740 '89 740 Cowl Removal To Fix Buzzing

Anyone know a comprehensive guide of how to remove the cowl on a 740? A guide with pictures would be a lifesaver.

I want to clean under the cowl because for a while now at random points when I am driving I will get the worst buzzing noise like a huge fly in the top portion of the dash. I'm thinking it could somehow be caused by dry leaves under the cowl or a quarter that found its way through the cowl (please don't ask how).

If this buzzing noise could have been caused by something else please advise me. Thanks in advance!

If the screens that block off the cowl slots have dropped down they will cause the “buzzing” sound you are describing. It can be so loud and violent sounding you might think the car is coming apart.

^^ Turns out mines has dropped down! I am glad to hear that's what it probably is.

That being said, I will need to know how to remove the cowl as well as secure and make sure that mesh remains in place. I heard there might be some things that could break when removing the cowl concerning the wipers. Knowing this, should I put an order in for whatever that is as well as any special tool I might need?

Thanks again for the help!

I removed the cowl a few times on my 940. I am pretty sure the 740 uses the same or at least almost identical cowl.
It is not very difficult and you don't need any special tools.

There are 3 bolts holding the cowl to the car. 1 on each corner (near the hood hinges) and 1 against the firewall in the center of the cowl. See picture below.

You have to remove the wipers first to lift the cowl.
To remove, lift the cap on the shaft, undo the nut and pull up the wiper. You might need to break it loose a bit because the shaft is grooved and they "lock" in position when you tighten the nut.
Once you've removed the wipers, remove the rubber caps that seal the holes for the shaft.

Once you have all that undone, wiggle the cowl free by pulling it towards the front of the car and lifting up.
It's a bit difficult to explain but you'll feel it when you get there.

The lower windhield trim will come with the cowl because it's clipped onto it (at least on the 940 and late 740's).

It's a good idea to check the wiper linkage and give it a bit of fresh lube since you're in there.

(EDIT: just noticed the cowl is from a RHD car because the second hole for the wipers is on the right side, but it doesn't make a difference to the process)

^ Thanks a bunch for the step by step explanation! I will try it tomorrow. Thanks again.

What Fa182 said is all correct. What I will add is that you pull the front edge of the cowl up slightly and then forward about 2". The back edge of the cowl slides into some plastic guides on the body and the outer edge of the cowl slides onto a plastic pin that is attached to the fender. That is what retains the cowl at the windshield side of the cowl. Once you have it loose, close the hood most of the way and it actually gives you more room to remove the cowl. Move the hood open to closed until you have the biggest gap between the hood and the cowl. Play with it and you will see what I'm getting at. You take it out toward the tail end of the car. The hinges are in the way to take it out towards the front of the car. It is a piece of cake if the hood is off. That said, don't remove the hood. They are even more difficult than a 240 to get right when they have been removed. When replacing the cowl make sure the back edge goes into the plastic guides. You can easily go right over them and the cowl will not pull down tight against the windshield.

Also wanted to ask: Is there anything I might need to be careful with sealing-wise? I'd rather be safe than sorry and have to pull drenched carpets out again. Thanks.

Are you sure water was leaking in from the cowl panel area? The (less common) known problem there is that plastic cover over the blower inlet can become dislodged and allow water a path in thru the fan intake ducting.

The more common problem (wet carpets) is failing sealant on the kick panel bulkhead vestigial vent covers. Often written up in this forum.

^ When I had a leak it was from a combo of bad engine bay seal + bad brake booster seal to firewall as well as a small leak from the kick panel seal. I fixed all of those and have a bone dry interior.

That being said, I don't want to mess up anything regarding the cowl removal which will cause a leak in the future.

There is nothing to seal on the cowl panel itself. As said above, make sure you reattach the blower motor "awning" while you are in there. Those are often loose and allowing water to get into the interior through the heater case.

Go to your auto parts store and buy a roll of sticky, black sealant.

I used 3M Windo-Weld Ribbon Sealler.

Stuff comes in handy for other things, e.g. sealing where the wiper motor goes through the firewall.

Mr. V said:

Go to your auto parts store and buy a roll of sticky, black sealant.

I used 3M Windo-Weld Ribbon Sealler.

Stuff comes in handy for other things, e.g. sealing where the wiper motor goes through the firewall.

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That's exactly what is used by Volvo. Butyl rubber ribbon. Messy stuff.

Just removed the cowl, cleaned, and reattached the mesh. I am still getting a buzzing noise around 30mph + when the car is otherwise cruising nicely and silently. At least I have reattached that mesh and have the peace of mind that it is nice and clean under the cowl.

I really hope I can figure out what's causing the upper-left dash buzzing. It's driving me insane.

Check to see if your windshield trim is loose at the top. That is the other part that can make that buzzing sound. I have this problem on a 1994 940 wagon I’m getting ready for resale.

May be something is dropped down the windshield defrosting vent?

PCH said:

May be something is dropped down the windshield defrosting vent?

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Now that I think about it, I replaced the defrost vent louvers a bit over a year ago when I got my dash pad. When I did that some pieces of the old cracked louvers may have fallen down. How would I take them out the vents? Thanks again.

daniels740 said:

...some pieces of the old cracked louvers may have fallen down. How would I take them out the vents? Thanks again.

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From under dash, kind of a hassle, lots of disassembly/reassembly there. Then there is always the (high) risk of creating more buzzing from reassembly things back in not the exact correct way because there's a lot of wires, tubes, vent hose, etc., under there, easier to create more problems than you solve.

I would identify the exact cause of the buzzing first before tearing into the underdash to chase some possible loose pieces of broke-off defroster vent louver plastic.

Some tips:
1. Wind related or engine/transmission/exhaust vibration related? Shift into neutral when it is buzzing real good. Does the sound persist or change?

2. Try using some blue painters tape to tape up all the windshield trim to the body and windshield and take it up to buzzing speed. Does the buzzing persist?

3. Roof racks? Some of these can buzz pretty good.

4. Ditto Winter tires.

daniels740 said:

Now that I think about it, I replaced the defrost vent louvers a bit over a year ago when I got my dash pad. When I did that some pieces of the old cracked louvers may have fallen down.

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Another tip: Has it been buzzing since then?

tintintin said:

Another tip: Has it been buzzing since then?

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Up until this year the tranny mount was completely done for. Because of all the vibration and noise in the cabin I can't tell since when the noise had been going on for. Now that I have all new mounts which account for a quiet cabin, I can hear the buzzing.

Unlike a 240, if something went down through the defrost vents and made it down into the blower motor cavity you can easily remove the blower motor and get it out of there.