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285/75/16 Mounted

yukon25008.1

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yukon25008.1 Senior Enthusiast

yukon25008.1

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04 yukon xl 2500 8.1 4l85e 4:10 rear.

 

I had goodyear ats 265/75, and switched to a pro comp x-terrain 285/75 i got cheap and now the truck feel/drives different, not so much the noise its just like the tranny is acting diffrent, and it doesnt seem to be shifting into to 4th or overdrive, really confused. ive had 285,s on almost every pickup/truck ive owned 7-8 and never noticed this before, What do you guys think is going on? the reason i went to the 285,s other than the look, was to knock down the final drive a little, with 4:10,s 80 mph on the highway is up there in the rpms

yukon25008.1 Senior Enthusiast

yukon25008.1

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I would think it is something transmission related that just happened to occur when you mounted the tires.

 

 

Right but what? like i posted ive had plenty of hd teucks gas and diesel and NEVER noticed these changes or feeling. it almost feels like its in tow/haul mode, and it really seemslike its not going into 4th

yukon25008.1 Senior Enthusiast

yukon25008.1

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Could have lost a clutch pack on the 3-4.

 

 

Ok, so again never had a problem before. how involved is repairing/replacing a clutch pack? does the tranny have to comeout? seems like a mechanical thing to me butany chance your program adjust for the tire height will take care of it??

Jennabear Senior Enthusiast

Jennabear

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Since you are having issues already, I would take it by a mechanic to see if it is a mechanical problem. You don't want to be messing with the transmission line pressures if it is not up to par.

davzog Enthusiast

davzog

Posted
Posted

You have increased the tire diameter and effectively changed the final drive ratio....that causes all kinds of issues. The speed sensor is confused and so is the ABS system as well as the tranny....

 

I had similar issues when I put the Hummer 17s on mine.....everything was different, including the brakes.

 

I hadBlackbear do a custom tune and everything went back on track...it does not take much to confuse the computer.

 

If yo do a search, you will fins a lot of guys going to larger tires wind up re-gearing the rearends....for exactly the same reason, to get things back where the computer can deal with the changes....

 

I was thinking about going to 35" tires with a lift kit on mine, and I know I will have to change the gears from 4.10 to 4.56 even with the Blackbear tune....that is just the way it is with the new trucks...

yukon25008.1 Senior Enthusiast

yukon25008.1

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I definitly understand what you guys are explaining, ive just never seen it before on any gm/gmc vehicle,

 

04 silverado 2500hd 285,s -6.0

05 sierra 3500 285,s -duramax

05 sierra 2500hd 285,s -duramax

03 sierra 1500 285,s - 5.3

01 silverado 2500hd 285,s -8.1

00 silverado 2500 285,s -454

89 silverado 1500 285,s -350

None of these vehicles showed any changes or acted any diffrent and they all had 285 or larger, thats what makes me more concerned with this one

What would make the yukon 2500 configuration/computer diffrent from the others escpecially the 04 and 05 models

masterp2 Enthusiast

masterp2

Posted
Posted

Shift points are based on speed and throttle position on many vehicles. The computer thinks you are going slower now. Program the tire size and you should fix the problem.

davzog Enthusiast

davzog

Posted
Posted

I can understand why you would not notice the differences so much with either a diesel or a big block engine. I had a Dodge cummins and put larger tires on it and I am sure the torque and power of the diesel overshadowed the tire change....

 

My son has a 2004 HD2500 with the 8.1 and 305s on it....never complained about shifting issues.

 

I believe (my opinion) that the 6.0 is for some reason more sensitive to ths tire changes because is it choked with the software for emissions, torque management, etc., , etc....and it does not have the extra power/torque to overcome the differences based solely on tire size.

 

I feel that when towing my 11,000 pound 5th wheel, the 6.0 is just barely adequate and if I retire and take a lot of longer trips, I would swap it for a duramax....it is ok for short hauls on flat terrrain, but a bit on the weak side for my liking. Actually, I wanted an 8.1 but GM quit making them just before I bought my truck, or that is what I would have....

yukon25008.1 Senior Enthusiast

yukon25008.1

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I think another reason im noticing it more is i purchased a magnaflow 12599 muffler for it got the oem muffler cut out but the new one isnt installed yet, its not real real loud, but i think the noise is making me notice the rpm diffrence.

So should i let it go for a while to see what happens before a tune.thats the tire size im going to stick with.

jro909 Senior Enthusiast

jro909

Posted
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it will take longer or less time to go into 4th, the bigger tire throws the speedo off and all that good stuff, i don't think your tires blew up the tranny..

Prokopchuk_9 Senior Enthusiast

Prokopchuk_9

Posted
Posted
I think another reason im noticing it more is i purchased a magnaflow 12599 muffler for it got the oem muffler cut out but the new one isnt installed yet, its not real real loud, but i think the noise is making me notice the rpm diffrence.

So should i let it go for a while to see what happens before a tune.thats the tire size im going to stick with.

 

when i installed the magnaflow cat back on mine, it would hold the rpm on the highway longer than it would before. like let off the gas at highway speeds, it takes a bit longer to idle down now...as for your tires. its just the tires man, they threw off your speedo. get somebody i.e. a tuner or your dealer to fix your speedo. i betcha thats what is goin on....

yukon25008.1 Senior Enthusiast

yukon25008.1

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Thanks guys, im gonna go out on the highway and see what happens at a higher speed. im gonna wait a while and see before the blac beartune,

yukon25008.1 Senior Enthusiast

yukon25008.1

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Ok, well if definitly goes into 4th. on the highway at 60mph and the rpms read 2200 (wow) and 2500 at 70 mph.

at 60 i put it into 3rd manually and went to 3000 instantly. how can i get the rpms a liitle lower besides tire height?

2200 at 60mph kinda sucks id really like to be around 1800 or so, and dont really want to go up to a 35"tire

???

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