Golf Mk3 brake unions - davemar
I'm just about to tackle replacing the brake pipes (they are corroded) on a Mk3 Golf. Looking at the 6-way union block in front of the bulkhead where the 2-in and 4-out pipes go it appears they are all M10 brake unions as you would expect...except one. One of them appears to be larger, it took a 13mm spanner instead of a 11mm spanner. The pipe is still normal 3/16" gauge, and I can't imagine an imperial union would be used. Is there such thing as a M12 brake union? I'm guessing this particular one was tapped out at some point in the past, so has a larger union on it.

I haven't crawled under the car to look at the connections onto the calipers. Would I be right in assuming that they'll also be M10 unions onto the flexible hoses too?

Golf Mk3 brake unions - yorkiebar
Its a regular size used a lot by ford, peugeot, vw etc etc.

Most motor factors will supply them easily enough.

Be careful it has correct 3/16 (4.75mm) pipe size because its also available in 1/4 and other sizes.
Golf Mk3 brake unions - pmh
Could it be original specn at manufacturing time so that wrong assembly is not possible?
--

pmh (was peter)


Golf Mk3 brake unions - davemar
That's a good point, as the two rear pipes run in parallel to a box near the rear-left trailing arm, it would be easy to get them mixed up. It turned out to be a 12mm union in the end, which I've managed to get hold of from my local trust motor factors.

I've now got the problem of trying to remove the pipes on the rear arms which are proving difficult to get off. One of the unions has rounded so the spanner won't grip, and I can't get either free from the flexible hose as they are both rusty and seized and generally horrible.
Golf Mk3 brake unions - madf
Mole grips work wonders on rounded threads after liberal dosing with vinegar (better imo than penetrating oil as more searching and the acetic acid appears to disslove some rust) and left overnight to soak.
madf
Golf Mk3 brake unions - piston power
as mentioned mole grips but better if you have 2 pairs, one on the nut the other on the steel part of the flexi and work it back& forth. hope your using one of those brake pipe flares that go in the vice much easier than the manual thing imop!!! good luck
Golf Mk3 brake unions - yorkiebar
All sound advice.

But if the hoses are as bad as they sound then please consider changing them too (not expensive) and it will make job a lot easier for removal too!
Golf Mk3 brake unions - Peter D
If this is a M/N type plate MK II I wold be changing the rear flexi's under the beam the rear slave cylinders which will be weeping and the rear pipework, and the front flexi's and associated pipework. Regards Peter
Golf Mk3 brake unions - davemar
It's a K-plate Mk3. I'm going to change the flexi pipes too, mainly because I can't remove the the metal pipes from those either. The trouble is the other end of the flexi pipes which connect to the pipes on the chassis side (rather than the trailing arm side) are also corroded badly and won't undo. No hope of getting a spanner to grip on those. They are attached via a piece of metal to the underside of the car. It would be nice if that pit of metal was removable, but that's also welded to the body, so can't remove that easily. In short I'm a bit stuck at the moment!! I tried some mole grips on the union that connects to the drum (just because it's the easiest to get to) and that was no good either, it just ground off more metal from the union.

If it was my own car in my garage I would get the angle grinder and MIG welder out and deal with these pipe mountings, but I'm away from power in this case (which also makes drilling things out pretty much impossible).

Golf Mk3 brake unions - yorkiebar
Sounds like you may need to cut these pipes off to free them from the guides and replace them too.

Not expensive just messy and awkward !
Golf Mk3 brake unions - davemar
I'll try and attack them with a hacksaw, though the left-hand is quite awkward with the brake compensator block (or whatever it is with all the pipes going into it) in the way. Hopefully I can put some new unions of the end of the remaining good pipes if I only nip a few mm off the end.

The nipples on the drums also look very rusty and potentially tough to remove.

Golf Mk3 brake unions - sierraman
I would not worry about rusty nipples,just replace the cylinders.They are not expensive and it would be 'spoiling
the ship' to leave them.I bet they will be wet anyway.Re 'Hopefully I can put some new unions of the end of the pipes',if the pipes are steel they will be very difficult to flare without using a vice mounted tool.I often find the easiest way,in the long run,is to replace the steel with Kunifer,a bit more work but it makes it all a lot easier.

 

Value my car