Shifting without a clutch question.

[scanzel]

My bus has the spicer six speed and I would like to learn how to shift without the clutch once it gets moving. What is the method or secret from you pro's on doing this without a lot of noise and grinding ? Is it easier upshifting or can it be done both up and down shifting ?

[Dreamscape]

Read this article by our own RJ Long here. Great information.

Maybe we can talk him into making it available here too!

http://www.busnut.com/bbs/messages/12262/16204.html?1167073154

[lostagain]

You can learn to shift without the clutch with practice.

However, I don't do it nor do I recommend it. It is great as long as a shift is done right and smooth. But if you miss a shift, there is 1000ft/lb of torque clashing with 40000lbs of bus, and it will break trans, drive line, diff, or axles in a hurry. The system was designed and built with a clutch: use it. Or go get an automatic.

I know a lot of truckers shift clutchless. Not a lot of bus drivers do. I never was a trucker, but in almost 40 years of bus driving, shifting without the clutch was always strongly discouraged by company mechanics for being too abusive to equipment.

Sure you can get good at it and shift really nice and smooth 99% of the time, but it is that one bad shift that will damage something.

You will find a lot of people who will tell you it is a good practice. Depends what it is you want to hear...

JC

[bevans6]

In theory it is simple - when you shift without the clutch you simply arrange for the gear and the main shaft to be turning at exactly the same speed and you can engage the gear without grinding.  Simplistically the gear is connected to the engine and the main shaft is connected to the wheels.  What you are grinding is actually the splines that sliding hubs slide along the main shaft on to engage the gears, they are hardened steel and about 1/4" wide and 1/4" deep, there are probably 30 of them for each gear.  they are a pretty exact fit.  I wouldn't try to shift without the clutch now having taken a Spicer apart to look inside, and having seen the damage on the dogs/splines.  

I have racing transmissions that use a remarkable similar design to the Spicers - except for size!  but their sliding hubs have only 4 or 8 dogs that engage the gears, and they are designed to be a very sloppy fit - and those gearboxes are designed to be shifted without the clutch up and down.  I can complete a shift in about a quarter of a second, and the faster the better.

So bottom line, if you can shift without a clutch more power to you, it's a great skill and might get you home if your clutch fails one day.  But I'm going to keep on double clutching MY personal Spicer that I own and have to pay for if I break it, and work on getting that down pat.

Brian

Brian

[Lin]

RJ Longs article is where to start.  When my clutch was going bad, I learned to shift without it and was surprised by how easy it was.  What made it easy though was having a tach so I was able to match my engine rpm to the rating of the particular gear at that speed.  For example, on my 4 speed 2000 rpm in first was around 1200 in second, so things went very smoothly.  It is only because I could shift without the clutch that I was able to drive the bus 200 miles to Bakersfield to get Don F. to change the transmission, so even if you are going to generally use your clutch, it is a good skill to know.

[Ed Hackenbruch]

When i was a kid i worked for a dairy farmer that had an old Ford flatbed that we shifted without using the clutch. Later on i used to do the same in 2 VW bugs and much later a Ford pickup. Haven't done it it many years though as i went to automatics.

[eddiepotts]

I have been doing it with my 6 speed spicer. I had a problem grinding going from second to third until I learned to double clutch. While I was figuring it out I had to get better at listening to engine speed before I would shift. I was always in a hurry. Now that I have the "talent" of knowing the engine sound to change gears I started shifting without a clutch. I have found if you just apply a little pressure to the shifter it moves almost like it knows it's time. If I had a tach it would be allot easier I think. I still do not recommend doing anything that can hurt your bus but if it is something your going to try no matter what I would like you to have your best shot at it. When I first received my bus I noticed a little sticker on the dash that said " this trans has a trans break. Do not push to floor while bus is moving or damage will occur " or something like that. So now I don't know how far to push in the clutch for full disengagement. I think I have not been using the clutch half the time I drive anyway. I am afraid of pushing the peddle in to far. I think you need to drive through town with allot of gear changing using your clutch and really listening to your engine and watching your tach. Know where the shift is at low rpms and don't force it. I do not like the shift from 1st to 2nd because the bus seems jerky but on up from there is a cake walk. Start by pulling out of gear into neutral first. Get that feel of the gears getting lined up and releasing. If You don't feel it, touch the throttle a few rpms and it will hit that sweet spot between the engine and trans turning exact speed. It will come right out into neutral. If you just learn this you will use 50% less of your clutch already.

