Bench bleed tips

[bugedd]

I am going to reinstall my master on the Bugeye and thought a bench bleed would be a good idea. Any tips on this? I went to my local auto parts store and they don't carry kits for this. And I don't have any extra flare fittings and brake line. Anything else I can use?

 

[zabond]

secure the cyl vice or clamp to bench, fill with fluid, slowly push piston down and hold, put your finger over the outlet to seal, slowly release the piston, repeat til all air is out, put a piece of tape over the outlet and reinstall, remove the tape and reconnect the pipe, don't push piston down again until pipes are connected and a bleed nipple is open, then bleed as normal
Russ

 

[dklawson]

If you want fittings, visit the plumbing section of the hardware store. Look for barbed hose fittings with a 1/8NPT thread. Chase those threads with a 3/8-24 die. (You'll have to work a bit at this... 1/8NPT is larger than 3/8-24). Place your modified fitting in the master cylinder discharge port. Use a length of rubber hose on the barbed fitting looped back into the MC reservoir.

As an alternate, IF you had (I know you said you don't) any left over old British hydraulic lines (they don't have to be new) cut the end off one leaving the nut in place and an inch or so of tubing. You can thread that into the MC and connect the rubber hose to the short length of tubing.

If you want to buy a kit, call local parts stores looking for Dorman part number 13910.

 

[bugedd]

And what brake fluid is best?

 

[dklawson]

And what brake fluid is best?

That question can potentially start a multi-page thread as people respond with lots of opinions. There are reasons for DOT-4, DOT-3, and DOT-5.

How much of the braking system have you replaced or rebuilt?

 

[glemon]

I have never figured out how I am going to put a line on an already filled MC without dripping fluid everywhere. My "bench bleed" method is crude, but easy, and has worked for me. I install the master cylinder, fill it, then loosen the attachment where the main brake line goes into the master cylinder, a couple turns or so. Then put a bunch of old rags under and around where the brake line exits the MC. Couple slow pumps until fluid comes out of the loose fitting (best with a helper, but I have done it alone) then tighten the fitting back up, remove the rags and bleed as usual. No special fittings/lines and minimal mess.

 

[dklawson]

I have also used the method glemon described. It's what I did for years before I found out there are kits with fittings and tubing. Like glemon said, bench bleeding is typically somewhat messy no matter what the method. Rags are your friend.

 

[bugedd]

Hey Doug,
The brake system was done by the PO, front disc conversion with larger rear drums. Thats about my extent of knowledge of it.

 

[dklawson]

My concerns are as follows.

The original brake rubber up to sometime in the mid-1970s was natural rubber. It was compatible with DOT-4 but not DOT-3. Any brake system fully rebuilt after the 1970s should have rubber that is compatible with DOT-3 and DOT-4. That must include all the rubber (cylinder seals, brake hoses, proportioning valves, etc).

Your car probably doesn't have original rubber brake parts left in it at this point. However, if you want to be 100% safe, flush the system and use DOT-4. Replace the fluid every two years or so to prevent problems.

 

[Gerard]

Regarding your question about bench bleeding, I don’t think you necessarily need to do that with the product I’ve provided. The MC is assembled with a special assembly lube, so you should be able to develop good pressure from the start on the brake side. The clutch side does not have a residual pressure valve, so they can be a little more challenging, however, if you follow the open-pedal down-close bleeder-let pedal up -repeat routine, it shouldn’t be too bad. The best solution is to add a remote bleeder to the slave cylinder. I’ve done that for the last 25 years and I can bleed a clutch in about 3 minutes. A speed bleeder works well also, but still have the issue with access. Whatever you do, make sure bleeder is in the uppermost port; sometimes they are assembled incorrectly.

 

[bugedd]

As I lay here sick with the flu, I have little else to do than ponder car stuff. Question, when replacing the master, why not bleed to the passenger front, the shortest distance, if the goal is to remove air and not do a full bleed?

 

[dklawson]

If you are really good and confident no air is in other parts of the system you can indeed do a partial bleed. However, it takes only a little more effort (and fluid) to bleed the whole system. If you do the whole system you will know that there is no trapped air AND you will have removed all the old dirty fluid that was in the system.

 

[Gerard]

I agree, especially the part about flushing all the old fluid out. Moisture, debris and degraded rubber bits will migrate through the system if your old fluid is contaminated with same, which it likely is.

If you are really good and confident no air is in other parts of the system you can indeed do a partial bleed. However, it takes only a little more effort (and fluid) to bleed the whole system. If you do the whole system you will know that there is no trapped air AND you will have removed all the old dirty fluid that was in the system.

 

[bugedd]

I had the brakes bled last year, but I suppose you're right. I have little else to do right now with the rain and being sick. About how many pumps does it take for the fresh fluid in the reservoir to rear the rear caliper?

 

[JPSmit]

how many pumps does it take for the fresh fluid in the reservoir to rear the rear caliper?

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