Could it harm the gearbox?

[Quixy]

Can anybody say if it's a problem to worry about or not?

I recently towed an old Volvo V70 (kerb weight of about 1650 kg) to a workshop. The distance was about 5km and we went about 20 km/h, but I still worry a little if it could harm the gearbox, engine, driveshafts or something else. It's 2017 Yaris XP130 1.33l 73kW gasoline 5-speed manual

[YarisHybrid2016]

As long as you didn't slip the clutch much to get it moving, it should be OK. Was it level ground?

[MikeSh]

Sounds like you did it correctly. You might have taken a little off the life of the clutch, but that is an extremely variable amount, so I wouldn't worry about it.

[TonyHSD]

That was not a good idea at all.
Even without any immediate affects on the car in similar situations  there are unwritten rules that should be followed exactly to prevent future trouble or worries. 
Never jump start a car with bigger Battery than yours, never towing a car larger and heavier than yours. The list goes on depending on the circumstances. No need to worry about it as you did it already but for your next time better refuse than help or it might be an expensive lesson. 
 

[MikeSh]

3 hours ago, TonyHSD said:

there are unwritten rules that should be followed exactly

Wot? How can you follow unwritten rules exactly?

We don't know what country the OP is in, so their circumstances might be very different from us. As long as there were no steep inclines or a lot of stopping and starting involved, then towing about 3 miles at 15mph or so really shouldn't be too taxing on the car.

That said: Is it a good idea? No, it's a risky procedure in several ways, so not recommended.

[Cyker]

Probably be okay, like trying to move off on a steep hill with a car full of people and luggage  

Probably the worst is some extra wear to the clutch and brakes, but that'll be made up by the fact you can now brag your tiny Yaris could tow a big hefty Volvo  

 

[bathtub tom]

I once moved a 20 ton trailer with a 15cwt van. Got it going, but thought I'd never stop it! Didn't bother to try and manoeuvre it into position and was grateful for getting it out of the way.

[Derek.w]

Im glad the welding was not compromised under all that strain.

Next time call a tow truck it may be cheaper in the long run.