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There is a nice section on brake upgrades in the 700/900 FAQ. Abe crombie describes the Jumbo brake conversion for ABS cars, and I describe the Big brake conversion for non-ABS cars with the 10.25 inch rotors. Last year I bought the Jumbo brake calipers and caliper holding brackets from a wrecked 1991 745T. I installed them at the end of the summer, and here are a few pictures. The Jumbo brakes are single piston calipers and you must disconnect and plug two brake lines which connect to the front calipers. Ordinarily a non-ABS Volvo has a dual master cylinder with dual front piston calipers. The pistons in these non-ABS calipers are hydraulically isolated from each other. Each brake ciruit in a non-ABS car takes care of a front piston on each side and one rear piston. When done with this conversion from non-ABS to Jumbo brakes, you have regular dual circuit diagonal brakes just like about every other car which I am familiar with. The picture below shows the brake line the the right front brake disconnected at the master cylinder and a plug in the port. The plug is ATE part number 1387506.
The picture below show the line to the left front brake disconnected at the brake junction block/switch and the same plug in the port.
This picture shows the line which was disconnected on my car at the left front brake.
The picture below shows the line which was disconnected at the right front brake.
This picture is a bottom view of an installed Jumbo brake. Notice the red polyurethane cone busings. Those cone bushings have been great. I have had no brake shimmy or warping with our cars, and good cone bushings have a lot to do with that.
This picture shows Girling brake components. The bottom calipers are dual piston calipers, one is ABS (one line), and the other is non-ABS (dual line). The top row shows the Jumbo brake caliper and caliper holding bracket as well as the pads for the early and Jumbo Girling brakes. The Jumbo brake takes the 1198 pad which is certainly more substantial than the 508 pad.
The Jumbo brakes do provide more stopping power than the Big brakes in my opinion. The area of the single piston Jumbo brake is exactly equal to the area of both pistons of the dual piston Girling caliper, I carefully measured them before installation. The Jumbo brakes do weigh a little more than the Big brakes, so you have a little more unsprung weight which is a very slight drawback. When I bought the new Jumbo brake rotors at a local discount parts store, the parts guy looked at the rotors and said "These can't be for a Volvo, they look like they are from a 1/2 ton pickup." The Jumbo rotors are 11 inches in diameter and a full one inch thick.
The stainless covered lines were purchased at an IPD garage sale. Stepping on the brakes in my car is like stepping on a rock, there is no give or sponginess to the pedal.
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