    
Bob uk
Unregistered guest
Posted From: 94.197.122.88
| | Posted on Sunday, 14 September, 2014 - 08:40: |    |
This posting is for the inexperienced pros go have a cup of tea instead.
All cars with hydraulic brakes.
Master cylinders are pumps they supply the pressure to the brakes if it fails then the brakes fail.
The master is super critical for the brakes to work, therefore it must be 100%
Repairing master cylinders with a service kit is acceptable but extreme caution must be exercised. Any damage to the bore piston or spring then the cylinder is SCRAP. Or the bore will have to be sleeved by a machine shop.
The SY cylinder is readily available and is a typical brit car cylinder which is quite robust and lasts well. Because of the length of the small bore feed pipe suffers from sometimes difficult bleeding. Because of this any problems buy a new one. They last so long that when they do fail they are well worn and not repairable. Some can be most times it's not worth the risk. Despite the power brakes.
Modern tandem dual line masters can also be rebuilt but service kits are rare and expensive and the same applies about wear.
So I am afraid that there's no magic trade secrets to save money. Well there are but all dodgy and secret because idiots will find out and actually try it.
To change a master get Haines workshop manual from Amazon second hand for £3.
Basically disconnect the pipes usually 2 or three undo two nuts pull the cylinder off the servo fit new one leave pipes loose fill with dot. When dot starts dribbling from the pipe unions tighten to 8 ftlbs and bleed as normal. Even without bleeding this should give a good pedal. The two servo nuts 25 ftlbs I guess refer to Haines manual. And some have electrical plugs.
SY cylinder fit it, leave pipes loose, when dot dribbles tighten pipes up. Then bleed. If the clipping point for the pipe is undone fit new self tapping screw rather than the shabby old one.
Wheel cylinders are much the same. Service kits are available. Some have springs inside. In general when the have dot between the dust cover and piston they are leaking, the pistons should move in with small resistance if not they are seized and probably scrap. They are cheap. However some of the older stuff is mega expensive and can be sleeved etc etc.
Calipers are because of devilish clever even ingenious design easy to overhaul if the bits are available. Which are piston, main seal, outer dust bellows, nipple and pins. It is permitted to fit one side only except some calipers come loaded with new pads. Either refit the original GOOD pads or fit new pads to both sides.
To rebuild calipers I like to split them to give them a good clean followed by soapy water and blow dry. If the piston is good then only a seal kit is nneeded. If the piston is scrap then a new one will make the overhaul price close to a lovely fully overhauled shinny one. A caliper piston is about £30 that's £60 plus £30 for seals which is nearly new money.
Rust above the seal in the caliper bore if really bad means scrap. Slight bits of rust use wire brush on a drill and give the seal groove a brushing. The.seal must sit properly in the groove. Smear seal and bore and piston in red rubber grease fit piston by hand pressure only. Leave piston out slightly. Then pack red rubber grease in around the piston and bore gap. Fit dust bellows and push piston in flush. The small o rings between the split should be replaced however they don't come with a service kit. I have reused them with no problems but apply sods law.
Do not clamp hoses undo the union and plug or cap. The brake bleed nipples from the front calipers on my car DO NOT fit because the caliper port threads are M10 fine. Not 3/8 UNF. Note a bleed nipple in a female union is not RR approved and must not be pressurised it may blow out because of only a few threads is possible but it will hold head pressure from the tank. So always pump down. In case a unauthorized person presses the pedal. If the caliper is still connected it will amputate one's fingers.
Clamping hoses can damage the liner which could leave a flap of rubber to work like a one way valve. Maybe not today but 6 months later.
On master cylinder systems if the brake pedal is slighty applied the inlet port(s) will be covered. If a piece of wood is used to hold the brake pedal down a bit then dot form the reservoir cannot flow.
When changing wheel cylinders ( or calipers not RR though except master circuit) use the above method. Fit the wheel wheel cylinder tighten pipes and bleed. Remove wood then bleed. Most cars by moving the shoes apart the cylinder can be fitted without removing the shoes.
Brakes shoes contaminated with dot should be changed. However if the shoes are boiled in soapy water they are often ok to use. If the axle seals has leaked then the shoes are scrap. If recovering rear shoes like this fitting a recovered shoe to each side is also even better Leading and trailing shoes!! don't get confused. Note some cars have thinner linings on the trailing shoe which look worn out check with Haines manual before fitting new ones.
One front drum brakes because of balance issues fit new linings if contaminated with dot. They may fit the rear brakes with luck. Reliant 3 wheeled cars are like that.
All cars in general handbrake should be adjusted by slacking off the cable or rods adjusting at the wheel then resetting the cable to suit.
Handbrakes that Work via the service piston. The lever MUST return to the stops that is fully off. Otherwise it won't self adjust. Same applies to automatic adjusters on drums.
On most cars the master is mounted on the bulkhead the bulkhead can crack so excessive movement of the servo and cylinder could mean a cracked bulkhead.(Saab). Or a brace to inner wing has been left off.
Note. A few professional mechanics when retracting pistons open the caliper nipple so that dot in the caliper does not return to reservoir taking dirt with it into the abs. (BMW and Jag.)
I hope the above is moral boosting to the owner who is new to brake stuff and give them the confidence to fix a dodgy braking system.
Any pros reading feel free to added useful stuff. Or criticise.
(Message approved by david_gore) |