Are you transfering from the New England Teamsters & Trucking Industry Pension Plan
http://www.nettipf.com
to the Western Conference of Teamsters Pension Plan?
http://www.wctpension.org
Download the Plan Document of both plans from their websites and see what they say about the subject. Every plan is independant, but some will allow you to combine your service from both plans so you don't loose out. In the New England plan, for example, read Article 13 "Partial Pensions Under Reciprocal Agreement."
You'll have to contact both funds to make sure they both actually have such a signed reciprocal agreement.
If you are transfering to the Central States region, most of their part-timers are in The UPS Pension Plan, a part-timer plan run by UPS and described in Contract Article 34, Section 1 (i).