MTFCA Forum

A friend of mine recently had a problem that I'd like to share with you. He has a 1922 Touring which is new to him. Recently the car suddenly started making a lot of (exhaust) noise. Inspection showed the pack nut split about 1/3 of the way around the circumference, with the crack spread about 1/16th of an inch apart. The exhaust pipe had a history of slipping out of the muffler so he had put a clamp on the muffler end.

In my '17 the pipe is free to move in the muffler and I've never had trouble. Could it be that clamping the pipe at the muffler contributed to the pack nut failure? Maybe the pipe is too short?

Never heard of an exhaust pack nut splitting around its circumference. I believe the exhaust pipe flange never properly connected with manifold bevel. The clamp at muffler end shouldn’t have any affect on brass nut. Yep, pipe too short..

Tim,
The repo stamped steel end mufflers have an inner pipe that turns so clamping the exhaust to the muffler will not restrict the exhaust systems ability to twist.

Ford never used an exhaust pipe clamp because the original exhaust pipe went all the way to the back of the muffler. The repo system essentially is using 2 pipes instead of one, a short pipe in the muffler and the exhaust pipe so a muffler clamp is needed for a repo system.

If he is using a tractor muffler or something other than the repo muffler, all bets are off.

Only later style mufflers had the pipe internal - on earlier cast mufflers, the pipe slid in partway - no clamps.

George House wrote: ↑

Mon Nov 04, 2024 11:10 am

Never heard of an exhaust pack nut splitting around its circumference. I believe the exhaust pipe flange never properly connected with manifold bevel. The clamp at muffler end shouldn’t have any affect on brass nut. Yep, pipe too short..

George,

I've never seen one break that way either, until I saw the one Tim describes. It's exactly as he states. I kind of wondered if the nut was way too tight to begin with.

Tim,

As to expansion and contraction of the exhaust pipe, it's hard to imagine the pipe pulling so hard during contraction as to actually part the nut. I would think the muffler bracket would bend first. In my case, the bracket on the muffler fatigued and cracked. I repaired it, then instead of bolting it up firmly to the frame, I placed a washer against the bracket ear, then a firm spring, then another washer, then finally, a double nut. It's firm, but allows the bracket to move as needed, without flexing and fatiguing it to failure.

How about the incorrect tool previously to turn the pack nut such as pipe wrench or chain vice grips like these:

On the earlier cast end mufflers, the pipe was free to expand/contract with heat cycles within the front end of the muffler. On the later cars with the full length pipe, the expansion/contraction was allowed by the flexing of the pressed steel bracket used to mount the muffler at the back.

This flexing allowance I believe was intended to relieve stresses in the exhaust manifold. If everything is bolted/clamped up tight, there is nowhere for the expansion stresses to go. Clamping reproduction mufflers at the front should not be necessary, but if it is clamped, the flex in the rear mounting should still handle the flexing.


Allan from down under

Richard I was there when the pack nut was installed using my original pack wrench. The flange on the repo exhaust pipe didn't seem to tighten properly so the nut may have been overtightened somewhat. We're going to replace the pipe also. I personally believe that the design of my '17 muffler is superior --- I especially like the little tail pipe that carries the exhaust away rather than coating some of the underside components.

May be the threads on the exhaust manifold need a good wire brush cleaning and hopefully the threads are still fairly sharp. Just a guess but over tightening of the nut with slightly compromised threads will eventually cause the nut to start to crack.

There may have been a cardinal sin committed here. If the flange on the pipe does not mate fully with the manifold, it should be re-worked until it does. Tightening the packnut to force it into place immediately stresses the manifold. A bent manifold is likely to already be mis-aligned with the flange. Without correction, things can only get worse.

Allan from down under.

The exhaust pipe is supposed to be free to slip in and out of the muffler as the frame flexes going through a ditch or from uneven pavement.

Putting that clamp on the muffler pipe usually breaks the tab off the rear area that bolts the muffler to the frame or pulls the exhaust pipe from the exhaust manifold or breaks the brass clamp.

The cast iron ends of the early mufflers do take the exhaust pipe slipped into the front of the muffler. It is free to expand and rotate with frame twisting. The reproduction muffles with pressed steel ends which I make work the same way. The exhaust pipe is a slide in fit into the front of the muffler.

