P38A Brake bleeding disaster

Hi everyone,

Just going to make this quick post before I completely lose my mind (already lost it in the garage and brake fluid is now everywhere)

Reviving a 1998 4.6 P38, been off the road around 12 years.

Brake calipers were sticking, as preventative maintenance I have replaced all the calipers. Flexible brake hoses look in good condition, new copper crush washers installed when bolting to calipers. New brake pads and discs.

Start the bleed procedure as per rave manual. I have 3 P38s and have performed this procedure by the book 3 times without any problems on the other ones...

Get to the end of the procedure, brake pedal feels terrible, mushy and no weight to it (despite there being no bubbles once finished each step)

Do the whole procedure again, brake pedal feels worse, noticeably went wrong this time when we started to use the pump to bleed the rear calipers (as per manual)

Going crazy, decide to start the procedure again...

Now at the first step, bleeding the lower bleed screw on the reservoir (after letting it first drip out), Im constantly getting bubbles from this lower bleed screw. Because of this, I am unable to bleed the brakes at all as I cant even get past the first step.

Please does anyone have any idea what's going on here, brakes were actually working pretty good for the couple of test drives I did with the vehicle, just sticking unfortunately even after removing all brake pads, cleaning carriers, greasing etc.

I have heard that o rings have to be replaced in the modulator for pre-facelift models, 1998 and prior, but from what I've read this only effected up until 1997.

If you've done it before with success then you should know what you're doing and are doing all 3 nipples in the right order. If you keep getting bubbles then assuming you're keeping the reservoir full then it must be sucking air in somewhere?

I never bled with the pump or diagnostics. Never had help either or problems, but know if you get air in the modulator it can be a serious PIA. It’s the nipple at the back people always forget.

kermit_rr said:

If you've done it before with success then you should know what you're doing and are doing all 3 nipples in the right order. If you keep getting bubbles then assuming you're keeping the reservoir full then it must be sucking air in somewhere?

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Yeah, I only wanted to mention that I did it before as I understand one of the most common problems is people don’t follow the procedure and then come crying for help.

I’m certainly doing all the nipples in the right order, and I’ve double checked they’re all tight. Fluid level always kept topped up as well. I’ll just have to take a brake from it (no pun intended) for now and try again later. So far though, I went out after posting this, doubled checked all the nipples were tight, and then started the procedure again - but had the same problem, constant air out of the lower bleed screw.

If you can clean up best as, perhaps put some cardboard underneath to find drips, go have a cup of tea and see what you comeback to? I would expect air getting in means it would drip somewhere

RangeRoller dt said:

If you can clean up best as, perhaps put some cardboard underneath to find drips, go have a cup of tea and see what you comeback to? I would expect air getting in means it would drip somewhere

Click to expand...

I agree, this is probably the best course of action. More than likely has to be a leak, I was just hoping it’s not a modulator off job as I’ve done it in the past and it’s not fun. Hopefully something shows itself, otherwise I think I’m going to try bleeding just the reservoir only, lower nipple, outer and then inner to see if we get any improvement.

Nipples are tight.. ooerr!!
Take it out and make sure the sealing surfaces are clean?

Was your helper following the procedure correctly ?

kermit_rr said:

Nipples are tight.. ooerr!!
Take it out and make sure the sealing surfaces are clean?

Click to expand...

Good idea, even though they are tight they may not be sealing correctly.

pwood999 said:

Was your helper following the procedure correctly ?

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Yes, they were reading it and doing the pumping/ignition when necessary. Honestly after thinking about it for a few hours, im hoping that maybe since we were doing all the bleeding over, and over and over again, that the brake fluid was starting to get aerated and would never bleed out correctly. Will be having another go off it after Christmas day, thanks for the suggestions!

MikeFl4 said:

Hi everyone,

Just going to make this quick post before I completely lose my mind (already lost it in the garage and brake fluid is now everywhere)

Reviving a 1998 4.6 P38, been off the road around 12 years.

