New Gears: Which Ratio?

[Dieselboy]

I'm considering a gear change. The 4.10s and 35s are not working out how I would like. The engine speed at 65 mph is a bit low, and just on the outside of the power band. It lugs, and the engine really has to work too hard to pull up hills. Boost is great so long as the engine speed is in the right range. I'm going for about 2100-2200 rpm at 65 mph.

I am considering a set of 5.13 Precision gears since I plan of 37" Goodyears in the future.

This is a big [read: expen$ive] upgrade, and I'm looking for second opinions.

[CleviteKid]

Hi David,

Your Toy is for fun, not towing, correct? How fast OVER 65 mph to you intend to run? My SAA engine in my 1984 is running 3.73 gears with 33" tires, and I see just over 2100 rpm at 80 mph. It really likes to run between 80 and 90, and will zip right up hills in 4th if it starts out that fast. Below 1800 rpm, it lugs down on the hills.

If you really want to run 65 mph, then your plan to turn 2100 rpm at that speed is a good one. Your gears (5.13:1) in conjunction with the 37 inch tires should give you about 15% more RPM at any speed than you are getting now. If you MUST run 80 mph for some reason (?) you will be at about 2600 rpm, which is fine for the engine, if hard on the ears.

PS: If I had it to do over I would have put in 3.90 gears, so I always recommend going for MORE GEAR - you will feel it in the seat of your pants, and enjoy it ! !

Dr. Lee :cool:

[Dieselboy]

I figure on 90% of the time spent will be unloaded and on the street, 5% is on the trail, and the other 5% will be towing.

Texas cops have a thing for giving out speeding tickets ;) , so with the legal limit being 70, I won't venture higher than 75.

Thanks

[Dieselboy]

After checking the pinion tooth engagement, I've settled on 4.88s. Towing is part of the plan, and these gears will fill the bill.

I'm also building a new D60 front, so I guess I'm committed now for the new rear gears:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7907873271

[Ratau]

Do the power band or sweet spot move much from naturally aspirated engine to a turbo engine? I am about ready to install the turbo. My Blazer runs on 33

[john8662]

4.88 gears? Whoa. I am working on lifting my 86 burb, I had planned for 44" tires, I was going to use 4.56 gears and a TH400 tranny with my 6.2L (Soon to be TD with TE06H). Good thing this project is still in the planning stage, I'll look closer at a gear ratio for my needs.

Dieselboy, you got a good deal on the gears on ebay!

John

[Dieselboy]

I did notice a change in the power band. Peak torque and the most efficient performance on the highway was right at 2000 in NA form for me. After the turbo, the engine did prefer about 2200 for the best balance between power and economy.

I am going to model my truck's rpm range after our 96 suburban's. My dad's truck turns about 2400 at 75, and when you drop to 65 or 70 on hills the engine is in the middle of the power band at 2100.

I use the calculators at www.4lo.com (http://www.4lo.com) to help determine my gear and tire combinations.

My truck does end up towing loads up to 9000 lbs about once every two months, but spends most of its highway time unloaded. 4.88s are a good compromise. Plus, I get a lower crawl ratio for better offroad performance.

Depending on what rear axle you're running, I'd use 5.13s or 5.38s for turning those 44s. Keep your sawzall handy since those tires have a way of self clearancing fenders. ;)

For 10 bolts, going higher (numerically) than 4.10s uses a very small pinion that isn't up to the task of towing, and in my opinion is not the best rear axle under turbo power. It's not a big deal for a front axle since the engagement is only part-time, but there's no substitute for a 14 bolt (semi or full floater). They're easy to find with 3.73s and 4.10s, and you'll spend the same amount or less that if you were to buy and install new 10 bolt gears. Plus, you get bigger brakes.

As for brands of gears, I like to get factory Dana/Spicer, AAM/Saginaw, etc. if the price is right, but usually they're quite expensive. Precision, Superior, and Richmond are excellent aftermarket gear providers too that are generally less expensive than factory.

[john8662]

Funny, on "modeling" gearing, I am using RPM information from my 95 K2500 burb with 4.10 gearing for a reference also.

