restarting drained hydraulic system - best method?

[tim]

Finally finished repiping the old horse and it's time for startup. I realised that there isn't any info on the process of refilling to hand so can anyone advise, i.e. which setting, normal or high? The brakes will also need bleeding, found some posts on that, i.e. bleed screw out 1/4 turn, run at 1000 rpm then pedal down on brakes until the bleed tubes are bubble-free (as usual with any caliper). And any further useful advice? I assume the pump won't need priming or is that wrong? The pipes drained out of course but there should be fluid left in the various systems?

[Dollywobbler]

Always a contentious point. Some say the pump should be primed, I've never primed a pump and have seen BXs behave just as badly whether primed or not.

Suspension on high and leave it running with the pressure regulator undone at first. Then tighten it. Could take several minutes to rise up. May respond from steering input, may not.

What I will say is check all of the bleed nipples will loosen before getting carried away. They often seize, especially on the rear wheels. If there's a problem, better to find out before you start trying to purge the system of air because if you have to remove a caliper to sort out a problem nipple, you'll have to re-bleed anyway.

You will also need some weight on the rear wheels. There are flanges on the base of the suspension arm, near the hub, that you can jack up on.

[tim]

OK, thanks for that!! Calipers have been rebuilt so no probs there. Why do the wheels need weight? I only have one jack so presumably one at a time, or just one, will do?

[Dollywobbler]

The rear brakes get power via the rear suspension units, cleverly giving adjustment for weight carried. If there is no weight on the rear wheels, the brakes will get no fluid and you therefore can't bleed them. I don't know enough about the circuits to know if you can do one side at a time.

[Mothman]

Just let me know if you need a hand or a foot to press a pedal bud.

Andy

[mat_fenwick]

Or wedge a piece of wood between the steering wheel and brake pedal to keep the pedal depressed. Thanks to Todd for that neat tip!

[Jaba]

Or wedge a piece of wood between the steering wheel and brake pedal to keep the pedal depressed. Thanks to Todd for that neat tip!

I use a broom from the seat to the pedal as I always have a broom of some sort to hand........

[MULLEY]

I always prime the pump & only stick the hose back onto the lhm tank once the bubbles have stopped. I then turn the pressure regulator on & off repeatedly upto approx 20 times. Once the regulator has been closed so that it can re-pressurise, i then put the car into high & wait a couple of minutes to see if anything happens, if not i give the car some revs for about a minute, nothing, then i turn the steering on full lock from side to side, its probably stiff as hell to begin with & should then get lighter & lighter as the air is purged out. I check the lhm reservoir whilst still on high for the lhm level & usual put some more in, half a litre+ approx (before i would have put in 2.5 litres into the tank, before priming the pump, so approx 3odd litres in total). I then press the brake pedal whilst turning the steering & then go up & down the height settings & it should start to move, it takes a while before it goes to the correct heights. Works everytime, although a bit time consuming. If anyone has got a faster technique that always works, please let me know

[kiwi]

So my lazy way of cleaning the reservoir then topping up and waiting for it to rise is not as easy as that?

[tim]

Just read the Haynes, maybe I should have done so first..... they state that the pedal simply needs to be pressed down rather than any weight or leverage applied to the rear arms themselves. I don't know about waggling steering - the front is on ramps, the rear on axle stands, it would have to be a pretty minimal wiggle! Maybe if I can get the brakes fully bled up first and the wheels on, this could be done after that.
Piece of wood trick noted. On a lot of hydraulic systems you need to 'pump' the system to get all the air bubbles out rather than apply continuous pressure to the pedal - I take it this won't be the case with the BX?

[Way2go]

i turn the steering on full lock from side to side, its probably stiff as hell to begin with & should then get lighter & lighter as the air is purged out.

If the wheels are on the ground and there is no power assist, you risk splitting the Hardy disk by turning the steering at this time. Don't ask me how I know!

[citronut]

no need for weight on the rear wheels at all, just get the suspension functioning and fully up on its highest setting ( with wheels dangling is fine ) before bleeding the brakes, with it fully up on high it opens the flow fully to the rear brakes,

not usually any need to prime the pump either,
just let it sit there on idle with the regulator bleed valve open for about two minutes, then hold the revs at around 2,500rpm whilst closing the bleed valve

regards malcolm

[MULLEY]

I like your easier method Malcolm, i'll give that a try next time

Never even thought about the hardy disc being damaged way2go would it only do that if it was on its way out anyway??

[Dollywobbler]

I'm just thinking - I think I've only ever had to the resort to steering input when the car was either on grass or gravel. Tarmac or concrete could be very different I guess.

Glad to be corrected about the rear brake bleeding. That makes life easier!

[RxBX]

Finally finished repiping the old horse and it's time for startup. I realised that there isn't any info on the process of refilling to hand so can anyone advise, i.e. which setting, normal or high? The brakes will also need bleeding, found some posts on that, i.e. bleed screw out 1/4 turn, run at 1000 rpm then pedal down on brakes until the bleed tubes are bubble-free (as usual with any caliper). And any further useful advice? I assume the pump won't need priming or is that wrong? The pipes drained out of course but there should be fluid left in the various systems?

Tim, have you not seen/read the thread for HP-PUMP PRIMING TIP ?

Hopefully it may be of help !



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