Manual shifting your auto for engine braking

[NickTransmissions]

I utilize manual shifting often when towing. It really helps going down a grade pulling over 15k. I try not to force the transmission to take the hit, I usually floor it momentarily to get the gear I want then move the shifter to that position, or Rev match a down shift. Yes, you can Rev match an automatic if you know what you're doing.

I agree with this approach and do it as well on steeper grades in my Tahoe (4L60E) if towing anything...

To all: Automatic transmissions that have overrun or other additional applied elements that come on when selecting a manual range setting are designed specifically to facilitate engine braking so you won't hurt the transmission if those elements are used judiciously and within their design limits.

 

[L31MaxExpress]

The main thing I want to install in the 4L85E is the Line to Lube kit I have. I have been told numerous times that the rear lubrication circuit greatly benifits from installing it and I now make enough torque that it should probably be addressed.

 

[L31MaxExpress]

I agree with this approach and do it as well on steeper grades in my Tahoe (4L60E) if towing anything...

To all: Automatic transmissions that have overrun or other additional applied elements that come on when selecting a manual range setting are designed specifically to facilitate engine braking so you won't hurt the transmission if those elements are used judiciously and within their design limits.

I like being at a slower speed, in a lower gear prior to going down a steep decline, especially towing. I disagree with those that just say just to use the brakes. It would be a really crappy time to lose a brake hose, caliper seal or master cylinder seal. There is a low area I go through going to the lakehouse that is 1/4 mile of 10% downgrade, followed by a narrow elevated bridge over a deep ravine and a 1/4 mile 10% climb back out. I slow to 25 mph and put the shifter in 1st even unloaded.

 

[NickTransmissions]

The main thing I want to install in the 4L85E is the Line to Lube kit I have. I have been told numerous times that the rear lubrication circuit greatly benifits from installing it and I now make enough torque that it should probably be addressed.

Did you drill the pump cover in your 4L80E for the line to lube?
If so, don't add any valve designed to provide line to lube if that .055 hole is already drilled otherwise you'll have too much pressure loss in that circuit.

I like being at a slower speed, in a lower gear prior to going down a steep decline, especially towing. I disagree with those that just say just to use the brakes. It would be a really crappy time to lose a brake hose, caliper seal or master cylinder seal.

Yep, brakes are the most important sub-system in any motor vehicle...Transmissions are cheap compared to what happens when your brakes decide to exit stage left...most likely, you'll be a fast follower.

 

[L31MaxExpress]

Did you drill the pump cover in your 4L80E for the line to lube?
If so, don't add any valve designed to provide line to lube if that .055 hole is already drilled otherwise you'll have too much pressure loss in that circuit.


Yep, brakes are the most important sub-system in any motor vehicle...Transmissions are cheap compared to what happens when your brakes decide to exit stage left...most likely, you'll be a fast follower.

My 4L85E has never been disassembled.

I value human life over the chunk of aluminum and steel. I had a master cylinder fail in an older vehicle once. It was working well one moment then the pedal was nearly on the floor the next moment. Getting stopped was not fun on rear drums alone, even though I did pull the shifter on the 700r4 into 1st gear at 70 mph. The brake warning light came on after I got stopped and I thought to myself that would have been nice to know earlier, lol.

Steering is also a very important sub system. I had a S10 once that broke a motor mount and jammed the steering shaft coupler against a header primary. That was a very interesting moment. All I could do was jab the brakes as the momentum carried me off the road into the ditch, luckily not hitting anything. I learned from that, if it can possibly move, it needs to stay far away from steering linkages.

 

[1998_K1500_Sub]

The "Brake" pressure is adjustable on the electronic transmissions. Brake table is in use for engine braking.

What version of the ECU supports tuning that table? I don't have my JET DST s/w handy so I can't check my 1998's OE ECU tuning at this instant... you often talk about using later model ECUs so it seems like a worthwhile question to ask.

Your "25% engine braking torque" assumption sounds reasonable back-of-the-napkin, to me.

 

[L31MaxExpress]

What version of the ECU supports tuning that table? I don't have my JET DST s/w handy so I can't check my 1998's OE ECU tuning at this instant... you often talk about using later model ECUs so it seems like a worthwhile question to ask.

Your "25% engine braking torque" assumption sounds reasonable back-of-the-napkin, to me.

I am going off back of the napkin numbers from the torque loss tables for the engine. I do not have one in front of me at the moment, but even at high rpm near redline and high vacuum the engine torque loss is fairly low numbers. Under 200 ft/lbs even on an engine like the 8.1L. The smaller the engine the less the number. A 4.8L has less torque loss than a 5.3L which is less than a 6.0L for example.

 

[1998_K1500_Sub]

<snip> so you won't hurt the transmission if those elements are used judiciously and within their design limits.

I usually goose the throttle when I'm downshifting for braking; the only thing I dislike is it takes the engine out of DFCO for a few seconds ... and DFCO really adds to the braking ... so I usually goose it, but not always.


(Edit: I assume everyone knows that DFCO means "deceleration fuel cut-off" aka "EFI shutoff on coastdown").

 

[L31MaxExpress]

What version of the ECU supports tuning that table? I don't have my JET DST s/w handy so I can't check my 1998's OE ECU tuning at this instant... you often talk about using later model ECUs so it seems like a worthwhile question to ask.

Your "25% engine braking torque" assumption sounds reasonable back-of-the-napkin, to me.

I do not have my laptop handy either. I think it exists on the black box, but do not quote me on it. I know it exist on the TBI trucks. The only one I have ever changed it on was a 454 TBI that I put a 4L60E behind.

 

[GrimsterGMC]

The problem with downshifting the 4L60/700R4 is your foot is off the throttle,TV cable not pulled,line pressure down,clutches applying slowly and lightly. All bad! I guess if you shift before you lift you can reduce the slippage by keeping the line pressure up during the downshift.

You make a very good point that I had overlooked. One of the reasons I originally started this thread was I had been reading about fully manual valve bodies and while I didn't think that would be practical in daily use but as usual it triggered my curiosity so I went for a drive to see what would happen. While I have always shifted down into drive for steep down hill runs, as overdrive doesn't engine brake, I found that downshifting into 2nd and 1st for a normal corner etc was quite a harsh downshift if you didn't wait for the revs to drop far enough first. I hadn't thought about the low line pressures due to closed throttle but found the downshifts to harsh to be practical anyway. I am impressed with all of the different perspectives that have been raised in this conversation, shows the true value of a forum like this.