As far as axles for my 86 burb, it has the 10 bolt stuff under it now. I have a 14 bolt FF sittting in the floor with 4.10 gears in it now for starters. I am waiting till I find that needle in a haystack (yeah a Dana 60 front) before putting them in as a set. I sure wish I could find a military truck that had the 4.56 geared axles underneat it for my project. But too far and few.

I am also new to 4x4ing, in that I want a tall rig, but for climbing what? Its flat as a panncake here in Lubbock. I was thinking 44 and 12" suspension lift. But this has been a long term project as I don't always have the cash for my toys nor the time. So parts collecting I go..

[CleviteKid]

Hey John!

Stop thinking about gears for a minute and tell us about the upcoming 82 C20 race truck . . . . .


Dr. Lee :cool:

[john8662]

Dr. Lee,

Well, its just a recently acquired truck that has the necessary goodies to make a good platform for some higher HP diesel. I must be jealous of your truck or something. smile.gif I am going to be using a 6.2 diesel engine that I have on the engine stand right now. For starters I want a set of 19:1 pistons, but I might go ahead and run with the stock ones in it till I have head gasket troubles. The plans are really basic, stick a 6.2 in, a good 700, a turbo (or two) and see what I can make this thing run like. There are several things I want to play with on this truck, because its such a simple truck (6.2, 700R4, 8lug 3/4 ton, 14B FF rear, 4.10 gears) and its plain, no power stuff on the inside. And best of all I got er real cheap, and in good shape.

Parts gathered right now:

+Complete Factory 6.5TD Turbo setup (GM4 turbo) to play with.
+6.2 Engine (original one is locked)

Looking for a supercharger or a turbo off an RX7 to play with...
And one big intercooler (going to use a cummins IC)

I don't know where this project is going, but I intend to stick with it, that and the 4x4 burb.

Thanks for your interest!

[Dieselboy]

Originally posted by john8662:
I am also new to 4x4ing, in that I want a tall rig, but for climbing what? Its flat as a panncake here in Lubbock. I was thinking 44 and 12" suspension lift.I've found the best setup for the 131" wheelbase is about 6"-8" total lift, and 37"-40" tires. I'll be running at the lower limit of that with 6.5"/37" in order to keep radial tires with road hazard protection. The truck is so long that you need to make up for the low hanging t-case, but go too high and you'll find that the new center of gravity is an impediment on the trail as things will get tipsy frequently.

I've been wheeling the suburban for several years now, so I would recommend a lift like the Tuff-Country 6" (what I have), a BDS 7", or a Rancho 5" setup. BFG MTs and Goodyear MTRs are my favorite radials in the 37" variety. You'll find that it doesn't take much to get these things trail ready, but be careful of two things: killing that low-hanging rear driveshaft, and narrow trails.

As for wheeling places, look up:
http://www.texasmotorizedtrails.com/
http://fwd-fwd.org/
http://www.texas4x4.org/
http://www.coloradok5.com/

There's some forums to cruise that are area specific, so you should be able to find a group to wheel with. It may be a long drive for you, but I'll let you know the next time my club goes wheeling.

:cool:

[dieselcrawler]

Hey all,
Not that I have a lot of info to draw on, but I thought my 4.56 geared truck ran well with 35's... a bit sluggish with the 39.5" boggers on it tho. It's nice and stable with only 6" of lift, and some work with a sawzall and a large hammer.
Latly, I swaped the gears for 4.10's, droped the truck to 4" of lift, and put a utility bed on it, with 235/75/16" tires. Will have it back on the road soon, hope it still runs good. We'll see. Put the gears in a gasser truck I have, wich I will be soon converting to a 6.2. I hate the carb on the gas truck. Been so used to idleing over every rock and bump, ran the gas truck out 4-wheeling last weekend, and hated it. Bump, caugh, sputter, cuss, repeat. That was bad enough, till I hit a bump hard enough to send the now-too-long front drive shaft (due to swaping the Dana 60 into the place of the Dana 44) into the transfercase, wich ripped it off the transmission. I had to get my friend to pull me home, with a 3500 lb Toyota no less. The shame...
Solution: Buy K-5 blazer w/6.2/700R4/NP208 and swap the whole mess into my K-20. And new drive shafts!
Sorry so long, got carried away... but that's my story for the week...
Greg

[waorth]

Hi,

imho, the TH400/NP208/4.56 combo is best with tires from 36" to 38".
This includes fourwheeling. :cool:

I've never experienced a hill to steep in low range.

