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Topic: Shift point adjustment and other things (Read 794 times) previous topic - next topic

Shift point adjustment and other things

Hi All,
  We are new (proud) owners of an 89 40FT GV....3208 Cat and I believe a MT647 Allison. I would like to lower the shift points some as well as delete the muffler for better breathing.
  Can anyone share wisdom from experience on these subjects?
  Also it only has 50k miles on it but being 30 years old I was wondering what I should be looking at replacing to help make sure its reliable. I was considering changing the air bags on the suspension, shocks maybe, full fluid and filter changes....should I look at doing anything with the air brake system?
   

Re: Shift point adjustment and other things

Reply #1 –
smartin9913,

Welcome to the ForeForum.

Congratulation on your "new to you" coach.

Is this an ORED (Oshkosh Rear Engine Diesel) chassis or U280? Side radiator or rear radiator?

Quite a few differences.

Re: Shift point adjustment and other things

Reply #2 –
Our U300 goes right up to the redline/fuel cutoff RPM on every shift if anywhere near full throttle. This is normal for a heavy duty truck engine. Lowering the shift point may have unintended consequences such as elevated EGTs, reduced coolant circulation, etc. Getting used to driving a big diesel motorhome is a lot different than a PU or car. The factory sets shift points for a reason.

Replacing the muffler with a resonator has been done by several members. Don't look for a lot of gain here but be careful of elevated noise levels. Some of the noise may be transferred to the coach and felt as increased vibration.

Post some photos of your air bags, especially the exposed area where the tires throw up debris. They can have lots of cracks and be OK as the rubber is really thick and has a lot of reinforcement between layers.  Our OEM shocks are fine. You could consider changing the air dryer to a spin-on type. Makes a 5 minute R&R at the most compared to a much more involved repair.

Pierce

Re: Shift point adjustment and other things

Reply #3 –
The 647 as far as I have done does have adjustable shift points via an Allison dealer.

The modulator which controls sensitivity to downshifts used to be set for heavy fire type vehicles. 

Both are adjustable as far as I know.

Have to drop the pan. 

Re: Shift point adjustment and other things

Reply #4 –
I have the MT647 transmission and had the shift point from 2nd to 3rd reduced slightly.  All gears shift at about 2500 RPM And that seems good.  I have the 3208T engine and things may be different behind some other engine.  Have a great day  ----  Fritz

Re: Shift point adjustment and other things

Reply #5 –
Smartin9913,  If starter are alternator have not been checked in last 5 years I would pull both and have rebuilt.  They both last a long time but with old grease and bearings not being lubed properly they usually don't quit slowly --today they work and tomorrow they don't . I'm sure others will chime in on additional things they would look at!
Chris

Re: Shift point adjustment and other things

Reply #6 –

 Welcome.
That sounds like the unit I was looking at in Louisiana.    Sounded nice and very cheap. 
  Most of my engine noise running down the road is intake noise  and some final drive humm. 
  I removed my muffler and the inside sound did not seem to change .
  I think that my bus has  the 643 and a down shift cable .  I changed my cable adjustment and lowered the shift point a couple hundred.

Re: Shift point adjustment and other things

Reply #7 –
Never heard of a rear engine diesel coach with any intake noise if it has a stock intake/air cleaner system.
The 10.4 liter 3208 is a 2800 RPM engine so while you may get away with dropping the shift points a couple hundred, that would be less than optimal for a Cummins 8.3 (2400 RPM) and a terrible idea for our 6V-92TA Detroit (2130 RPM). Just letting others who might get that idea.

Pierce

Re: Shift point adjustment and other things

Reply #8 –
The earlier shift is only at part throttle.  Wot Stays  the same  2600 or so. 
The intake has a loud resonance at 2000 rpm.  Did the same with muffler or without.

Re: Shift point adjustment and other things

Reply #9 –
Yes ORED......Thanks for all the input. Gives me a lot to think about. Mine is shifting out at 2500rpm except for high gear, it shifts at 2800.

Re: Shift point adjustment and other things

Reply #10 –
Oshkosh shipped me the first three hundred cat ORED and it would upshift at the same rpms as the 250hp ones.

Faster if you manually upshifted the coach.  Wrong.

Sent the coach to Allison Bob ware at S&J Chevy in Cerritos, ca to raise the upshift points and to set the modulator so at part throttle it would short shift more.

Weeks later I get a call from Indianapolis, Indiana from Allison.

The voice on the phone says "I am not calling you.  But why do I have a bill here for warranty adjustments from S&J?"

I explained that the shift points were wrong as was the modulator adjustment.

He said they set them the same as the 250's. 

I said that's great but the 300's had 10% more rpms. 

Got quiet on the phone.  He said Cat at the meetings had not told them that. 

He laughed that the local sales manager had had to fix a big companies brand new product.

Said they would raise and adjust.

Next coaches were raised.

The next coaches after that had the shift points raised to 2800.  And would hang in gear.

They went overboard.  Oh well.  Allison Bob fixed them all for me.

Had to reshim play out of the front axle and add additives and thicker rear axle oil to stop the slight gear howl under a load the stock rear axle had. 

Truck housing.  Not polished gear teeth.  At 40k miles you could pull the third member and on a bench reset the gears to eliminate the noise without the special oils. 

Quiet coach that shifted correctly without a steering wheel shimmy sold for more money profit wise and had happier owners