shifting us gear overdrive

[Black dawg]

I have this overdrive behind a t-19. I am having no trouble shifting the overdrive while accelerating, but trying to down shift the overdrive while maintaining speed or slowing down i get a long grind. I am sure I am just doing it wrong.

anybody drive this combo often? If you were cruising at highway speeds and wanted to down shift the overdrive, how would you do it?

 

[icanfixall]

From what I have read about this all your supposed to do is let off the throttle momentary. There may be a time limit for the shift spring to load up but once the power is off the trans it will shift quickly.

 

[Black dawg]

I figured somebody on here would have one, I guess I will get it figured out?

 

[chris142]

When downshifting you must give it more rpm so that the gears can match up.

 

[madpogue]

What's the gear ratio of the OD? Might be worth doing some math and figuring out how the gears/ratios overlap. It might work out better, when downshifting, just to downshift through the tranny gears, and only downshift the OD out when you're ready to start accelerating again.

 

[FarmerFrank]

I run a us gear / c6 combo and ill have to admit, downshifting kinda sucks.

If there is no load on the gear (coasting to a stop) and hit the toggle switch it shifts right away. This of course makes a clank/slam noise.

What I normally do is lightly push on the gas while holding the switch to down shift then let off the gas and start braking. That is if I have that kind of time

 

[suv7734]

I have this overdrive behind a t-19. I am having no trouble shifting the overdrive while accelerating, but trying to down shift the overdrive while maintaining speed or slowing down i get a long grind. I am sure I am just doing it wrong.

anybody drive this combo often? If you were cruising at highway speeds and wanted to down shift the overdrive, how would you do it?

OB member "The Warden" has a website with a lot of good information.

http://www.dieselwarden.net/temp/usgear/US%20Gears%20overdrive%20manual.pdf

 

[jaluhn83]

OD is 0.8:1

Make sure you're flipping the switch, waiting a couple seconds and then unloading the drivetrain. Don't unload it and then flip the switch - apparently this causes motor problems as it's designed where the motor preloads a shift spring and then the spring shifts the unit once it's unloaded. Apparently the motor isn't designed to actually shift the trans - not sure exactly how/why.

I would double clutch for a down shift - there's no sycros in the unit, so there's no way for the input rpms to increase unless you pull them up with the engine - ie double clutching. Shouldn't be that difficult once you get used to it.

 

[icanfixall]

This information is what I posted earlier on about the spring loading up. and then shifting. When the spring is loaded the shift is done quickly as you let off on the power just a bit. As just posted, there is no sychincros in the unit. Its direct gear to gear. This is not so in the Gear Vendors units. The gv have a clutch and a hydraulic pump that makes enough pressure when the truck or car reaches about 20 mph. The gv has no underdrive for the start bu the US Gear can cut down the first gear from the start essentially making it have a granny gear.

 

[jaluhn83]

Forgot to add the timeline - should take about 2 seconds to load the shifter - so hit the switch, wait 2 sec, then unload the drivetrain.

If you have an automatic or one that has the little 'lo'/'hi' lights on it, these are controlled by the actual movement of the shift fork, **not** the motor. So it is entirely normal to hit the shift button and have the indicator stay in the same gear until you unload the drivetrain.

There's no limit on how lo0ng you can drive with the spring preloaded - that is you can hit the shift button and then not actual unload and shift for a bit if you need to for some reason. I would recommend against doing this any longer than you have to as it will put a load on the shift fork and cause wear, could suddenly shift when you don't expect it to, or could theoretically pop out of gear causing damage. Sort of like driving down the road pushing on the shifter on a stick - not good for things, but not a crisis either.

Important to note that the US Gear/ DNE2 (same basic box) are *either* under/direct, *or* direct/over. So you either get a higher top end or lower 1st and can split the gears in between. GV is a over/direct only, despite the "under/over" they advertize.... to me this is pure bs on their part and is one reason I really don't much like them.

 

[madpogue]

You might be just as well off leaving the OD engaged and downshifting through the tranny, depending on the traffic, etc. Here are the ratios for the T19B, with/without the 0.8 OD:

1st - 4.02
1od - 3.22
2nd - 2.41
2od - 1.93
3rd - 1.41
3od - 1.13
4th - 1.00
4od - 0.80

So no overlap, but shifting down to third with the OD engaged takes you almost to 1:1. I reckon if I had that setup, I would probably keep in in OD until I was down to first or second.

 

[junk]

When my 89 was on the road. I remember using the US gear the same way either up or down. Basically pull the switch let the shift motor load up then lightly let off the throttle and clutch. Basically use it like another gear in the t-19. I found that method to be my smoothest shifts. Seams like you should be able to shift it without clutching, but that always seemed to make a lot of banging noises for me.

 

[Black dawg]

I have gotten more used to it, and have been able to shift it. It still isnt the smoothest thing to shift, but with no load on the pickup I dont know that it will be?

 

[Black dawg]

as an update, I have gotten to where 99% of the time the shift is smooth, with no noise other that a click. I really like it, and if I can find one to replace the gv in my suburban I will be doing so.

 

[crashnzuk]

I was gonna comment that the GV units are no better when shifting down. You tend to get a big thud out of the drivetrain, really sucks. Rev matching helps sometimes, and not others. The ratios are so near each other on the splits, I only use it as an O/D with this transmission.
Travis..