Searching for an answer on RPM's

[TheKassman]

Here is the scenario: I am traveling on the freeway at 60mph in six gear (allison 3000 six speed; Cummins 330hp). My tac reads 1,600 rpm. I look down 15 minutes later and same speed but now 1,800 rpm. I glance down a half hour later and 1,600 rmp. I glance down a little later and 1,900 rpm. later, 1,600 rpm. All on flat level ground same gear same speed.?????

[DD788Snipe]

Originally Posted by TheKassman

Here is the scenario: I am traveling on the freeway at 60mph in six gear (allison 3000 six speed; Cummins 330hp). My tac reads 1,600 rpm. I look down 15 minutes later and same speed but now 1,800 rpm. I glance down a half hour later and 1,600 rmp. I glance down a little later and 1,900 rpm. later, 1,600 rpm. All on flat level ground same gear same speed.?????

Your Allison is hunting. Its shifting back and forth from 6th to 5th and back 6th. You need to be running at 62 to 63 mph at 1800 rpm for it to stay in 6th gear. Also there is a mode switch on the gear selctor. When running on straight and fairly level terrain make sure you put it in economy mode. The light will light up. You have to do that everytime you shut off the engine. In economy it locks up the torque converter I believe so your trans doesn't wander between the 2 overdrives.

[wolfe10]

We have no idea if your transmission is indeed shifting gears or if the tach is not accurate.


Easy to tell.


Next time this happens (RPM goes up), use the down arrow on the Allison shifter to go to 5th gear. What does RPM do?



Then up arrow/push "D" to select 6th. What does the RPM do?

[Skip426]

This could just be the trans controller locking and unlocking the torque converter , depending on engine load .

Is this a new issue , on a coach you've had for a while ... or a new to you coach??

[wolfe10]

Originally Posted by Skip426

This could just be the trans controller locking and unlocking the torque converter , depending on engine load .

Is this a new issue , on a coach you've had for a while ... or a new to you coach??

His Allison 3000 should not be locking/unlocking. If it were, it should set a code. The 3000 torque converter is locked in higher RPM 2nd and always in all higher gears.


Might be a good idea to check for diagnostic codes. Takes two minutes from the driver's seat. See instruction in your Allison owners manual or we can post. VERY easy to do.

[gmcgene]

Kassman,

Assuming your coach speed remained at a constant 60 mph and you never heard the engine speed up or slow down then you are describing "normal" (not correct) behavior for the 1998 Alpine tach. I have the same coach, OEM tach, and issue.
My tach isn't as erratic as yours but my speedo is far worse. It fluctuates and is so inaccurate that I have to rely on the gps to know what my the coach speed is.

Search the forum and you'll find several posts from me and others on this tach/speedo problem. Posts other than mine were for newer Alpines that have different speedos.

There used to be a shop near you in Riverside that specialized in repairing/rebuilding mechanical speedos for old cars. Don't know if they worked on electronic instruments or if they are still in business.

If you find a solution be sure to post it here.

[TheKassman]

I always run in economy mode. Also, it it is hunting between 5th and 6th why does the selector always say 6th. it says 6th when it is at 1,600 rpm and 1,800 rpm.

[TheKassman]

speedo seams accurate. My Odometer stopped working so I had a GPS speedo-odometer installed. There is only 1mph difference between the two speedo's.

[c_oneil]

Originally Posted by TheKassman

I always run in economy mode. Also, it it is hunting between 5th and 6th why does the selector always say 6th. it says 6th when it is at 1,600 rpm and 1,800 rpm.

I think your transmission gear LED is displaying the selected gear at all times and does not change to display the actual gear if it were to downshift.

[wolfe10]

If you have the ONE WINDOW Allison selector, as Carter said, it only indicates the "pre-select gear", not the gear you are actually in. So, even at a stop, in gear, it will read "6".


If you have the TWO WINDOW Allison selector, the left window is as described above, the right window indicates the gear you are actually in.

[RiverBurt]

I don’t know where there’s a perfectly flat stretch of road in windless conditions the distance you travel in 45 minutes at 60mph. Transmission is just doing its job. Run in economy “Mode” and it will downshift to 5th less often, but drop below 60 (slightly) on uphill stretches and in headwinds (even those so slight you can’t feel them).

[gmcgene]

My 1998 Alpine and I assume all the early coaches have the single window gear indicator as Brett described. It displays selected gear as described by Carter.

Only exception is when the PacBrake is engaged and the Allison downshifts to 4th.

Have you verified whether or not the Allison is actually shifting when the rpm changes?
I'm betting the tach is malfunctioning.

Maybe another 1998 Alpine owner with the early OEM instruments will join in the discussion and report their experience.

[wolfe10]

Originally Posted by gmcgene

My 1998

Only exception is when the PacBrake is engaged and the Allison downshifts to 4th.

Actually, it is working EXACTLY the same.


It is displaying the "pre-select gear"= the gear toward which the transmission will shift as RPM perimeters are met.


Your pre-select gear for exhaust brake is 4th. Note: any gear could be programmed into the ECM for the exhaust brake pre-select gear. I have had several reprogrammed to 5th gear, and use the down arrow to select lower gears.

[RiverBurt]

Another way to identify grades and winds you don’t realize are there is to leave the exhaust brake on. It’ll tell you!