[kyle4501]

I took some friends with me to bring one of my buses home. I was the only one who could shift it without grinding the gears. My technique to up shift was to take it to ~5 mph below the governed speed - let off the throttle and stab the clutch as I pulled it out of gear - let it 'rest' for a moment in neutral - gently nudge the shifter towards the desired gear. After it was in the next gear, I'd get back on the throttle.

To down shift - I came to almost a complete stop & slipped it into 1st & worked my way back up to the desired gear. 

It is more a matter of technique than clutch useage that avoids the problem of grinding gears - I've heard lots of drivers grind gears even though they were double clutching and, I've seen gears shifted silently & smoothly without a clutch. You should know in short order if clutchless shifting works for you. 

[gus]

I do it all the time with my 4-sp Spicer. It is easier going up than down. I don't clash gears any more than I do using the clutch.

The real difference is timing, you have to take your time between gears. It takes a while but you will get the knack of it.

I don't do it down-shifting on a climb, then I double clutch as fast as possible. Shifting without the clutch uphill causes too much loss of speed. The quickie double clutch takes the bat of an eye to do and is smooth as silk 90% of the time.

If you miss a clutchless shift you just go back to normal double clutching.

I've driven 18 wheelers but their transmissions are completely different, they have air shifts and transmission brakes -  this makes a world of difference.

[lostagain]

If you miss a shift and clash gears with the clutch pedal down, the engine is isolated from the transmission and drive line. All the tension and binding is relaxed, and although noisy, little damage occurs.

Clash gears, or get hung up between two gears without the clutch, and there is no give anymore, and cumulative damage happens to trans gear teeth, bearings, u-joints on the drive line, diff, etc.
Without using the clutch, the whole drive train from engine to drive wheels is rigid, except for the brief moment while the tranny is in neutral. Going from neutral into gear, if the rpms don't quite match, first the gear teeth will take a beating as they grind against each other, then as they engage/mesh with a jerk, the shock is taken by other parts, and I don't think it is good for them.

I have never met a driver that could shift flawlessly every time all day, day after day. Even the best grind gears once in a while.

I'm only a shade tree mechanic, but it seems like elementary logic to me...

JC

[TomC]

When I changed the 13 spd transmission to the Allison HT740 in my truck, the PO had to overhaul the transmission at 350,000mi.  I changed it at almost 1.2 million.  So I got 850,000mi out of my transmission and the clutch was original.  My suggestion is to upshift without the clutch but use the clutch for down shifting-that's what I did and obviously it worked.  Good Luck, TomC

[kyle4501]

When I changed the 13 spd transmission to the Allison HT740 in my truck, the PO had to overhaul the transmission at 350,000mi.  I changed it at almost 1.2 million.  So I got 850,000mi out of my transmission and the clutch was original.  My suggestion is to upshift without the clutch but use the clutch for down shifting-that's what I did and obviously it worked.  Good Luck, TomC

But Tom,   you've got skills!      

[buswarrior]

All of these have been written from a driver's view, with the exception of brian and lostagain...

It is amazing that risking abuse to the transmission continues to be a sought after badge of honour, or sign of having arrived as a big rig driver.

The rebellion against the rule makers continue?

No transmission manufacturer has recommended clutchless shifting.

No sane person who has paid for the repairs and downtime continues the practice.

As noted, once you've seen inside a transmission to see what parts are grinding against one another, and which way, you'll be likely to just use your clutch.

A multi-speed truck transmission has gears spaced at most 400 rpm apart at the redline, much closer than that when progressive shifting a modern 4 stroke. We historical bus types are looking at 600 rpm gear spreads and bigger for every shift. That is a much smaller target to hit.

There is a misconception that using the clutch to shift somehow uses it up. Not true.

You use up the clutch on take off by revving the engine while engaging the clutch, you use up the clutch by resting your foot on the pedal while driving, lightening the clamping force of the clutch and allowing some slippage under load,you use up the clutch by having the engine speed and road speed wildly mismatched at engagement.

