam, it should fit nicely and have essentially NO WOBBLE when you try to move the end of the torsion arm. If that inner bushing is damaged .. or more likely it gets pressed further into the beam so that the arm does not fit through it.. then the arm can move in all kinds of weird directions - like 1/2" or so at the outer end. If the bushing is intact and just moved too deeply in the tube, it is possible to pull it back into position, but it's not easy. It's a tough job just getting to the point where you can check the inner bushings. I'd try the steering damper first. It's the only REAL solution to the problem.

Adjusting brakes is 'magic' on a vee, but there should be NO pressure on the system while you're adjusting the shoes. Bias is set by pressure regulation, not by shoe travel distance. The 2 most important issues with vee brakes are
1). They should STOP THE CAR when you need them to.
2). They should NEVER 'drag'. If you are not applying the brakes, then the wheels should roll freely. ANY drag on any wheel will KILL your top end speed.

BTW ... where are you in Alabama? I'm guessing you bought Mike Chandler's car. If so, you probably know Mark Rothermel ..or you need to. Try to get with Mark or maybe Sherman to talk about the car BEFORE you take off to your first race. However, since Mike was racing it occasionally, it's reasonable to assume it's mostly OK to get on track.

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Originally Posted by Steve Davis

BTW ... where are you in Alabama? I'm guessing you bought Mike Chandler's car. If so, you probably know Mark Rothermel ..or you need to. Try to get with Mark or maybe Sherman to talk about the car BEFORE you take off to your first race. However, since Mike was racing it occasionally, it's reasonable to assume it's mostly OK to get on track.

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I did not buy Chandler's car. I called him about it a couple of days after he made a deal with the new owner. And I get frequent tips from Mark Rothermel as I see him often at club meetings. I met Sherman last summer at Barber, and he's been helpful as well.