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TCC Lock-up

Just for the record... I was wrong above... When at highway speeds and TC is locked, letting off the throttle drops RPM's to about 1,000, BUT tapping the brake DOES NOT drop the RPM's to idle. Dropping to idle (from tapping brakes) only happens when I'm going slower with the TC already unlocked.

However, what I mentioned doing in post #15 should apply to ANY automatic (truck/car/whatever) with a lock-up TC, regardless of year.
 
bmxdkj said:
Dennis...the truck is completely stock. Also, at 60, when you "goose" the throttle, the RPM's do climb with the speed.
Click to expand...

OK, then you can confidently say the TC isn't locking as that's a physical indication. However, this also means that I'm out of the conversation as the others can offer better expertise than I can! :) I guess you're back to things like the brake switch and sticky solenoids?

The only other thing I would add is that I would wonder if low ATF (or old ATF) could cause this problem? Just talking (typing;)) outloud - maybe someone else can verify.

Good luck!
 
Some simple math with ratios of gears and tire heights put you at around 2500rpm with 5.13 gears. So its probably locking.

So its not really high for the gearing. Taller tires would bring the RPMs down. A 35" tall tire would bring it down between 2200-2300 @ 65mph, the tires he has are no talller than those on a 3.73 geared truck, at less than 32" tall.

The fact that RPMs climb with speed is an indication its locked, because if its not it would either downshift or jump in RPMs within the gear without accelerating. Thats even what you had stated before Dennis.
 
Ooops - let me back track a bit (in regards to my first sentence in post #43). I misread post #42 to mean that the RPM's jump not in relation to speed - my bad on that - reading too fast, I guess.

Yes, if the RPM's climb proportionally to speed, it is locked. If they jump a few hundred RPM's immediately (before your speed really starts to change), then it is NOT locked. Whew! :)
 
Late to the party here, but......I'm geared at 4.63 and at 55 mph I'm at 22 -2300 rpm's.......so with the 5.13 gears (that was an option, most HD's are 4.63's) and the 225 70 19.5 wheels his gearing should be a tad lower, running 65 mph at 2500 rpm's sounds about right.

Matt and I had a discussion that brought us to the conclusion that my 4.63 gears and my 19.5's should bring me down to "about" 4.10 gearing, as opposed to a regular 3500 dually with 16" wheels, that are "usually" geared at 4.10.

As far as TCC lock up......When your rolling at 55-65 mph and you push the go pedal, speed and rpm's increase in sync, it's pretty safe too say your locked up.
For me as well there is no jump in rpm's when I hit the brake while locked......just a WAG, but, programming might be different on a HD to take in account for the weight factor.

Unloaded with me (220)......I'm weighing in at 96 to 9800 lbs, depending on fuel, consistantly.....I'm at the scale regularly.
 
Brooklyn Tow said:
Late to the party here, but......I'm geared at 4.63 and at 55 mph I'm at 22 -2300 rpm's.......so with the 5.13 gears (that was an option, most HD's are 4.63's) and the 225 70 19.5 wheels his gearing should be a tad lower, running 65 mph at 2500 rpm's sounds about right.

Matt and I had a discussion that brought us to the conclusion that my 4.63 gears and my 19.5's should bring me down to "about" 4.10 gearing, as opposed to a regular 3500 dually with 16" wheels, that are "usually" geared at 4.10.
Click to expand...

Thanks for that input, thats what we were missing and wasnt sure how accurate the ratio math was.

Also, just realize the wheel size doesnt matter, its the tire height, so where duallys with 16" wheel may have had short 225/75/16 tires, there are plenty others with 4.10s that have taller 265/75/16 or 235/80/16 tires that would be just as tall as 225/75/19.5. To get down to the level of 4.10s, using 4.56/4.63 gears you would need 35" tall tires.
 
the gear ratio comparison is only truly comparable with the same height tires. If you have 3.42 gears vs 4.10 gears with the same 28" tall tires it would be ratio of gears to determine RPM differences. At 55mph locked OD the 3.42 truck is at 1800rpm. 4.10/3.42 * 1800 = 2157rpm for the 4.10 gears at 55mph but since they use taller tires factor in that tire height ratio 28"/31" * 2157 = 1950rpm at 55mph for the 4.10 guy with 31" tall tires.

