Originally Posted By: MolaKule
Quote:
tqh: Is it bad for the transmission - as long as I keep the rpm within a reasonable range (< 3000 rpm)
Consider this, high temperature in a transmission degrades the fluid through oxidation, and increases wear in the clutch packs, etc.
Using a transmission in a lower gear to do your braking raises internal transmission temperatures.
Brakes jobs cost much less than a tranny replacement.
I think a better approach is to anticipate the hill and slow at the top so your descent speed will be slower as well.
I think it comes down to frequency, duration, grade, and the ability of your transmission and its cooling system (if any) to keep everything working within its normal parameters. I would not downshift for a 30 second downhill coast where one or two moderate applications of the brakes would suffice. But I did keep the GP in 3rd for most of a 15+ mile downgrade coming down a mountain in 50F weather and kept an eye on the tranny fluid temp (one of the readout options on the digital dash info system) to make sure it did not get too hot. With the engine at about 2,000-2,500 rpm with very little load and moving at 55-65 mph, the cooling system had no problems keeping tranny fluid temps in check (making the uphill trip in 3rd was a completely different story!). If you do use engine braking regularly and it does (or you suspect it does) increase tranny fluid temps, I would definitely keep a closer eye on the ATF and change more frequently, perhaps following the severe service interval.
Edit: And as dermapaint said, I would not drop more than one gear, unless I had to crawl down a hill due to slower vehicles in front of me at a speed that would otherwise require constant brake application to maintain a safe following distance.
Additionally, my father used to (don't know if he still does as I do not drive much with him anymore) use engine braking nearly every time he would exit the freeway and never experienced any tranny issues in his Toyota, Nissan, Kia, or GM vehicles that were kept for more than 100k miles each before being totalled or sold to one of us kids (who never experienced any issues, AFAIK). Before finding BITOG, I did not realize transmissions or engines could/do give people so many problems or require rebuilds/replacements before 200k miles!