brake bleed screws

Post by **Dominic** » Sun Jun 10, 2007 6:16 pm

Hello All

Some advice would be appreciated please. I attempted to replace the brake fluid today, to find that the rear bleed nipples are seized very tight. I obviously want to avoid damage and replacing anything unnecessarily, so my question is: just how much force is safe to use on the spanner? The rear cylinders, being a sliding fit, have a tendency to twist along with the bleed screw, which in turn imparts a bending force to the brake pipes. Is it safe to use a penetrating oil here, or even very careful use of heat? Or is plain bog-standard brute force ok? I intend to replace the actual bleed screws as these are somewhat corroded. The fronts are luckily quite new, and turned readily.
Any advice would be gratefully received!
Thanks,
Dom

Post by **picky** » Sun Jun 10, 2007 6:20 pm

I would wire brush them to remove corrosion from the screwthread, then apply some release oil and leave it a while to soak in. I wouldnt use any heat, unless you are replacing all of the brake fluid as the heat might effect the brake fluid.. i dont know. Better safe than sorry.

Picky

Post by **Alec** » Sun Jun 10, 2007 6:47 pm

Hello Dom,

I would avoid heat as it is likely to damage the seals. Picky's suggestion is best first step, but be aware that such as WD40 is not a penetrant, Plus Gas is better in this situation.
Be prepared that the bleed nipple may well shear off and you have the choice to try and drill and re-tap the cylinder or simply replace it.

Alec

Post by **alex_holden** » Sun Jun 10, 2007 6:57 pm

picky wrote:I wouldnt use any heat, unless you are replacing all of the brake fluid as the heat might effect the brake fluid..

Not to mention, brake fluid is highly flammable.

Post by **Alec** » Sun Jun 10, 2007 7:07 pm

Hello Alex,

not when it's within the brake system.

Alec

Post by **bigginger** » Sun Jun 10, 2007 7:11 pm

Not when it's out of the brake system either. Both Cam and I have tried to set it on fire, he failed and I managed to after several minutes with a blow torch. There's even a video of it on here somewhere. Can't remember where the story came from - anybody?

Post by **bmcecosse** » Sun Jun 10, 2007 8:13 pm

Remember these bleed screws are the strange course thread (what is it ??) - not the normal 3/8" unf.

Post by **Alec** » Sun Jun 10, 2007 9:20 pm

Hello BMCE,

all the bleed screws I have are 3\8" UNF, if the Morris's are different, 3\8" UNC?, which is very unusual. surely they are not a Whitworth thread?#

Alec

Post by **bmcecosse** » Sun Jun 10, 2007 9:43 pm

Dunno - the rear wheel cylinders have a different course thread for the pipe connections - but maybe I am wrong in thinking the bleed screws are different - maybe they are indeed 3/8" unf. You have got me thinking now - will be checking up tomorrow night

Post by **alex_holden** » Sun Jun 10, 2007 9:47 pm

The bleed nipples are the same all round. They screw into a banjo fitting on the rear.

Post by **bmcecosse** » Sun Jun 10, 2007 9:53 pm

Aye - but I was thinking that thread is same as the brake pipe thread - which is course at the rear of the car. Too late tonight to go rummaging!

Post by **mickessex** » Sun Jun 10, 2007 11:15 pm

The thread is BSF on the rear bleed nipples. I had this problem a couple of days ago. The bleed nipples had rusted solid. I eventualy manage to get them out, problem being it left behind rust deposits inside the brass banjo's. I thought I managed to clean it all out but when I screwed in the new bleed nipples that I had just bought, they wouldn't seal. I ended up buying new brass banjo's as well.

I recommend doing that anyway for what they cost, ESM sell them, but don't forget the copper washers small and large. it will also make it easier in the future to bleed the brakes.

Mick

Post by **alex_holden** » Sun Jun 10, 2007 11:25 pm

Oh, I stand corrected. I could have sworn there was no difference between the front and rear bleed nipples. I think the banjos on the rear brakes are the same as the banjo on the master cylinder, so I suppose the fitting that screws into there must have a BSF thread too...

Post by **steve4063** » Mon Jun 11, 2007 7:17 am

on my trav i tried to nick a rear screw of the 4 door to put on the front and it wouldn't fit!!!!!!!!!!

so not sure no doubt someone will correct me but i think some are dif sizes

Post by **bmcecosse** » Mon Jun 11, 2007 7:39 am

Thanks Mick - thought I was goiong daft there fgor a while! So it's BSF on the rear axle - and UNF elsewhere on the car. It may be of course that aftermarket 'banjos' are same as mastercylinder ie UNF - but I knew the originals were a coarser thread (now thanks to Mick identified as 3/8" BSF) and this certainly applies to the T piece on the axle too although I am not sure about the flexi pipe there - does the rearward Bundy pipe have a UNF or BSF end fitting ?? Or does that T have 2 x BSF and 1 x UNF port - or does the flexi have BSF male end - and UNF female end ??? Wow - complicated isn't it!!

Post by **Alec** » Mon Jun 11, 2007 7:47 am

Hello BMCE,

it certainly is, why do we have all these different threads?. If only they had left Mr Whitworth's excellent design as standard! (It has a better thread form than all the successors) I think that the TPI on both BSW and BSF are similar to UNC anf UNF, indeed some BSW and UNC do coincide and will assemble.

Alec

Post by **bmcecosse** » Mon Jun 11, 2007 8:26 am

Whitworth and UNC are same 16 TPI - but one has 55 degree angle and the other 60 (can't remember which), BSF is 20 TPI and UNF is 24 TPI (all in 3/8" size). I can only imagine that the rear axle brakes were sourced from one factory and the rest of the car elsewhere!