Cleveland Brake pistons:O ring groove dimensions

The place to raise issues, ask questions, swap ideas and discuss anything related to aircraft engineering, maintenance and building.
NB Any opinions expressed in this forum are not necessarily those of LAA Engineering

Moderators: John Dean, Moderator

Post Reply
Ian Law
Posts: 213
Joined: Wed Jan 02, 2008 11:00 am
Location: Devon

Cleveland Brake pistons:O ring groove dimensions

Post by Ian Law » Fri Oct 17, 2014 5:23 pm

I have an old set of Cleveland brake callipers for my Boredom Fighter project and since they didn't have pistons with them, when I bought them, I have turned some new pistons on my lathe. The cylinders are believed to be Cleveland part number 061-00601. The pistons are 1.500”OD & about 0.5”deep and are of a simple cylindrical form. After many attempts, I finally managed to extract this information from Parkers in the USA and don't fancy engaging with them again, to obtain dimensions for the O ring grooves.

I sized the O ring grooves using information for reciprocating rings from various websites. The O rings are a good fit, but seem excessively tight in the cylinders -too tight for me to risk pushing the pistons fully home in the cylinders, in case I can't get 'em out! I have lubricated the O rings with hydraulic fluid & this doesn't make much difference.

Could anyone who has some expertise with Cleveland brakes advise me exactly what the correct groove dimensions should be for my home made pistons and how tight a fit the assembled piston/ O ring should be? The pistons, without O rings, are a free and smooth fit in the cylinders.

I keep looking on e-bay for suitable replacement pistons, but haven't had any luck so far.

Ian

nuggets
Posts: 19
Joined: Mon May 14, 2012 6:25 am

Re: Cleveland Brake pistons:O ring groove dimensions

Post by nuggets » Sat Oct 18, 2014 5:25 pm

hi

can,t help you with the dimensions but i used the air line from the compressor or you could use a bicycle pump to push the pistons out of the calipers , bleed nipples locked and just blow through the fitting for the brake line :wink:
Paul Dennington
039741

Ian Law
Posts: 213
Joined: Wed Jan 02, 2008 11:00 am
Location: Devon

Re: Cleveland Brake pistons:O ring groove dimensions

Post by Ian Law » Sat Oct 18, 2014 8:03 pm

Many thanks Paul and I had considered using compressed air ( carefully ... ) to persuade the piston out of the cylinder, and will use this method.

Having rechecked all the dimensions of the groove for the o ring, today, I think that the groove should be about 6 thou deeper, to equal the recommended depth for the 1/8"D O ring I'm using. No idea how I miscalculated this, in the first place and I'm sure this is the cause of the problem! The groove width seems OK.

I'll try to re-machine the groove to the correct spec in my much less than perfect and ancient lathe, if I can make a suitable small tool to get inside the groove without fouling the chuck jaws. Very quick & simple with a decent lathe, but a challenge for me with my antique tools.

If not successful, I'll have to start again from scratch with new bar stock and be a lot more careful next time!

Measure twice and cut once!

Ian

Post Reply