Britax marathon install w/sb, but not lockoff?

Today I got my hands on a marathon70 to try rear-facing in the civic. Latch was a pain. (The car's side of it.) I wanted to install with seatbelt, but I could not get the lockoff to close. Two instructors tried and failed. One said I could just use a locked seatbelt instead. The other looked in the manual, but could find no mention of whether you could or couldn't. Anyone know?

Yeah, you don't have to use the lockoff if you lock the seatbelt.

Did you try closing the lockoff before tightening the seatbelt?

http://webapps.easy2.com/cm2/flash/generic_index.asp?page_id=36117991



Britax Child Safety, Inc - MARATHON 70 Installation with Seat Belt & Lock-offs Product Demo

Visit Britax Child Safety, Inc
MARATHON 70 Installation with Seat Belt & Lock-offs Instructions
1. Getting Started
2. Lock-off Change Notice

3. Rear Facing Installation Using 2 Lock-offs

4. Rear Facing Installation Using 1 Lock-off

5. Forward Facing Installation Using 2 Lock-offs

6. Forward Facing Installation Using 1 Lock-off

Lock-off Change Notice
In the spirit of continuous improvement, BRITAX has revised the lock-off installation method for all BRITAX U.S.A. next generation convertible car seats (ROUNDABOUT 55, MARATHON 70, BOULEVARD 70, BOULEVARD 70 CS, ADVOCATE 70 CS), allowing you to use only the lock-off closest to your vehicle seat buckle instead of requiring you to use both lock-offs. This change applies to both rear- and forward-facing installations and eliminates the occasional convenience button interference issues that have been observed. This change only applies to U.S.A. car seats; all Canadian next generation child seats manufactured on or after August 1, 2010 were produced utilizing the single lock-off installation method.

The change was implemented in production on October 5, 2010. All seats with a manufacture date of October 5, 2010 or later should be installed using only the lock-off closest to the vehicle seat buckle. A kit can be requested free of charge for seats manufactured that instructed use of both lock-offs. To request a kit, contact BRITAX Consumer Services at 1-888-427-4829 with the serial number and manufacture date of your seat.

Rear Facing Installation Using 2 Lock-offs
Installing your car seat rear facing using the vehicle lap/shoulder seat belt and two lock-offs

Rear Facing Installation Using 1 Lock-off
Installing your car seat rear facing using the vehicle lap/shoulder seat belt and one lock-off

Forward Facing Installation Using 2 Lock-offs
Installing your car seat forward facing using the vehicle lap/shoulder seat belt and two lock-offs

Forward Facing Installation Using 1 Lock-off
Installing your car seat forward facing using the vehicle lap/shoulder seat belt and one lock-off

 

Push the seatbelt into the channel for the lockoff first before closing it. That makes the seatbelt conform to the lockoff shape a bit and makes it easier to close the lockoff. There's a definite sweet spot to the lockoff and it's not at the very end of it--http://carseatblog.com/7495/britax-convertible-lockoff-tips-and-guidance/ .

Today during lunch they showed us the britax video on how the lockoffs work. I didn't get a chance to try the marathon 70 again, but the video really helped. Thanks!