How I mounted a Britax HiWay child seat in our BMW E39

(If you want to avoid reading and want to go directly to how things were done, skim through the legal disclaimer and then skip directly to the mount description.)


We have a -00 BMW E39 523i Touring for transporting our family. That is indeed a great car, IMO. But with our youngest child growing out of the 0–9 kg baby protection, it was time to squeeze in a rear-facing child seat for her together with the already mounted rear-facing child seat her older brother sits in. What seat should we choose, in what seat should we mount it, and how should we mount it?

The E39 Touring is not a small car. It is actually pretty big. So are child seats... (At least the rear-facing ones. And like most other Swedes, I believe in using those as much and long as possible.) In the passenger seat (passenger airbag deactivated by authorized BMW dealer and seat belt switched to the non-stretching kind) our son has his Britax MultiTech. A seat we really dislike in many ways; hard to clean, takes huge amounts of space, covers all of the right side mirror, etc. etc. For some reason the mirror was fully visible when we bought the seat. Anyways. The seat is a test winner when it comes to security, and that is a really good thing. But, would it be possible to cram in another child seat (obviously not a Britax MultiTech) in the right rear seat or elsewhere? And what seat would that be?

NB! This is how I did it in our car, not an official guide from the manufacturer. I have no responsibility, legal or other, towards anyone or anything that uses this guide and for some reason runs into trouble and wants to blame me. Everything on your own risk, etc. etc. yada yada. This is simply the web page I wish I had found on the WWW when I set out to investigate what child seat to use and how to mount it in our car.


Like most Swedes, I believe in using rear-facing child seats as much and as long as possible. The downside with the rear-facing child seats is the huge amount of space they consume. Bad memories from standing in the parking lot outside the baby dealer testing child seats with a child that grew tired of it all after the first seat did not inspire to use that strategy this time around. So I posed a question in the Swedish BMW enthusiast site's forum, asking if anyone could recommend a good seat that would fit my usecase.

To summarize, I was recommended 3 rear-facing child seats for the E39:

It seemed to me that the Britax HiWay would be the first thing to try. There were forum members writing that the HiWay is perfect to put in in the E39 middle back seat since it is not that wide and thus fits in between the front seats. This seemed really good since my 184 cm mean I need/want to pull back the driver's seat pretty much to sit well. So we ordered one with free delivery from a shop not very far away from where we live in order to easily be able to go back and return it if it would not fit. (With the prospect of not having to go anywhere if it would fit.) When delivered, we could conclude that yes, the Britax HiWay fits perfectly in the E39 back seat's mid position! (We also concluded that no, it does not fit behind the front passenger seat with the Britax MultiTech in it if the son's legs are supposed to be on the trip as well...)


Now, our car does not have ISOFIX (it came in the 2nd half of 2000 on the E39, and our car was manufactured in February that year), but nor does the Britax HiWay so it really does not matter. (The iZi Kid comes in an ISOFIX version that is said to use less space than the non-ISOFIX version of said seat.) But there is nothing in the floor where the straps could be fastened on this car. (An issue it seems to share with a lot of other cars.) One alternative is to fasten them in the driver's seat, but then all drivers must use the same seat position. That is a no-go for me and my ~15 cm shorter wife who drives the car as (ir)regularly as I do.

For the E39 Limousine, there are child seat fastening brackets no. 72118187599 listed that are not to be found for the Touring. The reason is that these are to be mounted in the hat shelf behind the back seat and is some mandatory equipment in North America or something. Regardless of what, they do not help mounting a rear-facing child seat in any E39, at least not for the front-facing mount belts and at least not in Sweden. But I was handed a link to this universal car seat mount loop set which I ordered. Now all I needed was an additional T50 Torx socket for the seat rail M10 screw. Then I was all set to start tinkering:

This is what the universal fastening loop set looks like.

Bummer, I would need to drill it in order to make room for that pin coming up next to the M10 mount screw. Or perhaps I could slide it in underneath and have it at a 45-something degree angle? No, then the edge goes in against the transmission tunnel and the mount hole cannot be aligned with the rail screw hole.

At this point I scrap the idea with the mounting loops to try another approach where the fastening belt is directly mounted instead.

Use the T50 Torx socket to unscrew.

Screw loose! Notice the thread-locking fluid; of course I use that when I mount everything again.

Here is the fastening belt that is to be fastened.

The theory is to lift the rail and hook up the belt loop under the rail and around the pin next to the screw hole (to get the belt somewhat further back than if we had the belt around the screw instead).

Even if the driver's seat is in its most forward position, the rail is hard to lift. I squeeze in a screwdriver to hold the rail up in order for me to get the belt in using both hands.

The belt loop is now around the pin. I have the M10 screw loose in the rail just to keep the belt loop away from the screw hole.

Screwdriver removed. I pull the belt gently to make it align itself somewhat and to see if the theory seems to hold. The small drawing illustrates the relation between the belt loop and the pin.

Time to fasten the M10 screw! Thread-locking fluid is applied.

Tighten screw to, well, what torque? I have no idea. If you know, please let me know and I will update this page! For now, it is “what felt enough”.

There! Now I pull the belt really hard to see if it seems good. I think so.

Plastic cover re-attached.

A cheap way to protect the seat somewhat.

Seat in place, attaching straps and mounting it as per the manufacturer's installation instructions. (On the passenger side I fasten the belt in the passenger chair since that one does not need to be moved, with the Britax MultiTech in front and all.)


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