New Master Cylinder Bracket Bolt size

[Anglefire]

On the basis that the Club shop is now shut, I thought I'd ask here!

I bought some new brackets for the Master cylinders from the Club shop and thought I'd have a look at changing them tonight whilst the bakeoff was on.

Clutch came off easy enough - I have a bag of UNF bolts and thought I would replace the ones holding the cylinder onto the bracket - and can't find the right size one - even the originals won't go in. ? They go about halfway in and then go tight. I've tried some metric bolts and they are worse.

It might just be that the nut is slightly distorted from being welded - but don't want to wreck them without being sure of the size!

Oh and this is for a Spitfire 1500.

[Pete Lewis]

Cyl to brkt should be 5/16" x 24 unf  2 off

Bracket to baulkhead  is 1/4"unf   4 off 

Pete

[Anglefire]

Thanks Pete - I bought new bracket to bulkhead bolts - but forgot to order the cylinder to bracket bolts - but have bought a selection of UNF bolts - though not sure they are 24UNF unless that is the standard thread?

[Pete Lewis]

24 pitch is pretty standard 

Pete

[Anglefire]

Thanks Pete - I'd worked that after I googled it

[Anglefire]

Got some new 5/16” bolts and they don’t fit either. I’ve not had chance to ring the shop yet. I might get some time tomorrow but work (yes I know it’s a four letter word) is a bit hectic- especially as I’m off next week so have a load of stuff to get done this week 

[Pete Lewis]

Well the next option is are they 8mm x 1.25    

Pete

[Anglefire]

I've got metric bolts and they don't fit either!

[Anglefire]

I've had it confirmed from the shop that they are 5/16 UNF as original.

Must just be a bit tight with the powered coating and welding process. I have a tap so I'll run that down the threads.

[Pete Lewis]

Makes you wonder why its a weld nut , if it was a loose nut you could get at the two fixing so much easier 

As often you have to remove the bracket and cyl as a sub assy to get on the lower bolt.

And thats probably how it worked on the assy line 

[Anglefire]

The clutch one is easy to get to - not so the brake. And the bolts on mine are ruddy tight so removing it without taking off the brake lines and putting the lot in a vice. 

[Rabbit]

Some of these brackets do have, unfortunately, either stove enamelling down the threads or occasionally some weld offshoots (?), I ran a second tap and bottoming tap down all of them but wondered if you had an early one that had not been cleaned out? It is though 1/4 x 24 UNF thread as Pete stated, not metric at all. 

[Anglefire]

4 hours ago, Rabbit said:

1/4 x 24 UNF

Its a 5/16" actually - I've not had chance to run a tap down yet - not sure I'll get anytime over the weekend as I have to do some twiddling on the heating control system and then pack my bag before I have to get the train to Manchester on Monday evening and catch the big bird.

[Rabbit]

SORRY, yes 5/16, a typographical error on my part! Sorry.

[Anglefire]

Finally got around to tackling this, this afternoon whilst SWMBO is out

Ran a tap down and bolts went in just fine. 

Then took it out for a spin - as it's not been out for what seems like months! Went very nicely - span up to 5500rpm with ease - no misfires, nothing - and sounds really nice It is using too much oil though - probably rings - and the pressure is still lower than I'd like - so I will change it for some 20-60 Millers in and see if that helps. If not, I'll drop the engine out - but it won't be for a while - I'll just keep adding oil!

Oh and I put a new pivot pin in on the clutch - as the old was really badly worn - stepped probably 2-3mm on two sides. Clutch seems to work much nicer now too!

 

[Colin Lindsay]

Glad to hear it! So they were UNF?

 

[Anglefire]

Yep 5/16" UNF - when I put the tap down it just bound up very slightly, then you could feel it cut the crap that was left in the thread and it went down all the way nicely.