Two piston calipers with ABS...or 4 piston calipers without ABS.

This is a question i have often wondered about,but seeing a 240 based in Japan,which i presumed was Two piston calipers with ABS. I wondered which would pull the car up quicker in an emergency:Two piston calipers with ABS...or 4 piston calipers without ABS? Ive never been a 240 with only TWO piston calipers,but the difference between another car i own which only has TWO...and the 240,there is only winner. The 240. I have had near misses with the 240,which would have been accidents,if it were not for the 4 piston calipers.

It depends on driver skills in braking without ABS and skid control. But the 4 piston calipers seem to help even with that.

So im wondering what you peeps think? To not have ABS or to have,that is the question.

Comments

  • Vee_QueVee_Que @Vee_Que South Eastern suburbs Melbourne.
    edited September 2016
    You've looked at a 740 if it has two piston calipers, all 240s had the same caliper, even with abs. The surface area of the pistons is the important part combined with the pad size.


    You cannot compare the calipers directly. Slide calipers work almost as well, the pressure is distributed pretty evenly. However racing cars use more pistons that are a similar total fluid usage (bore size of a single piston caliper vs a 4 piston total swept area) to be able to run bigger pads and have the fluid pressurise quicker basically.

    The reason your 240 may not let you down is more due to pad choice, tyre choice and how well the brakes were bled through. if the brakes lock the tyres, your exceeding the tyres grip, if they don't, then the pads aren't gripping the rotor very well in order to stop in combination with the old brake fluid.

    I wouldn't ever fit abs to a car that never had it, I can drive to not lock up most of the time when emergency stopping. So its not needed.
  • Quantity of pistons isn't relevant, the total surface area of the pistons available for the fluid to act against, and the surface area of the pads and rotors determines effectiveness.

    In the case of 700/900 series cars, the 940 single piston calipers actually have more surface area in all these areas than the twin piston setup used on 740T etc.

    As for ABS, it generally pulls the car up sooner than an otherwise identical car without ABS, because you can mash the pedal and give the calipers full hydraulic pressure, without locking the wheels.

    Maximum grip occurs just before traction breaks, and ABS keeps grip in this range.

    It is possible to equal or exceed this on a car without ABS, but it takes skill and concentration to modulate the pedal to keep the tyres near the limit of grip without locking the wheels. In a panic situation few people can do this.

    ABS can increase stopping distances on soft dirt, because the quickest way to stop on soft dirt is to lock the wheels so that a mound of compacted dirt can form in front of the tyres. In pretty much all other situations, ABS wins.
  • Abs is mixed bag on solid ice
    Great on patchy ice though
  • Also
    Diamiter of the brake rotor matters a lot as well

    A single piston on a 336 rotor will destroy near anything on a 280mm rotor setup

    If we want some truely amazing brakes though we need to look at aircraft setups using multi plate setups with 360* pads

  • Vee_QueVee_Que @Vee_Que South Eastern suburbs Melbourne.
    Quantity of pistons isn't relevant, the total surface area of the pistons available for the fluid to act against, and the surface area of the pads and rotors determines effectiveness.

    In the case of 700/900 series cars, the 940 single piston calipers actually have more surface area in all these areas than the twin piston setup used on 740T etc.
    The pads on the late 740/760 vs the jumbos is minimal, the pedal travel does not change so the surface area cant be much bigger, the rotors are thicker though.

    So yes, quantity of pistons is relevant for performance braking.
  • Pedal travel with boosted brakes is a funny thing

  • Some interesting comments. I can wish for a 240 with 4 piston calipers and ABS. I just love the 240 brakes! I have agressive pads on them though. What are cost of rotors and pads compared to your safety? Worth the money!

    Has anyone seen ABS on any 240's in Australia?, Ive seen one,which was a personal import from the UK.
  • Angus242164Angus @Angus242164 Western Victoria
    edited September 2016
    The pads on the late 740/760 vs the jumbos is minimal, the pedal travel does not change so the surface area cant be much bigger, the rotors are thicker though.

    So yes, quantity of pistons is relevant for performance braking.

    When I did the conversion on my '85 760T years ago I did the maths on the pistons, the original Bendix twin piston caliper had less surface area on it's two pistons combined than the "jumbo" caliper had on it's single piston.

    The pads on the jumbo setup are somewhat larger side by side, and when doing the maths on the rotor friction surface area the "jumbo" also came out on top, despite the 0.25" diameter reduction.

