View Full Version : 33" Tires + 3.42 gears+ 4L80E = Bad News!
DA BIG ONE
09-18-2005, 15:50
After taking trip and driving locally, I can say I'm not happy at all with combo I have chosen.
70 mph mpg is great, however anything other than level road tranny downshifts and motor temps climb with egt's (pre turbo) @ 1,000+ deg.
Skyway bridge in Tampa/St Pete area has become a PITA w/my setup. Before 33" tires there was no downshift on this bridge and truck temps were ok, now it struggles over bridge.
Even on interstate going over overpasses is a problem. I'm thinking without load I have this problem, can only emagine issues loaded, forget towing even a motorcycle, or two.
Going back to 245/75/16 for now, maybe even look around for diffs with lower gears to switch out later on.
markrinker
09-18-2005, 15:52
A set of 4.10s shouldn't be hard to find. That should do the trick, but don't expect to set any fuel mileage records!
DA BIG ONE
09-19-2005, 00:42
Originally posted by Mark Rinker:
A set of 4.10s shouldn't be hard to find. That should do the trick, but don't expect to set any fuel mileage records! 3:42:1 are great w/245/75/16 and I mean great. In the mountains dosen't even break a sweat, no constant down shifts and this is w/load. I feel that the tranny control is just right too.
I would like to get complete diff assemblies to cut down on labor. I figure it would be a good time to learn how to work on the 14 bolt IFS too.
Considered the stand alone tranny controller, but don't know if it can be retrofitted into my burb "that %#$@# autotrac"?
Anything other than highway driving mpg takes a big dump. From a stop it still has lots of getup and go.
I remember 3.08's in my 6.2 w/700 r4 (lower 1st gear) Jimmy was great all around. 700 R 4 was a problem in the stay working area, but eventually that was fixed.
markrinker
09-19-2005, 03:29
Too bad we aren't closer - I'd offer to trade you for the gears in #2. I always run stock rubber so its actually under-geared for what it does.
Just about my experience, switch from 4.10 to 3.73 and bigger tires : slightly better unloaded,
with my truck camper, lost TCC lock up in any hard pulls,
TCC lock up switch does work, but you need to
down shift to 3rd prior to hill.
I have a 4.10 front unit from a 1 ton with 4.10 ratio if anyone is interested.
DieselDavy
09-19-2005, 05:04
I'm looking for a 3.42:1 complete diff. If anyone has or knows where I can find one, let me know. After 335,000 miles, mine took a dump while my daughter was driving it! Can you believe that? After only 335kmiles! Darn thing!
Dave
Originally posted by DieselDavy:
I'm looking for a 3.42:1 complete diff. If anyone has or knows where I can find one, let me know. After 335,000 miles, mine took a dump while my daughter was driving it! Can you believe that? After only 335kmiles! Darn thing!
Dave DieselDavy, I have a 14FF with 3.73s complete if you are interested, and I am also in Terre Haute.
Email is below:
DieselDavy, I have a 14FF with 3.42s complete if you are interested. About 50,000 miles. contact me at "gmc65td at aol dot com"
Marty Lau
09-19-2005, 07:06
Originally posted by DA BIG ONE:
[QB] 3:42:1 are great w/245/75/16 and I mean great. In the mountains dosen't even break a sweat, no constant down shifts and this is w/load. I feel that the tranny control is just right too.
/QB]This what I found too, and I live in Montana and we do have a few mountains here. I also found that with a modestly modified 6.5 the 3.42's tow up to about 7500 lbs pretty well.
So why not just hang with the stock tires and live with your set up sounds like you have been pretty happy with it?
DieselDavy
09-19-2005, 07:55
Andy and John,
Thanks for the quick response. I should have said the truck with the bad rearend is a half ton. I would have to get new rims and tires if I went with your rear diffs. I'm looking for a Corp. 10 bolt. The junk yards say they could sell one a week if they had them. I guess I'm going to have to keep my eyes open for junk trucks in farm lots or something.
thanks again,
Dave
Originally posted by DieselDavy:
Andy and John,
Thanks for the quick response. I should have said the truck with the bad rearend is a half ton. I would have to get new rims and tires if I went with your rear diffs. I'm looking for a Corp. 10 bolt. The junk yards say they could sell one a week if they had them. I guess I'm going to have to keep my eyes open for junk trucks in farm lots or something.
thanks again,
Dave 10Bs are everywhere, I sold 3.43 gears just about 6 months ago, check out ck5.com!
DA BIG ONE
09-19-2005, 11:44
Originally posted by 16ga SxS:
</font><blockquote>quote:</font><hr />Originally posted by DA BIG ONE:
[QB] 3:42:1 are great w/245/75/16 and I mean great. In the mountains dosen't even break a sweat, no constant down shifts and this is w/load. I feel that the tranny control is just right too.
