Switch Heater
Q:
My '96 Dodge Ram pickup has a heater/air-conditioning problem that I can't figure out. When the heater is on without the defroster, the system sometimes jumps to defrost for no particular reason. It doesn't seem to matter how long the truck has been running or what the weather conditions are. It seems that the problem is somehow related to acceleration. The problem happens when I'm entering a freeway onramp or leaving a stop light and accelerating for a substantial distance. Why is this? Is this a difficult problem to fix?
Trevor Porter
Flagstaff, AZ

A: It sounds as though you have a defective heater/air-conditioner check valve. Other '94-'96 Dodge Ram pickup owners have also reported this problem. The check valve doesn't seem to stay in position under hard acceleration. Dodge released a replacement check valve (part number 4677204), which should solve the problem. The other solution is to drive like an hourly employee running errands in the company truck.

Gimme A Brake
Q:
How many times can rotors be turned? My '94 Toyota SR5 seems to go through brake rotors quicker than any other truck I've ever owned. The truck is two-wheel-drive, with the 3.0L V-6 and automatic transmission. I live in hilly country, but my brake problems seem to be much more frequent than those of ny of my friends who drive trucks on the same roads.

My brakes have a noticeable amount of brake-pedal pulsation, which I find very annoying. I've had the rotors turned twice. The current rotors are replacements because the ones that came on the truck were too badly worn to turn. It was suggested to me that besides living in the mountains, the lack of asbestos in modern brake pads creates more heat, which warps the rotors. If that's true, can I still find brake pads with asbestos?

The first time I had the rotors turned, they worked fine. The second time, I took them to a place that charged less, and I've been experiencing more brake squealing. Is there an obvious reason for that? Do you think there's a connection, or is it just a coincidence? What can I do to get more miles between brake jobs?
Allan Pindroh
Kalispell, MT

A: The number of times you can turn a set of rotors depends on how much metal is left. There is a factory-specified minimum thickness that no responsible shop will exceed. Those specs are usually stamped into the rotor. You may need to clean the rotor with steel wool to see the minimum thickness. The number of times that the rotors are turned affects their ability to dissipate heat. The more times the rotors are turned, the hotter they tend to run, leading to more warpage in a relatively short amount of time. In general, two times seems to be about all the average rotor can be turned.

Having the rotors turned (always turn them in pairs; front or rear pair on four-wheel disc-brake vehicles) can sometimes cost nearly as much as replacement rotors, which is something you should consider any time you're thinking of having a set of rotors turned for the second time.

As to why the rotors squealed more after switching shops, the second shop might not have done a good job of sanding or cleaning the rotors. Turned rotors should be sanded for a random crosshatch finish. They also need to be thoroughly cleaned to eliminate any tiny metal particles that can get imbedded in the brake pads. Both of these situations can cause squealing.

Blaming the lack of asbestos for the excessive warpage doesn't make sense. The old asbestos-based brake pads were more harmful to rotors - not less. Our biggest gripe about asbestos-free disc-brake pads is that they generate a lot of brake dust, which translates to more-frequent wheel cleaning. Since you have the squealing problem, there is a very slight possibility that the budget shop didn't do a good job.

Brakes pulsate when the rotors warp. To not pulsate, the rotor surfaces need to be totally flat and parallel to each other. The standard parallel tolerance is 0.0005 inch. Runout tolerances typically range from 0.002 inch to 0.005 inch. This means that it doesn't take much of a variance to cause problems.

Rotors are traditionally turned on a lathe after the rotors have been removed from the truck. Some shops offer rotor turning while the rotor is still attached to the vehicle. This method ensures that the machine work is true to the axis of rotation. Since you've had repeated problems, it might pay to find a shop that can do in-place rotor turning.

Any wobble in the brake system can lead to premature rotor wear and brake-pedal pulsation or vibration. Something as seemingly simple as improperly tightened lug nuts can lead to warped rotors. That's why lug nuts shouldn't be installed with a powerful air wrench and should be torqued to the manufacturer's specs. Loose wheel bearings can cause unwanted vibration, too.

A final thing to check is how you or anyone else who regularly drives your truck treats the brake pedal. Some drivers rest their foot on the pedal. Even a tiny amount of constant drag can generate excessive heat and lead to warped rotors.

Tow Woes
Q:
I'd like to use my '72 Chevy Fleetside shorty to tow an enclosed tandem 26-foot race-car trailer or 20-foot day cruiser. The truck has a relatively new Goodwrench 350 engine, but still has the original (I think) turbo 350 transmission. I've had problems in the past with transmission failures in other trucks due to overheating. I plan to install an auxiliary transmission cooler. Would it be helpful to install a transmission temperature gauge, or is that really necessary since I have the cooler? Does it matter what the transmission temperature is as long as you can't smell hot fluid? What temps are normal for a transmission?
R.L. Ingram
via e-mail

A: It helps to stay cool if you want to tow without woe. Heat is public enemy number one for automatic transmissions, so anything you can do to keep heat at bay is good. We learned the hard way about towing a car trailer on a 100-degree day with a Chevy pickup equipped with a stock turbo 350. Excessive heat fried the transmission's friction plates.

The transmission was rebuilt with B&M Performance Products parts designed for tow-and-go applications. Besides all the heavy-duty internal components and tow-style torque converter, we added a big auxiliary cooler; a thermostatically controlled auxiliary fan with a manual override switch; a larger B&M transmission pan; and a transmission temperature gauge. We filled the transmission with B&M Trick Shift fluid and never had the slightest towing problem after instituting those upgrades.

A transmission temperature gauge is a very useful addition for anyone serious about towing. Most automatic transmissions should operate at 225 degrees or less. When temperatures top 240 degrees, the additives in the transmission fluid start to break down. That leads to that dreaded burnt-smelling fluid. If temperatures continue to rise to the 260-degree plateau, internal seals can lose their sealing capabilities. Then internal and external leakage begins. At about 300 degrees, the clutch plates start slipping. When temps reach 315 degrees or more, the clutches and seals burn up, the transmission oil is wasted, and the transmission is soon history.

With a transmission temp gauge, you can spot potential trouble before it strands you on the side of the road. Although we installed a thermostatically activated fan, we preferred to watch the transmission temp gauge. On big hills, we engaged the fan as soon as any heat increase was indicated. We pulled a loaded car trailer from Los Angeles to Seattle through several mountain passes in the middle of summer and never saw the transmission temperature leave the safe zone.

You can monitor the transmission temperature in a single location or, if you want to be extra well-informed, on the inlet and outlet side of the cooler. For two locations, you need two sending units and a toggle switch on the dashboard so the gauge can read one side or the other.

It's a good idea to use as large a transmission cooler as possible on a tow rig. The ideal mounting location is in front of the radiator, which shouldn't be a problem on most trucks. This mounting location allows the cooler to receive fresh air first.