Breakdowns, Accidents, Green Angels and Mechanics in Mexico
If you feel something going wrong try to pull over immediately. As there are usually no shoulders, this can take time. If you must stop on the highway place the florescent triangles out to warn drivers of your stopped vehicle. It is also advisable to have someone wave a flag.
People often stop to try and help. During one breakdown in the middle of nowhere, we had farmers, bus drivers, taxis, agriculturalists, municipal police, highway police and truck drivers stop to give us a hand.
Do not be surprised if they do not have a tow truck large enough for your vehicle. The mechanic often just come to the vehicle with a set of tools. We were towed behind by a farmers flatbed truck all the way to Leon some 60 kms away.
Dylan Bell with a bus on fire in the background
It was quite the experience getting whipsawed as we traveled up and down hills. No brakes. No steering. Praying those thick yellow ropes held.
Rule of thumb is to have someone stay with your rig to protect it against vandalism while the other goes for help.
Green Angeles are a fleet of green trucks and jeeps that travel the major highways throughout Mexico twice every 24 hours. 
They are paid by the Mexican government to help tourist who have broken down on the road. They carry gas, some spare parts and a CB radio. You are expected to pay only for fuel or supply costs. Tips are appreciated.
Green Angels for help and information
While their English is often limited, their mechanical skills are legendary.
Mechanics
Mechanics in Mexico are everywhere. In general, they have an incredible reputation for repairing parts that are impossible to buy locally. You will find that they can do amazing things and that they will charge you very little. Our experience has been very good.
We have broken down a few times and have direct experience. They managed for example, to get a completely flattened air conditioner working. They actually fabricated the fan out of metal just to fit our rig. The fabrication was $25.
While the mechanics are usually very competent, many vehicle parts and supplies are limited. Remember to pack extra fuel and air filters and any other small parts that may falter.
If you have an emergency while driving, call the Ministry of Tourism’s hotline or (55) 5250-8221, extension 130/297, to obtain help from the “Green Angels,” a fleet of radio dispatched trucks with bilingual crews. Services include protection, medical first aid, mechanical aid for your car, and basic supplies. You will not be charged for services, only for parts, gas, and oil. 
The Green Angels patrol daily, from dawn until sunset. If you are unable to call them, pull off the road and lift the hood of your car; chances are good they will find you.
Mechanics like our amigo in Lázaro Cárdenaz make breakdowns a little less frightening.