Best practice for swapping brake lines and calipers?

[youngsyr]

Hi all, just about the swap the front brake calipers on my Porsche 996 turbo for the larger OEM six pots. Thought I'd take the opportunity to replace the 20 year old OEM brake hoses too.

Looking at them, I could attach the new hoses to the new calipers and fill and bleed these very easily off the car - just crack the bleed nipples and use a large syringe to inject brake fluid into the inboard side of the new hoses until fluid comes out of the bleed nipples. Then close them and keep the new hose above the caliper. Hey presto - no air in the calipers.

Problem comes when it comes to connecting the new hoses to the car's hard lines. Now way to stop a little air getting in here, I don't think.

So, my question is - am I wasting my time pre-filling the brake calipers and should I just leave them dry, fit them to the car and then bleed the calipers as normal?

Thanks!

[shakindog]

Fit calipers then bleed them up.
faster,less hassle and less brake fluid all over the place.

As it’s a pain to clean up and will corrode paint if not cleaned up fairly quickly.
That’s if the new calipers are painted.

[youngsyr]

shakindog said:

Fit calipers then bleed them up.
faster,less hassle and less brake fluid all over the place.

As it’s a pain to clean up and will corrode paint if not cleaned up fairly quickly.
That’s if the new calipers are painted.

Thanks - the mess and eating paint were the aspects that made me think that filling them off the car might be better - would be very simple to ensure minimal spillage at the caliper side and could be cleaned up quickly. The drips would probably be more where the brake hoses connect to the hard lines deep inside the wheel arch.

[donkmeister]

From bitter experience, only have the flex/caliper disconnected for the minimum of time you need to do the swap, or cap off the pipe if you need to leave it off.

I once made the mistake of leaving a caliper off whilst waiting on parts and after several weeks disconnected it went from being a 5 minute bleed job to a ball-ache as the fluid had slowly syphoned itself out of the system and drained the ABS block. Not fun.

[youngsyr]

donkmeister said:

From bitter experience, only have the flex/caliper disconnected for the minimum of time you need to do the swap, or cap off the pipe if you need to leave it off.

I once made the mistake of leaving a caliper off whilst waiting on parts and after several weeks disconnected it went from being a 5 minute bleed job to a ball-ache as the fluid had slowly syphoned itself out of the system and drained the ABS block. Not fun.

Thanks - did you not realise that the system would syphon just by gravity?

[donkmeister]

youngsyr said:

donkmeister said:

From bitter experience, only have the flex/caliper disconnected for the minimum of time you need to do the swap, or cap off the pipe if you need to leave it off.

I once made the mistake of leaving a caliper off whilst waiting on parts and after several weeks disconnected it went from being a 5 minute bleed job to a ball-ache as the fluid had slowly syphoned itself out of the system and drained the ABS block. Not fun.

Thanks - did you not realise that the system would syphon just by gravity?

No... I'll blame a combination of cold weather and being pissed off with it, but I literally had no idea despite it being so obvious in retrospect.

I'll only do that once

[youngsyr]

donkmeister said:

youngsyr said:

donkmeister said:

From bitter experience, only have the flex/caliper disconnected for the minimum of time you need to do the swap, or cap off the pipe if you need to leave it off.

I once made the mistake of leaving a caliper off whilst waiting on parts and after several weeks disconnected it went from being a 5 minute bleed job to a ball-ache as the fluid had slowly syphoned itself out of the system and drained the ABS block. Not fun.

Thanks - did you not realise that the system would syphon just by gravity?

No... I'll blame a combination of cold weather and being pissed off with it, but I literally had no idea despite it being so obvious in retrospect.

I'll only do that once

Well, in the words of the great Tony Beets (gold miner): "All lessons cost money. Good lessons cost lots of money"!

I suspect the brakes will gravity bleed themselves if you just cracked the nipples and left the car for a week or two, with you topping up the reservoir as required.

[Pit Pony]

Upgraded front brake calipers on a mk2 cavalier once to mk3 cavalier GSi spec.

Somehow I dropped the copper washer and never realised. Went for a test drive and it all seemed fine. Then I noticed the brake fluid all over the wheel and inner wing and floor. Then I found the copper washer, still attached to the Old brake caliper.

Oh how we laughed.

[tr7v8]

My late fathers (gone 32 years) trick still applies. Remove reservoir cap, place plastic bag under lid reattach lid, fluid can't come out so it is in a vacuum.
This stops the brake pipe completely emptying. Less fluid to bleed out when the empty caliper & hose is attached.
Another point if the hoses haven't been moved since it was built be prepared for the hose to brake pipe to be solid & that means making a new brake pipe. I keep a reel of copper, brass unions spare just for this, you may be lucky.

[youngsyr]

Pit Pony said:

Upgraded front brake calipers on a mk2 cavalier once to mk3 cavalier GSi spec.

Somehow I dropped the copper washer and never realised. Went for a test drive and it all seemed fine. Then I noticed the brake fluid all over the wheel and inner wing and floor. Then I found the copper washer, still attached to the Old brake caliper.

Oh how we laughed.

Ooof. Did it wreck the paintwork?

[youngsyr]

tr7v8 said:

My late fathers (gone 32 years) trick still applies. Remove reservoir cap, place plastic bag under lid reattach lid, fluid can't come out so it is in a vacuum.
This stops the brake pipe completely emptying. Less fluid to bleed out when the empty caliper & hose is attached.
Another point if the hoses haven't been moved since it was built be prepared for the hose to brake pipe to be solid & that means making a new brake pipe. I keep a reel of copper, brass unions spare just for this, you may be lucky.

Will give your late Dad's plastic bag trick a try! RIP.

I'm hoping the hard brake line to brake pipe union will be tucked up out of the way and not too badly corroded etc. If it is, there are 3 connections I can try to undo to get the new caliper fitted, so hopefully one out of the 3 will shift!

[Krikkit]

tr7v8 said:

My late fathers (gone 32 years) trick still applies. Remove reservoir cap, place plastic bag under lid reattach lid, fluid can't come out so it is in a vacuum.
This stops the brake pipe completely emptying. Less fluid to bleed out when the empty caliper & hose is attached.
Another point if the hoses haven't been moved since it was built be prepared for the hose to brake pipe to be solid & that means making a new brake pipe. I keep a reel of copper, brass unions spare just for this, you may be lucky.

Only works if you're only disconnecting one at a time

If I'm replacing the flexis but want all 4 calipers off, I'll fold then zip-tie the old lines shut to help the fluid stay where it should, then you can attach one corner at a time.

That, or invest the effort in properly bleeding out the ABS etc, very often there's a service method for it. Sometimes a pressure bleeder is enough for simpler units.

[julianm]

I bought one of these recently & was pleased with how it avoided rounding off the union nuts on my Subaru - first time they had been touched in 14 years - neat idea - different sizes available - https://www.ebay.co.uk/itm/324343020748?hash=item4...

[lexusboy]

Get something to hold the brake pedal down whilst disconnecting the hoses as that will stop 99% of the brake fluid coming out