Is it necessary to bench bleed a new master cylinder?

[Bailes1992]

Following on from THIS thread, I've just ordered a new master cylinder for my Wife's car.

Is it necessary to bench bleed a new master cylinder before installation? I've a lot of mixed arguments now.

What makes me even more curious, I cannot find a MC bleeding kit here in the UK. I can import a Dorman unit from the US for about £30. But there are none here in the UK.

So is bench bleeding required? Or fit the new master cylinder and bleed the entire braking system as one?

 

[wag123]

The reason why you want to bench bleed the master cylinder is that you don't want to push a bunch of air into the braking system. You can "bench bleed" a master cylinder when it is mounted in the vehicle, before you attach the vehicle's brake lines to it.

 

[joegreen]

Yes it helps get the air out of the master. You would be surprised how many air bubbles keep coming out. Plus on the bench you have the ability to move the master piston the whole travel to remove all air.

 

[Creekside]

I’m not sure you’d need a kit, we had a bunch of tiny plastic hose barbs that usually weren’t the perfect thread match but would thread into the ports, take a piece of vacuum line or similar hose and route it back into the master cylinder reservoir. Fill with fluid and pump it with a screwdriver or something until you didn’t see bubbles in the fluid that was recirculating.

 

[benjy]

going is important but stopping is lifesaving!! bleed it! prolly some you tubes if you search

 

[Blueshound]

I don't know your specific vehicle, but bench bleeding the master cylinder is usually just as a time saver. Basically to prevent having to run air all the way through. But it is definitely messier and a real pain in the neck to connect brake lines. Unless the service manual requires it, or if you already have the equipment, you can probably just install it dry and bleed afterwards.

 

[Jarlaxle]

Following on from THIS thread, I've just ordered a new master cylinder for my Wife's car.

Is it necessary to bench bleed a new master cylinder before installation? I've a lot of mixed arguments now.

What makes me even more curious, I cannot find a MC bleeding kit here in the UK. I can import a Dorman unit from the US for about £30. But there are none here in the UK.

So is bench bleeding required? Or fit the new master cylinder and bleed the entire braking system as one?

Yes. It's easier to do on the car. No kit needed, just two ~30cm lengths of brake line.

Install MC. Connect the lines to the ports, and run them back up to the reservoirs. Slowly pump the pedal until you no longer get bubbles. Hook up the lines, bleed, and you're done.

 

[Soft Cars]

All you need are two brass barbed hose fittings and two lengths of clear plastic tubing. I wish I could provide the thread sizes, but that shouldn't be too hard to find out. Clamp the master cylinder to something stationary or get a vise. Get a large Phillips screwdriver to push the plunger in; like a #3 or #4 Phillips with a large handle. Keep pushing the plunger until there are no more bubbles going into the master cylinder reservoirs.

 

[Chris142]

Yes. 100% necessary. You don't need a "kit". Just an extra set of fingers

 

[Astro14]

Yes. It is absolutely needed.

Well, unless you want crappy, underperforming brakes with air in the lines, and a bunch of posts saying, “Told you so!”

 

[JeffKeryk]

Better safe than sorry! Have fun with your brake master service.

 

[Jetronic]

Following on from THIS thread, I've just ordered a new master cylinder for my Wife's car.

Is it necessary to bench bleed a new master cylinder before installation? I've a lot of mixed arguments now.

What makes me even more curious, I cannot find a MC bleeding kit here in the UK. I can import a Dorman unit from the US for about £30. But there are none here in the UK.

So is bench bleeding required? Or fit the new master cylinder and bleed the entire braking system as one?

After installing the new MC, push the brake pistons back all the way, this will push fluid through the MC and air into the reservoir.

 

[Trav]

Following on from THIS thread, I've just ordered a new master cylinder for my Wife's car.

Is it necessary to bench bleed a new master cylinder before installation? I've a lot of mixed arguments now.

What makes me even more curious, I cannot find a MC bleeding kit here in the UK. I can import a Dorman unit from the US for about £30. But there are none here in the UK.

So is bench bleeding required? Or fit the new master cylinder and bleed the entire braking system as one?

Yes bench bleeding is important but there is no need to buy anything special, just get a piece of brake line with 2 nuts that fit your MC and cut it in half, put a bend in it and attach 2 pieces of tubing. 5 min job, I make these sort of little tools out of nicopp line.

 

[wpod]

Yes. It is absolutely needed.

Well, unless you want crappy, underperforming brakes with air in the lines, and a bunch of posts saying, “Told you so!”

I told you so is the best part of anything. Never tell the wife I told you so!

 

[nthach]

I’ve always bench bled an MC for install if possible. It might be possible to do a gravity bleed, but some cars use weird MCs *cough*GM*cough*.

 

[eljefino]

It depends.

Some master cylinders are tilted back at the firewall and have fittings down low. If you don't bench bleed them level, there'll be a triangle of air at the forward upper part that never makes it down the lines and out the bleeders.

Other MCs are either installed level or have the lines tapped up top or in a way they self-bleed.

If your MC comes with instructions to bench bleed, or your service manual states same, you'd better do it. Otherwise, it's optional but probably a good idea.

 

[Bailes1992]

Thanks for your advice all. I'll grab some cheap copper brake line and fittings and make up my own kit.

After installing the new MC, push the brake pistons back all the way, this will push fluid through the MC and air into the reservoir.

I love this idea. However, I've just fitted brand new front brakes so have nowhere to push the piston unless I take the pads out and pump the pistons out a little first.

 

[Gus_Mahn]

I haven't put a master on in decades, but I watched a friend bleed one at his shop last month. The master he was doing had simple plugs for the master. None of the hoses that I was expecting. He just pushed the piston in 10-15 time until no bubbles floated back up through the reservoir. I've always bleed them at the master/line junction, but I think air that high in the system will eventually find its way back out through the master.

 

[Jarlaxle]

All you need are two brass barbed hose fittings and two lengths of clear plastic tubing. I wish I could provide the thread sizes, but that shouldn't be too hard to find out. Clamp the master cylinder to something stationary or get a vise. Get a large Phillips screwdriver to push the plunger in; like a #3 or #4 Phillips with a large handle. Keep pushing the plunger until there are no more bubbles going into the master cylinder reservoirs.

99% of the time, it's much easier to do on the car.

 

[Jason2007]