R&R flex pipe

Had a of a time replacing the 2 flex pipes today. My questions are...
1) is it mandatory (DOT rules) to have any flex pipe on the exhaust?
2) what's the trick to getting the new flex pipe on?
3) can/should the ol' metal bands be reused?

 

Take a file to prep the inside of the pipe. New clamps. I use as much hard pipe as possible, but you need flex in certain places. You need flex. The engine and frame will flex at times. Hard pipe all the way would break

 

Always new clamps. Flex pipe is spiral and I've had good luck trying to "thread" it on. I always put a wire wheel on my die grinder and cleaned all the rust and debris off the solid pipes.

No idea if there are rules against not having flex pipe but I would for sure have a section of it, especially if you've got a truck with an air ride cab that has the exhaust hanging from the bottom of the cab. You need that flex where the cab pivots.

Even on a truck with the exhaust under the frame you'd want that flexpipe because your stacks are usually attached to the cab. I know the top stack mounts can flex but you want a little bit of give on the pipe as well.

 

Excellent answers. Thank you both. Time to get some more tools.

 

Definitely need some flex pipe as others have mentioned. Another problem that wasn’t mentioned was putting too much stress on the turbo exhaust housing.
I actually know of one where the back of the housing broke off from a rigid exhaust. It was on a farm truck that gets abused and had sloppy engine mounts but I can’t see a road truck being immune to such problems. I also think the turbo housing might have been a cheap reproduction because it sure seemed pretty thin. As far as reusing the band clamps it can be done successfully if they’re not stretched funny. I generally won’t do it on a customer truck but have done it several times on my own trucks.

 

I find the bolts are always NFG once they come out.

 

They make a product for slip joints. Looks like black grease. I saw a Mechanic using it once at a Peterbilt Dealership. Some type of paste, that also hardens and fills small gaps. I’ve never used it myself. Sure made the job look easy. A little grease or WD wouldn’t hurt. I had a hard time recently, changing the elbow off the turbo. It was stuck inside the flex. PB Blaster and an hour of pounding with a hammer finally got it out. I use the good SS full wrap clamps with a flare in them. They last almost forever. I usually buy a couple new ones for the outside elbows when replacing, and re use the best of the old ones underneath. I keep any of the old ones that are still in decent shape. They’re expensive but worth it. The cheap flat stretch type with aluminum foil packing always leak and break if over torqued. I cut the stacks off 4-5” at the bottom last time I replaced mufflers. Swapped them so the dents and faded chrome is on the inside. Anything to save a Buck, Lol. With the new shiny saddle clamps, good full wrap band clamps and elbows, my 20+ yr old stacks still look good. Whatever that black stuff is called, maybe exhaust paste? I’ve seen it before while taking the original exhaust apart. It crumbles apart, looks like carbon, but it’s the paste. I’ve seen it for sale, just never used it. Good for sealing the slip joints. Avoiding the small leaks. My FLD only has one short piece of flex. I upgraded the pipe off the turbo, from a short 1/4 turn, to a full S style. Now the flex no longer breaks every couple years. The straighter, with less stress points near the ends, the better. You want it to flex in the middle of the run as much as possible. Mine used to break at the turbo flange end. I’d have to buy 3’ of it every 2-3 yrs. Now it’s shorter and lined up straight, and has lasted over 5 yrs. so far.

 

Spend the money and get the good stainless flex pipe, that galvanized garbage stuff you'll be lucky to get a couple years out of anymore.

 

Yep spend money on the 304 stainless not the crappy 409. Also get some good pre-formed 304 stainless clamps. Grand Rock and Donaldson both make quality clamps. I sometimes notch about a half inch slot with a cut off wheel in a couple or 3 places around the end of the flex if it's in a difficult area. Don't notch it too far tho.

 

You can also use the copper based anti-seize compound on the joints to keep them from corroding and make it easier to take apart much later.

Hacking old pipes apart is pretty much par for the coarse tho.