Mark Hartley's son, Jamie, has been given just months to live.
The 22-year-old and his brother Kyle both have Juvenile Huntington's Disease.
Mr Hartley said Jamie's condition had accelerated over the past month "so essentially Jamie's got not a great deal of time left with us".
The family, from Blyth, are bike enthusiasts so he posted the request for a sidecar on Facebook to a few dozen friends.
"I put my phone down and about two hours later I picked it back up again and there was 400 messages," Mr Hartley said.
A ride involving hundreds of bikers is planned for Sunday.
Juvenile Huntington's Disease is an uncommon form of the condition, causing stiffness, tremor or muscle twitching, seizures and difficulty speaking.
It is terminal but the timescale can vary.
A father who asked for a sidecar so he could take his dying son out for one last motorbike ride has had an overwhelming response.