Manual shifting your auto for engine braking

[L31MaxExpress]

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.

I would have to go through the 700r4s line pressure schematics, but I recall the line pressure jumping up on its own when a gear lower than OD was selected. I know reverse has a huge bump and I recall moving the shifter to a lower gear also bumping it.

 

[Scooterwrench]

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.

And warp the rotors and eggshape the drums.

 

[NickTransmissions]

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.

I have had the same experience once in a GM Saab 900...Brakes were working one second, then they weren't. Luckily I was still in my neighborhood when it happened and limped it back to my house a couple hundred feet...

CK Performance is coming out with a 4L80/85E line pressure regulator valve that's supposed to have some improved design features over stock and the Sonnax valve...Spoke to him this AM and he's thinking it's about 6-8 weeks out so if you're not going to be doing the work in the immediate near future, it's another option for you.

 

[L31MaxExpress]

Actually a couple of minutes of searching confirms this. Manual 1st and 2nd should have full pressure irregardless of TV position. I do not have a 4L60E vehicle, but it is also possible GM left the same configuration in the manaul valve operation on them. Maybe Nick knows if the line pressure jumps in a lower manual gear on the 4L60E.

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[NickTransmissions]

I would have to go through the 700r4s line pressure schematics, but I recall the line pressure jumping up on its own when a gear lower than OD was selected. I know reverse has a huge bump and I recall moving the shifter to a lower gear also bumping it.

You're correct...Pressures below are a good generalization of what to expect from the 700R4:

PND,D3: 60-75 PSI at idle
R: 90-110 PSI at idle
2/L: 165-190 PSI at idle

Depends on what boost valve and pr spring are used and assumes TV cable geometry and adjustment are optimal.

 

[L31MaxExpress]

You're correct...Pressures below are a good generalization of what to expect from the 700R4:

PND,D3: 60-75 PSI at idle
R: 90-110 PSI at idle
2/L: 165-190 PSI at idle

Depends on what boost valve and pr spring are used and assumes TV cable geometry and adjustment are optimal.

Towing a heavy trailer from a stop or towing a boat out of the lake, I always used Manual 1st gear with a 700r4. I did that mainly because it would upshift to 2nd too quickly at part-throttle for my liking. I recall it having an additional clutch pack activated that helped eliminate load off the sprag. I also always used manual 2nd when I ran it down the track for both the burnout and launch. I let it 1-2 shift on its own, then did the 2-3 shift manually.

 

[NickTransmissions]

Towing a heavy trailer from a stop or towing a boat out of the lake, I always used Manual 1st gear with a 700r4. I did that mainly because it would upshift to 2nd too quickly at part-throttle for my liking. I recall it having an additional clutch pack activated that helped eliminate load off the sprag. I also always used manual 2nd when I ran it down the track. I let it 1-2 shift on its own, then did the 2-3 shift manually.

Yes, that's the correct way to use that trans (or any trans) when towing...If a vehicle is to be used predominantly for towing and hauling, I always pair that guidance with a custom low stall converter, deep pan and giant aftermarket trans cooler w/fans to help things along and better keep trans temps in check.

 

[L31MaxExpress]

Yes, that's the correct way to use that trans (or any trans) when towing...If a vehicle is to be used predominantly for towing and hauling, I always pair that guidance with a custom low stall converter, deep pan and giant aftermarket trans cooler w/fans to help things along and better keep trans temps in check.

I could see the desire for a lower stall speed, but I never liked the way it loaded the engine trying to get rolling from a stop, especially uphill. I used the S10 converter in the 700r4 in my G20 van. Drove like stock until I nailed it and then it would flash up to ~2,800 rpm. I always run an auxiliary cooler after the in-radiator cooler and used a deep pan. I had a stock 4L60E deep pan on the 700r4 in my G20. I re-wired my 700r4 back to factory to fix the wiring after the guy that built it had it setup to lock the converter only in 4th gear. From the factory in 83 it locked in 2nd, 3rd or 4th. It used the ported vacuum switch through a vacuum delay valve and the TVS on the intake manifold in 2nd and 3rd and a pressure switch to lock it regardless of vacuum or coolant temperature in 4th.

When I swapped ot from carb to TBI, I rewired it again to duplicate the 1992 G20 4L60 wiring. The TBI computer locked it in 2nd, 3rd and 4th after that. The TBI computer had lockup tables for low gear (2nd & 3rd) and high gear (4th) that were adjustable by MPH vs TPS along with a minimum speed for lockup and release. Above ~20 mph they would lockup even during acceleration. It took heavy throttle opening to keep the converter unlocked in 2nd and 3rd under 60 mph and WOT (99.6% TPS) to keep it unlocked above 60 mph.

 

[NickTransmissions]

Actually a couple of minutes of searching confirms this. Manual 1st and 2nd should have full pressure irregardless of TV position. I do not have a 4L60E vehicle, but it is also possible GM left the same configuration in the manaul valve operation on them. Maybe Nick knows if the line pressure jumps in a lower manual gear on the 4L60E.

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I believe manual 2 and Low Reverse line pressure strategies are the same in the 4L60E (and 4L80e) as the 700R4/4L60 but don't hold me to it as it's been ages since I've done a line pressure test on a transmission and cannot remember for sure.

 

[L31MaxExpress]

These are the maximum trans temps I see on my 4L85E at the sensor on the MPS on a 105F day. Moroso Deep pan, in-radiator cooler and a M7B auxiliary cooler. I found it odd that the transmission temps actually decreased 4°F on a WOT passing pull, the cooler flow must spike dramatically at WOT and higher rpm. Converter stalls 2,900 rpm behind my 383 making ~500 ft/lbs and it has a 3.73 gear in a ~7,000 lbs van.

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