Cowl Rust - Ford Forums

s-code · 07-07-2001, 14:28

OK all you Mustang gurus. I was talking to a buddy of mine the other day, who is fairly knowledgeable about Classic Stangs. I asked him what he thought about cowl damage due to rust. The unknown plague of any Classic Stang, "Is it there or not?" He said that he figured the majority of Mustangs had some degree of cowl damage caused by rust, just because of the poor design. He agreed that a car left sitting for many years was probably more likely to have it than one that was well taken care of, but it was still a possibility. What do you all think? Do the majority of Classics have some degree of cowl rust? And, if you answer yes, what percent would you think it would be? I am also going to post this on a couple of other sites and will pool all of the answers and let you all know what the majority opinion is.

66PonyStang · 07-11-2001, 19:48

Yeah, my 66 has some issues with the cowl. I really need to get it fixed up. It's holdin' now and I've got it garaged, but I'd like to get it fixed sometime soon.

Apparently alot of people have that problem with their older 'stangs....

geegee · 07-22-2001, 17:42

Cowl rust is the bane of the early Mustang but its fairly easy to treat if not advanced too far. How do you find out?

a. look up under dash at the left cowl vent intake. If it is clean all around the air intake, then there is a 50% chance its okay. The right should be checked similarly but with the heater in the way, its even harder to inspect. Any evidence of water, white powder or corrosion in these areas indicates advanced cowl vent problems.

b. if it looks okay with under dash inspection and you still want more insurance of the condition, then take the car to an aircraft maintenance shop having a bore scope. A bore scope will let you see inside the grille, and after removing the fender splash guard, let you look at the outside edge of the cowl vents. This inspection will cost you $50 or so but then you'll know for sure.

If you know you have cowl vent rust, then there's two repairs worthy of consideration:

a. Top hat repair. Plastic top hat inserts can delay cowl vent corrosion for a long time if they are used correctly. Correctly means to remove the fenders, remove the air vent and heater assemblies, cut inspection holes in the upper cowl vent sheet metal (below the upper fender line) and clean all debris and treat the cowl vent are with POR-15. This is a pain in the tokus, and all work has to be through a 2"x8" hole but this is a lot easier than the repair to be discussed next. After the cowl vent is treated then the plastic top hat is inserted from the bottom with a liberal amount of body adhesive. The hole is then closed by welding or brazing. This repair will be good for a very long time provided the cowl vent is not too far gone...Expect this repair to cost between $500 and $600. This repair can be done without damage to existing paint.

b. Cowl vent plug repair. American Designer makes cowl vent plugs that are nice fabrications of the cowl vent area. To install these, the fenders and hood come off, the windshield and gasket come off and about 100 spot welds are drilled out to permit removal of the upper cowl vent sheet metal. Extreme care must be used at all times since the drilled sheet metal must be reused and the windshield lower edge must not be damaged. Once the cowl vents are exposed, the bad cowl vents are cut out and the surrounding sheet metal prepared for the cowl vent plugs. It is a very good idea not to disturb the left wiper post if at all possible, meaning cut around it even though the left cowl vent plug has the flat for the wiper post. The reason being, the best fit of the left cowl vent plug may displace the flat slightly and then leave inadequate flat space for mounting the wiper post. The wiper post position is critical since:

a. the upper cowl vent grille hole must match exactly
b. The height of the post is critical in order the chrome ring and special bolt fit when the assembly is welded.

The cowl vent plugs are fitted making sure not to increase the height of the overall sheet metal assembly. Note: if the height is incorrect, the wiper post fittings will not fit. The fenders will bend up such the moldings won't fit and the whole job will go sour. Note: it is almost impossible to correct the work so it must be done correctly the first time.

In leaving the left wiper post in position, then cutting the new cowl vent plug to match, much less effort is required. This is, of course, dependent on how far the corrosion has advanced toward the wiper post.

The right cowl vent plug is not as difficult since the wiper post is not near the vent hole.