Greg: with 235/75 R16 the diff of your 14b full floater will act like a plow. ;) Hope you won't do any 4x4 with that setup.

David: from time to time I'm thinking about more lift than just my 2". But aside from the costs, there's lot of technics to be considered
- dropped pitman arm or crossover steering
- driveline angles
- additional stress to all componenets
- less handy when using onroad (as a daily driver)

I've seen a few of 8" lifts - even here in germany - and I like them. But for me, 2" and 37" tires are a good compromise.

Happy wheeling :D
Walter

[john8662]

Dieselboy,

thanks for the links and info about trails. I'll study those a little more. Right now I need a rig to "learn" in. My project 86 burb is still quite from finished, or even road worthy right now.

Thanks for the invitation next time your team goes trail riding. Let me know and I'll see what I can do to make a trip there, its not THAT far... I probably wouldn't be able to bring a 4x4 to drive off road (the 95 is 4x4 but not for offroad, its just a sticker on that rig). But if you want to talk about trucks and offroading, I'm game, or go with.

Are you going to the Rendezvous?

my email is awesomechevyman @ yahoo.com (since my cox mail is down)

later..

[Dieselboy]

I wish that I could make it, but my prof has refused to let me work around a scheduled test and a lab. I told him about the rendezvous two months in advance, and asked if it was possible to work something out. I offered to do all the work/test/labs in advance, but he declined.

I even tried to say that I had a special tutoring session with Professor Bigley of the University of Montana, and Doctor Swanger of the University of Miami. He wasn't buying. ;)

Soon enough I will graduate, and I'll just take some vacation time. :cool:

[john8662]

now thats comedy, professor Bigley of Montana and Dr. Lee of Miami, though not far from the truth smile.gif .

I am still considering, but I wish this Rendezvous was more like the older format. The pull-off would be nice to witness, although I don't know if there will be many 6.5's contending, mostly Dmax. I have never been to one though, still kick myself for not getting off work to go to the Rendezvous that was held at the Dmax engine facility and AMG engines.

Bummer you couldn't get away from classes, I am not that close in my degree, so I take my summers off to work.

John

[CleviteKid]

Whaddaya mean, "Not far from the truth" ?

Look HERE, U of MIAMI (http://www.miami.edu/UMD/CDA/UMD_People_Details/1,3191,dqGGl1ufroxy_e_0,00.html) for me.

And ask Jim about his position at U of Montana, from which he retired to run www.TheDieselPage.com (http://www.TheDieselPage.com) full time.

Remember, here at TheDieselPage.com we stay very close to the truth, we don't need to make up stuff.

Dr. Lee :cool:

[dieselcrawler]

He He Heee, I know the stock tire size/14b FF combo will equal almost negitive numbers in ground clearance... I will be limiting the dually truck to on-road use, and keeping the the other one, (currently a gasser) for off roading. I'm a big fan of simple, low lift set-ups... no body lift, 6" suspention lift, steering arm correction, and wheel the wee out of it... trim fenders if more clearance is needed. I clear 40" boggers on the play (gas) truck with the help from a sawzall, and hope to go to 44's, and 5.13 gears. And no more lift, of course.
As to the dually, I drove it for the first time today, with the newest set up. open 4.10 gears, 235/75/16 tires. Seems to run just about right. About the same rpm range as with 4.56 gears and 35's. Being lower (4" lift, not the 6" it had), and with the dual wheels, it handles well. should be sweet when I add a turbo some day...
There's a new picture of the truck with duallys and new bed in the photo album in my sig...
Greg

[john8662]

Dr. Lee,

Gee, looks like I was totally wrong again, figures... no more jokes from me.

[Dieselboy]

This is how I spent my latest paycheck:
http://www.oliverdiesel.com/images/gears/14ffgears.jpg

4.88:1 Precision gears for the 14 bolt and an install kit - all Timken stuff (sorry Doc! ;) ). 8 teeth on the pinion, and 39 teeth on the ring gear. I was concerned that the pinion would be too small, and that marginal tooth engagement would not lend itself to towing. This stuff is still huge; though not quite as large as the 3.73s and 4.10s with which I have to compare, but it's still darned big.

