What thread size in '90's master cylinder?

[Jettadoor]

Hello, could anyone tell me what the actual thread specs are for my MC? (1990 Jetta).I have a NPT 1/8 27TPI tap that fits enticingly into a steel union but think it could be M10 1.0.  I don't have a tap this size to try out.

Unfortunately I need to run a tap through some threads in my MC and would like to use the right one to avoid problems 

Thanks!
Philip.

[bvolks73]

I'm not sure of the size but it's the same as the bolts that hold the pressure plate to the crank. I've used them many times to block off the brakes to one wheel in a pinch when I've blown a line or a cylinder.

[Jettadoor]

Thanks bvolks73, I've been a bit busy the last couple of days, sorry it took a while to acknowledge your reply.

I'm pretty sure that makes it M10x1.0. The similarity of the pitch (27 tpi and 25.4 tpi) and the pipe thread profile make it all too easy to screw up!

I'm following up on this because I did a couple of searches before posting my query and couldn't find anything. If someone else needs to know in the future, hopefully it will come up!

I dug up from the depths of my addled memory an occasion when I had to undo the very bolts you speak of!

Many moons ago, when I was working as an apprentice at the local VW dealership, one of our customers had been to his corner garage for an oil change. Now I know that guys who work in local repair shops have to be familiar with dozens of makes and models of cars and deserve some respect but this guy, after checking the brake fluid, prestone, battery, etc. took a look into the timing hole on top of the tranny. Things looked a bit dry in there, he thought, so he decided to add some auto trans fluid!

It took our customer about 2 hours to make the 30 miles to our shop!! I had to take off the transmission and undo the whole clutch/p.p mechanism to clean off all the oil that had been giving him a slight case of slipping clutch  

I felt a bit sheepish when, on firing up the engine after cleaning up and changing the clutch, oil was p*****ng from the starter, so I had to take that off and take it apart and clean it too!