Once the area is finished, it is coated with POR-15 or similar anti-corrosion treatment, primed, painted and then the top grille sheet metal is welded in place. If all goes well, the dimensions of the complete project match the original dimensions within very close tolerances. If dimensions are off, then other pieces having to be replaced must account for the error.

The bottom line for this job is it is very expensive and should only be attempted by body shops having a sheet metal artist and all the right tools. It is almost never done correctly by an amateur on the first attempt. It is almost never done correctly by a professional on the first attempt. If you want this done right, take it to an experienced, professional shop. Expect it to cost at least $1,200 (exterior unpainted, prime only). Full paint normally follows this repair.

jas24zzk · 10-27-2006, 07:18

Brazing should never be done any car (unless its electric silicone bronze) as the flux's used for brazing are corrosive. It is howver ok,IF you can clean up both sides.

Quote:

It is almost never done correctly by a professional on the first attempt.

I must be lucky then!!!
My first attempt came out perfect...not bad for a bloke from a smash background!

On the original question, Mustangs seem to fare better than most other marques, as the lower cowl was galvanised from factory. This at least gave the unpainted area's a chance. As your freind suggest a car sitting has a higher probability of issues, as this allows water to sit in lower lying area's. Movement of the vehicle permits, the water to move about and head for the drains.
Even with movement, life under trees can generate problems, as leaves block the drains quite readily, and this stands for ANY car. I have seen cowl leaks repaired simply by blowing out all the crap that has accumulated, and unfortunatley for an early stang this often means guard removal any how.

As our learned friend above suggests, a top cowl removal can be problematic if care is not taken with alignment on reassembly. There are two factors to ensure proper realignment.
1) before you begin, drill 2 1/8" holes through the windsreen lip, and 2 through the firewall lip...in an area that is not going to be replaced. (don't put em in spot welds) Upon reassembly, putting self tappers through these 4 holes will place the top cowl so close to factory that the tolerances originally built in will ensure proper panel alignment later.
2) The manner in which you unpick the spots. (on a 65/66 there are 142 welds) The ONLY way is with a flat bottomed spot weld drill. You can buy them commercially, but i prefer to grind my own. The best thing youcould do i s buy one commercially, and then use it as a reference to cut your own. that way you can make a few in different sizes to suit different size spots.

Cheers.
Jas

**Big Block Ford** · 10-27-2006, 15:33

This is an old thread but yes cowl rust is a problem in early Stangs but I'm not sure it is really poor design but more from poor assembly line production. I don't think the cowl area was painted correctly or rust prevention wasn't carried out in this area.

I guess back then rust protection wasn't as good as it is these days and there is new technology and methods used to prevent it better.

Gearhead99 · 11-24-2006, 17:11

Back in the 60's there wasn't alot of rust prevention done to cars.

Who back in 1966 would of thought the Mustangs would still be around and in such a demand 40 years later.

jas24zzk · 01-12-2007, 04:14

Dave, you obviously didn't read my post very carefully did you.
or maybe you disagree..

.............but what would i know about this subject....

Jas

FB1965 · 03-21-2008, 20:05

I removed the cowling on my 65 fb and replaced each stove pipe section.This took a long time working 2-3 hours a day.I do know that if your checking out a old one to buy,and wonder about cowl leakage,check the floors first and the carpet.If theres rust or the carpet is wet,there is a problem.Mine had even rusted thru the panel behind the glove box.Now my only problem is it sets and dumps transmittion fluid when the seal drys out.Just need to drive it more than once every 6 mo.

artstang · 07-17-2008, 12:56

The 1965-68 Mustangs are proned to rust around the cowl vents area due to side drain holes simply get clogged and water sits in. The 69-70 you are only dealing with one side cowl vent. I have replaced a cowl vents by removing the windsheild and top panel or cut the panel just above the cowl. Most Mustang vendors sells cowl vent panel replacement.