Brake calipers were sticking, as preventative maintenance I have replaced all the calipers. Flexible brake hoses look in good condition, new copper crush washers installed when bolting to calipers. New brake pads and discs.

Start the bleed procedure as per rave manual. I have 3 P38s and have performed this procedure by the book 3 times without any problems on the other ones...

Get to the end of the procedure, brake pedal feels terrible, mushy and no weight to it (despite there being no bubbles once finished each step)

Do the whole procedure again, brake pedal feels worse, noticeably went wrong this time when we started to use the pump to bleed the rear calipers (as per manual)

Going crazy, decide to start the procedure again...

Now at the first step, bleeding the lower bleed screw on the reservoir (after letting it first drip out), Im constantly getting bubbles from this lower bleed screw. Because of this, I am unable to bleed the brakes at all as I cant even get past the first step.

Please does anyone have any idea what's going on here, brakes were actually working pretty good for the couple of test drives I did with the vehicle, just sticking unfortunately even after removing all brake pads, cleaning carriers, greasing etc.

I have heard that o rings have to be replaced in the modulator for pre-facelift models, 1998 and prior, but from what I've read this only effected up until 1997.

Click to expand...

Sounds like air got drawn into the modulator somehow. Bleed the modulator using 3 litres of fluid (with an Ezibleed kit or similar to make it easy on yourself) and then start again. Top up fluid at each step because it can get lower than you think.

MikeFl4 said:

Yes, they were reading it and doing the pumping/ignition when necessary. Honestly after thinking about it for a few hours, im hoping that maybe since we were doing all the bleeding over, and over and over again, that the brake fluid was starting to get aerated and would never bleed out correctly. Will be having another go off it after Christmas day, thanks for the suggestions!

Click to expand...

Is the sphere good ,its not leaking a tiny bit of nitrogen into the system,just a thought..

dubbleRR said:

Is the sphere good ,its not leaking a tiny bit of nitrogen into the system,just a thought..

Click to expand...

Not that much i doubt

Grrrrrr said:

Sounds like air got drawn into the modulator somehow. Bleed the modulator using 3 litres of fluid (with an Ezibleed kit or similar to make it easy on yourself) and then start again. Top up fluid at each step because it can get lower than you think.

Click to expand...

dubbleRR said:

Is the sphere good ,its not leaking a tiny bit of nitrogen into the system,just a thought..

Click to expand...

kermit_rr said:

Not that much i doubt

Click to expand...

Thank you all for the replies! I finally got a chance today to have another go off it.

So to answer your comments first.

Yes, certainly got air in the modulator, I bought a 5l drum of brake fluid so no issues there. Don’t have an easy bleed kit but I was able to get around that, will detail below.

Sphere is certainly bad, pump runs on the second pedal press but before bleeding the brakes felt fine. Weak sphere shouldn’t stop me from completing the first step of bleeding the modulator though, will just affect breaking power.

So, I had a look over the whole system after leaving it on the lift for a few days. No leaks thankfully, so looks like we are ok on that front. Pedal still had no resistance when I tried it first.

Tried the first step of bleeding again, same symptoms as before, constant bubbles and fluid, never a constant fluid stream. So decided to bag the Rave method and do it my own way. Had my assistant pump up the pedal 4-5 times, opened the lower bleed screw on the reservoir - fluid shoots out in the bleed tube. Do this a few more times, now we were only getting fluid and no bubbles. Finish it off by doing a couple of pumps following the Rave method (nipple open, pump pedal, nipple closed etc) and now no longer getting air.

Move onto the front left caliper, instantly complete loss of the pedal feel. We decided to keep going following the method anyways. Did all the steps, no bubbles on all calipers and modulator, so certainly no air in the system to be found using the Rave method. Pedal still light though.

So we decided to scrap the Rave method and do what felt right. Bled out the modulator again by pumping up pedal and opening the screw. Bunch of bubbles came out, repeated until the pedal was nice and solid (and there were no bubbles). Let the accumulator fill up with ignition on, topped off reservoir and called it good.