They'll be installed in a couple of weeks, and I'll let y'all know how it works out.

[ 09-11-2004, 08:14 AM: Message edited by: Dieselboy ]

[CleviteKid]

Clevite made engine bearings, and never made tapered roller bearings. Timken is also a fine classic Ohio company (from Canton) and as the inventor and major developer of tapered roller bearings, they are the brand of choice. Excellent selection on your part.

Dr. Lee :cool:

[dieselcrawler]

DieselBoy,

Got that Dana 60 under the front of your truck yet? What's the plan/time frame you're working with there...? I assume you're gonna swap that and the gears in the rear around the same time, huh?

Have you had meny problems with your current frontend? Aside from the fact that the D60's are just plane awesome, what is prompting you to swap?

Greg

[Dieselboy]

The Dana 60 is still under construction. I'm an undergrad on a budget, so don't hold your breath too long. I anticipate getting the 60 under there around Christmas or early 2005, but it won't have a center section or axle shafts until several months later.

The plan is to get the axle in place with crossover steering and all new bearings and seals. Bumpsteer is driving me mad. Then, a Detroit and 4.88s for the front remain (the ring & pinion I got off ebay turned out to be a 5.87 ratio :mad: , so I'm still looking). Like most projects, I need to go in stages as the money is available.

The 10 bolt has served me very well, and I plan on keeping it for another project. It's got plenty of life left in it, and all new bearings and seals with only 50,000 miles on them.

Basically I just can't resist the allure of 1 ton beef - got 60? :D

[john8662]

Got 60? Yes! I just scored a M1008 truck with a matching set of axles for my Project Suburban smile.gif ! Its VERY hard to find a D60 for my budjet. Luckily its already geared 4.56 so it'll work for the tires I am thinking about. I know the rear has a locker, anyone know if the front on these rigs has a locker or if its open carrier?

[G. Gearloose]

D-boy,
why did't you leave the axles alone a just switch to an M465 to get the rpms? you might have even gained MPG. just curious.

[jcomp]

I'm also an undergraduate on a budget, but I was able to trade a little 9mm pistol (92FS) for a huge differential (D60). :D

I still need to do the brakes and bearings, and I'm going to do the kingpins and u-joints while I'm at it. I wish I could squeeze a detroit and some 4.88s into the budget. Maybe someday, like when I get a real job again. smile.gif

[Dieselboy]

I'm a big fan of the 700R4, plus I've gone through hell and high water to get one that works well. I just prefer my auto.

A standard would be cool, and an NV4500 will probably find its way into a future project. Who said Cummins? ;)

PS: My 92FS is just too much fun to trade!

[waorth]

John8662,

if it's from a M1008, the front carrier will be open.

Other CUCV Models however (M1028, M1031) did come with a Trac-Lock in the front.

Regards. Walter

[dieselcrawler]

DieselBoy,
I hear ya on the bump steer problems, crossover is in my plans for the winter projects. I have the arm I need, just need to find a good 2wd gearbox. Haven't really started looking all that hard tho eather.
You say you've had good luck with your 700r4 trans, why so? What mods have been made to it to make it so great, and what can I do to mine to make it strong? I plan to put it in my dually truck, but refresh it with a rebuild kit when I do. If I stay with a manual TC lockup sw, and a big cooler, think it will live?

John, the M1008 would have an open diff, my m1028 did have a D60 w/limited slip. (That frontend/14FF rearend now lives in my K-5!)

Greg

[Dieselboy]

Originally posted by DieselCrawler:
DieselBoy,
I hear ya on the bump steer problems, crossover is in my plans for the winter projects. I have the arm I need, just need to find a good 2wd gearbox. Haven't really started looking all that hard tho eather.
You say you've had good luck with your 700r4 trans, why so? What mods have been made to it to make it so great, and what can I do to mine to make it strong? I plan to put it in my dually truck, but refresh it with a rebuild kit when I do. If I stay with a manual TC lockup sw, and a big cooler, think it will live?

John, the M1008 would have an open diff, my m1028 did have a D60 w/limited slip. (That frontend/14FF rearend now lives in my K-5!)

Greg Greg,
You can get a rebuilt 2wd Chevy box from West Texas Off-Road tapped for hydraulic assist for $150 + shipping. That's where I'll probably get mine when the time comes. It's as good a deal as any parts store offers.

