Hydraulic brake bleed fail - try again or replace?

I'm only going to answer an aspect of your question; you can apply it to your brake how you wish.

Firstly, Certain Tekro models are fiddly to bleed but also feel like they need bleeding if the pads are worn down, so if you haven't put new pads in, I suggest you do that first.

When something like this comes into a commercial workshop and this amount of time has effectively been wasted, there's a strong argument for replacing the brake, giving better value for the customer and putting the mechanic's time back into another job that pays the bills.

When you are in another scenario where conservation of materials is important and you are time rich, you can play with bleeding this as long as you like, though you may already have learned all you need to know.

Meanwhile, SRAM Level, Shimano's entry-level hydro brakes and even new Tektro brakes are easy to set up, easier to bleed and don't cost very much, especially when compared to a workshop hourly rate.

There is a unifying theme with bleeding Tektro and similar brakes: disregard the written procedures, don't trust the contents of any bleed kit to give you what you need, aggressively modify the kit parts, and make up your own rules. I follow manufacturer instructions faithfully when they work, like for Shimano, but for the Tektros and Promaxes of the world, it's all choose your own adventure. I do this for money and I hate there being that level of subjectivity and uncertainty in the process, because bike mechanics deciding they're going to make up the rules is often what precedes bad service, but here it has to be embraced. There is no other choice if you want to provide good service because the instructions as writ and the bleed kits as offered are nonsense.

For the nipple fitting, put a tiny zip-tie around the hose where it fits on the nipple and cinch it down. Or, if the tubing is expanded from use (i.e. from being put on some other chunkier nipple), cut it down. Or rob a different size from other kit. Everything is chaos and it's on you to make a connection that doesn't leak.

For the sideways lever bleed port, do the entire bleed with the lever angled so the port is up. Position it and the other controls on the bar as needed to achieve this.

For your nipple quandaries, I would start by removing it and examining what's going on where it's supposed to be holding the fluid in. You might find a ruined or out of place seal/o-ring, or some other kind of damage or debris. The problem you're describing there is pretty odd, as would be needing to replace the bleed nipple completely with a syringe fitting. You might be able to get that to work and replace the nipple without disturbing things, or you might not, depending on how it's put together underneath.

Usually seals/gaskets being ruined, missing, or out of place shows up as failure to contain the fluid somewhere on the brake, like between the halves of the caliper for example. It's common to see the effect happen a little under pressure if you squeeze the lever repeatedly. If the problem really is a fluid leak, you should be able to find the fluid somewhere. I wouldn't settle on that conclusion otherwise, although it is true that it seems likely it's what's going if they develop excess travel from feeling good quickly over a short ride. You could try bleeding again and do a bunch of hard test squeezes after the caliper syringe is off but before you remove the lever one. For the most part, the system doesn't care whether the bike is in motion, so that will likely reveal any issues and save you the hassle of taking it all apart and riding it first.

Finally, be paranoid about the lever o-rings throughout being in place and in good condition. The bleed screws usually have them and the syringe fittings also have them, and they don't always stay in place on either, so sometimes you wind up with 0 or 2 where there's supposed to be 1.

They could have some kind of defect or broken/worn part. There are some brakes that basically don't work. But, two hydros demonstrating the exact same problem so soon on both brakes following a bleed hints pretty hard at there being some kind of problem with the bleed procedure, especially combined with that defect or wear not being apparent anywhere and also no visible signs of fluid leak. Also by the same token, be paranoid about the integrity of the hose connections whenever there are inexplicable problems with hydros. Hose connections are a place where a factory can do the same thing wrong twice.

I just got my front brake of the same model bled to a point where I'm happy. There's still a bit of sponginess, but the bike will stop.

A few tips I found helpful:

1. As Nathan said, put zip ties on all barb fittings. The tubing slipped off a barb twice before I smartened up and slapped some zip ties on there. Time to clean up two puddles of oil now...grrrrrrr

2. I'm assuming you have the same model as I do (Orion 4 piston), where the lever bleed port is on the reservoir pointing towards the handlebar at approximately a 45 degree angle. I followed Tektro's instruction to bleed with the lever parallel to the ground, unlike Nathan's recommendation to do it with the port skywards and lever pointing at the ground. With the Nathan method, I found that oil would always spill out of the port when unscrewing the syringe, while much less did with flat levers. However, I think I'm creating an air pocket in the reservoir with this method, so if you can get it to not leak, the Nathan method is probably better. An intermediate angle would likely be great too.

3. On the subject of leakage, I found it greatly beneficial to use the syringes to generate some pressure or vacuum before disconnecting them, depending on which one:

   • Use the lever syringe to draw a slight vacuum (no more than 1mL worth). Then disconnect the caliper syringe.
   • Next, use the lever syringe to generate a bit of pressure. Disconnect the lever syringe afterwards.

   Generating a vacuum will prevent residual oil pressure and gravity from causing leakage at the caliper. Creating some pressure will force a bit of extra oil into the system so you can hopefully minimize losses while putting the bleed screw in.

   In retrospect, I don't see why generating pressure would actually help. I think creating a vacuum for the lever syringe removal would work just as well if not better because the oil will be retracted back into the lever, even without a second syringe doing the pulling. However, making pressure worked pragmatically, so that's all I can recommend for now.

4. Have your bleed screws ready and attached to the torx driver bit with a magnet before disconnecting their respective syringes. You want to install them as soon as possible to minimize leakage.