Master cylinder kits

[Forumadmin]

The MC on the SA failed in Stratford. Investigation showed that the kit used for rebuild many years ago was perhaps past its best but there was no sign of what the problem was except wear on the sleeve. The symptom was that the brakes needed bleeding just before journey to Stratford and then required pumping on the way to the rally field to acheive some braking. This could have been due to a weak seal spreader.

I have rebuilt half a dozen MCs using the NZ kits but they came in two varieties, an early one with a black seal spreader and a late one with a white seal spreader . It is thought the later may cause air to be drawn into the unit and should not be used. I do not know if an NZ kit was used to rebuild this failed unit.

The unit I used to replace the failed unit had a black spreader NZ kit. Note assembly order is important and the unit should be tested on the bench to see if it returns easily after full extension. Slight misalignment will make it stick.
and these instructions https://jowett.net/jowettorg/jowettnet/ ... brakes.htm

Drummond gave me a new kit from JCS which should be to original specification and this was compared to the NZ kits and the failed unit.

20220627_172752.jpg

Late NZ spreader, Early NZ , out of failed unit, new JCS .

The NZ kits also have a white plastic sleeve that goes aroung the piston that replaces the original aluminium one. This will have a different coefficient of expansion which Scott thinks may cause issues. I think, but am not sure, I have used these plastic sleeves in the SC and Jav without issue.

[Forumadmin]

It is very probable a full NZ kit was used for this rebuild as it had the white plastic sleeve. On further consideration the failure may have been due to the white plastic sleeve rather than the outer seal or spreader. I would really need to check the Jav and SC to see what they have in them and consider the mileage done by each. The SA certainly did the Switzerland tour but I am not sure about the Baltic tour with that M/C. The symptoms were unusual in that air was getting into the system and the brakes needed bleeding. The final failure was more likely to be the failure of the recuperating seal but this may have been caused by the plastic sleeve.
It is easy to do wrong analysis, remember the wrong sequence of events and jump to the wrong conclusions.

More to come as we get information from other's experiences.