However, when Ford went to the pressed steel ends, the exhaust pipe went clear to the back of the muffler. There is no sliding joint. Any flexing was absorbed by the pressed steel rear mounting bracket. Perhaps this was a backward step if those brackets were prone to breaking. Personally, I have never seen a broken bracket, even on the most rusted out/thin muffler ends.

Allan from down under.

Some replacement pack nuts are chamfered top and bottom, which is incorrect. The originals were chamfered only at the top.

Only time I lost my exhaust was on a tour where we went to Tijuana. Right when we got to the border, it fell off so I went across with a straight pipe. In those days you could drive right across. No waiting in long lines as it is today. Fixed it when we got back to the hotel on our side of border!
Norm

A couple of things come to mind.

Was any of it 'new' in more recent years? If so, it might have just been pulled together to work. No harm, no foul, but you do enough of these things you find that the near perfect manifolds and the new bronze nuts need a little bit of dry fitting. I'm pretty sure the nuts are made full, but can't prove it. I simple mount new or old manifold in a vice and 'work' a new nut on by 1/4 turn cw, then 1/8 turn ccw, repeat until there is a very small gap where the flange will seat. My conclusion about the nut being the culprit is solely based on yellow metal dust left on the bench when done-knowing the yellow metal is softer than cast iron.

Then I mount the tail of the pipe with a zip tie. Fit the front of the pipe loosely, twisting the pipe to stay where it belongs until I have the nut seated on the flange. While it may seem angles are wrong, with patience it will all work out perfectly. Use that final tug on the pipe to align before the final tug on the wrench

Then I go to the back, slide the muffler on and examine where the mounting bolt hole needs to be. Sometimes get lucky, other times find need to trim 1/2"-3/4" off the repo tail pipes to get things 'right' without forcing things and still have expansion room. Slide muffler back on, bolt her up, go back up front.

Using the correct BAOW (big *** original-style wrench that weighs 15 pounds. I had originally used a big Rigid pipe wrench for a decade or so, sort of worked but needed a bunch of reseating, then started borrowing a BAOW from someone, then finally got my own BAOW and life became a dream) I do a final tug to just seat the nut. Turn on car, let her get good and hot, listen for a leak-usually none, but I forgot this last step once, buttoned everything up, and after the first ride had to do another 1/4 turn.

I bought one of these several years ago and it does a great job of tightening the nut without any fear of rounding the corners of the nut like the original open end wrench.
It fits the 2 inch nut very closely and the gap will slip over the pipe. An extension and a ratchet is all you need to snug the nut up. I bought it off of Ebay.

The car I had when the pipe fell off had a bent chassis on the right side which lowered the manifold about 2 inches. This put the pipe and muffler out of alignment. That could be your problem too, so try the pipe on the manifold first and see if it is aligned with the muffler. This same problem causes the steering to pull to one side because the ball joint is also misaligned with the radius rod ball which pulls the front axle to one side. If this is the cause, the best fix would be to remove the body from the chassis or replace the chassis or straighten it first. This problem changes the fit of the doors as well as the exhaust system and the steering.
Norm

I've been using original pack nuts all my life. I like the early design, 3Z better than the later design.

I agree with George. Dry fit everything before snugging up the packnut. This includes an initial nut tighten and a check that the tailpipe will allow the muffler to be bolted to the frame If you have to stress it, take the pipe off again and bend it to make a good fit.

Allan from down under.

You really do not need a muffler. I have a friend and he and his son run straight pipes. Model T's do not make much noise.

A couple of years ago when I drove to Dearborn my muffler broke free. The bracket on the muffler where it connects to the frame snapped off. The exhaust pipe banging on the rear axle housing alerted me to the problem. The exhaust pipe also bangs up and down on the fuel line when this happens so I guess I was lucky. I also had a U-bolt on the front of the muffler and I think this caused the entire exhaust system to stiffen up and it broke.

I ended up at Autozone and purchased a muffler hanger. It turns out I was close to the shop of Dallas Landers and he ground off the remainder of the bracket on the muffler. We installed a tail pipe to the muffler and hung the tail pipe to the muffler hanger. This allowed my exhaust system to move forward and aft so it was now flexible. There was no way to get the U bolt off the front of the muffler. When I got home I installed a new muffler so the exhaust pipe could move in and out of the muffler, and I reattached the tail pipe to the hanger like before. Seems to be better than fixing the muffler to the frame.