Bench bleeding a new/rebuilt brake master cylinder

[Pete_89T2]

Would it be acceptable to install the MC on the power brake booster, and "bench" bleed it using the brake pedal? Would still be using the plugs/tubes that came with the MC per instructions, seems the only difference is I'd be using the car's brake pedal linkage to operate the MC instead of clamping the MC to a bench and manually pushing the cylinder. Just think it would be less messy to install the MC dry vs. wet, hence the question.

[djmtsu]

That is the way I did mine on my old 626 turbo, since I didn't have a vise. It worked fine for me.

Now I have a pressure bleeder, much easier!

[Pete_89T2]

Originally Posted by djmtsu

That is the way I did mine on my old 626 turbo, since I didn't have a vise. It worked fine for me.

Now I have a pressure bleeder, much easier!

That's good to hear. I have a pressure bleeder too, just wasn't sure if that method would work properly when starting with a dry MC. I figured the air trapped inside a dry MC during assembly might be too hard to fully remove with the pressure bleeder alone without first doing a bench bleed, since the MC piston stays put when you use the pressure bleeder. Think I'll try bench bleeding the MC in car first, then hit it with the pressure bleeder to bleed the entire system.

[C. Ludwig]

Use the pressure bleeder. No need to do the bench bleeding when you have that. Much easier.

[TitaniumTT]

mmmm pressure bleeder... Maybe I shoudl put that on my Sears want list.

You can "bench bleed" while on the booster, just pull the check valve off the booster.

[josh18_2k]

only one i know of is the Motive. are there any other/better designs? motive is pretty damn cheap and seems to be amazing

[Pete_89T2]

Originally Posted by josh18_2k

only one i know of is the Motive. are there any other/better designs? motive is pretty damn cheap and seems to be amazing

The Motive unit is what I got. It has the pressure gauge on the tank, and came with an assortment of caps, cost was less than $50. For what it does, it is a great product. Unfortunately the Motive kit I got didn't come with a cap that is an exact fit for the MC's on my FC, and the "universal" cap they included in my kit is just too clumsy to use -- no room to route the chains under the MC and secure it, so I could never get it to seal properly. Solved that problem by fabricating my own cap with a junkyard MC cap from a 90's vintage Mazda, a brass nipple and some sealant. My homemade cap works on my FC, and also fits my '03 Mazda Protege5.

[djmtsu]

Originally Posted by Pete_89T2

The Motive unit is what I got. It has the pressure gauge on the tank, and came with an assortment of caps, cost was less than $50. For what it does, it is a great product. Unfortunately the Motive kit I got didn't come with a cap that is an exact fit for the MC's on my FC, and the "universal" cap they included in my kit is just too clumsy to use -- no room to route the chains under the MC and secure it, so I could never get it to seal properly. Solved that problem by fabricating my own cap with a junkyard MC cap from a 90's vintage Mazda, a brass nipple and some sealant. My homemade cap works on my FC, and also fits my '03 Mazda Protege5.

This is exactly what I have, and how I use it. Still can't get it to work on the BMW.

Did yours come with a BMW cap? Lol, if so send it my way, and I'll send it back when I'm done (or bring it to DGRR).

Seriously.

[Redshft]

Originally Posted by Pete_89T2

The Motive unit is what I got. It has the pressure gauge on the tank, and came with an assortment of caps, cost was less than $50. For what it does, it is a great product. Unfortunately the Motive kit I got didn't come with a cap that is an exact fit for the MC's on my FC, and the "universal" cap they included in my kit is just too clumsy to use -- no room to route the chains under the MC and secure it, so I could never get it to seal properly. Solved that problem by fabricating my own cap with a junkyard MC cap from a 90's vintage Mazda, a brass nipple and some sealant. My homemade cap works on my FC, and also fits my '03 Mazda Protege5.

I've been thinking of picking up the motive, but the stories I'd heard about the fumbly "universal" cap on the Mazda's has made me hold off.
Do you have a picture you could post of how you fabricated it? I'm pretty sure I know what you did, but I like pictures to verify things.

[djmtsu]

It literally is just a Mazda cap with a hole drilled in the middle, a barb fitting put in the hole, and then JB weld or something else that seals REALLY well (has to hold up to psi).

I wonder if the Miata cap they sell fits?

[Redshft]

Honestly, that is what I had pictured. I guess I just didn't believe it was that simple.

[Pete_89T2]

Yup, it's that simple -- djmtsu gave an exact description of my homemade cap. I can post some pics tonight if I have time. The only caveat is to make sure the donor junk yard cap still has a good rubber seal/washer under it -- you'll need that for a good seal with your MC when you screw it down.

The cap I picked up in the yard was from a '90s vintage 626, and it fits my FC ('89T2) and my '03 Mazda Protege5, so it might fit the Miata as well.

[TitaniumTT]

Something about pressurizing a fluid that can strip paint kinda bothers me. What about the air-comp powered vac ones that pull fluid from the calipers?

[djmtsu]

Originally Posted by TitaniumTT

Something about pressurizing a fluid that can strip paint kinda bothers me. What about the air-comp powered vac ones that pull fluid from the calipers?

Meh, its only like 10psi to get it all done. I can usually get 2-3 calipers done before I have to pump it some more.

Another way is with a simple oil hand pump (think like what the Tin Man uses to stay lubed).

Fill it with brake fluid, attach a hose to the end, and then onto the bleeder. Pump it so there is fluid to the end of the hose, crack the bleeder and pump it up through the lines to air escapes at the MC.

I've done it that way too. Works great too.

[Pete_89T2]

Originally Posted by TitaniumTT

Something about pressurizing a fluid that can strip paint kinda bothers me. What about the air-comp powered vac ones that pull fluid from the calipers?

^ Which is why you need a really good seal between the cap & the MC. I had the same concerns until I tried it -- IMHO, pressure bleeding works SO much better and is faster than vacuum bleeding. I've used the Mityvac hand pump vacuum method before and won't be going back - I can get a rock hard pedal via pressure bleeding in a fraction of the time it took me with the Mityvac. And no sore hands from the repetitive hand pump action.

Pressure bleeding works very well with only 2~5 PSI pressure; just enough to push the air bubbles & fluid out the bleeder screws without risk of blowing any seals. So if you buy or build one for yourself, just make sure it has a gauge.