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PostPosted: Wed Sep 10, 2014 4:26 pm 
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Joined: Thu Aug 11, 2005 10:45 am
Posts: 464
Location: Ames, IA
Diesel Tailpipe Replacement-Upgrade – We were traveling the last 400 miles of a trip at night and had an exhaust system failure in-route that allowed the tailpipe to swing down and melt the corner out of the black tank (the tank was empty). At home the next morning, I noticed the tailpipe hanging down, pulled on it, and the tailpipe swung upward removing a blob of plastic from the tank. I repaired the black tank using a hot air plastic welder and welding rod while it was on the coach. The tailpipe failure is likely a problem limited to Born Free diesel coaches.

The exhaust system failed at the joint just behind the rear axle where the 3 inch diameter tailpipe was installed inside the 3.5 inch Ford factory exhaust pipe. Had I realized the original tailpipe was undersized and restricting exhaust flow, I might have installed the new tailpipe just for the improvement in performance and reduction in exhaust gas temperature. If I had known that a tailpipe failure would also damage the black tank, I for sure would have replaced the tailpipe. This replacement-upgrade was on a 1999 Born Free 24RB with a 7.3 PowerStroke Diesel (all stock with no performance modifications). If you have a diesel Born Free, it might be worth checking the size of your tailpipe compared to the size of the Ford factory pipe located in front of the axle.

The owner of my local independent muffler shop said the 7.3 diesel should have a 3.5 inch tailpipe and he could only bend pipe up to 3 inches diameter. He also said that if I wanted to do it myself, the local Superduty Truck Parts store would have the 3.5 inch diameter parts for the job. So, I removed the tailpipe, took some measurements and went to the Superduty store for parts. They had an assortment of aluminized parts by Donaldson—everything needed for the job except an appropriate turndown tip.


Photo 1

Photo 1 above shows the layout of the old and new tailpipes. I dry-fitted the front portion of the assembly under the coach to measure and mark the bulk tube for cutting. I measured to insure that the rear hanger would clamp and align vertically with the joint of the 90 degree elbow and the bulk tube. On our 24RB model, it required 29 inches of bulk tubing for the tailpipe assembly. The pipe is 1/16 inch thick and cuts easily with a hacksaw (I used a Sawzall). Donaldson parts are easy to assemble: the elbows are 3.5 inch O.D. on one end and 3.5 inch I.D. on the other end; the connector is 3.5 inch I.D. on both ends; the bulk tube is 3.5 inch O.D.; and the 3.5 inch clamps hold it all together. The parts can be welded instead of clamped. The photo also shows the difference between mandrel bent curves—which maintain the pipe diameter, and crush bent curves—which reduce the pipe diameter.


Photo 2

I clamped the tailpipe loosely in place and adjusted the angles as necessary before the final tightening. I was able to install the new tailpipe without raising the coach. The clamp on the right shows the new tailpipe clamped over the Ford factory exhaust pipe. The 3.5 inch I.D. joint on the 45 degree elbow is installed over the 3.5 inch O.D. Ford factory pipe at the axle. There is an exhaust pipe hanger welded onto the factory pipe, but there is enough room to clamp on the new tailpipe. The clamp in the middle holds the two 45 degree elbows together.


Photo 3

The 2 clamps in the center are on the connector for the 45 degree elbow and the bulk pipe. The 2nd clamp from the left in Photo 3 connects the end of the bulk pipe to the 90 degree elbow and attaches to the vertical rear tailpipe hanger. I used a Magnaflow turndown tip. The 16 inch long turndown tip was too long. To make it fit, I cut 3.25 inches off of the end of the 90 degree elbow pipe. I also cut 1.25 inches off of the connector end of the turndown tip leaving enough room for it to slip on and clamp to the 90 degree elbow. It hangs down more than I’d prefer, but it is not as low as the caster wheels on the bumper. The turndown tip has a nicely finished exhaust port that was too pretty to cut. If I drag it a couple times, I’ll probably remove an inch from the turndown port by making a parallel cut to the existing opening.


Photo 4

This photo shows some of the Donaldson parts with their numbers.


I used Donaldson parts and a 16 inch Magnaflow turndown tip that had to be modified. A tip that is 12 inches long would probably be better as no cutting should be required. Banks makes a 12 inch turndown tip that might be worth investigating.

3 – Donaldson 3.5 inch Bulk tubing (pipe per foot) P206335: $7.58 = $22.74
2 – Donaldson 3.5 inch 45 degree elbow pipe P206281: $33.06 = $66.12
1 – Donaldson 3.5 inch 90 degree elbow pipe P206342: $36.92 = $36.92
6 – Donaldson 3.5 inch Clamp J000228: $4.59 = $27.54
1 – Donaldson 3.5 inch Connector P206373: $15.58 = $15.58
1 – Magnaflow turndown tip 35178: $70.10 = $70.10 ... B000XQO2BO
Total (without tax) = $239.00

Donaldson Exhaust Parts – Dealer locator ... cator.html

As an option to doing the work, you could buy the parts and have a local muffler shop do the installation.

Submitted by:
Chuck Meadows
'99 24RB PSD

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