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RS Turbo ABS operation

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Old 13-05-2009, 01:47 PM   #1
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Default RS Turbo ABS operation

Afternoon all,

Does anyone know exactly how the ABS System on an Escort RS Turbo works?

I know the basics of the mechanics:
• 2 pumps run with belts off the driveshafts
• Return feed from each of the pumps to the reservoir
• There are "Wires" connected to the pumps
• Feeds from the master cylinder go through the pumps
• Load compensator valves on the rear beam.

But how does it operate, are the "Wires" connected to sensors within the pumps? Are there sensors at the wheels? What does the system do in a lock-up situation and how?

I have some ideas floating around in my head about "Replacement" ABS systems and would like to know more about the RS Turbo one.


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Old 13-05-2009, 06:41 PM   #2
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A brief description of the mechanical ABS system fitted to Escorts and Fiestas:

From 1986 onwards, an anti-lock braking system is available as standard or as optional equipment on some Fiestas, and Escorts.
The system compromises four main components: two modulators, one for each brake circuit, and two rear axle apportioning valves, again one for each circuit. Apart from the additional hydraulic piping the remainder of the braking system is the same as for conventional models (with the exception of the RS Turbo model, which has larger drums, and larger calipers and discs).
The modulators are located in the engine compartment and one mounted each side of the transmission, directly above the drive shaft inner constant velocity joints. Each modulator contains a shaft which actuates a flywheel by means of a ball and ramp clutch. A rubber toothed belt is used to drive the modulator shaft from the driveshaft inner constant velocity joint.
During driving and under normal braking the modulator shaft and the flywheel rotate together and at the same speed through the engagement of a ball and ramp clutch. In this condition the hydraulic pressure from the master cylinder passes to the modulators and then to each brake in the conventional way. In the event of a front wheel locking, the modulator shaft rotation will be less than that of the flywheel, and the flywheel will overrun the ball and ramp clutch. This causes the flywheel to slide on the modulator shaft, move inward and operate a lever which in turn opens a dump valve. Hydraulic pressure to the locked brake is released via a deboost piston allowing the wheel to revolve once again.
Fluid passes through the dump valve is returned to the master cylinder reservoir via the modulator return pipes. At the same time hydraulic pressure from the master cylinder causes a pump piston to contact an accentric cam on the modulator shaft. The flywheel is then decelerated at a controlled rate by the flywheel friction clutch. When the speed of the modulator shaft and flywheel are once again equal the dump valve crosses and the cycle repeats. This complete action takes place many times a second until the vehicle stops, or the brakes are released.
The load apportioning valves are mounted on the rear crossmember and connected to each rear suspension arm via a linkage. The valves regulate hydraulic pressure to the rear brakes and in accordance with the vehicle load and attitude, is such a way that brake force at the front brakes will always be greater than that at the rear.
A belt break warning switch is fitted to the cover that surrounds each modulator drivebelt. The switch contains an arm which is in contact with the drivebelt at all times. If the belt should break, or the adjustment of the belt is too slack, the arm will move, closing the switch contacts and informing the driver via an instrument panel warning light.

The system above, was probably very good in 1986, however even the newest systems are over ten years old now. The mechanical parts inside wear, and the ABS system becomes flawed. Sometimes not releasing a wheel, sometimes not releasing both wheels, under hard braking. Mine for instance was very intermittant, sometimes working very well, and sometimes not at all. I fitted a pair of second hand modulators in an attempt to rectify this problem, to which the problem worsened.
I took this opportunity to remove the system altogether, and upgrade to a better system. This compromised of nothing more than getting a few parts from another Escort(XR3i). I used, master cylinder reservoir, compensators, and the front pipework


Last edited by studabear; 13-05-2009 at 06:43 PM. Reason: cut and pasted the wrong info
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Old 13-05-2009, 07:35 PM   #3
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:Hmmm, so it's all mechanical then. Thanks for the info though!

Basically I'm trying to work out ways of fitting something like a Cosworth or late Sierra ATE System. Maybe even something diferent all together. What happened was I read Retro Ford and there was a Cortina in there with Sierra Cosworth ABS fitted. Me being me thought "Hmmm that is quite a good trick, I wonder if I could do that.......". I really need to stop reading that mag, the cars in there always give me barmy ideas!

The mechanicals of the Cosworth system would fit quite easily, all I'm not sure of is the sensor setup. I know the Sierra systems have an ABS sensor that fits into the hub with a trigger wheel of some sort fitted to the drive shaft. Dont know what sort of trigger though

I'll have a longer think!

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