Shifting W/O clutch

[Mr_Roboto]

Basically with double clutching, you are matching the engine RPM to the road speed for the gear you are shifting into. This is necessary in most big trucks since most are not synchronized (since synchros are extra weight, and another part to wear out / break).

To upshift: clutch in, trans in neutral, clutch out, drop engine 300 RPM, clutch in, shift up one gear.

To downshift: clutch in, trans in neutral, clutch out, increase engine 300 RPM, clutch in, shift down one gear.

It isn't as hard as it sounds, once you learn how you do it automatically. (The 300 rpm difference is for the Super 10 trans, other gear spacings will require different RPM changes). In practice, to get the 300 RPM increase, you blip the throttle and catch the right RPM as it is coming down.

When it's cold my wrecker's synchros don't work, so I get to practice double clutching......

 

[Mont91]

Good description.

The purpose of double clutching of course is to use the clutch as a synchronizer. So engage the clutch when you think the engine is at the proper RPM to match the gear you are going to engage. Disengaging the clutch before shifting into gear prevents grinding if there is a slight discrepancy in speeds.

I think double clutching is easier on synchros than floating and seems to help with wore out synchros, but if you are trying to avoid pushing in the clutch it is not much help.

On the '88 the stiff hard to push clutch was because of the wore out linkage under the dash.

 

[zigg]

I float my gears all the time. Have all my life, and never have worn out anything doing it.

My present T-19 shift smooth as can be without the clutch, and I also have a splitter on it that I also shift without the clutch. I pulled it all apart a couple years ago to replace the input bearing that was chattering, and it was as new inside with no wear on any of the gears or synchros, and it has over 350,000 on it!!

I think you'd acutally have to see a synchro unit to understand what it actually does, and there is very little to wear out. It's much like a disc brake in how it works, but using the friction of brass against polished hardened steel to slow spinning gears. If you think about it, you are more likely wearing the synchro's out much more by stuffing it into the next gear without any concern for engine speed/rpms, even with the clutch in, than you are by carefully and with experience lining things up without load and then gently drifting the parts together. When you are floating gears, the synchros are doing nothing at all, you are only aligning the gears and then sliding them together.

One definately gets very good at it over time, and I can upshift and downshift all eight gears all day long, and never miss a beat, or grind anything. I've driven big rigs, with Eaton splitters, and same thing. Use the clutch to start out in 1st, and then never touch it again all day. Millions of miles like that, never a problem or failure...

Just my .02

Zigg

 

[93turbo_animal]

The old trannys like the t-19 and stuff that use 80-90 gear oil are easy to float gears the thick oil slows the gears a bunch how ever the newer trannys with ATF don't hardly slow down any. so it takes a lot more to match RPMs also the thing is when you start wearing out the syncros the gears will want to start to grind and the gear doesn't get shoved all the way onto the next gear increasing your chance of stripping the nose off the gear set. I just got done replacing a synchro and input shaft in 7 spd eaton I think cause the driver rides with his hand on the shifter wore out the synchro and the ripped the splines off the shaft cause it wasn't fully engaged