    My "jumbo" setup came from a '90 740GL, but is identical to any 940. I also didn't notice a difference in pedal travel, probably because the piston surface area isn't sufficiently different between the two setups to be able to feel it at the pedal.

    I personally haven't seen an ABS or SRS equipped 240 in Australia, only photos from other countries.
  • Angus,"SRS",do you mean airbag? Ive got a 240 with air bag. It says SRS on it. I dont know what "SRS" stands for though. Glad i have the airbag. I saw at pickles 2 months ago,a 1993 940 with an airbag...and it deployed. So im confident mine would go of. Hard to believe its rocket fuel pellets that ignite and fill the bag with the gas from it. Not as quick as my other "airbag" though. :-)
  • I have a SRS equipped 1993 240, still does not have ABS...

    I have been tempted to wire in an ABS setup from a USA car and probably will do in future with the work on the 1993 245 I have
    The main reason for it to get ABS is because if I mash the brakes in a panic it will help
    I need to import a fair few bits to do it.... so wont happen until the container comes over with the next load of my stuff
  • As an enhancement to the three-point seat belt system, your Volvo is equipped with a Supplemental Restraint System (SRS). The Volvo SRS consists of a driver's side airbag with a driver's side knee bolster. The systems is designed to supplement the protection provided by the three-point seat belt system.
    The interior of an SRS-equipped Volvo loos very much the same as any other. The only indications of the system's presence are the "SRS" embossed on the steering wheel pad, and the knee bolster beneath the steering column. Also, the SRS diagnostic receptacle is indicated on the center dash panel.
    The airbag is folded and located in the center of the steering wheel. It is released only during certain frontal or front-angular collisions, depending upon the crash severity, angle, speed, and object impacted.
  • Yep SRS is the system that detects impacts and controls restraints in addition to the car's seatbelts, so in later model cars, airbags in various positions, including dual stage airbags, and seatbelt pretensioners.
  • 1993 240s typically have abs on the front.
    The factory even had the hardware setup for the rears (read diff mounting points and maybe the harness) but Aust models didn't get the full monty 4 channel.

    I looked into getting the 240 diff from this car, but the ratio was poor at 3.31 so I passed, plus getting a lsd diff centre for 1031 is near impossible.

    I was more interested with using the sensor wheels for traction control and I regret I didn't pursue that now.

    Swedish models likely have the full system though. It would also have been a matter of cost from Bosch as the full system would have cost a lot at the time.

    I learnt, saw, and discussed this with the late Gerry McCarthy who is sorely missed in the Volvo tech community.
  • 1993 240s typically have abs on the front.
    The factory even had the hardware setup for the rears (read diff mounting points and maybe the harness) but Aust models didn't get the full monty 4 channel.

    I looked into getting the 240 diff from this car, but the ratio was poor at 3.31 so I passed, plus getting a lsd diff centre for 1031 is near impossible.

    I was more interested with using the sensor wheels for traction control and I regret I didn't pursue that now.

    Swedish models likely have the full system though. It would also have been a matter of cost from Bosch as the full system would have cost a lot at the time.

    I learnt, saw, and discussed this with the late Gerry McCarthy who is sorely missed in the Volvo tech community.

    I was thinking of importing a 1993 240 wagon from Japan or the UK,with the full ABS setup. I dont know if it would be expensive,but Im interested. Im not sure how the new import laws would affect this though.
  • Vee_QueVee_Que @Vee_Que South Eastern suburbs Melbourne.
    It seems futile given how there would be no advantage in the real world and just lots of cost.
  • Wait, have you ever mashed the brakes on a car with abs? Totally works, even early systems.
  • Id like abs because, can you guarantee you are ready to control a skid every time? No. Its for emergencies. So i'd like it,esp on a 240! Wonder if ABS needs much more brake fluid? With all that extra pipe,must do. Just a thought.
  • Angus242164Angus @Angus242164 Western Victoria
    edited September 2016
    The early generation systems like were used on 240's aren't as effective as newer systems, as the valves and electronics available at the time limited how quickly the valves could pulse, but it still makes a difference to stopping distances.

    Not much extra fluid in the system, maybe an extra 500ml at most.

    I wanted to fit ABS from a 940 to my 760T, as I was doing a couple of roo avoidance stops a week typically. It would have been an easy conversion as I already had a 940 diff, struts and brakes on the car, but I stopped driving it daily and didn't bother.
  • Vee_QueVee_Que @Vee_Que South Eastern suburbs Melbourne.
    I find the early abs unit too intrusive. The tyres make more of a difference than the abs does.
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