Reboring Master Cylinders

[chuck hahn]

Seeing that front master cylinder kits for the 78-79 1000s are like hens teeth i was thinking why not rebore the masters to accept an available kit. Has anyone done this or know of anyone that has?
Also i was wondering if another early dual disc master such as the 78 750E is the same bore size as the 1000. If so, was thinking i could use a 750 kit for this master cylinder. Its leaking out from the handle end seal.
What are the bore sizes for the 750 and 1000? How do i tell by the markings on the bottom of the masters? Im not schooled on the codes for masters.

[Grimly]

Point of related info that might be of some use...
The dual disc master cylinders on the 850 79 (early caliper type) and the 80 (later caliper type) are both 5/8".
Given Suzuki's tendency to re-use as much as possible, it's likely they're the same setups for the 750 and 1000.

[Nessism]

All GS dual front disc bikes use a 5/8" bore. Single disc are 14mm.

There is almost no chance of finding an appropriately sized and configured plunger to allow a small overbore of the master. There are guys that overbore, but they sleeve the master back to stock size using a stainless steel liner. That doesn't solve the lack of master kits problem, though, and such sleeving jobs are expensive.

Given the large selection of low mileage and new 5/8" bore (or 16mm) masters on ebay and the like, trying to bore the master makes doesn't make economic sense.

[chuck hahn]

Ed.. So in theory any 16MM kit can be used "for parts" and i can swap the seal on the piston into my existing piston? Am i reading too much into your info?? I dont need all the other stuff in a kit. .I just need the seal on the piston itself.

[Nessism]

Ed.. So in theory any 16MM kit can be used "for parts" and i can swap the seal on the piston into my existing piston? Am i reading too much into your info?? I dont need all the other stuff in a kit. .I just need the seal on the piston itself.

No. The ID and width of the new seal needs to be the same as those on the old plunger. And while close in size, GS masters for dual disc bikes are 5/8", not 16mm.

[chuck hahn]

OK.. So im seeing kits for 14mm and 16mm. So the early models with dual disc are 14mm..correct? What im trying to figure out what bikes used the same size and style seal on the piston as the 78 1000 so i can buy a kit to scrounge a seal from.