Situation No. 1

Bohacz ray
Hot Rod Farmer
Email “The Hotrod Farmer” Ray Bohacz with your machinery-related questions. Visit his site for te...

It has been a rough winter, and the gravel road from your place out to the paved two-lane road is more washboarded than ever. Your wife tells you her car has a terrible rattle coming from the front end. It sounds metallic, as if the bumper is coming off. Concerned for her safety, you take it for a ride, and she is correct – it makes some racket like a barrel of bolts. You decide to turn around to head back to the farm to check it out, and you notice when you gently apply the brakes, the noise stops. Baffled, you ask some of your friends if they have any ideas. This is what they say:

A. Farmer A thinks the front wheel bearings are loose, and when you step on the brake, the caliper holds the rotor from moving in and out.

B. Farmer B says the shock is loose, and with the brake applied, it limits the wheel travel.

C. Farmer C says the anti-rattle clips on the pads are either worn or missing.


D. Farmer D told you that once a car gets a rattle, you can never get it out.

Situation No. 2

You are having breakfast with some buddies at the café in town, and this question comes up: Why does an older diesel engine run poorly for a minute or so in the cold weather even though the fuel is not gelled? The guys at the table offer these explanations:

A. Farmer A states that the reaction zone has not yet been established in the cylinder.

B. Farmer B says Farmer A is making things up. He has been farming for 40 years and has never heard of that. He says the fuel is not gelled, but the cold makes it too dense, and the engine cannot burn it.

C. Farmer C believes the glow plugs are not working.

D. Farmer D blames the ULSD fuel today and calls it junk.

Situation No. 3

You caught the rally in beans with some talk of China coming back into the market. While running a few loads to the elevator before the market pulls back, you notice the engine in the semi is running more boost than usual. You also see when this happens, the EGT goes higher. Not wanting to stop hauling, you just modulate the turbo boost by easing out on the throttle. That works, and you sell all your old crop at a good price. However, you are now worried the truck may have a problem with the turbo that will eat up some of your profits. When you get home, you pop the hood and find a small rubber line hanging by the turbo. You connect it, and everything is now back to normal. At lunch the next day, you ask four of your friends if they know what happened and what the hose is for. They are anxious to say:

A. Farmer A says he thinks the hose puts boost pressure to the injection pump.

B. Farmer B is stern in stating it is the boost sensing hose to the wastegate actuator.

C. Farmer C is confused since the turbocharger is controlled by the throttle pedal.

D. Farmer D believes the hose somehow tells the turbocharger to shut down if you use the Jake Brake.


Situation No. 1: Farmer C is correct. The anti-rattle clips are either missing or have lost their tension. The clips are used to keep the brake pad tight against the caliper and not allow them to rattle when the piston is retracted. On some vehicles, ineffective anti-rattle clips will make you think the bumper is falling off. To test if the noise is the brake pads, drive over some bumps and then do it again with the brake pedal slightly depressed so that the pads hug the rotor. If the rattle goes away or is greatly diminished, the pads are the culprit.

Situation No. 2: Farmer A knows what he is talking about. In both a gasoline and diesel engine, a reaction zone needs to be established. That is where the heat from the flame travels to the not-yet-combusted region. Since an older diesel has no other heat source (new diesel engines keep the glow plugs on after the engine starts), the flame becomes partially quenched until the reaction zone is established. On a gas engine, this occurs also. Still, only the flame speed across the bore is impacted; the operator of the engine is unaware of the lack of a reaction zone.

Situation No. 3: Farmer B understands the system. Most but not all turbochargers use an internal wastegate that is controlled by a wastegate actuator. The hose that fell off on the subject engine supplies manifold boost pressure to a sensing spring. At a specified setting, the manifold pressure overpowers the spring. As a result, the wastegate is opened, bypassing exhaust flow to the turbine wheel.  

Email “The Hotrod Farmer” Ray Bohacz with your machinery-related questions. Visit his site – Farm Machinery Digest  – for technical articles and to listen to his Idle Chatter podcast, which has listeners in 83 countries. Also tune into Farm Machinery Digest Radio on Sirius/XM Channel 147.