Ring and Pinion strength 3.83 vs 4.11

[deneric]

I have a 79 FJ40 w/ 4" SUA and SBC 350. After doing some research here in the tech area I found out that my stock axles have 3.83 gears in the pumpkins. I always thought the 40's came with 4.11's. I am planning on putting 35's on this summer and my next upgrade will be a rear locker ( at least a year out). Ultimately I would like to re-gear it, but have heard that as you increase the r&p it gets weaker. Is this true? Since I have the V8 power would it make sense to leave the axles alone and concentrate on at Orion TC with lower gearing, or will I have to eventually re-gear the axles anyway. I will eventually put a selectable locker up front (have sag PS) and would rather do new r&p at time of locker install instead of doing them at separate times. As with all the knowledgable people on this site, any and all comments and opinions are apprecieated!!! Hopefully this makes sense.

Eric

 

[matt.mcinnes]

I have a 79 FJ40 w/ 4" SUA and SBC 350. After doing some research here in the tech area I found out that my stock axles have 3.83 gears in the pumpkins. I always thought the 40's came with 4.11's. I am planning on putting 35's on this summer and my next upgrade will be a rear locker ( at least a year out). Ultimately I would like to re-gear it, but have heard that as you increase the r&p it gets weaker. Is this true? Since I have the V8 power would it make sense to leave the axles alone and concentrate on at Orion TC with lower gearing, or will I have to eventually re-gear the axles anyway. I will eventually put a selectable locker up front (have sag PS) and would rather do new r&p at time of locker install instead of doing them at separate times. As with all the knowledgable people on this site, any and all comments and opinions are apprecieated!!! Hopefully this makes sense.

Eric

Yes its true but you should have no issue with 4.11 I run 4.56's on 35's and a high torque 2F, as you move more towards the 4.88's then it becomes more of an issue

Buy quality

 

[venpick]

Ive got 4.88 and a v8. Zero problems. with 35" tires the 4.88s made the speedometer fairly accurate. Ive commented on this in another thread if you are going to put in a locker make sure you know what ring and pinion gear you want because you dont want to have to keep taking apart your differentials just for laughs. it cost money.
to quote randys ring and pinion

Here's 4 Reasons To Change Your Gear Ratio. (ring and pinion)

If you have larger than stock tires on your vehicle, the benefits of gearing CANNOT BE MATCHED BY ANY OTHER MODIFICATION TO THE VEHICLE!

By regearing it is guaranteed that:

1. TORQUE TO THE REAR AXLE WILL BE GREATLY IMPROVED
Even a simple change from a 31" diameter tire to a 33" diameter tire will affect the amount of available torque by 10%.

2. STRESS TO THE DRIVELINE WILL BE GREATLY LESSENED
Modern day transmissions cost $600 or more to perform a basic overhaul. Driving with even a 10% larger tire will result in the transmission being under the same load as always being driven on an incline. The transmission may not suddenly fail, but the life will definitely be reduced by thousands of miles.

3. ENGINE EFFICIENCY WILL BE REGAINED
RPM alone does not affect fuel mileage. An undergeared vehicle (as the result of oversized tires) will result in a substantial loss of fuel mileage. Also, just as with the transmission, your engine life will greatly be reduced.

4. SPEEDOMETER/ODOMETER ACCURACY WILL BE REGAINED
With kits in the $100+ range to calibrate speedometers after tire swaps, it seems pretty important to have an accurate speedometer, which can also be fixed with a simple gear change.

Don't put a bandage on a serious problem. By installing the proper gear ratio, easily determined with our gear calculators, you can save thousands of dollars and days of vehicle downtime, plus have a little fun to boot.

 

[venpick]

I really like the part that says benefits cant be matched by any other modification to the vehicle

 

[rookie54]

Bottom line: Put in 4.88's(bigger if extreme) for 35's and remember that doing both F/R R&P is kinda key. Lower T-case and such be sweet addition, and if you have a 5-speed you are in like flyn. Yukon makes a nice set.

 

[deneric]

So Venpick,

I understand what you are saying. Going to 4.88's will take a huge strain off of the drivetrain, axles, and help out in the engine performance dept. as well. I agree that I don't want to be pulling apart diffs every summer, but to do it right I would have to have both r&p sets as well as both lockers all before I start the work. I would like to use ARB's front and rear, but am seriously considering an Aussie for the back and ARB up front. Then sometime in the future I can replace the rear with an ARB. What considerations to eventually putting in a 4:1 orion t-case. How will that affect my low range? Sticking with the stock 4 speed and a 4:1 orion with 4:88. Math is not my strong suit. Any comments? When thinking about axles, I will run the stock birfs until they break (which I understand can be sooner than later once a locker is in there) and upgrade to Bobby longs.