As noted the clutch disengages the power from the weight and lets the little hardened splines and gear teeth rattle against one another and match speed, with no more than their own spinning mass behind them for energy. With clutch engaged, those splines are forced against the very edges of one another with the mass of the spinning engine, potentially under power, on one side and the weight of the vehicle moving down the road on the other, as they are pushed along the shaft by your shifter use.

Neither forces are very easy to change to a different speed for the metal bits to align and slide together.

The heavy duty transmission shop near you has a bin full of shafts with twisted splines from getting it wrong.

It is very possible to completely wear out/burn up a clutch in the city in under an hour by using bad take off techniques.

It is also possible for the clutch to last the life of the drive train in city driving.

See RJ's article.  http://www.busnut.com/bbs/messages/12262/16204.html?1167073154

Now, if your shifting is good using the clutch, you get the gears in without any clunk,smooth as a hot knife through butter every time, no grinding, rattling or other sign that anything is less than perfectly aligned for many miles of shifting, you already have the timing to simply remove the use of the clutch from the equation.

I am with Tom, it's one thing to clutchless shift against an engine that is not being fueled, it is a whole 'nuther thing to be pulling the shifter with the engine under power. I am a fan of using the clutch for range shifts and for downshifting. Anything that is likely to be stressful on the parts, clutch gets used.

It is your ride, and your money, get a tutor and do what makes you happy!

happy coaching!
buswarrior

[bevans6]

BW, I like your exposition of what's happening, makes it very vivid.  One thing I read a lot is about the gear teeth and what they are doing during a shift - the answer is nothing, the gear teeth are constant mesh with their mate and never move in any way to effect a gear change (except for reverse).  All of the gears in the transmission are constantly spinning and in perfect mesh.  They aren't straight cut either (again except for reverse), they are helical cut to reduce noise.

For fun, I went out and took a couple of pictures.  The first picture is of a 4 speed Spicer, input/fourth gear and third gear, with the sliding hub towards third gear so you can see the splines and the teeth on the input gear.  They are less than 1/4" across and you can see the rounded portion where the sliding hub engages them.  When wear occurs that rounded  bit gets bigger.

The second picture is showing  the first/second gear sliding hub, which is also the mainshaft gear for reverse.  You can see how huge the reverse gear is (around 10" in diameter, and very heavy) and that is what you are sliding around when doing first/second shifts.  You can see the helical cut second gear, and the splines and teeth that are engaged.  These teeth are larger than the three/four teeth since they transmit a lot more torque, they are little over 1/4" wide and you can see the same rounded wear pattern on them.

If you look at the first picture again, you get an excellent visual of how the transmission actually works.  The top gear in the picture is the input gear, it's part of the input shaft that the clutch rides on.  Power comes into the gearbox from the engine via the input shaft and the input gear.  Below and to the left you can see the countershaft gears.  They are constantly in mesh with the input shaft gear and the main shaft gears.  Power comes in via the input shaft and gear, is transfered down to the countershaft and then back up to the main shaft gears, so there is a gear reduction between the input gear and it's countershaft gear, and then again between the countershaft gears and the main shaft gears, that lets the pairs of gears be smaller and more compact.  When you select a gear, the sliding hub locks that gear to the main shaft so it can transmit it's power out the back.  When you select fourth, the input shaft is locked directly to the main shaft for a 1:1 ratio.

[kyle4501]

Never a good idea to shift gears while the drivetrain is under a load. That is one of the reasons they included a throttle & clutch. Use them as necessary.

So, yes, normally using a clutch is the way to shift. Shifting without a clutch brings potential problems - while damage may be likely, it is not guaranteed. . . .

Some people are 'tuned in' to the machinery they are operating - others, not so much.

I know guys that can tell when a inside dual tire is flat on the trailer just by the way the steering wheel feels. I've also heard of an instance when the driver didn't notice when a whole axle came out from under the trailer he was pulling. 

Driving style & technique matter more than simple use of the clutch. SILENT gear changes is required for maximum life of the transmission.   
So, do what is required to get that. - For me, I'm gonna use an automatic.