Delay in shifting?

[patterbery]

My 2004 Bounder 38N has the MH3000 trans. Recently, I've noticed that when I shift from reverse to drive, drive does not engage, the 6 flashes. If I select neutral for a ten count, then select drive, drive engages normally. The opposite is also happening going from drive to reverse. No warning lights & normal shifting otherwise.

[Skip426]

Have you tried pulling codes from the trans controller ?

Checked the fluid level using the shift pad?

Engine idle speed normal ?

[153stars]

First thing thought was higher idle holding it back. Not necessarily extract same description ,but high idle keeping from shifting delaying fwd. or rev. has been discussed .

[patterbery]

I'll check the idle speed the next time I crank it up.

[wolfe10]

Correct:


If idle speed too high, the "D" will just flash.


If that is not the issue, use the up/down arrows to check for DIAGNOSTIC CODES. This can be done with the engine off. Push up and down arrows TWICE to access the diagnostic codes (first push get you to oil level check).

[RKins]

Another thing to check is that the chassis bank has a good charge on it. Allison trannys need good voltage to operate.

[stang37]

I was told by Allison tech to always stop in neutral before shift from reverse to drive or drive to reverse. I do not remember why but I follow his directions.

[CaptainGizmo]

My 4000 is finicky. If I roll slightly or don’t have my foot on the brake, it won’t shift into gear at all.

Yesterday, I had to actually shut the motor off and restart to get it to shift.

Not sure this is the way it’s supposed to be.

[deandec]

Originally Posted by stang37

I was told by Allison tech to always stop in neutral before shift from reverse to drive or drive to reverse. I do not remember why but I follow his directions.

This advice could solve the problem.

[patterbery]

Dean, my shifting procedure hasn't changed in 5 years with this coach. At a dead stop with the brakes applied, I shift from D to N to R. This will result in a flashing R and the trans will not go into reverse. Then, I'll select N for ten seconds then into R. The trans goes into reverse. The opposite, going from R to N to D has the same result, I have to wait 10 seconds in N before selecting R. Before I get a local Allison service writer involved I'd like a little common knowledge if it's available.

[Ted Lambert]

I am familiar with Allison and have rebuilt many ZF transmissions.
I used to dyno all the trannys after rebuild.
In my opinion the valve body may be a little dirty.
This could prevent the computer not seeing a complete dump of the pressure so what may happen is the transmission is telling the computer not to shift because there is a clutch engaged as the lack of pressure drop is indicating.
That is why pausing in neutral allows the pressure to drop allowing the shift.
Shift inhibitor prevents damage to the tranny.

Possibly there is nothing wrong otherwise.

Some people who rebuild transmissions short cut and don't clean the screens and the ports in the valve body.

Just my opinion.

[patterbery]

Hi Ted. Sounds as if a trans fluid and filter change is in order. The trans has all most 90K on it but, I can only speak for about half of those miles. I'll call around to see which shop can give me the price for the service. Thanks for your response.

[R.Wold]

probably been said above, but ALWAYS go through neutral before changing from a forward gear to reverse or the reverse to forward. ALWAYS.

[R.Wold]

Originally Posted by CaptainGizmo

My 4000 is finicky. If I roll slightly or don’t have my foot on the brake, it won’t shift into gear at all.

Yesterday, I had to actually shut the motor off and restart to get it to shift.

Not sure this is the way it’s supposed to be.

I think this is to avoid shock loading the drive train