Not common. 8.1 Allsion combo truck speedo issue.

[04blackgmc]

Long story short my customer swapped from the factory 3.73's to 4.56's and 33.2" Tires.

Well with this truck the Gear/Tire calc table is blank.

Now from the factory GM in the tune put ratio as 3.73 and trans 4.10.

I corrected the truck to 4.10's and change the VSS tires revs and now instead of 10 mph off it's only 5. Has anyone dealt with this? Just trial and error for this app or what?

[Ghostnotes]

Subd

My son is going to do the same thing with his 2500HD 8.1 soon.

Hello from the G8 Board......

[04blackgmc]

Yea maybe Staff can add this table? I wish I could tag people lol.

[rynez06]

Why can't you just do the calculation and input the data by hand ? It's not hard.

[04blackgmc]

Why can't you just do the calculation and input the data by hand ? It's not hard.

I did. still isn't correct. That's why im asking now

[rynez06]

Post up your file before and after correction , let's see if we can help.

[04blackgmc]

huber 8.1 truck.hpttry1.hpttry 2.hpttry3.hpt

[Road]

Trans needs to be set to 4.10 and ratio needs to be set to 4.56

[04blackgmc]

Cool I'll flip those and see if it helps.
Thanks!
Never ran across the issue but I don't normally do these.

[Road]

Some os don't have trans ratio w/Allison don't know why. My 8.1 w/Allison has 5.38 and speedo is accurate.
Mike

[Ghostnotes]

Nice to see someone got some answers in regards to the 8.1/Allison. Got the engine about 90%. The tranny on the other hand...............

[04blackgmc]

Tried the above nothing i do will get it closer than 5 mph off. Set the rev nothing changes..

[mecanicman]

Have a gps? Post your tune as it is now. Do 60 mph by the gps and post what Hpt says your speed is. I'll look this evening.

[04blackgmc]

try3.hptwtf.hpt

Have a gps? Post your tune as it is now. Do 60 mph by the gps and post what Hpt says your speed is. I'll look this evening.

Yep i GPS confirmed.

Ill post the changed ones

[04blackgmc]

Bump!

[Road]

Try this something doesn't seem right with the speedo segment see if the checksum will flash these settings.

Mike

[DSteck]

It'd probably be prudent for people to go look up the formula for the diameter of a circle.

[Road]

My bad I used a speedo calculator from a different OS and copied over Trans rev per mile to dist - trans. DSteck I slept trough English class so your adjective's are out of my thinking range. The end result is he is needing help calibrating his speedometer so if you would use all that effort you put in trying to be smarter than everyone else and help fix the problem at hand it would be better for the community. It's a shame a dumbass has to speak first before a smartass will chime in. I have the upmost respect for you but if you would use you knowledge to help us instead of belittling us I think we could get along better.

Respectfully
Mike

[DSteck]

Did you miss the picture I posted with the appropriate settings?

[Road]

Did you miss the picture I posted with the appropriate settings?

I saw it that's how I figured out my mistake. Sorry for the rant. I was just trying to help.

I apologize
Mike