It’s got good pedal feel now (just like my other P38s), stops good and normal. Took it for a quick drive, felt great, nothing odd to report. Checked over everything when we came back and it all was good so stuck back on all the dust caps.

I know what some of you will think “there’s no way you can properly bleed the brakes on a P38 without following the procedure 100%”.
Before experiencing this particular P38 I would have to agree. Well unfortunately, the procedure just wasn’t working on this occasion.

If the brakes were not working beforehand, I would have dug deeper and probably removed the modulator/rebuilt the master cylinder. But since the brakes were perfect before (just sticking rusty calipers) I couldn’t see any reason how a component could have just failed (master cylinder/modulator) by just removing and flushing with new brake fluid.
It’s parked in the garage now on its wheels this time, I’m looking forward to driving it some more over the next few days. If there are any negative developments in the brakes, I’ll update this post. Otherwise, just another P38 fixed and back on the road for now!

For air inside the modulator you got off easy that time. Well done

MikeFl4 said:

Thank you all for the replies! I finally got a chance today to have another go off it.

So to answer your comments first.

Yes, certainly got air in the modulator, I bought a 5l drum of brake fluid so no issues there. Don’t have an easy bleed kit but I was able to get around that, will detail below.

Sphere is certainly bad, pump runs on the second pedal press but before bleeding the brakes felt fine. Weak sphere shouldn’t stop me from completing the first step of bleeding the modulator though, will just affect breaking power.

So, I had a look over the whole system after leaving it on the lift for a few days. No leaks thankfully, so looks like we are ok on that front. Pedal still had no resistance when I tried it first.

Tried the first step of bleeding again, same symptoms as before, constant bubbles and fluid, never a constant fluid stream. So decided to bag the Rave method and do it my own way. Had my assistant pump up the pedal 4-5 times, opened the lower bleed screw on the reservoir - fluid shoots out in the bleed tube. Do this a few more times, now we were only getting fluid and no bubbles. Finish it off by doing a couple of pumps following the Rave method (nipple open, pump pedal, nipple closed etc) and now no longer getting air.

Move onto the front left caliper, instantly complete loss of the pedal feel. We decided to keep going following the method anyways. Did all the steps, no bubbles on all calipers and modulator, so certainly no air in the system to be found using the Rave method. Pedal still light though.

So we decided to scrap the Rave method and do what felt right. Bled out the modulator again by pumping up pedal and opening the screw. Bunch of bubbles came out, repeated until the pedal was nice and solid (and there were no bubbles). Let the accumulator fill up with ignition on, topped off reservoir and called it good.

It’s got good pedal feel now (just like my other P38s), stops good and normal. Took it for a quick drive, felt great, nothing odd to report. Checked over everything when we came back and it all was good so stuck back on all the dust caps.

I know what some of you will think “there’s no way you can properly bleed the brakes on a P38 without following the procedure 100%”.
Before experiencing this particular P38 I would have to agree. Well unfortunately, the procedure just wasn’t working on this occasion.

If the brakes were not working beforehand, I would have dug deeper and probably removed the modulator/rebuilt the master cylinder. But since the brakes were perfect before (just sticking rusty calipers) I couldn’t see any reason how a component could have just failed (master cylinder/modulator) by just removing and flushing with new brake fluid.
It’s parked in the garage now on its wheels this time, I’m looking forward to driving it some more over the next few days. If there are any negative developments in the brakes, I’ll update this post. Otherwise, just another P38 fixed and back on the road for now!

Click to expand...

I would be tempted to give that front left caliper a good look. Make sure the bleed nipple isn't leaking or the seals on the caliper itself.

Grrrrrr said:

I would be tempted to give that front left caliper a good look. Make sure the bleed nipple isn't leaking or the seals on the caliper itself.

Click to expand...

Yeah, I just went out now to check over everything after it being left overnight. No fluid leaked out anywhere I can see and the brake pedal still feels the same so I’ll call it good for now.