Hi,

I have an F700 bucket truck that has a 534 engine in it. There is very little left of the muffler, and I would like to replace it. The Y-pipe comes from the engine and collects into a single 3" OD exhaust tube. The local muffler shop suggested that I use a 2-1/2" ID inlet muffler with a 2-1/2" to 3" adaptor to connect to the exhaust tube from the engine. I mentioned this to the guy I bought the truck from, and he said that the smaller muffler would create too much of a restriction, and the valves would burn up in the engine. Any thoughts on this?

Secondly, the person that I bought the truck from, suggested not revving the engine past 3000 RPM, or the engine may come apart. Are there any time-proven guidelines on this?

Thank you,
Greg

 

There are tons of 3" mufflers, mostly for folks who want to make their SUV louder. Gibson, Magnaflow and many others sell them.

Google "3 inch muffler" and find a 3" inlet with 2 3" outlets on ebay.

Google "3 inch truck muffler" and finally find some truck stuff like this:

Grand Rock Truck Exhaust Systems - Performance Exhaust, Performance Exhaust System, Diesel Performance Exhaust, Heavy Truck Exhaust, Performance Muffler, Quiet Performance Muffler, High Performance Muffler, Truck Muffler, Exhaust Muffler, Diesel Perf

According to many posts, these things run the exhaust manifolds red hot as it is, so no point in adding back pressure.

And I would head the 3000 rpm warning. Lots of OLD iron flinging around in there just waiting to be liberated....

 

85E -I had been to E-bay, and had found many 3" mufflers for the little sports cars that you described. The key word that I lacked was the word "truck". I will check again. Thank you. Greg

 

Greg, Save yourself time & money, go to any heavy truck place such as Freightliner, International, Mack, etc. A muffler for this kind of service is just that, A muffler. I have used many farm tractor andheavy truck mufflers on these engines over the years with no ramifications. The engine should live long at 3000, but can turn to 3200 easily. The key is to keep the bottom end tight, and sometimes the cost of dropping the pan and installing a set of inserts is well worth the money. These engines seem to pull hard around 2200-2800, so why beat em to death at 3000-3200? These engines are pullers, not speed demons.

 

Scrapiron - I've noticed that the Allison seems to shift nicely when the rpm range is as you mentioned, and overall, the truck gets up to about 50 mph fairly quickly - in about 1/2 of a mile or so. If the engine is revved up to 3000 rpm, it doesn't really seem to get to speed any more quickly than at the lower rpm's. Am never in a hurry with this vehicle anyway. My real reason for redline concern is in the event the transmission should happen to downshift when I already am at about 2800 rpm. This may send the engine into redline according to the previous owner (who had to replace an engine for this reason).

 

Greg, If you can, please find the ID tag on the tranny, &give me the numbers. With the age and application, I am assuming it to be a 545. The 545 & 540 are identical on the outside, but the 545 has a PTO gear. It could also be a 643, but would be a longshot. The vehicle speed is really a function of the 3rd member, and these trucks generally came with a gear in the 7.5 to 1 range(7.42 was real popular). You could greatly inprove your speed performance, and economy by upgrading to an Eaton 2 speed unit with a top side of about 5.66 or 5.83. the bottom side will be about what you have now. I am in Iraq right now, so I don't have references handy, and am doing this from the top of my head. If you are running 10.00X20 tires, a 5.83 will give you 63 MPH @ 3000.( Just a quick figure, i don't have my calculator).The 534 should pull a 5.13 real well, unless you are real heavy, and in a lot of hills. The Allison was not bad about sudden downshifts unless forced to it. The most common problem with a mechanical Allison is the kickdown linkage as it controls most of the operating pressures.I would suggest that if you are not comfortable with the performance, take it to an old fart mechanic, and have him look it over. Keep good ,clean ,and proper fluid in it, and you should have no trouble from it. The 534, in my experience has but one mechanical weakness, and that is the main, & rod bearings. watch the oil pressure closely. I always run a very good, tight gauge with 1/4" aeroquip lines to it. this makes the gauge very quick to show any changes in pressure. I ,personally change out the rod bearings at about 65-70, 000 intervals, adjusted for idle & work time. One observation I go by is if the engine is somewhere in the 2000-2500 range & pulling, just back off the throttle. If the oil pressure increases over about 5or 6 psi, you may have the mains needing attertion. Inversly, if you are at a high idle, & punch it hard, and oil pressure drops as much, it is probably time to get some rod bearings.I guess that I am rambling a bit, but am trying to share what I know. If you wish to communicate off forum, you can e-mail and I will provide phone numbers, as long as such does not break rules. I am new here, and would hate to be kicked out this early. Thanks much. Scrapiron

 

Scrapiron -

This computer is not at my house, so it sometimes takes a while for me to see a post.

This bucket truck is used almost entirely on my own property for storm damage control on my trees. Whenever there is a storm, there almost always are several trees that the tops are partially clipped, and a lot of the branches are still hanging in the top of the trees. Driving down the road is something that only happens a few times a year, and that is when I drive to help a friend who has a tree that needs attention from a storm as well. Even though I don't drive it much, I was concerned about over-revving the engine when coming to a hill. Also, the muffler does not really make a difference when on my property, but across the road, I choose not to attract unnecessary attention. For the $50 bucks or so for a muffler, it would be a good idea to get one.

Thank you for your ideas!

Greg

 

Hi Greg:

What year is your truck? Ours is a 73 with a 477 motor and it also was in bad need of a muffler. The Y-pipe is a 4" OD pipe. After phoning several local muffler shops I found several who could get a muffler to match. Are you close to a NAPA store? Our local store has a book which list all sorts of mufflers based on specs like 3.5" OD inlet with 2ft long body and 9" round barrel (width). It only took a matter of about 10min of flipping through pages to locate a muffler I could use and they even had it in stock at there local warehouse. My search also turned up several local shops which specialized in mufflers for larger trucks. At any rate, if you are close to a major center you should be able to find what you are looking for.

An interesting though I had is your truck has a larger motor with a smaller exhaust. Could this be that back pressure is not really critical. Just wondering.

PaMnd

 

PaMnd - My truck is a 1978. I looked at the pipes, and they all look like they could be stock, but it is old enough that you never really know for sure. Thanks for the tip on NAPA. There is one not too far away, just never made it there. As for the back pressure question, I don't know very much about these big engines (didn't know a 534 existed until I had one), and was hoping someone would chime in that knew. Thanks again, Greg

 

I am running a 3" magna flow muffler on my john deere 4020. it sounds awsome and is not too loud considering it is a straight through design. Any way it is stainless steel and if it will live on a tractor that is always under load im sure it will be happy on your truck.