    
Bob uk
Unregistered guest
Posted From: 94.197.122.93
| | Posted on Saturday, 13 September, 2014 - 08:40: |    |
It's all very well me extolling a virtuous brake fluid but someone has to do the virtuous deed.
To the amateurs changing dot is daunting and if they knew how simple it really is to do then maybe dot would would changed in all cars thus preserving the bits of the hydraulics longer and therefore cheaper so for the pros take a nap.And for the disinterested take the car to the shop.
Conventional brakes which we all have ( I wish I could use my car for everything but I not rich enough) As discussed a litre of dot is about a fiver from a supermarket which is enough and a bit more to to change the fluid. It's less the a gallon of go go juice and therefore not doing the deed is a as silly as a hat full of frogs. Dot doesn't store well so don't bother trying to save dot. Lhm has an indefinite shelf life. When bleeding any fluid taken out is IMO scrap.
All cars with hydraulics systems have a reservoir.
Some such as Citroen have an easily removed tank. Simply remove tip out and refit fill up. The system will not require bleeding. However a quick bleed would be even better. Even if just the oil in the tank is renewed it would be better than not changing it at all.
A lot of conventional master cylinders have plastic reservoirs that come off. Providing the brakes are not applied then removing the reservoir will not put air in the master.
Pre SY cars have lovely bottles that look nice and easy to quickly drain.
To bleed the rest simply open bleed nipple one at a time and let fluid run under gravity. A egg cup full from each nipple and a bit more for luck.
Note some cars have a valve on the front circuit that stops flow until the rear has about 30 to 50 psi. These won't gravity bleed and the rear must be bleed first. Mainly USA cars which drum rear and disco front.
Should the system have air due to repair work gravity works up to a point.
To get all the air.
Vacuum bleeding is the way to go.
On RR master cylinders the 1/4 bore feed pipe will if a strong vacuum is used tend to suck air via the push rod hole past the piston seals. So gentle suck only.
The rams can't be bleed like this due to the ride valves in the way. They are done squirty into bottle.
The power can be sucked though the returns which are bottom feeders in the tank. The tank can be drained like this. So by sucking both calipers on one wheel the fluid can be changed. However any dirt in the tank could be pulled though the £1200 brake valves. So I like to suck it out of the tank by lid off etc etc.
The power brakes will all so gravity bleed which will show dodgy hoses up.
Because a little bit of air could get trapped in the brake valves a squirt in the bottle is needed from each power caliper. Or if you can't be bothered the two front calipers on one wheel. Replace any iffy nipple dust covers.
The spheres when the the system is discharged ( not the spheres but the system) have virtually no dot or Lhm in them so as soon as the engine is started they fill up with new oil so they look after themselves. Unless that area has been opened up if so a pump down will push any air to the tank. 60 pumps. If the pumps has been opened up fill tank and wait 30 mins to allow the air in the feed pipes to bubble back or crack the feed pipe at the pump joint a bit and give the pipe a wiggle. Or both.
Pressure bleeding I don't like because any mistakes or pipes blowing off and it's air in the system or brake fluid all over the car. Silicon oil will get loaded with air.
Abs systems will bleed as normal on conventional systems however some ABS are trapped systems which means dot is trapped behind valves so the ABS should be cycled.
RR ABS I don't know so a look in the tech book is a must.
Pump and squirt is still a good method but can cause froth. Dot recovers in a short time if this happens I like to call it a day and battle on next day. However an hour will help a lot. Silicon takes days and is s##t to bleed it even froths pouring it.
Sealy do an excellent vacuum bleeder that runs off a compressor which is what I had at plod garage and to change dot in say a Volvo T5 took 10 mins.
The Sealy bleeder holds 1 litre of dot or power steering oil in a translucent bottle.
To change the dot in any car put the pipe in the tank pull the trigger slurp. Fill tank with dot. Put the pipe on each nipple slurp. Job done.
The bleeder is £40 on special offer. Don't forget the air line connector and PTFE tape.
Does lhm as well. And any thing else that needs sucking.
It won't suck gear oil out of axles for that I have a 1and a half hp version which takes 5 litres of nasty evil oils that are damaging my beautiful cars innards.
Clutches can be bleed by gravity providing the nipple is above the pressure port in the slave. Also if the piston is pushed in with a poky thing that won't damage any thing and air will be pushed back to the master. Do this a few times and the system will work fine. Some car I take the slave off and leave the hose connected and give the slave full stroke a few times and jobs done. If the clutch release brg is firmly fixed to the fork then the fork arm can be used. Ford and others are clip fitted so don't.
Incidentally the vent holes are necessary to allow dot to expand and contract due to temperature change. Pressure would cause the brakes to apply and a vacuum would suck air in though seals.
(Message approved by david_gore) |