Can anyone assist me in understanding the working of the brake compression tube - part no 2569 on the link attached http://www.smallfordspares.co.uk/plate.phtml?PlateID=5
I am determined to try and get some better braking from the cable & rod system I have on my car. I have read the description on Page 47 of Stephens - Ford Specials Book which seems to suggest that there should be some movement within this tube to allow the pedal pressure to close the compression tube whereby the spring inside is forced back to eventually apply the rear brakes. Or have I misunderstood it completely?
My tube seems to be completely solid, and I cannot see how you dismantle it to get to the spring inside - the nut on the end just rotates.
Alternatively has anyone got such an item they can let me have/ borrow etc?
Both Small Fords and the FSOC do not list this item within their spares lists.
Thanks
Tony Brooks
Interesting, a non hydraulic ' relief ' valve that works the other way around. Looks as though you are correct. On application the 'Balance' lever 2556 pulls on the front brakes and pushes part 2571 (plunger) within the tube against the spring, small application pushes the spring with little pressure against the end of the tube and the rear brakes come on lightly. Further application pushes the spring in further, this reacts increasingly against lever 2473, in turn pulling the rear rods with more movement and finally the the spring will become coil bound (maybe) and the rears lock up, or runs out of movement to prevent this. As we know, hydraulics work the other way around.One assumes that when new, the 'piston' lives in a greasy tube. To lock up the rear brakes, take out the spring and re-adjust so that front and back start to come on together, rod tension then depends on relative lever lengths front and back. So, has the spring been removed or has it been jammed in and stayed there?
ReplyDeleteI have a Dellow with Girling cable brakes and have
ReplyDeletepersevered for years to get them right until a new MOT tester gave me
instruction on how to set them up. The Dellow does not have the Compression
tube but I quote from ‘Automobile Brakes and Brake testing by Maurice
Platt 1938 book’
‘The compensator at the lower end of
the pedal is connected to the forward pull-rod and is also coupled to a cross
shaft by a compression rod embodying a sliding spring loaded joint, This spring
maintains a slight degree of tension throughout the system when the brakes are
free and also serves to prevent rattle in the various joints. Consequently the
designers are able to permit sufficient play in the joints to ensure free
action without lubrication. Care should be taken that the sliding joint in the
compression rod works freely and that the clearance of about 1/16 inch is
maintained between the plunger part and the end of the tube in which it fits,
when the pedal is off ‘
I hope this answers your question. It strikes me it is nice
to have rather than fundamental but if you have it should be maintained.
Recently I replaced all the clevis pins and yokes both front and rear.
Then hear is the tip. Get all 4 wheels off the ground. Tighten up the brake adjusters
on each back plate until the wheel starts to bind. Ensure all the front and
rear compensator links are in a position where a pull on the front of rear rod
will exert a mechanical advantage on the link. You do not what the compensators
to have gone past the centre line so there is no mechanical advantage. Adjust
the individual brake cables to ensure the compensators give this advantage. You
may need to slacken the adjusters to do this. When these are set adjust the
main cable to ensure they are taught and will just start to pull the brake
pedal on. Slacken the back plate adjusters one or two notches until the wheels
are free. You are now set up. On the brake test for the first time I managed to
lock all 4 wheels Eureka!
Mudplugger2
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Thanks Mudplugger2 - I am on the track of a replacement Compression tube - mine looks as if it has been brazed up and I will then follow your advice.
ReplyDeleteHi Tony I have one if you are stuck You can ususally free off the tube by removing it from the vehicle and soaking in diesel. Then you lightly tap the outside with a small hammer to free off the piston There is also a air hole drilled through the tube that must be kept clear Put back together with the piston well greased The spring loaded end is the opposite end to the nut and threaded rod - this is to provide adjustment - there should be about 2mm to 3mm clearance. The idea of the compression tube is to make the front brakes come on slightly ahead of the rear. The mechanical brakes work OK when they are set up as per the workshop manual - this included centralising the shoes, making sure the expanders are free to slide and getting the swivel trees in the correct alignment, they are a bit time consuming to get adjusted the first time round but it is well worth the effort I found no problem going down Porlock hill in the Pop after doing the Lands End the brakes still worked fine and pulled up square. Ken
ReplyDelete