PDA

View Full Version : engine braking


Gnat5680
July 7th, 2006, 21:45
so im starting to engine brake alot more now. you know down shifting going down a hill.

heres the question.
How many gears are in a 95 country? second, if im doing around 40 and down shift to 3rd gear and the tach does not go up over 2000 rpm can i drop down to 2nd?

i would have searched but i didn't think i would find anything.

creeperjeep
July 8th, 2006, 16:47
If you want full control you should look into brettm's aw4 shifting products.
http://www.awshifting.com/

kennzz05
July 8th, 2006, 19:54
brake pads are cheaper than a tranny stop downshifting. I read this reply in hot rod about your question hope it helps, makes sense.When i first got my license i hand shifted the old dodge dart all the time wasnt long b4 it needed a tranny rebuild sorry dad! guess all the neutral drops didnt help either!

old_man
July 8th, 2006, 20:55
Trannys hold up better than brakes here in the mountains.

WB9YZU
July 8th, 2006, 21:19
so im starting to engine brake alot more now. you know down shifting going down a hill.

heres the question.
How many gears are in a 95 country? second, if im doing around 40 and down shift to 3rd gear and the tach does not go up over 2000 rpm can i drop down to 2nd?

i would have searched but i didn't think i would find anything.

Manual or Automatic ( I can never remember who has what rig).
A manual 5 spd has 5 gears.
An AW4 automatic (used in 87 and up XJs) has 4 gears, 3+OD. 3rd gear is straight through; 2nd and 1st have gear reduction and are useful for engine braking.

Tom is right on, if you do mountian driving, you will find yourself engine braking and here is why: When you use you brakes for an extended period of time, they will fade and become useless. I have seen SUVs with white smoke coming off all four corners at the bottom of a long grade and wondered how they heck they got it stopped!

When you engine brake, you bypass that whole problem and things are just peachy at the end of the grade.

That being said, I have an automatic on the XJ and I generally do not use engine braking in everyday driving or on mild grades. I do use it when I am hauling a trailer (slowing to a stop), or going down a very steep grade and want to save the effectiveness of my brakes. I have not had a problem with the engine over reving while engine braking. The torque converter just doesn't reverse couple that well.

My YJ is another matter. Since the YJ is a manual, I upshift and downshift at will and almost never touch the brakes unless I am going to actually stop. Since the manual is directly coupled, I downshift gradually and rairly miss a gear to avoid over rev.

Matthew Currie
July 8th, 2006, 21:27
brake pads are cheaper than a tranny stop downshifting. I read this reply in hot rod about your question hope it helps, makes sense.When i first got my license i hand shifted the old dodge dart all the time wasnt long b4 it needed a tranny rebuild sorry dad! guess all the neutral drops didnt help either!

I don't think you can generalize about downshifting from what happened to a Dart after a lot of neutral drops! Anyway, it might depend on when and why you're downshifting. Manually up and down shifting an automatic to change the shift points and eke out performance can be pretty rough, especially if you do it abruptly. It's a different thing from using engine braking on hills. The engine is doing the braking, not the transmission. I notice that the owner's manual recommends downshifting when loaded or towing to avoid overheating the transmission. Downshifting without using the brakes is likely to be easier on the transmission as well as the brakes, because it won't be slipping and hunting for gears.

RichP
July 8th, 2006, 21:41
I've not owned an auto since 77 and that was the only one I ever owned. That said, my wifes Oldsmobile cutlass has two drive postions, normal D and a D with a circle around it [Over drive] Around here in the poconos it stays in D not OD, OD is reserved for the flats and interstate. She drove with it for a few years around here in OD and we ended up putting a new tranny in. In D it does pretty good and downshifts going downhill if you take your foot off the gas, not enough to stop it but enough that I'm not replacing pads every year...

Harlee&Tahoe
July 10th, 2006, 08:40
Is engine braking hard on the motor? Any effect on engine parts rings and such? 4.0's are notorious for blow-by, would this make symptoms worse?

dmillion
July 10th, 2006, 08:52
brake pads are cheaper than a tranny...
A tranny is WAAAY cheaper than a funeral! You live in Maryland, where the "mountains" are really just big hills, so maybe you don't know this, but brakes can and do fail. Usually from overheating, usually from overuse. Here in Colorado, if you find yourself riding the brakes then you need to downshift.

Engine braking is not hard on the motor, but it will cause you to use more gas than just coasting. Nonethless, remember my first sentence above. The corollary is that the little bit of extra gas you'll use is ALSO a lot cheaper than a funeral!

