new belts on diesel motor squeaking

No its not normal

Once a belt starts to squeak the rubber is usually glazed and will not get better. I'm guessing that the belt was not properly tensioned when installed or that it was just too long(wrong belt) to be properly tensioned.

We need more information:

What engine?

What belt?

Automatic tensioner or manual tensioner on that belt?

Miles on coach?

Were the belts replaced as PM or was there an issue. If an issue, were all the items driven by that belt hand spun to check for failing bearing? Alignment of pulleys?

Wolfe10 - Engine is a 350 Cat. We don't know which belt. We had the main front seal replaced. While they had the engine blown apart I had them replace all the belts as PM. I don't know the answer to your other questions. I can hear the noise from the rear in the drivers seat!

I could be a belt is loose.

The Caterpillar C7 very likely has two belts:

An old fashion V belt that drives only the water pump. So, crankshaft pulley, water pump and manually adjusted idler pulley. THIS BELT IS CRITICAL-- if loose, the water pump may not turn and engine will overheat. It can only be checked from below-- driver's side of engine between block and fan shroud. It doesn't need to be bar tight, but should not be loose.

The other belt is a serpentine belt which drives the accessories. So, crankshaft pulley, alternator, A/C compressor and automatic belt tensioner.

Here is a good video on belt tensioners from Gates Corp: https://www.youtube.com/watch?v=uTLV5IU_IMM

BTW, it if the old belts did not squeal, it could be something as simple is the wrong belt-- if an inch or two longer than the correct one, tension would not be correct. Or the new belt(s) may not be installed properly-- perhaps a groove off.

Call Freightliner with your VIN and get the correct belt part numbers/belt description and compare with what they put on: Freightliner 800 385-4357

thegriffins wrote:
Just had all the belts replaced on our diesel Freightliner chassis. Before we left we noticed they were squeaking very loudly. We had the repair man check them. He sprayed belt dressing on them and it helped for literally a minute. He told me to drive it a while and the squeak should go away. It has been driven about 60 miles. It's now squeaking louder than ever. Is 60 miles not enough? Is this normal? Was the mechanic just trying to get me out the door?

you have two belts or one? Most diesel pushers have a serpentine drive belt and a regular V groove just to drive the AC compressor
Does It sqeak just sitting there idling or only on acceleration?
Big difference on what the problem may be
also need to determine which belt is the culprit

Actually, many Cummins engines have a separate belt for A/C.

Most Caterpillar engines (3116, 3126 and most C7's) have a separate belt for water pump with the serpentine belt driving A/C compressor and alternator. The theory here is that a bad bearing on alternator or A/C compressor will not cause overheating/shutdown.

Take a cake of soap rub it on the inside of the belt if you can reach it. It should stop, unless there is something wrong that need an adjustment.