QuestionQUESTION: is mechanical abs possible in cars? (no digital system
allowed)
if yes please tell the complete working of it with description
or send any link where i could get it or copy paste the matter
thank you
ANSWER: There used to be a device (sorry, can't remember the name) which acted as a sort of hydraulic ABS. It consisted of a damper that absorbed the pulses in the brake system pressure that occur when wheel locking occurs. Also, Ford and Lincoln had an Anti-skid system that they used on the MKIV and T-Bird back in the seventies. It was tied in with the Hydro-boost brakes and acted to cut pressure to the rear brakes when the wheels began to lock, but I'm not sure how it worked. If you are looking to adapt a system to a non-ABS car, the only feasible way I can think of doing it is to use a dual master cylinder with a balance bar. This has to be adjusted to prevent one axle from locking up before the other, which is simple but time-consuming to get right. It is the most common system used on road-race cars and works well once you get used to it.
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QUESTION: thanks for your answer. i really appreciate it as it was the
best one i have got for this question. but i am also sorry
because now i have many questions for you.
q.1 what is the difference between tandem master cylinder
and dual master cylinder. which one is better. why.
i think in tandem the pistons are in series one after
another whereas in dual they are parallel and are connected
by a linkage which you are calling balance bar.
q.2 i am using disc brakes on all four wheels. do i need
metering valve?
q.3 do we need to adjust proportioning valve according to
our requirement or it gets adjusted automatically. i mean to
say that i want 35% braking in front wheels in my car
whereas in usual car it is 65%, so can i use any
proportioning valve used in other cars or do i need a
special one or do i need the same old proportioning valve
and need to adjust it by same method.
q.4 i am taking out the braking percentage on front wheel
and rear wheel by calculating the reactions on front wheel
and rear wheel in case when brakes are applied on all the
wheels i am getting the reaction on front wheel to be 0.32
times the weight of car and on rear wheel 0.68 times the
weight of car. so my braking percentage on front wheel is
32% and on rear wheel is 68%.
is my method correct?
i know this is a whole lot of questions for a busy person
like you. i will be very thankful for you precious help also
if you can get any other or remember anything else on
previous abs question, post it
thank you
Answer Actually, you will hear these terms used interchangeably, especially when referring to the cars of the sixties (which is when dual master cylinders became mandatory on most cars). The tandem master cylinder is used primarily because of its lower cost in mass production. Dual, or side-by-side, master cylinders are generally only used on racing or high-performance cars, as they provide a method of adjusting the balance between front and rear braking. This can be necessary to adjust for different tires, brake pads, and track conditions.
If you are using four wheel disc brakes and a tandem master cylinder then you will need a proportioning valve intended for use with four-wheel discs. If you use the dual master cylinders with a balance bar you won't need a proportioning valve. The purpose of the proportioning valve (which all factory-built cars have) is to keep the rear wheels from locking up under hard braking. The setup with the balance bar is for the same reason. If the rear wheels lock before the fronts they lose friction (sliding on the pavement like a puck on ice) and will allow the rear of the car to come right on by in what we all know as a spin. If the front wheels lock first it is generally safe and can still be controlled. The balance bar on side-by-side dual master cylinders is adjusted until the rears will not lock before the fronts. Then you are good to go.
Very few proportioning valves are adjustable front-to-rear. You can buy manual valves that are plumbed into either the rear or the front (almost always the rear) which then allow you to dial down the hydraulic pressure going to the rear and prevent any skidding or spinning. You pretty much want full pressure to the front wheels at all times, as they do most of the work as the weight shifts forward under braking. Rear pressure is dialed back to prevent spinning, that's all.
You can use this kind of math to set up or design a system, but it only goes so far. Under heavy braking, even on a rear- or mid-engined car, the front wheels are going to do over half of the braking. On a front engined car they will do around ninety to ninety-five percent of it. On many small front-wheel-drive cars the rear brakes are mainly there for the parking brake function and do little or nothing to slow the car down. But always remember: give the front wheels all you've got, and back off the rears until they will not lock up. Really, the whole art of brake design pivots around that necessity; the rear wheels must not lock under any braking conditions. This is why digital ABS is so wonderful; you can run the rears right up to the point of locking and the computer will prevent it from happening.
