Double flare or bubble flare for 740 brakes

[Offgrid]

I'm having loads of problems sorting out the rear brakes on Cinderella. I'm concerned that I may have to cut the brake pipe where it joins the caliper hose. This means I will have to replace the union nut. That isn't too hard a job it seems, but I need to know the type of flare so that I can buy a kit. My feeling is that it is a metric bubble flare, but there is an alternative that was used at the time, and this is the double flare. Each needs its own specialist kit, and they aren't interchangeable. Does anyone know the flare type for a 1988 744 which came with a B200E engine?

[Forrest]

I’d be reasonably confident it will be a DIN or Bubble flare. That’s what I used on my 1997 V90 Mk1 with no problems. I think this may have been the article I read at the time when I was scratching my head over the matter.

http://www.fedhillusa.com/?page=flare

This is definitely the kit I bought and used.

https://www.amazon.co.uk/dp/B01B5GJ6KW

https://www.amazon.co.uk/dp/B084GT322T

https://www.amazon.co.uk/dp/B093DDT4YJ

https://www.amazon.co.uk/dp/B00U2IS6SS

https://www.amazon.co.uk/dp/B01MD1OO0K

Whilst that flare tool (which is not currently available) had excellent reviews and worked very well its one flaw is that it needs to grip quite a length of straight pipe. Therefore, if you have a bend too near to the flare you have to cut off you might not be able to fit both the nut and the tool onto the available straight pipe. This was the case with mine so I ended up re-making the whole section from the ABS module to flexible pipe in the wheel arch. This enabled me to put the nut and the flare on first and then make the final bend.

I have since also bought, but not yet used, this kit which looks more suited to forming a flare on a limited length of available pipe.

https://www.amazon.co.uk/gp/product/B00170V64G

It doesn’t have such good reviews though.

If you’re doing this sort of job for the first time, like I was, it’s worth practicing on a scrap piece of copper nickel tubing before doing the piece to which you are going to be trusting your life. I found using a bit of grease on the tool made it work better and form a more consistent flare.

Final tip is not to be tempted to use just copper tubing. It isn’t strong enough and might lead to an MOT fail, or worse.

[J liddy]

Excellent tutorial as always forrest I need to get the rear brake hoses changed on my 1995 900 volvo they are original so probably past there sell by date! But concerned if I attempt it myself I can't free the hose at the copper union end of the fitting !I have the flare nut spanners and access to a blow lamp from a retired plumber he said he can help as he knows safe temperature and pressure to put on that nut what are your thoughts?

[Offgrid]

Thanks Forrest for that excellent and informative post. In fact I have managed to undo the union nut, and on looking at the thread, |I see that there is a small unthreaded section on the end. I believe that confirms your opinion that it is a bubble end.
It might be worth considering my experience and difficulty with removing the hose section. The first thing I did was to cut the hose to allow me to remove the caliper. I then pumped the brake into a small plastic water bottle to examine the fluid. It looked black and evil, almost as if it was 35 years old.

I tried to undo the union nut with an 11mm flare wrench with no luck, and I was concerned that I would roll the corners on the nut, as I had managed to do this with the other end of the hose. I'd been spaying with WD40 for 3 or 4 days to try to make things easier. I then applied some heat with a plumbers torch, and the last bit of hose blew out of the coupling with a bang. Even after this, I had no luck in trying to unscrew the nut, and, in fact, the remaining bit of hose coupling started to revolve in the retaining bracket. I decided that I needed a decent pair of mole grips, as all of mine were a bit old and shaky. I bought this pair from Screwfix - https://www.screwfix.com/p/magnusson...9-225mm-/6610v . I was lucky as they were on sale with a £2 reduction. They were great, and did the job by holding the pipe end securely whilst I eased the flare nut back and forth to loosen it. It was a slow process undoing the nut, and was accompanied by a lot of squeaking. The pliers were probably a bit too large for the job, but they did provide a very secure grip on the hose remnants. The length was OK, but the jaws were difficult to get around the hose end, and it would have been better to use a pair with a slimmer curved jaw.

Take care to save the spring separator that is on the cable end,. You will need that ( or a new one ) when fitting the new hose.

[Forrest]

Originally Posted by J liddy

I have the flare nut spanners and access to a blow lamp from a retired plumber he said he can help as he knows safe temperature and pressure to put on that nut what are your thoughts?

If you've got someone with professional experience prepared to help definitely accept it.

The risk heating brake unions is that they will explode. Never heat one without at least opening the nearest bleed nipple and taking the cap off the fluid reservoir. As you can read in Offgrid's update above that isn't necessarily enough to avoid a bang.

I had a very similar experience to him. I was working on the front calliper nearest the ABS pump so I decided to remove the hard line from the car to work on the recalcitrant nut. Like Offgrid, I cut the flexible pipe leaving about an inch of rubber on the end of the nut. I first tried grips on the brass flare nut and a socket and impact driver on what was left of the flex-hose. This just caused the brass nut to spin and the grips quickly to grind the flats down to a cylinder. I then decide to heat what was left with a MAPP torch until I heard the threads crack. Well, the first sound was the almighty bang of remaining inch of rubber being propelled from coupling like a rubber bullet. I happened to have it pointing straight up. I never saw where the rubber bit landed, but my estimate from the power of the "shot" was the garden two doors down the road - and these are 1/3 acre plots!

I think what happens is that there is air trapped in the crimp where the rubber hose connects to the metal nut. This air probably also gets supplemented with traces of the flammable chemicals one has been using over the previous few days to try and loosen the threads. The effect is noisy and potentially dangerous. However, in my case, having recovered from the shock and ascertained that no one had been hit I was then able easily to unscrew what was left of the union! Of course, my exiting flare nut was useless having been ground down to a much smaller cylinder by the earlier attempt. My only reason for still wanting to get the union apart was the hope that I could get away with cutting a minimal amount off the flare and reuse the hard line.

[J liddy]

Hi forrest just asking if you woud be going to the V.O.C.national rally 30th June woud be good to see you there as its in your part of the country .I will be traveling from stoke on trent