Newbie Question: what happens if I drain all the brake fluid

[AdrianBrewster]

Replaced my brake lines with some extended ones. I had some fitment issues and while I was fussing with it I apparently I let too much brake fluid drain out. Every video I’ve watched suggests that you always keep an eye on the fluid level and not let it drop too low. I am already going to have to bleed all of the brakes. Is this really an issue? Can I just fill it up and bleed the brakes on all 4 corners or do I need to do anything additional? Do I need to bleed the master cylinder or is bleeding at the wheels sufficient?

 

[Devbot]

Yes you will need to bleed the master. And in doing so, will probably need to bleed the lines all over again.

 

[phattyduck]

The procedure is different whether 01/02 or 96-00.

Here's the '99 procedure:

And yes, if the master went dry, you'll have some extra work to do. See above. Also expect air bubbles in your ABS unit, which may be hard to bleed out.

Good luck - and next time, put a cap in/on the line when you open the system up...

-Charlie

 

[AdrianBrewster]

That picture of the shop manual was very helpful. Thank you! I do have a 99 so it sounds like bleeding the master should be fairly easy.

I actually did have it capped off. That’s the frustrating part. I bought some vacuum caps off Amazon, capped the hardline, went over to my bench to try and fix the extended brake line fitment and the cap apparently failed because when I came back to the 4Runner there was a puddle of brake fluid. It looks like it only drained from the rear of the reservoir. The front is still full. Seems off to me.

Is there a picture of the shop manual on how to bleed the abs unit?

 

[Brian.]

It looks like it only drained from the rear of the reservoir. The front is still full. Seems off to me.

Is there a picture of the shop manual on how to bleed the abs unit?

That would be an indicator that you have a bad plunger seal in the master, usually this is felt as a slow creep in the pedal once stopped and as the pedal is held firm. Granted, my knowledge is from the small engine world (motorcycles, atvs and the like) with only a Single chamber master, I've no clue how the secondary chamber would impact this... regardless, your master isn't performing as it should.


As for the ABS, somewhere in the '99 models the ability to actuate via techstream (toyota software, can be found for free online and the adapter to connect car to PC is about $20) became available, my 99 isn't one of them. So I "bleed" the ABS by doing the normal brake bleed, then getting the ABS to trigger (slamming on brakes while on a loose surface, I have a1/2 mile gravel driveway that works) a few times, then doing the normal brake bleed again. You burn through some brake fluid, but it's simple enough.

 

[Devbot]

Is there a picture of the shop manual on how to bleed the abs unit?

I could be wrong, but I think the method is to just go a slick road (gravel, dirt, mud, what have you) and purposely try to lock them up a few times so the pump cycles. Then afterwards you bleed the lines yet again :brick:

 

[Bad Luck]

That would be an indicator that you have a bad plunger seal in the master, usually this is felt as a slow creep in the pedal once stopped and as the pedal is held firm. Granted, my knowledge is from the small engine world (motorcycles, atvs and the like) with only a Single chamber master, I've no clue how the secondary chamber would impact this... regardless, your master isn't performing as it should.


As for the ABS, somewhere in the '99 models the ability to actuate via techstream (toyota software, can be found for free online and the adapter to connect car to PC is about $20) became available, my 99 isn't one of them. So I "bleed" the ABS by doing the normal brake bleed, then getting the ABS to trigger (slamming on brakes while on a loose surface, I have a1/2 mile gravel driveway that works) a few times, then doing the normal brake bleed again. You burn through some brake fluid, but it's simple enough.

It’s more likely because the front and rear brake fluid circuits get fluid from different areas of the brake fluid reservoir. There is a shallow divider between the front and rear fluid intakes in an attempt to keep some fluid available to the front or rear in the case of a fluid leak on either the front or rear.

 

[gamefreakgc]

That picture of the shop manual was very helpful. Thank you! I do have a 99 so it sounds like bleeding the master should be fairly easy.

I actually did have it capped off. That’s the frustrating part. I bought some vacuum caps off Amazon, capped the hardline, went over to my bench to try and fix the extended brake line fitment and the cap apparently failed because when I came back to the 4Runner there was a puddle of brake fluid. It looks like it only drained from the rear of the reservoir. The front is still full. Seems off to me.

Is there a picture of the shop manual on how to bleed the abs unit?

If you have a 96-98 with the old ABS system (a rectangular box with a bunch of brake lines in and out) it can only be bled successfully with the engine running. I just had a heck of a time getting a small bubble out of mine that was causing a soft pedal. There is no procedure in the FSM for bleeding the ABS, it just says to bleed the lines until there's no more air coming out. Except that the ABS unit sits so high up that it's very hard to force a bubble all the way down to the brake caliper.

 

[AdrianBrewster]

If you have a 96-98 with the old ABS system (a rectangular box with a bunch of brake lines in and out) it can only be bled successfully with the engine running. I just had a heck of a time getting a small bubble out of mine that was causing a soft pedal. There is no procedure in the FSM for bleeding the ABS, it just says to bleed the lines until there's no more air coming out. Except that the ABS unit sits so high up that it's very hard to force a bubble all the way down to the brake caliper.

I have a 99 so hopefully that makes it a little easier. I will say, only the back part of the reservoir is empty. The front is still pretty full. Which part of the reservoir runs to the ABS module? Fingers crossed it’s the part that still has some fluid in it.

The back part of the reservoir is dry and I’m leaving it dry until I finish my tundra brake upgrade so I don’t have to worry about the mess.

 

[brillo_76]

I have a 99 so hopefully that makes it a little easier. I will say, only the back part of the reservoir is empty. The front is still pretty full. Which part of the reservoir runs to the ABS module? Fingers crossed it’s the part that still has some fluid in it.



The back part of the reservoir is dry and I’m leaving it dry until I finish my tundra brake upgrade so I don’t have to worry about the mess.

All brakes lines run through abs. I belive only the 01 and 02 have the integrated abs and master cylinder unit.

Sent from my SM-A505U using Tapatalk

 

[gamefreakgc]

I have a 99 so hopefully that makes it a little easier. I will say, only the back part of the reservoir is empty. The front is still pretty full. Which part of the reservoir runs to the ABS module? Fingers crossed it’s the part that still has some fluid in it.

The back part of the reservoir is dry and I’m leaving it dry until I finish my tundra brake upgrade so I don’t have to worry about the mess.

The problem is when you take off the master cylinder to bench bleed it, it will still have air in the lines. That air will get pushed into the ABS unit and then you'll have to bleed it out. You will know if you have air in the system if you bleed the brakes with the engine off, you'll hear either crackling noises in the line or a louder groan or creak. It should be whisper quiet.

 

[AdrianBrewster]

The problem is when you take off the master cylinder to bench bleed it, it will still have air in the lines. That air will get pushed into the ABS unit and then you'll have to bleed it out. You will know if you have air in the system if you bleed the brakes with the engine off, you'll hear either crackling noises in the line or a louder groan or creak. It should be whisper quiet.

Do I have to bench bleed the master cylinder? Can I bleed it on the vehicle and then hopefully avoid exposing air to the ABS module?

 

[Bad Luck]

Do I have to bench bleed the master cylinder? Can I bleed it on the vehicle and then hopefully avoid exposing air to the ABS module?

You can bleed the master cylinder in the vehicle with the help of an assistant, but you already have air in the brake lines between the master and the abs module. There is no avoiding that you will need to bleed the master, bleed all the brake lines, go activate the abs pump, rebleed all the lines, repeat as necessary. Make sure you keep an eye on the fluid level in the master. If you run it dry again you will need to start all over.