Beyond that I will add that a lot of people just use their brakes wrong when in the mountains. They hold the brake down just a little bit, dragging them just enough to slow themselves down a little, and ride all the way down the mountain like that. BAD IDEA!!! First downshift so that the engine controls your speed mostly. Second, when you have to brake step on the brake hard enough to really make a difference, and really slow yourself down some. Then get your foot completely OFF the brake and let engine braking control your speed for a while. If your speed slowly creeps up then, when you have to, brake again enough to make a real difference and then get your foot completely off the brake again. If your speed jumps up quickly then you need to downshift even further.

I have seen a pickup truck lose its brakes and go off the side of a mountain road. Luckily for the driver the drop-off was only a few feet and he survived. Every year there are a few who don't. Don't be one of them!

Rick Anderson
July 10th, 2006, 10:49
Everyone makes valid points here, may I restate the concept better:

Brakes are cheaper than Drivelines (its more than the tranny, clutch, the axle, U-Joints and motor mounts are all taking a beating as well).

But Drivelines are cheaper than ENTIRE VEHICLE AND/OR YOUR LIFE

IMHO, Engine Braking is uneccessary for normal slow downs and stops and you should just use the brakes and avoid the shock and strain on the rest of the driveline.

BUT there are lots of abnormal stops and slowing that will overheat the brakes, and when they overheat they fade and/or fail. There are lots of accidents at the bottom of mountain roads from people that can't stop because they overheated their brakes riding them all the way down the mountain.

Understand how your brakes work, and look over your driveline while someone revs the engine or puts it in gear with the brake on to strain it, you'll see the stress's and you can figure out when its appropraite to just use the brakes or use engine braking to keep the vehicle at speed down extended hills/mountains.

Someone was asking if engine braking is bad for the motor? Perhaps, if the motor isn't particularly strong, riding down the mountain side while engine braking could put your engine under an extended off proper A/F ratio, the motor had to be pretty out of tune or poorly designed for it too bad enough to be anything but negligent. Mostly its everything in the power train BUT the motor, that takes the shock and strain, although not bad, its still adds up and adds to the wear.

Back in the CARB days, I had a friend thought he would save gas by turning the motor off as he engine braked all the way down the mountain side. Think about how a CARB works, all he did was turn off the ignition while the motor still turned, it continued to suck gas thru the motor BUT didn't burn it. At the bottom of the mountain, he turned the ignition on again and the entire bottom of his truck exploded in a fireball and blew the entire exhuast off the Pick-Up, leaving charred and burst pipes and mufflers on the road. The motor was fine, he just needed an entirely new exhaust.

RichP
July 10th, 2006, 15:51
A tranny is WAAAY cheaper than a funeral! You live in Maryland, where the "mountains" are really just big hills, so maybe you don't know this, but brakes can and do fail. Usually from overheating, usually from overuse. Here in Colorado, if you find yourself riding the brakes then you need to downshift.

Aparently you have never been in western maryland, I remember one hiway there that had a 5mi very very steep downgrade with a T at the bottom, straight ahead right on the top of the T was a 500ft high rock wall with about 200 crosses on it... I remember one turn on the blue ridge parkway that was so sharp you could see your tail lights in your rearview when going around it, Granted not alot like the rockies but they are there...

Matthew Currie
July 10th, 2006, 17:23
Couple of observations:

Normal slowing down does not need downshifting, at least on an automatic that works well; the tranny will downshift as needed. Needless shifting of gears is not going to do the drive train any good. But long descents are a different matter. This is not beating up on the drivetrain. There's no more abuse of drivetrain in using it to slow the car down than there is in using it to speed it up, which is what you do every time you touch the gas pedal. That's what it's made to do.

I remember reading the owner's manual for the 58 CJ5 we had in our family when I was a kid (and which I wish now that I hadn't sold, despite its rusty frame and bad valves). Practically every page reiterated: "don't ride the brakes, use the engine as a brake." Of course, the CJ5 had disastrously bad brakes, so perhaps they were just hedging there, but the Jeep folks certainly were not of the opinion then that it was bad for the engine.

Take the shuttle bus down Mt. Washington some time. Last time I was there, at least, they used ordinary one-ton GM vans with automatic transmissions. They do not touch the brakes all the way down unless they encounter an obstacle. They rely entirely on extra-low geared differentials and engine braking.

In my argument here, though, I'm assuming that one uses the shifter gently, at appropriate times, not smoking tires or trying to get sporty performance out of a slushbox.