I’ve got a 94 Mazda B2300, 131000 miles.I drive it on the freeway at normal speeds, take my foot off the gas to let someone merge or something and then put my foot back on the gas I hear a load bang. Sort of like a hammer hitting metal. Doesn’t make the sound in 1st 2nd 3rd or 4th just 5th gear. Crawled under and all the mounting bolts / structures appear solid. The drive shaft has about 1/4 inch of play in it with the car parked in neutral (I know it’s not good to get under with it in neutral but I blocked the tires… Is 1/4 inch of play normal…??? Any other thoughts on what it might be…??
New driveshafts have to be made for the truck and they work great and have u-joints that can be replaced. They cost about $600 and you should have a shop do the work because sometimes the new shaft is too short or long and has to be redone.
When you get the new one, make sure that the rear end of the truck is at the right height. A driveshaft that is perfectly straight will wear out the universal joints fast. They need some angle so that the needle bearings can rotate slightly in order to get the benefit of lubrication and so they don’t wear in one spot on the bearings.
how does the drive shaft itself go bad? I can see the ujoints but needing a new drive shaft…?
What do you mean by 1/4" of play? If the engine is in neutral and you can turn the front of the driveshaft back and forth 1/4", the play could be in the driveshaft or in the rear axle. If it’s that much play between the front and back of the driveshaft, I’d be surprised that it’s still in the car and not on the roadway. But that much play through the entire rear axle doesn’t sound as bad. Can you hear a gear growling coming from the rear when you accelerate or decelerate but not while coasting? If so, you might want to have the rear axle checked.
Do your accelerate/decelerate thing in 4th, then shift to 5th and repeat. If it only does it in 5th, it’s the transmission. Those Mitsubishi 5-speeds have a tender 5th gear. Does it make noise when in 5th (overdrive)??
I’ve seen this before. Have you messed with the springs or suspension (Maybe to raise the truck body)?
If so, you maybe got a U-Joint aligned too straight. It needs some bend in it to work. Get it perfectly straight, and it will sometimes lock (Just like the gimbal lock they were worried about on Apollo 13). You get a bang, with no explanation as it pushes the shaft sideways.