Is it OK to force downshift with auto tranny?
 

Hi folks,

Say I'm going down a hill, or pulling onto a highway off-ramp at around 45-55 MPH and I want to cut some speed.. Can I shift down to the L (or whatever is directly below D, the one that limits the tranny to 3rd gear)? Is that going to wear out my transmission, even if I follow the gear-speed limits on the speedometer?

Thanks!

the synchronization required to get the speed at 45 mph will almost certainly be too much. Id avoid soing that until youre at 25 or so. wear is almost certain at such high speeds, IMO, considering the RPMs these cars do.

I've never heard anything bad about it, but I personally wouldn't use the engine/tranny to slow down. I *do* use it to limit speed though, just not to slow me down to that point. Brakes are a whole lot cheaper than engine parts. ;)

John
'79 300SD

[QUOTE Brakes are a whole lot cheaper than engine parts. ;)/QUOTE]
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Cheaper than tranny parts also !

Check your owners manual... gives good info. about how to use the auto trans.

I checked last night. I guess I was only downshifting around 25 or 30 MPH. But I see your point... Brake pads are cheap.

Thanks!

The transmission will have to use its internal friction lining in the clutch packs and brake bands to engage the lower gear and pull the engine up to the higher RPM.

So, no it will not break anything, however, it will obviously put more wear on the transmission. If you use your brake pads twice as much, then they will last half as long. If you make the transmission do twice as many shifts that require a lot of work on its part, then the friction materials will last half as long. Get the idea? If you require a part to do a lot more work, it doesn't necessarily break anything, it just reduces its life.

AND it is MUCHO CHEAPER to replace brake pads than transmission bands.

I don't like to force downshift. I do shift into L (2nd) at some stoplights when I need extra braking force. I noticed that I get much better engine braking below 1500rpm. I think boost has something to do with low effort above that.

Upshifts are different. I use my shifter kinda like a manual to control shift points.

I keep it in L all the way to the automatic shift to 2nd at 4k.
Up to S at 3500rpm.
Up to D when I reach the speed limit or 3500rpm (Whatever comes first.)

My 617 kind of struggles above 3500, otherwise I'd be choose to be at 4000 before shifting.