VOLVO DISC ROTOR COMPARISON
© by Anthony Hyde, Australia 5/2009

INTRODUCTION : Volvo enthusiasts at some time or another consider bigger brakes. Disc Rotors are a component needing understanding. Rotor measurements have been made for ventilated discs 240 / 740 / 940 Turbo, with a 'scale relationship' drawing for easy understanding.
In certain years 240's also came with solid front discs eg 1985 (no internal ventillation), but most years are ventilated. Rear discs are solid.

NOTES:

The 240 rotor / disc is more inboard.

The 740 rotor is larger in dia than the othersand stands alone in that it vents to the outside (air is scooped from the hub region and passes internally up thru the rotor to vent out the top), but note its still the same thickness as a 240. With the tall & slim rotor, warpage is a risk so make sure the hub mounting surface plus the wheel hub are clean and flat, with wheel nuts torqued up evenly.

For rotor / disc ventilation, the 240 and 940 designs scoop air from the rotor outer diameter and passes thru to vent down near the hub. So in an evolutionary sense, the 240 design line -evolved- into the 940 Jumbo, with the 740 version disappearing.

Volvo learnt a brake lesson with the 740 rotor with thousands of owners reporting warpage, and hence the 940 Jumbo rotor was designed with a better width to diameter ratio, meaning wider and less tall, and changed disc ventillation direction.


VOLVO ROTOR / DISC BASIC DIMENSIONS - by Anthony Hyde

240 Front OD=263.3 mm (10.36") 22 thick, Hat 150 OD (4 piston caliper)           
240 Rear Disc diameter = 281 mm

740 1988-95 OD=286. 7mm (11.28") 22 thick, Hat 160 OD (double piston caliper, smaller pad area than Jumbo)

940 Jumbo OD=280 mm (11.033") 26 thick, Hat 150 OD (smaller OD, but thicker, single larger dia piston caliper, larger pad than 740)

Hat diameters - The Jumbo is the same design as the 240 rotor hat design with the same inside ventilation system, the Jumbo difference being a much thicker rotor thicker and larger outside dia 280 vs 263 = 23.4 mm).


One 240 upgrade 'out there' is fitting Mazda RX7 Turbo brakes onto a 240 front. Both are 4 pot calipers, with the Mazda being all alloy vs the Volvo Girling being heavy cast iron. The upgrade uses the 740 rotor that you can see is outboard by 11.5 mm. Therefore Volvo factory 15"240 rims (5 spoke Gemini 16x7" will fit with a 3mm spacer) will interfere with the RX7 / 740 setup, as normally on a 240 the rim sits very inboard. Solution is aftermarket rims 16" or better still 17" and larger with better clearance and offset. For higher force brake applications, the combination of the Mazda caliper and larger dia Volvo 740 disc improves decelleration.

Thanks to Peter Linssen & others on Turbobricks for discussion on Jumbo 940 brakes.

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