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Exhaust Brakes vs. Automatic Transmissions
Q: I will be purchasing my first diesel soon to tow about 8,000 pounds of boat, fuel, and gear. It will probably be a used 1-ton (F-350 or Ram 3500). I would like to have an automatic transmission for my wife but would also like to add an exhaust brake to help slow things down. Someone told me that factory automatics can't handle exhaust brakes. Can you give me some advice on whether or not this is true?
Louis Wacker
Nashville, Tennessee
Shown here is a complete BD...
Shown here is a complete BD Diesel Performance exhaust brake kit for a Ford 7.3L Power Stroke application. Notice that a lot more than just the exhaust brake is included, as wiring and a transmission pressure control device are also added to ensure the exhaust brake works properly with the rest of the vehicle.
A: Whoever told you stock automatic transmissions can't handle exhaust brakes is right--sort of. What happens is that on a steep grade, the stock transmission will only know that you let your foot off the throttle, so it will decrease the internal hydraulic line pressure within the transmission. What the truck doesn't know is that it might have 10,000 pounds behind it, pushing it down the hill. When this happens with little-to-no line pressure, the transmission may slip, because there's insufficient line pressure to hold the clutches engaged. The good news is there is a relatively easy fix for this problem.
We talked to Harvey Grant, of J&H Performance (www.jandhperformance.com, [530] 245-0176) who installs at least one exhaust brake a week, to get the lowdown on what's needed to make sure the transmission lives. Grant advised us that for an exhaust brake to work properly, the transmission must be able to lock the converter on a downgrade, as well as provide sufficient line pressure. Fortunately, this is a known issue with exhaust brake installs, so companies such as BD Diesel Performance, ATS, and Banks offer transmission control devices that will work in conjunction with exhaust brakes to ensure the transmission is not damaged.
Just in case you're wondering why you'd need to spend the money for a little extra braking power, we have this tidbit for you. In the last few years, Grant has seen exhaust brake-equipped trucks go 100,000 miles on the original brake pads! So in summation, yes, exhaust brakes can hurt automatic transmissions if the line pressure remains at stock levels in the transmission. Newer computer-controlled transmissions, such as the Allison transmission found in '01-and-later GMCs and Chevrolets, have enough built-in computer controls to be able to handle exhaust brakes without any additional modifications.