UKC

Is there a way to adjust the return spring on drop bar levers?

My shimano sti lever worked fine with rim brakes but my new frame has internal routing for hydraulic rear brake rather than cable stops. Ive run a good quality housing full length to the mechanical disc caliper, but it wont return fully despite all adjustments I can see on the caliper.

Just wondering if theres an adjustment screw for the return spring on the lever?

I don't think so (speaking for 105, Dura-ace, SuperRecord and Acera).  The return spring for rim brakes and mech disc brakes is in the brake, with only a lightweight spring in the lever.  The Acera bike I have (a folder) has mech disk brakes - the cable outer runs all the way to the caliper and a built-in cable-outer stop, which is part of the brake assembly.  If you just squeeze the caliper on its own, the spring is quite strong.  If you hold the caliper closed, the spring on the brake lever itself is quite light.  Have you checked that the cable is not taking  any sharp turns (curves should be  the curve of a hand holding a mug of coffee at the sharpest)

As said above, the spring is really in the caliper. What brake caliper are you using?

Trp spyre also tried avid Bb7

Yep cable is as well rounded as can be

Did you use a new cable and is it one of the Teflon coated ones? They can sometimes shed the coating, which can then make them sticky. Personally, I always try and run a bit of lube through the housing, too.

I would start by disconnecting the cable from the caliper and see if it runs freely through the housing. If not, try and identify if it's getting stuck in the housing or at the lever end.

ive ordered a jagwire pro polished wire, will try that instead of the regular stainless steel one ive got in at the moment and will report back. Im not hopeful but aside from throwing money at it im not sure what else to do

Does the lever return if you disconnect the cable from the caliper?

Can you fully return the lever by hand, or can you feel resistance or something stopping when you try.

Have you checked that you've not crushed the liner on the cable housing when it was cut to length? I insert an old cable  inner into the housing before I cut it to stop it deforming when I cut housing to length.

I tend to file the end and use a small nail to round out the hole again.

yep

no resistance

I always open the end with a small allen key, no obstructions.

As per previous replies it’s the mechanical disk brake end that’s struggling, a common problem with mech disks and internal routing. I recall seeing a “hack” for this at a cyclocross race where a compression spring was added over the cable inner sitting between the calliper lever (near cable clamp) and the barrel adjuster. It gave the calliper lever a bit of extra return force to compensate for the extra drag of the internal routing. You just need to be careful that the spring doesn’t fully compress before the brake goes firm.

Thanks I had thought of that but don't know how to decide what strength of spring to choose and cba buying many to try.

I've temporarily tied a tough rubber band from the seat stay to the caliper arm 

Yep, jagwire polished wire did the job, works great now