/QB]This what I found too, and I live in Montana and we do have a few mountains here. I also found that with a modestly modified 6.5 the 3.42's tow up to about 7500 lbs pretty well.
So why not just hang with the stock tires and live with your set up sounds like you have been pretty happy with it? </font>[/QUOTE]I've been considering this too! Guess I'll use the 285's for off road only.
DA BIG ONE
09-19-2005, 11:48
Originally posted by rjwest:
I have a 4.10 front unit from a 1 ton with 4.10 ratio if anyone is interested. Is this a complete IFS differential, or straight axle?
IFS from a 96 1 ton, VERY little 4x4 operation.
Never plowed ( florida truck ) I bought a
3.73 and removed the IFS unit about 60 k miles on it. Jacksonville area...
DA BIG ONE
09-19-2005, 14:59
Originally posted by rjwest:
IFS from a 96 1 ton, VERY little 4x4 operation.
Never plowed ( florida truck ) I bought a
3.73 and removed the IFS unit about 60 k miles on it. Jacksonville area... Is it a 14 bolt unit, 14 bolts connecting both halves?
john8662
09-19-2005, 15:35
Hmm, anyone got a 3.42 front IFS for a 3/4 ton Heavy Duty? I can have the rear end on my burb setup for 3.42's but no one wants to touch the front, so I figure that it would be easier to swap out the front IFS axle.
rjschoolcraft
09-19-2005, 15:46
What's so scary about the front? I've been into mine to replace the carrier. It's not too tough. In fact, it's easier than the rear.
DA BIG ONE it is a 11 bolt ifs.
pn 15573206. out of 1 ton
unit is 1996, with long axle a 2000(newer solenoid). swaped them to not have to change wiring...
DBO, I was interested to see how you liked your setup. I'm eyeballing a set of H2 wheels and tires(LT315/70R17) for my K2500 sub and think I'll be ok with 3.73 barring any tire fit issues.
[ 09-20-2005, 08:34 AM: Message edited by: MJEasly ]
nathan71
09-20-2005, 07:12
DieselDavy: I have front and rear 10 bolt, 3.42 axles off an 86 half ton in central Ohio. nate_cotton at amanda dot k12 dot oh dot us
MTTwister
09-20-2005, 11:58
I hate to interrupt the swap meet smile.gif but, with a 3.73, would I be better off staying with 245/75's ( only 5000 on the spare) or eventually go to 265/75's which would / should require buying a new spare( oh and hacking the VSSB) ? Any benefits? the rpmcalc.xls doesn't show a whole lot of drop, so's anyone have any opinions? THanks.
[ 09-20-2005, 12:43 PM: Message edited by: MTTwister ]
DA BIG ONE
09-21-2005, 01:17
Originally posted by MJEasly:
DBO, I was interested to see how you liked your setup. I'm eyeballing a set of H2 wheels and tires(LT315/70R17) for my K2500 sub and think I'll be ok with 3.73 barring any tire fit issues. I like the setup very much, but I have to correct the shifting/lockup issue to make it efficent.
My torque out put still allows the burb to accelerate from a stop, or passing on highway like a high powered car.
I'm thinking that your combo will yield somewhere around 3.40:1, I find the 4L80e w/stock program responds well at this ratio, but remember lockup in 4th will be about 55mph.
My issue is between 45 and 60, then the downshifting problem on hills because of final drive. Looking at 2 different tranny control units to see if this can fix issue?
Marty Lau
09-21-2005, 05:50
Originally posted by MTTwister:
I hate to interrupt the swap meet smile.gif but, with a 3.73, would I be better off staying with 245/75's ( only 5000 on the spare) or eventually go to 265/75's which would / should require buying a new spare( oh and hacking the VSSB) ? Any benefits? the rpmcalc.xls doesn't show a whole lot of drop, so's anyone have any opinions? THanks. Tom;
With the wider tires you will increase your rolling rersitance and areodynamic drag which may negate some or all the difference in tire size. You might consider 255/85/16's just a bit wider but should be giving you the the added size. I have also considered 235/85/16 the are larger than the 245/75/16 and since they are narrower would also decrease rolling resistance, I talk with a fellow who went that route and he was not happy with the handling, so I have hung with the stock 245/75/16's.
DA BIG ONE The resister accross the Trans temp sensor will make 4th hold TCC lock up untill a 3rd down shift is required ( throttle position).
Alos 3rd would lock up at about 43 MPH on your setup. 2nd at about 30 mph.
cheap way to test more expensive options IE: see if power is there for 4th, IF it shifts to 3rd with the resister switched in, it needs to shift,,,
no more power left in 4th..
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