DIY: Re installing the heater box

Bmachine

Bmachine

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There are a few threads on removing the heater but not many on reinstalling it. Here is the way I did it. Please add / correct as needed:

As discussed elsewhere, re building this box is quite an undertaking and many agree that it is best to leave it to the pros. That is what I did. New heater core and rebuild by sfdon's shop. (one of my metal air directing flaps is missing)

EDIT: I was just reminded that if you want to do this yourself, @eriknetherlands wrote an excellent how to here:

DIY - Heater unit rebuild

My pay back to the forum; here's my approach to rebuilding the heater box from my E9. Not sure how this compares to e3, but let me know and I can possibly merge. I'll likely chop it in roughly three pieces; removal, disassembly, repair and rebuild. I haven't installed it yet myself, so i can't...
e9coupe.com e9coupe.com

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The unit is attached to the angled section of the firewall by four M6 nuts. First thing to do it to test the threads on the captive studs coming down from the firewall. Because this unit is pretty hard and cumbersome to remove, it is very easy for the threads on these studs to get damaged during deconstruction. So just try and screw a nut on each of them to make sure they go on smoothly. The last thing you want is to maneuver that big unit in position only to realize you can't screw the nuts on because the threads are toast.

In my case, sure enough, everyone of them was damaged. They are very hard to repair because they are fixed in a difficult position. You can't use a die bc it's the first threads that need repairing. What I ended up doing is getting my friend @tygaboy to split an M6 nut in half with a very thin cutting wheel. Then I wrapped both halves on the stud above the damaged threads and unscrewed them down in order to repair the threads. After they were reasonably clean, I ran a die on them to finish the cleaning.

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Start bringing the box into position. Because the bowden cables are still attached, and inevitably there are lots of cables and things in the way, it takes a bit of doing to get it in. I found that it helped to get it close enough from the inside and then pull it up from the outside. Be sure to guide the two heater hose connectors through the hole in the firewall.

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Unless you have someone else to hold the thing from above, it is very difficult to get the unit to move on the studs and stay there until you go and get the nuts on. I ended up setting a few wood pieces against the gear shifter until I could see the beginning of the threads poking through.

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Because it very hard to get to these studs, a bit of preparation is needed. First, you need large washers. The holes in the mounting plate of the heater box are quite large and standard M6 washers go right through them. So you need large washers. The factory diagram calls for wave washers. But a bit of research points out that these type of lock washers really don't do very much and that modern thread lockers like Loctite are better. So I thread a nut onto a bolt, add the large washer on it, wrap some tape around both of them so they stick together, push them onto a socket, apply a bit of blue Loctite on the stud and then try to screw the nut and washer combo in place.

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A combination of several sockets, extensions, wobbly adapters, and ratchet wrenches is needed as each stud has its own level of difficult access.

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But, eventually it gets in there

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What a nightmare job. I completed this recently, and no amount of preparation can make this an easy install. Just when it looks like that heater box will never again fit, it will eventually slide into position. I think at one point, I had to resort to a bottle jack, ever so gently, pushing up on the dashboard/tray to get a couple of mm clearance, for the unit to fit where it was supposed to go. Whew! In my experience, going slow, having lots of light, and observing every touch point, helped me see where I had to exert some pressure or twisting motion to get the box and the studs to line up where they needed to be. All in, works well, looks great. Happy with results. Like others have said, do not want to do that ever again.
 
Bo - Thanks for posting the details. I appreciate the extra effort it takes to document the steps - particularly when the job itself is already tedious!
I'll be referring to this post as I have this same effort to tackle at some point in the not too distant future. Oh, and are you busy that day? :p
 
Things that make this challenging job easier:

Even though technically it is not difficult, the reason this job is a pain is because it is in an awkward position and the studs are sometimes very difficult to reach. So making the ergonomics as good as they can is key. Here are a few things that helped me:

- Have the car elevated. Ideally it would be on a lift. Mine in on four jack stands so I don't have to bend down so far each time.
- Have as much stuff out of the way as possible:
- Remove glove box
- If you are lucky to have the windshield out, now is the best time to do it. It allows you to access it from both inside and outside at the same time.
- Have the seats out
- Remove the steering wheel
- Have the whole area super clean. Remove all old carpets, glues, sound proofing and clean all with acetone.
- Have excellent lighting. Best are small lights with magnets so they can be placed anywhere.
- Have very good knee pads
- As mentioned in the first post, be sure to test and clean the threads on the studs before you do anything else.
- Allow plenty of time and be ready to have to retry things a few times. It took me about 4 hours at a leisurely pace.
- And, of course, read as much as possible about the procedure on this forum beforehand.
 
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Bmachine said:
Oh, crap, was there a thread on this already? I checked in the DIY section and did not see it. Thank you Erik.
Click to expand...

Well, there is currently only a thread on the rebuild of the unit, but it does not cover the reinstall. It just ends with " The install is the reverse" orsomething along those lines.
This thread is a good continuation!

Just to link both threads,
The rebuild DIY is here:
Thread 'DIY - Heater unit rebuild' https://e9coupe.com/forum/threads/diy-heater-unit-rebuild.38896/
 
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