3.07's and tires size question(kinda long)

[MMiller]

I was under my 90 the other day. The way the truck runs down the road I assumed it had 3. 55 in it. Going down the road in drive felt a lot like my 93 in 4th gear. Anyway, I was under the truck the other day and looked at the tag on the diff, and it says 3. 07. I have not pulled the cover to verify, but I can't think why anybody would put the wrong tag on a diff.



Here is my situation. I am going to use this truck for offroading, ie lockers, flexy suspension, 36-40" tires, BUT still drive it on the road, to run parts, cruise,etc, not "daily driven". I know with the 3spd it will not be a interstate cruiser, but I still want to run down the two lanes without winding all day. I will still leave it set up to do very occasional towing, not heavy, long trips. My 93 works awesome for that. Someday I would like to run an OD/Lockup auto in it, but that won't be soon so I will set the truck up with the 3spd. Also this truck will eventually get all kinds of power upgrades, after the trans is set up to hold them.



Will the 3. 07s be too tall? I know of gassers guys running 4. 56 to 5. 13 with these tires sizes, BUT this is not a gasser. I was thinking 3. 55 would be adequate, and could switch lower later if needed. With these axles I can't do anything but 3. 07 correct? Also if lockers could be found for the 61F and 71R could they be put into a 60F and 70R or would I be stuck buying another set if the 3. 07's are too tall?



Now the auto. I know the 727 is tough, and the converter is lackadaisical like most. It will surely hold lots of fuel, and twins with a good converter, VB, rebuild, won't it?



Sorry for the long post. I pretty much got my 93 figured out, but the 90 is a little different beast.



Michael

 

[Philip]

A lot of the early auto trucks came with the 3:07 gears in them. The sticks got 3:54's because they have a OD gear in them.



3:07 is the only gear you can use in that case/carrier assy.



As far as a locker about the only thing out there is the ones that replace your spider gears. But I have not gotten any 4x4 shops to tell me if the 3:07 will take the one for the 3:54 and up carrier.



The 3:07's are a tall gear. With that size tire I do not know how bad it will kill it down. I have the 3:07's with 235's on it. In 4X4 low lock. I can run almost 60 MPH.

 

[MMiller]

The lockrites are good units, I run one in the front of my 75, but I would like to get full detroits for the 90. The drawback of the lockrites are they are only as strong as the carrier they are in. I would hate to break one, they sound like they are hard to come by, carrier wise. I feel when I get the cummins running hard, lockers and boggers/swampers on the truck I need all the strength I can get.

 

[RGT]

I bet you could sell those 3:07 axles real easy and you should have no problem finding some 3:54's or 4:11's to replace and build. with the 40" tires you should havee decent top speed.

 

[Philip]

Finding a used carrier would be hard to do. Most larger junkyards do not part out model 70 axles. They sell them off to rebuilders or rebuild them in house.



If you want steeper gears as stated by RGT there are members wanting the 3:07 rears that would trade in a heartbeat if you are close to them.

 

[MMiller]

I knew that trading would be a viable option. I already have one pm about that.



I was just wondering if the 307 would indeed be too tall for what I want to do. Sounds like I need to find out about the locker deal first, as far as avalibility. If I can only get the lockrite style then I will probably choose to swap out gears.



Thanks for the input and keep the info comming.



Michael

 

[1stgen4evr]

The 3:07s

A very interesting thread. I have just bought an 89 with 3:07s. While I have no plans for off road (not a fwd) I am also curious as to the result of different transmission and tire selection. I have an automatic od 92 and 93 that are exactly the same with 3:54 rears. The motor speed is a tad higher (no tach) with the 89. (235 85 16 tires on both) I want to run a 3:07 behind an OD with lockup torque converter and behind the Getrag to see what it does for mileage. I am not satisfied with the 727 although it is plenty strong. I am going to swap some rears around and see what I get.



For the off roading, couldn't you have a second set of tires and run them only when you are doing the off road. The tread wear isn't going to be the best when you are running highway miles and they are somewhat noisy as well. With low range, the 3:07s will work good enough as far as ratio but I think the difficulty is going to be in the front as to lockers.



There are plenty of options as to swaping out the axles and most likely would be the cheapest in the long run. There are several parts trucks on the classified right now.



While I have no experience with the strength of the 3:07, I have seen several comments on the forum as to ripping out/roasting the rear. Can anyone comment as to the actual strength of the 3:07 rear. I do know that they are hard to come by and if you roast them, you are down for the count.



Another possible solution. Buy another truck. Build the current truck for off road only. Trailer it to the off road location and you can even run red fuel. No tag, no insurance, no taxes cause the courthouse nit wits won't even know you have it. I have talked with folks who have bought a CTD for 1500 dollars. A few bucks to get it highway worthy and that is the daily runner. If you honestly consider trying to run a truck that is set up for serious off road, you will find that the additional truck is the cheapest in the long run.