 

[deneric]

Rokkie 54-

Where you at in P-town??

 

[matt.mcinnes]

When thinking about axles, I will run the stock birfs until they break (which I understand can be sooner than later once a locker is in there) and upgrade to Bobby longs.

Time for Bobby Longs My 2F would break a stock birf with 35's and 4.56's R&P every trip out, even broke a pair at the same time

 

[rookie54]

I'm in SE PDX, and so's my 40. If you wanna talk shop hit me up. rookie54@hotmail.com

 

[deneric]

So it is a reassignment of priorities again. I guess the most logical progressions would be Bobby longs, lockers with new pinions front and rear, and then whatever direction I choose to go with t-case gearing. Unless of course I break something else and need to rework it. I fully believe in doing it right and doing it "once", but sometimes it can drive me crazy trying to figure out in what order to do stuff. Regarding the lockers, I have always felt that working on the differentials is somethign left to professionals, dealing with backlash and gear mesh and the like. Has anyone just done it on their own, or do you recommend paying the $$$ for an experienced professional? Thanks again for all the info!!

 

[rookie54]

you should hit me up before you go crazy i can recommend a great local mechanic to you and tell you what worked for me.

 

[rookie54]

http://www.leonardsoffroad.com/page/page/2502926.htm

 

[venpick]

I found a calc so we dont have to do math. BC4x4.COM four wheel drive, 4x4, offroad and fourwheeling site. at the very bottom of the page but the final gear ratios are as follows.
stock right now with 4 speed h2 and transfer with 3.8 ring and pinion your at 26.85:1.
4 speed with stock transfer and 4.88 ring and pinion 33.78:1
4 speed with orion and 4.88 69.29:1

As for the birfields. I thought I could nurse mine along for awhile but they failed on the very first trip with the lockers. I only had a rear locker and 4.88s for years but as soon as the front locker went in POW birfield time. so better plan on some longfields. I have old marfields and they are doing fine with my current set up. ive been told that 39 size tires are the biggest you can go with that set up.
As for doing the work yourself just depends on how mechanical you are. I think that any one can do what i did and just take your third member out and take the new gears and lockers to a shop to have them set up then reinstall them yourself. if your really daring the instructions to set up your ring and pinion back lash are on this web site some where. good luck these things are continual money burners gotta love it I think your 79 already has rear disk brakes but if not this is a good time to add them since youll have the entire rear axle aprart. lol money money who needs it. i dont even like money

 

[venpick]

Really the only cost to keep taking your differential / axle apart is the $5 ish???? seal kit for the axle seals, plus the front knuckle kits run $90 ish, and the differential set up cost is around $250 so try to do you ring and pinion and lockers at the same time. if you cant afford it all at once you just have to add that to the cost of your time. its not horrible but its nice to save it for something else too. I use that orange silicone gasket maker for the pumpkin and a bottle of that will usually make a couple gaskets.

 

[Mace]

3.70 is your original axle ratio.

The numericaly higher Ring and pinions have a smaller pinon head (less teeth). But it is not really that much of an issue with a LC axle.

What tranny are you running? an overdrive can alter opinions on ratio choice..

 

[greenmachine]

what years have what gears? I search, but then always end up finding threads like these. If someone could just post it up here that would be great.

 

[Mace]

to 77 is a 4.11 (coarse spline)
78 is a 4.11 (Fine Spline)
79 to 84 is 3.70 (fine spline)

(these are model years)

 

[John Smith]

If it were me I would swap out your diffs for some 4:11 fine splines and put your money into a crawl box. That is the route I went and am very happy. My tired old 2F powers the 40 down the hwy on 36s just fine. Your V8 should have no problem. If you blow a diff up wheeling at an event the chances of finding a 4:11 diff is much higher than a 4:88

 

[Ducks]

what years have what gears? I search, but then always end up finding threads like these. If someone could just post it up here that would be great.

Follow up question - what are the gears in the t-case based on year?

 

[Mace]

to 74 2.3
75 to 84 1.9 IIRC