Tranny Cooler

DesertRace21 · June 30, 2004

Hey guys. I have a 2000 Z-71 with an RCD lift and 35's on it. Everything about the drive train is stock. I was wondering if Z-71's come with a tranny cooler or if I should add one on it... I do not really use overdrive because the tire size, but I am going to be towing. I live in southern california and race Desert trucks. I am only 21 and cannot really afford a hole lot due to the racing budget and the truck payment and the southern california price of gas! However, those of you who live here or have traveled around here know where I am towing. 2 major grades: The Grapevine, and Cajon Pass!!! My speedo stays at about 70 up the hill and does not kick down.. adjusted speed accoring to GPS and other trucks would tell me that is somewhere near 85. With the toyota i race and trailor being about 5k lbs. I would like to be able to get up the hill without working my tranny which may mean manually running it into 2nd gear and cruisin at 60 mph or so to keep it in the power band for torque to get up the hill. Any tranny cooler suggestions?

snoman · June 30, 2004

You need two things, a cooler and a new set of gears if you want to tow properly. You are too tall now since OD is not usable and that adds to tranny strain when not even towing. Towing will realy add more strain with stock gears and have poor tow performance. Second gear towing on interstate hills is not cool or good on tranny. I would suggest you install 4.56 gears in that truck and a aux cooler. They would yeid a 2000 RPM cruise in OD at 65mph with your setup and about 2800 RPM in drive at that speed with would give you much better power on hills for towing without downshifts. I figure you may have a 3.73 now and if you 4.56's would reduce tranny strain 25% at any given cruise load and boost power accordingly. It would make a big difference in the way the truck drove too. Even with a cooler, your tranny my not last long towing because you would be severly overloading it in your trucks current configuration because with those tires and gearing it is already "towing" because of added strain.

az'03Silverado · June 30, 2004

Hey DesertRace, I know exactly what you're talking about. The Grapevine and Cajon both suck. When you see semi-trucks creeping up the grade at 5mph you know it's a b***h of a hill. I went up Chiriaco Summit on Sunday (east of Palm Springs) on my way back to AZ and my '03 4x2 was empty (just me and my dad) and pushing 70mph it was in and out of 3rd and OD. I'm not sure about the gearing. It sounds like snoman explained it well. But, if you can save your pennies and put on an aux tranny cooler you'd be in good shape. Especially down the road when it's saving you costly tranny repairs. Just my $0.02. Good luck at the races!!

snoman · June 30, 2004

Do not think so, if OD is worthless now he will really strain it towing. Want to try a hill? Try the 6000 ft climb to the Eisenhower tunnel at 12000 ft on I-70 west of Denver, that one is a REAL ball buster!

az'03Silverado · June 30, 2004

Hey snoman, I have a question. Is changing the gearing just a matter of gutting the diff and replacing the gears or is an entire new rearend required? What does that run in $'s ? It sounds like with the tall tires and towing he'll need to do the gears.

P.S.-- I'll have to check out the Eisenhower tunnel some day. Sounds like fun!

snoman · June 30, 2004

Hey snoman, I have a question. Is changing the gearing just a matter of gutting the diff and replacing the gears or is an entire new rearend required? What does that run in $'s ? It sounds like with the tall tires and towing he'll need to do the gears.

P.S.-- I'll have to check out the Eisenhower tunnel some day. Sounds like fun!

Depends on rearend. He most likey has a 10 bolt so it is pretty cheap parts wise (gears on line are about $140 a set give or take) and there is no need to replace bearings if rear end is in good shape and not high mileage or bearings look good. You re-use housing and carrier in that axle and you just need a new crush sleeve for preload on pinion bearings and some shims and a new pinion seal. They are not that hard to set up if you are mechically inclined and have the present of mind to take your time and tear it down a few times if needed to change shims to get pattern on teeth correct. You cruch the sleeve after everything is set and I usually set pinion to be a hair deep on pattern on a 10 bolt becuase when you torque it to crush pinon sleeve to preload bearings it usually pulls in a 001" or so and brings contact area "out" just a tiny bit to the right spot. Regular tools will work but I would add a dial indicator to your tool tray to check and set backlash.

DesertRace21 · June 30, 2004

4WD.. what about front gears?

snoman · June 30, 2004

4WD.. what about front gears?

The 8.25 IFS is actually a bit easier to to do. You do have to drop the whole front pig from truck but it is not that bad and it has preload/shim adjusters for carrier bearings built in to case so you only have to shim the pinion manually (change shim packs as needed) and you can set it upon the bench which is easier (to my old bones anyway) than under the truck.