My 700R4 is an Art-Carr "towing special" and built for the low end torque of a diesel. It's got the updated valve body, K case, 1200 stall lockup converter (with a switch in the cab), 30 spline input, and is rated for 400 hp. I am very pleased with it thus far. It was competitively priced, and came with some excellent service. Right now, I have a B&M 24,000 GVW cooler on it with a spin on filter, but I will upgrade to the 28,000 GVW cooler at some point.

[smcghan]

OK I have what I think is an odd ball. At least the tranny shops gave me a look like I was nuts when I needed to rebuild my trany. Any way it's a 82 k10 6.2 4 speed (3 speed w/o.d.) A 833 new process I found out. 3.08 10 bolts f@r. with 31's. 150k miles new timing set, h20 @ fuel pump. All new gasket's through out. New clutch set, w/ new linkage etc. The problem NO POWER!!! Well it runs great the diesal shops are quite happy with it.the injecter pump has ben set at 4 1/2 degrees. First gear isn't low enough so I have to slip the clutch to get started. All is well til I go to 4th (O.D). Then it slows down as soon as I come to any incline until I shift down to 3rd then it picks up speed. I know I need to change gears but I don't know if 3.73 or 4.11 is the answer. Eventually I will put 4 in. lift, and 33's or 35's. I would like to find a turbo. But that's another wish. Any help would be very appreciated. Steven

[Dieselboy]

Check out 4lo.com

There are some great calculators there. Plug in your numbers, it will help you decide what gears are right.

Consider a cruising speed of 1900-2100 @ 60-65 mph.

[84 Convert]

Smcghan, you do have somewhat of an oddball, I've been through the same thing with my GMC. It is a stock GM offering, but ask anybody but a really good parts guy and they'll say "I can't find an application for that!"

As far as rpms with gear ratio... I have 255/85R16's on that truck with 3.73 gears. About 1900 rpm @75 mph. These tires are somewhere between 33" and 35". Even with the BBC it really likes 80 and above. The gasser will pull hard from 400rpm up, but cruising at below 2100 seems to lug it a bit. I'm really afraid I'll be wishing for 4.10's when the 6.2L returns to its proper resting place.

Hope this helps!

Gregg

[Dieselboy]

Performance Report:

In a word, wow! If you put this thing in drive, you had better want to go forward. It's like I have it in 4-lo all the time. The Detroit chirps more frequently in turns, but it's not violent at all. Interestingly, in town performance isn't that different. Cruising on the highway is where these gears make themselves known. :D

75 mph @ 2400 rpm gives 5.5 - 6 psi of boost and 550 - 600 on the EGT. Locked up in 4th, lean into it a little bit and it's easy to gain speed on hills with boost topping out around 12 psi before the 700R4 tries to grab 3rd. Thank goodness I installed extra sound deadener some years ago; I think it would have been a little loud otherwise.

The real fun in all this was watching my friend set up the gears. I had never seen the guts of my 14FF disassembled, and had never seen a rear end set up. The attention to detail was awesome. Backlash is set at .010, and we ended up shimming the pinion to .023 to get a perfect pattern. Drive side was perfectly centered, and the coast side had the slightest bit of toe in.

My speedo is highly inaccurate now, and I need to rebalance my rear driveshaft. One mod begets another. :rolleyes:

After the 500 mile break-in, I'll see how well these BFGs can hold on to the pavement, and give a towing report.

...now if I could just find some time to install these 6.5TD injectors I have... ;)

:cool:

[ 10-03-2004, 03:47 PM: Message edited by: Dieselboy ]

[Dieselboy]

First tankfull - 520 miles - 1/2 highway & 1/2 in-town Aggieland

16.5 mpg

I expect that a full run on the highway at 65 (2000 rpm) will yield 17 or 18 mpg.

[Ratau]

David

I had the same problem with speedo calibration. I replaced the in line reversing gearbox with a home made one. The gears are 39 and 32 build into a aluminium di-cast box.. that

[Dieselboy]

I finally ordered a speedo correction unit:
http://www.oliverdiesel.com/images/speedocorrection/reductionunit.jpg

It's about 2.75" long, so there's no interference:
http://www.oliverdiesel.com/images/speedocorrection/length.jpg