• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

M/C bench bleed

rrTor-Red

FBBO Gold Member
FBBO Gold Member
Local time
6:13 PM
Joined
Sep 1, 2010
Messages
2,313
Reaction score
858
Location
USA
I have a new M/C installed and lines hooked up. It's like a 50/50 census as people say to bench bleed it BEFORE putting it in the car. My issue is this: Why bleed it first just to do it all over again? Also, I don't want to spill fluid on a freshly painted car. Guess, if I have to, take it back off and do it. What do you do?
 
It's usually easier to bench bleed the MC before installing it but you can also do it on the car. It'll just take a bit longer to get the air out of the MC and the lines too. When you bench it, all the air is out of the MC before you put it on.
 
Thanks a bunch, Cranky.
 
I've never ever bench bled anything and never had any trouble bleeding my brakes our hyd clutch. To me it's just taking a chance of dripping fluid everywhere that isn't necessary?
 
Wont Dot 5 Fluid, not Eat through paint?
 
What is a good fluid to use? I hear about DOT 5 but not sure if I've ever seen it in auto stores.

- - - Updated - - -

I've never ever bench bled anything and never had any trouble bleeding my brakes our hyd clutch. To me it's just taking a chance of dripping fluid everywhere that isn't necessary?

Exactly what I was thinking.
 
I bench bleed the master cylinder on a vise before installing it. No muss no fuss. It gets all the air out of the mc and yes, you will get a bit of air in the disconnected lines. But bench bleeding is allot quicker than second guessing yourself on skipping this step.
 
I always use DOT5 silicone fluid on all my Hot Rods, mostly because it does not eat paint. I do bench bleed M/C's to save some time. I have been successful in hooking up the distribution at that point, and then, bleeding at that location,by untightening and pressure and tightening at that point. Basically bleeding at the line connection and catching it with a rag. Works Great for me.
 
If you bench bleed your MC either off or on the car, you will spend a lot less time under the car. I've got an old nasty moving blanket I put under the MC and over the fender so I don't make a mess or screw up the paint. I use DOT3 but if you use DOT5 that's fine, just don't mix 'em together.
 
I think that when you bench bleed you push the piston in as far as it goes. When it's mounted on the car the piston may not go all the way and that small amount of trapped air will give you a fit getting it out through the wheel cylinders.
I bought a cheap kit for bench bleeding. Has an assortment of fittings and short plastic hoses to recycle the fluid into the reservoir.
 
i bench bled mine as well. put an old blanket as Moparsmitty said, and went one step farther with painters plastic. i had to configure a contraption to hold the m/c with wire and a 2x2 to hold it near the mounting surface on the firewall while getting under that blah, blah, blah dash.
 
It is your choice just make sure the MC is level so you get all the air
 
I think that when you bench bleed you push the piston in as far as it goes. When it's mounted on the car the piston may not go all the way and that small amount of trapped air will give you a fit getting it out through the wheel cylinders.
I bought a cheap kit for bench bleeding. Has an assortment of fittings and short plastic hoses to recycle the fluid into the reservoir.

Thank you ! I think you answered a problem I have had that has bugged me for some time now . I was hoping that in time, it would work out the air bubbles on it's own.................................MO
 
I think that when you bench bleed you push the piston in as far as it goes. When it's mounted on the car the piston may not go all the way and that small amount of trapped air will give you a fit getting it out through the wheel cylinders.
I bought a cheap kit for bench bleeding. Has an assortment of fittings and short plastic hoses to recycle the fluid into the reservoir.

Exactly. My pedal does not quite bottom out mc, so I'm presumably one of those guys who would have had a hard time bleeding the brakes.

Also, if I were you I would just gravity bleed all 4 wheels at the same time. Works great. I have 4 mason jars and 4 lengths of 1/4" tubing and just let them drip to purge old fluid. Once the new fluid is coming out, I get under each corner and check for bubbles, then close the bleeders when they look good. Works perfectly and let's you get other things done while the brakes bleed themselves. Just remember to keep an eye on the reservoir.
 
Exactly. My pedal does not quite bottom out mc, so I'm presumably one of those guys who would have had a hard time bleeding the brakes.

Also, if I were you I would just gravity bleed all 4 wheels at the same time. Works great. I have 4 mason jars and 4 lengths of 1/4" tubing and just let them drip to purge old fluid. Once the new fluid is coming out, I get under each corner and check for bubbles, then close the bleeders when they look good. Works perfectly and let's you get other things done while the brakes bleed themselves. Just remember to keep an eye on the reservoir.

When working by yourself we find ways to get it done!
I've done what you said with a clear jar or bottle. I've even done one wheel at a time (doing farthest from MC and work your way back) and pumping the brake knowing that the container has plenty of fluid and the reservoir too so not to suck any air. Works!
Some vehicles are harder than others. These new cars with the ABS systems really get the trapped air / spongey peddle. I've never had to use the "pressurised" bleeding apparatus yet but I guess they do better?
 
When working by yourself we find ways to get it done!
I've done what you said with a clear jar or bottle. I've even done one wheel at a time (doing farthest from MC and work your way back) and pumping the brake knowing that the container has plenty of fluid and the reservoir too so not to suck any air. Works!
Some vehicles are harder than others. These new cars with the ABS systems really get the trapped air / spongey peddle. I've never had to use the "pressurised" bleeding apparatus yet but I guess they do better?

Dang right, we do. I have a pressure bleeder because of my recent brake issues. I thought maybe some air was getting caught up in my line lock so I tried the pressure bleeder but for our old cars it does no better than the old gravity or "pump and squirt" method lol.
 
Makes a little more sense to me now to bench bleed to ensure getting all of the air out. The new on is on my car with new SS lines, etc. I've never even put fluid in it yet for this reason because I figured why do it twice. Now I will be benching. Leaning towards getting DOT 5 fluid if I can find it

Thanks guys!
 
I've never installed a mc without bench bleading first, its just standard procedure.
 
Please bench bleed, whether you do it on or off the car just do it ! I do mine on the car. I use to extra master cylinder lines and loop them back to the reservoirs, a few pumps of the pedal and done. If you get some to pump the pedal for you, you can watch for bubbles. Sometimes a quick, fast pump is needed for getting the last little bubble out of the piston if the pedal wont bottom it out .....
 
Auto Transport Service
Back
Top