RPM Shift Light

Doug1968 · May 09, 2010, 08:20:45 AM

Fellows,

I am curious if any of you are using an RPM shift light to easily monitor your engine RPM. These devices are very common in the race world and it seems logical that this same process could be used in our buses with manual transmissions. Without looking at the tachometer one could easily see the light come on which would alert you to the proper RPM for downshifting. This light could be set to match the RPM split between the transmission gearing. As the engine RPM drops to the set point the light would come on and you would take the transmission out of the gear, move up against the governor and move the transmission into the next lower gear.

Seems as though the issue with downshifting is getting the gearing properly meshed. This light may be very helpful and you would not have to look at the tach.

Has anyone tried using a RPM light?

Doug

Ace · May 09, 2010, 08:39:53 AM

I'm very familiar with the shift light as I used one in my drag car when I had the 5 speed but soon went with the automatic! The same with the bus. I had a bus with a manual trans but after driving it a while, I NEVER used the tach to shift! It became almost a natural to feel your engine speed and know when to and not to shift! In my opinion, a light used in a bus would be a waste! It doesn't have to be as precise as in a drag car where every millisecond counts!
Sorry!

buswarrior · May 09, 2010, 09:15:53 AM

Related to Ace's comments, just get out and do some driving and you'll forget all about this.

You only have 4 shift points, and they are pretty much stationary due to the rpm spread between the gears.

that's a fancy way of saying you shift them all at pretty much the same rpm point.

In no time, you'll get an ear for the right pitch, time to shift.

happy coaching!
buswarrior

Lin · May 09, 2010, 09:24:38 AM

Now, the tach can be really useful if you want to shift without the clutch. Other than that, just shift when the gear tops out.

redbus · May 09, 2010, 09:32:18 AM

On the other hand I've got a son in law that need a hand to the back of the head when it is time to shift.

bevans6 · May 09, 2010, 09:54:13 AM

I just use the speedometer. I upshift when it hits the governor, and downshift when it hits 55 mph or 30 mph on the way down. The "rev matching" to do a seamless downshift is foot on the floor in neutral, and hit the double clutch really fast. It's when you aren't quick that it talks back to you. I see no need for either a tachometer or a shift light. You can't over-rev it, and you know darn well when you are under-revving it.

Brian

Lin · May 09, 2010, 10:21:00 AM

Brian,

I am sure that one can master no-clutch shifting without a tach, but it makes a huge difference for the beginner. I started doing it when we were having clutch problems. The tach made it so simple that I found clutching to be an unnecessary waste of energy.

Chopper Scott · May 09, 2010, 01:39:26 PM

To be honest with you even the Allison auto's are basically manually shifted. Throw her in 1 and the converter locks up and you feel it hit the governor. Then on to second and so forth. Letting the tranny do the deciding ends up with it shifting to soon. It actually is more of a "seat of the pants" type of deal. A few trips and you'll have it down.

belfert · May 09, 2010, 05:26:26 PM

BW says that anyone who doesn't manually shift an older Allison will have unhappy passengers. I have a newer Allison B500 and the only time I manually shift down is when I need more braking from the Jakes. When I'm a passenger the tranny seems to shift just fine on its own. I didn't buy an automatic to spend all my time manually shifting it.

I've never owned any vehicle with a manual transmission and don't intend to if I can help it. I have driven some old 1946 Chevy trucks and those were a pain to drive with the double clutching and all that. We were told never to downshift while moving which could be a pain when needing to slow down. The trucks were never driven above 10 to 15 MPH as they were used on a fairground.

Van · May 09, 2010, 05:54:09 PM

LOL! I"ve got a 740 and am now back to shifting it manual, helps a lot in seting up for a grade, haven't spilled a beer yet

Unfortunately my clutch days are over. I recall how bad I got beat up when I joined this merry crew

, now the only gauge I watch is the Temperature, I know exactly how much over the speed limit I am traveling with it to the floor

.

Ace · May 09, 2010, 06:24:48 PM

Van I also have a 740 but never have had to shift it manually! It's tied to a 8v92. What's yours again? Even mt recent trip to the hills of Carolina, I never up or down shifted manually and it never down shifted on its own!

Dreamscape · May 09, 2010, 06:30:35 PM

I guess we'll have to wait for someone's response who has used one, you might be the first to try it out. I'll be second!

Funny, I didn't see Allison mentioned in the original post.

Paul

Chopper Scott · May 09, 2010, 06:43:18 PM

Mine's a 740 behind an 8v71. No way I would just put it in 4th and be happy. Pulling grades I have to shift her down to 3rd or even second manually when the rpm's get low enough. I manually upshift it also from a start beginning in first. I was just using that as an example for the original poster concerned when he needs to shift his manual.