Question Locking Mechanism for Seatbelt Install- Chevy Silverado

Hello,

We recently purchased a 2008 Chevy Silverado (extended cab) as our secondary vehicle. We have a Safety 1st Onside Air as our secondary carseat. We originally installed the carseat behind the passenger seat (rearfacing) using LATCH. However, since the rear seat is not very deep, this meant that we couldn't comfortably sit in the passenger seat. So... we are moving the carseat to the middle of the backseat (still rearfacing). Since the middle position doesn't have LATCH, we are doing a seatbelt install. However, we are having trouble getting a tight installation. My question is:

How do I get the seatbelt to lock? Do I need a locking clip?

The only other seatbelt install I've done is in a 2001 Chevy Impala. In that car, you pulled the seatbelt all the way out, then it would automatically lock as it went back in. It doesn't seem like the Silverado belts work the same way. I am far from a car seat expert, but I am determined to keep my daughter as safe as possible in the car and want to do everything correctly.

In case it matters, my daughter is 15 months old, 31 inches, and 24 pounds. She will stay rearfacing in this seat until she hits 40 lbs or has less than one inch of room above her head. We will likely replace this with another convertible, perhaps with a higher shell.

Thanks in advance for your help!

Your seat belts lock at the latch plate, so all you need to do is route the belt, buckle, tighten, and check to see if it's holding. Sometimes it will slip if the angle of the webbing relative to the latch plate is not flat enough, and if that's the case you can unbuckle it, give it a half twist, and rebuckle. Check for movement at the belt path only with a firm handshake. If you go to 6:11 in this movie that is the type of belt you likely have although yours might not look exactly the same: [ame="http://www.youtube.com/watch?v=DD1Z3Kbs5xE"]How does your seat belt lock? - YouTube[/ame]

I believe that seat has a standing height limit of 36" - but I'm Canadian and our specs are different so please check. It's not a seat that goes by the 1" from the top rule, so you'd need to switch her out when she reaches either 36" or 40lbs.

Thank you so much! This is very helpful. I will definitely check the manual on the height limit issue.