Master cylinder conversion for 105's - Alfa Romeo Bulletin Board & Forums
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post #1 of 4 (permalink) Old 02-15-2010, 08:02 PM Thread Starter
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Master cylinder conversion for 105's

Replacing a Dunlop master cylinder with an ATE on a standing pedal 105

My ’66 Sprint GT came with a Dunlop cylinder which I rebuilt when I restored the car. However, I could never get a firm, high pedal. With time, the pedal dropped further and further before the brake shoes made contact. Bleeding the system would improve things, but with no apparent leaks, I surmised that the master cylinder was somehow drawing in air. After some research on the Alfa BB (see thread at: and a conversation with Jim “Papajam” Neill, I decided that a new master cylinder would fix my problem.

I had always disliked the design of the Dunlop cylinders – with the inlet at the far end (which faces the rear when it is mounted in the car), and outlet in the middle, these cylinders rely on an auxiliary valve to shut off the supply as they begin to build pressure (see first photo below). This design with its extra valve always seemed overly complicated. I suspected that pitting on my old cylinder was causing the valve to leak, resulting in the low pedal.

Alfa used master cylinders from a variety of manufacturers (Bonaldi, Dunlop, and ATE) on the early 105’s with floor mounted, or “standing” pedals. The ATE cylinder has a more conventional design than the Dunlop – fluid goes in the middle, and out the end, as it does on most other master cylinders. I believe that the Bonaldi is similar in design to the Dunlop. The ATE mounts to the pedal box in the same manner, has the same mechanical dimensions, and accepts the same diameter tubing, flare types, and threads on the input and output lines (see second photo below). The only difference is that the location of the inlet and outlet ports is reversed (see third and fourth photos below).

Based on these similarities, I decided to replace my rebuilt Dunlop with a new ATE. Tony Stevens of AlfaStop in the UK supplied me with an ATE-style cylinder (apparently, this is a reproduction, not made by ATE) See: AlfaStop - passionate about Giuliettas (vintage Alfa Romeo Spares/Parts) . Installing the ATE cylinder proved fairly easy – although the locations of the input and outlet ports are reversed from the Dunlop, there was ample give in the lines to allow them to be realigned with a little bending. I did need to remove the exhaust system, exhaust heat shield, and transmission mount, as well as loosen the pedal box, to gain working space.

With the ATE cylinder installed my brakes work great – the pads contact the disks with much less little pedal travel than they did with the Dunlop. Given that the ATE is a bolt-on replacement, I would recommend this conversion to anyone experiencing problems with a Dunlop master cylinder.

Two additional thoughts:

The biggest glitch I encountered in completing this job had nothing to do with swapping brands of master cylinder - it had to do with the two special bolts that hold the cylinder to the pedal box casting. Those bolts have a round head with two flats that fit into receptacles cast into the pedal box – these are supposed to prevent the bolts from turning as you tighten the nets. As with many 40-year old parts, my receptacles were worn, and no longer gripped the bolt heads, which allowed them to turn as I tried to loosen the nuts. I substituted 10mm X 75mm allen head screws for the special bolts – there are holes in the casting that allow an allen wrench to reach the bolts (the fifth photo shows the two bolt head types).

Alfa used several different master cylinder suppliers and sizes on the standing pedal cars. Hydraulic parts were supplied by Dunlop, Bonaldi, and ATE. Master cylinder diameter varied with the presence or absence of power brakes. Unboosted cars used cylinders with diameters of Ύ”, 13/16”, or 20mm. Cars with boosters came with 7/8” or 22mm cylinders. AlfaStop carries many, but not all combinations of cylinder diameter and manufacturer – if you are making this conversion, be sure to order the right one for your car.
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Jay Mackro
San Juan Capistrano, CA

'63 Guilia spider
'65 Guilia Sprint GT
'67 Duetto
'91 164L

Last edited by Alfajay; 02-15-2010 at 08:05 PM.
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post #2 of 4 (permalink) Old 02-16-2010, 12:25 AM
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Because of the swap in the thread pitch of the inlet and outlet connections, what do you do? Interesting thread.


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post #3 of 4 (permalink) Old 02-17-2010, 01:35 PM
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You bend the hard lines to fit. At least that's what I did on putting a later [Bonaldi?] MC on a TI that originally had a Dunlop MC on it.
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post #4 of 4 (permalink) Old 04-13-2019, 06:48 PM
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Rats, and double rats.
Nice idea, substituting this 20mm ATE-copy m/cyl for my leaking 22mm Bonaldi, but stymied (for now) by the much taller ATE m/cyl body not fitting under the floor of my RHD 1600 GTV.

Adding a second banjo fitting might give enough room, I thought. Nope. Too tight for one by 15mm or so, still.
I thought about relieving the floor, coz "it'd be hidden under the seat". Nope. Not under the seat. It wouldn't be the end of the world, but quite noticeable.

Custom bracket may be the only solution, lowering everything by 15ish mm, unless anybody has another idea?
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