Brake Fluid change, without T4, using the "gravity" method
 

Hi all

There's been a couple of threads recently re brake fluid bleeding/changing.

On MikeTrident's informative "Brake Fluid" thread, Marinabrian posted about a "gravity" bleed method he uses which I'd never come across before.

I'd always used the " rubber tube with a split in it, and pump the brake pedal" method on my previous classic cars - no ABS, dual circuit, T4-option modern stuff on any of them! :D

Today provided the opportunity for another "satisfying job whilst on lockdown" and I had a go at the full fluid change using Brian's gravity method.

It worked perfectly, so I thought I'd post up a separate thread for anybody who might be interested but perhaps is also unaware of this method, or following the other threads.

What I did, and some comments.....

Background

I've had my current V6 for two years now. I'm not sure of all it's previous service history but I know prior to me, it had sat in a garage back yard for 5 years and not moved. :eek: :eek:
The calipers had been painted red at some time and paint was covering the bleed nipple/caliper joints too, so probably the fluid was much older than 5 years.

Here we go

1 . About a week a go I started wirebrushing and PlusGassing all the bleed nipples.

2 . First of all I used a large syringe to take out fluid from the Master Cylinder, down to the bottom of the "neck" of the cylinder, and put fresh in .. just to start the supply of new fluid from the start.

3 . I started with the nearside rear wheel. Jacked up, axle stand in place, more PlusGas/ wirebrushing and, picking up on another tip from a thread, I heated up the caliper for 5 seconds with a small gas blowtorch and squirted the nipple again with PlusGas to cool it down.

4 . Using a snug fitting, hexagonal 9mm socket and a T bar so as to apply even pressure (another thread warned about using an open or ring spanner as the twisting is harder to keep "central"), holding my breath and fretting for a couple of seconds as my twisting effort increased, the nipple came undone rather than snapping off or rounding off. Result!

5 . The same procedure worked for the other three nipples too. I was SO chuffed about this bit. So I highly recommend the PlusGas / wirebrush and gentle heat steps if (like me) you are concerned about the nipples snapping off.

6 . A clear length of tubing was pushed onto the nipple and into a clear container, and loosening the nipple half a turn saw old fluid rising up in the tube and then over the top of the loop. See picture.

7 . The next stage took AGES.... I wasn't expecting fast flowing fluid but it was SOOOOO slow! It probably took an hour and a half for the first half a litre of fluid to end up in the container. Perhaps that's indicative of the age/ thickness / viscosity, I don't know. It did get a tiny bit quicker as (I guess) the new fluid displaced the old but God it was slowww. :duh: I can understand why some folk on here use a pressure system to "push" the fluid through....

8 . As most people will know, the next caliper was offside rear, then nearside front and finally offside front.

9 . Because of the slow draining process you get the chance to do other little jobs. Just had to check the Master Cylinder every 5 minutes and keep it topped up with fresh fluid.

10. The front calipers drained down faster than the rear, so do remember to keep an eye on the Master Cylinder. I didn't let the new fluid level drop anywhere near the "neck" of the cylinder.

11. I can understand that T4 might be needed to get the last 40ml or so out of the ABS bit, but the brake pedal is rock hard so I'm happy (actually, it was good before the change but at least I know the fluid is fresh and I didn't seem to c0ck up anything else!) :D

I've attached a picture of some of the old fluid (plastic container) and new fluid (see the jar next to it) so there's a definite difference in colour. Was the old fluid REALLY bad? ... had it been changed before? :shrug: What do you think?

In summary although very slow, this method is definitely a useful one. But of course if any of the nipples had snapped off I would not feel as smug as I do this evening! :D:D:D

Sorry for the long thread ... hope it's useful at some time for someone else.

Stay safe folks

John

Lovely post :D

I tend to use the gravity method quite a lot as I’m normally working alone when I’m doing these jobs & I find it’s usually very successful with 75/ZTs I have however recently bought a pressure bleeder but not one of those horrible ones you attach to a tyre valve, I hate those things, I bought the type that’s a round pot bellied container with a pump handle on the too

I'm now plus gassing bleed nipples and what a clever idea, put the lid on the jar with a hole big enough for the pipe from the bleed nipple... why did I not think of that?

macafee2

It's clearly very slow and therefore easier to manage single-handed, but what advantage does a 'gravity' bleed have over a 'pressure' or 'vacuum' bleed? I can't put my finger on it.


TC

It saves the expense of a pressure or vacuum pump! :D

Oh ... and when Mr Amazon knocks on the door it saves the wife saying "OMG WHAT have you bought for your car NOW?!"

:D :D :D

John

Ah, I see. It was the mention of 'without a T4' in the title that threw me.


TC

Was it obvious from the colour change when the new fluid had reached each caliper?
How much new fluid did you use?

post 13 shows a/the sequence for bleeding
https://www.the75andztclub.co.uk/for...=217015&page=2

macafee2