Scarab brake fixes are required now on most Ducatis and MV Agustas, as they were pretty badly made to start with. These brakes were a very poor copy of the Lockheed calipers which were starting to appear on racing motorcycles in the late 1960s. The brakes really were being made in a gentleman’s shed for reasons we go into in the long version of this article in The Inside Line members part of The Motorcycle Broker website. We also explain, in the longer version, why Ducati’s green frame had Scarabs at the front and a Lockheed caliper on the rear. To read the full version of this article, click the link here and subscribe free to The Inside Line. Once logged in, go to market analysis and scroll to the end of the page where you can find a much more detailed and longer version of this article. We will now show you why these brakes are problematic and it is also the reason why most green frames had their front brakes upgraded, losing their Scarabs in the process. Let’s have a look at the caliper and what we’re left to deal with today.
Badly machined when new
Most of these calipers were badly machined when new. They are made in two halves, splitting length ways with a piston and a pad in each half. There is a transfer port from one half of the caliper to carry brake fluid to the other half. These holes and ports were drilled by hand and were often located in the wrong place for fluid to pass from one half of the caliper to the other. The O ring often also blocked fluid from transferring between the two halves of the calipers. The hole in both calipers, which is supposed to push each piston outwards to press the brake pad, is poorly drilled and forces fluid at the side of the pistons rather than behind them. This prevents the pistons from squeezing brake pads which squeeze the discs and just builds up pressure in the master cylinder. Such poorly manufactured brake calipers are at the heart of seriously poor braking for the motorcycle.
Scarab brake caliper repairs
There are a few Scarab brake caliper repairs that work really well and the calipers then offer pretty good braking. The holes transferring fluid from one side of the caliper to the other need to be re-machined correctly. This is a one-shot fix, get it wrong and the cost of saving the caliper is much greater and it will have to be re-anodised. A really good machinist who is prepared to take this job on for the initial repair will need to be found. Most will turn you away as it is a time consuming and costly repair. Fortunately, we managed to get the repair spot-on first time for the Amelia Island green frame which meant we retained the original anodised finish and patina. These calipers were so poorly made when they were new, there is no guarantee that a repair can be completed without damaging the original anodise.
Scarab brake piston replacement
Scarab brake piston replacement is not straight forward, but it does offer the opportunity to repair the problem of brake fluid not getting behind the pistons. Firstly there is no availability of replacement pistons for Scarab brake calipers, but Lockheed pistons are still available. However, contrary to popular belief, these pistons are marginally too big and don’t fit. Many companies working on green frames claim that the Lockheed pistons are a perfect fit, but they are definitely not. Either you can have new stainless items made, or you can modify the Lockheed items. As you can see, the Lockheed items have a right angle between the side of the piston and the back of it. To remedy the problem of fluid not reaching the back of the piston to push it out towards the pads, it is possible to machine a radius on that right angle to allow fluid to the rear of the piston.
Nipples
Nipples are another problem with these calipers, as they often corroded into the aluminium, because the original nipples were poorly chromed steel items. Once these nipples have disintegrated, they will need to be very carefully machined out of the caliper body. New stainless steel items will need to be fabricated from scratch and carefully machined to create an air tight, and brake fluid tight, seal. This sounds all very straight forward, but it is a long and tedious job which should only be undertaken by a machinist who understands the job and has the skill to get it right. Again, if this job is in any way substandard then a very costly repair will need to be undertaken and the original anodise finish will be destroyed.
Scarab brake caliper repair
These Scarab brake caliper repairs transform them from marginally better than useless to really rather good brakes. As well as the calipers themselves, there are serious issues around the master cylinder as well, which we will go into soon. If you need your Scarab brakes repaired for your Ducati or MV Agusta, contact The Motorcycle Broker and we will ensure that your classic stops the way it should have stopped when it was new.
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