So if you are starting with 4.56 gears and 31" tall tires, and you know you are at 2200rpm at 55mph, then take larger tire and factor the ratio to determine your "effective" ratio. 31"/35" * 4.56 = 4.04, so then you will feel like 4.10 gears with 35" tires and the rpm would be the same ratio difference 31/35 * 2200=1950rpm just like the 4.10 guy with 31" tires. Getting lower gears is often how trucks upsize in tires without losing all their power to the ground. Military trucks often have the really low gearing, but have big tires to drive off road over logs and stuff, so the axles clear a certain specified height.

The math is not 100% accurate though because of loading differences, but its close when using data off your own truck for the calcualtion.
 
Would these calculators be of any help? Reading this thread just got me wondering and I started googling.

Convert metric tire size to inches: http://www.4lo.com/calc/gearmetric.htm Then, use the next calculator...

Find your RPM (at various speeds) with different tire sizes: http://www.grimmjeeper.com/gears.html

I think our transfer case is an NP241 (needed for that second calculator)?

There may be slight differences in one manufacturer's tire height size to another, but I think for your purposes this would work just fine.
 
For tire sizes I just take the width, divide by 25.4 to get inches, then multiple by then you have to use the second number as a percetage to get wall height.

225/75/R15
So 225/25.4 = 8.86" 75% of that is 8.86 * 0.75 = 6.644" wall height, multiply by two because its above and below the rim, 6.644 * 2 = 13.28", then add the rim size 13.28 + 15 = 28.28" tall

However its never perfect, and rubber is a little shorter by a quarter inch or so, and when mounted it sags, but some of that expands at speed, so the sag isnt a big deal. I always like knowing what it is I am calculating instead of trusting the website calculator things, but those tools are good for quick reference, especially that gear ratio calculator, does a lot of math for you if you have the info.
 
There may be slight differences in one manufacturer's tire height size to another



I've seen as much as 1" diff in diam from 1 tire manf to another
 
Yes it varies, I look at that on thier specs before buying, and then factor in tread height reduction over time and my once 28" tall tires were more like 27" tires when they came off :)
 
Yeah, it is fun doing some math. In fact, I started playing with taking a given RPM and tire diameter and converting that to MPH. First factoring in gear and axle ratio to get tire RPM. Then factoring in tire radius and eventually converting from inches/minute to miles/hour. Granted, it's not rocket science, but it's kinda neat to do it yourself!
 
DennisG01 said:
Yeah, it is fun doing some math. In fact, I started playing with taking a given RPM and tire diameter and converting that to MPH. First factoring in gear and axle ratio to get tire RPM. Then factoring in tire radius and eventually converting from inches/minute to miles/hour. Granted, it's not rocket science, but it's kinda neat to do it yourself!
Click to expand...

I'd rather stick needles in my eye!......."If one train left California at 2pm traveling at 50mph and another train left.....":???:

I hated those friggin questions!:mad2:
 
For what its worth, My 98 Tc stopped Locking up a month or so ago I bought a new Solenoid and The Sonnax 34994-01K kit, I had to drop the Valve body to get the roll pin in and out but it locks up great now, right at 45 mph
 
raceday--- do you have more detailed info on doing this solenoid swap? My TC is randomly not locking in when it should. From reading I've done it could be the CTS on the coolant crossover also. I haven't had time to do any troubleshooting yet. If it is the solenoid then that's getting into a new area for me.

Don
 
Alright guys, had a chance to snag a scanner from a mechanic friend of mine...(hard to get as he's real busy, but got a chance to use it on his lunch)..The TCC is locking up 100%. The RPM's climb with the speed, but I'm just wondering if its the gearing in this truck as it did come with the 5.13's. So I do want to thank everyone who helped me figure out that my problem wasn't really a problem at all. I did write down a lot of useful info from this thread. I do wish this truck ran around 1800-2000 RPM around 65 or so. The turbo seems to run out of steam around that speed. Truck goes like a bat out of hell, but still, I personally feel safer with the motor running around 2000RPM since it seems to be "at home" there. Thank you again everyone!!

Brooklyn Tow...real quick...since you have an HD...how tight is your exhaust with the 3" DP...I'm looking to get a 4", but not sure if I have the room, since its already really cramped with the bigger frame. Any thoughts?
 
Handcannon...I am interested in this swap as well, since the twin to my truck DEFINITLEY does not have a lockup...that truck runs around 2800-3000 RPM around 65 mph. I got a chance to take a ride in that thing today as well. That comes up with some soleniod code.
 
Next time it needs rubber pick up some 35" tires and your cruising will be much more enjoyable, with a little loss in acceleration off the line. Changing tire height also requires to modify the VSSB module to correct the speedometer and PCM's speed input. The VSSB modification isnt a big deal.
 
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