by Marc James Small in the April 1977 RootesReview, edited by Tom Calvert
Regarding the article on servo unit rebuilding by Antoni Wojtowicz and M. del Prado in the August, ’77 issue, the system is truly fine and honing does appear to work, though not to be vitally necessary. I’ve rebuilt them both ways, and the decision as to honing would appear to rest on whether the metal has been “pushed” into a ridge at the lip of the bore. If it has – and this is fairly rare, as the rubber seals are softer than the neoprene used in cast-iron units where ridging is much more common, then honing should be used to bring it back to a uniform bore, but carefully, since the aluminum used is a terribly soft substance. If the ridging is too severe, then rebuilding should not be contemplated, since the overall diameter will then be too great for the seals to hold.
Second, the relocation of the vacuum cylinder is positively vital and my rebuilt units were locking up after a few days and I simply could not figure out why until I disassembled a junker unit that was leaking and suddenly realized the three bolts holding the vacuum unit to the assembly were very, very tight–and then it dawned on me that I had not been tightening the bolts in my rebuilt units down sufficiently and they were shifting in service, causing lock-up.
a) Ensuring the entire interior surface is sanded down with 400 grit and crocus cloth until it is absolutely, relentlessly clean and smooth.
b) Ensuring the grease (Girling Black Leather Grease) is used only on the inside of the leather seal in quantity and sparingly on the outside: this grease hardens in service and will cause binding and lock-up.
c) Loosely assemble the cylinder to the hydraulic unit, put the vacuum piston and spring in without the rubber under the leather seal, and push down four or five times to ensure the bushing, cylinder, piston etc. are aligned properly.
d) Then gingerly allow the spring to free the piston, gently remove them, and have a friend tighten the bolts snugly.
e) Then get out a cheater and so forth and put a godawful strain to tighten ’em down–I did mine to 100 pounds or so, but then I don’t have a vise to use.
f) Then test when the seal has been put on the piston and the grease squirted around. If it doesn’t move promptly to the end of the piston, it’s not free and has to be loosened, realigned and tightened anew. (The book says it should free up in “half a second”. I don’t know if this is accurate.)
Lastly, many of the warnings in the manuals vis a vis brake systems are paranoid overkill: brakes can generally be rebuilt even when there is pitting, scoring etc. But the decision to do so should not be taken lightly as there is a greater chance of unexpected failure. I won’t do it now, but I have when bread was scarce and parts unobtainable, and it’s never failed to hold – so far! But Alpine / Tiger systems are single cylinder and there isn’t the margin of safety present as there is in the newer dual systems.