1stgen4evr

James

 

[MMiller]

I agree james,



I bought the 90 for $2500. It came with new BFG's 305's, new aluminuim wheels, and 6" or so lift already. I believe I got a good deal. I use the 93 for truely daily driving, towing, hauling etc. I will set the 90 up for offroading, and it will be very able in the end, but I wouldn't enjoy it as much if I couldn't get in a drive it to the grocery store, parts store, up town on Saturday night. Heck my 75 with the 440 is set up for truck pulling, and off roading, BUT it still runs on pump gas and goes to town. I really enjoy driving a competitive pulling truck, that offroads well, and is still street worthy. In the end I will set the 75 for truck pulling and quit off roading it. That way I can make the body nice, and look good on the street and track. The 90 is an old farm truck, already beat up body wise.



I took the 305' and wheels and put them on my 93. I will use the wheels that were on the 93 for the 75, then put the steel wheels and swampers on the 90. I know the mud tires will not road "great" and will not wear "great", but it will not see an extreme amount of highway miles. If it gets to be getting many highway miles I will indeed get some tall street friendly tires.



I'm not really new to offroading/pulling/ trying to drive them on the street, just trying to figure out how to get the 90 setup.



By the way james, the visor is boxed up on the bench ready to ship. Just gotta get the wife to get it to ups soon. Sorry for the wait .



Michael

 

[tugboatphil]

Originally posted by 1stgen4evr

Can anyone comment as to the actual strength of the 3:07 rear. I do know that they are hard to come by and if you roast them, you are down for the count.

James,



I drove my 90, with a 3. 07 rear, to about 303k. Will admit that I never checked the oil. Had seals replaced on the axle a couple of times and figured that it was ok.



Was about 300 miles from home one time and heard a loud pop. I thought it was just a big rock hitting the underneath. Drove another 50 miles to a friends house, for the night. Looked under the back and a piece of gear tooth had apparently broken off and hit the spinning gears, which propelled it through the case and out the back. The hole was up high, so I lost some oil, but didn't run dry.



Pulled the cover and patched it with JB Weld (hooray for JB!). Fished out 3 other small pieces that had been there for who knows how long.



Drove the rest of the way home to my son in laws garage and that's when I found out just how far gone everything was, and that no new replacements were available.



Would anyone consider putting their 3. 07 in their will for me???

 

[Philip]

The issue I see with the 3:07's and off roading is you will not be close to the engine power band.



You haven't stated the type of off roading you do. If it is mudding where wheel speed might help out a lot. The the 3:07's will give you wheel speed.



If you are into rock crawling. Then I would step to a deeper gear or you will need to add a reduction box before the transfer case. The 3:07's with tall tires will not be good for this app.



I hit 89 MPH in 3rd against the governors. What are you doing on MPH with the taller tires. Mine are 31" tall.

 

[MMiller]

Well as far as wheelin, I do see almost all. Not been to Moab on the rocks. I don't mud race anymore. But my friends and I go trail riding in Wisconsin, and here in Iowa. Some mud, some sand, mostly steep trails. We all would like to go to Moab Utah and the Badlands in Indiana. Out here in the midwest there ain't a whole lot of rocks. If I every got into that I would put a doubler kit in and have two low gear reductions at the t-case. It uses the low side out of a NP203 tc and then the 205 bolts to the rear of it. That way a guy could run double low. I would only do that if I ended up in the rocks. My buddies are running 44" tires with 5. 13's auto trans, and solid big blocks. Another buddy is runnin 49" irocs with 6. 13 or something in rockwell axels. These trucks are dedicated trail trucks, with full on hydralic steering, radiators behind the cab, and full cages, one of them has king coilover suspension on all four corners of his truck. Another buddy runs 38" swampers with 4. 10s and 460 with an auto. No custom transfer cases just regular truck parts. My 75 with 4spd and 4. 10's handles 36's easily. We always run lo 4 off road. Most of us have modified so we have 2 lo on straight sections of trail, for slower travel speeds. Then just push it into 4lo for the harder sections. Most of us are using big blocks that only rev to 5-6000 rpms too. Set up for low end torque, well as much as you can get from a gasser!



Again these are all gassers, I'm not ready to build a full on trail truck, with 44's yet. I am very confident that I can run a taller gear then 4. 10s with the tire size I want, but am not sure the 3. 07s will do the job.



I have wheeled my 93 with the 3. 54s before the injectors, and it is WAY overpowering the 33" BFG MTs. With some PODs, pump tweaks, and other mods, along with a tighter transmission I think the 90 should be able to turn 38" tsl, 39"boggers, or 40" tsl's.



I know a lot of this is bench racing and probably not many have tried, but am I on the right track? I have impressed alot of people with the 93, and with the auto in the 90 I believe it will work a little better. Its time to bring some smoke to the timber!



Michael

 

[MMiller]

Here's some more info. I just got off the phone with my buddy that runs the 38's, 410's and 460 with the C6 auto. At 70 mph he is turning about 2800 rpms. I think this would be a little too slow gearing wise for my diesel. With 3. 54s I could run 70 without hitting the governor, or am I not figuring correctly? I also am thinking that in low side I should be able to turn the tires easily. Am I missing anything here?



Please keep the info coming.



Michael