Seat Belt Question..slippage?

I Ordered a seat belt from Juliano's to hold down my daughters' child seat....it seems to be abel to loosen up a bit after tightening. Anybody run into this problem?

Any recommendations for a better belt that won't slip?

 

Call or store and talk to joe about your problem. 1 800 300 1932

 

what type of seatbelt? What type of child restraint? If it is a seatbelt with a sliding latchplate, such as the type pictured here:
the problem may be the angle of pull on the webbing, and where the latchplate sits when routed through the child seat. Here are a couple pics to help explain.

shows the webbing getting close to a 90 degree angle to the latchplate, it could allow it to slip.

showing how flipping the latchplate will pull the webbing at a greater angle and positively lock the sliding lock bar in the latchplate.
(These pics used for demonstration only, Belt Positioning Booster seats need to be used with a shoulder harness)