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Old 07-23-2007, 10:50 PM   #1
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D35 strength??

Alright so heres my deal. Im runnin 33's on the Sport I bought 2 months ago. When I got it she was already lifted about 4" so the tires clear fine. Only problem is one of the several previous owners has geared the axles far too low for the tire size, I believe it has 4.88's. So now Im going to be trading my cousin for his 35's since he is selling his truck anyway and he doesnt care. Only thing Im concerned about is the ability of the Dana 35 to hold up to the larger tires. It wouldnt be too big a deal but it has been locked up with a Detroit locker as well. It does great now with the 33's and locker off road but highway speed is killing me. Luckly, it got the Super 35 kit so it also has Alloy 30 spline shafts in it. Now my only question is, can that kit hold up to 35's with it being locked and all?? I realize the new shafts are pretty strong compared to stock and Im pretty easy on my skinny pedal but what are my chances of breakin a shaft. I dont really have the $$ to be carrying trail spare 30 spline shafts with me. With bigger tires I should gain back a little more of my top end which I badly need though. Does anyone have any experience with this kinda situation

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Old 07-23-2007, 10:56 PM   #2
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Old 07-23-2007, 11:19 PM   #3
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So your basically sayin Im screwd?? Even if Im careful its still gonna snap the shafts?
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Old 07-23-2007, 11:22 PM   #4
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I'm going to be putting on 33s when I get my lift. I was told to re-gear to 4:56 which would give me the same ratio as the Rubicon with 31s and 4:11 gears. Then I was warned to upgrade the axles because the D35 wouldn't hold long to serious abuse. The risk is even greater with 35s. IDK for sure, just from what I've been told you'll snap the axles.
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Old 07-23-2007, 11:31 PM   #5
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Dare I thought thats what the super 35 kit was for, and he has a detroit locker carrier or is that the lunch box type in the 35 housing?
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Old 07-23-2007, 11:38 PM   #6
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Old 07-23-2007, 11:41 PM   #7
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Crap man I had no idea, But heck thats why I read everything I can.
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Old 07-23-2007, 11:43 PM   #8
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I would think with some care you should be fine with the super 35 kit. Everyone says the 35 will break regardless, but that can't be the case or so many wouldn't have had them for so many years. If handled right and not abused with the super 35 kit you should be fine. I am definitely not saying anyone here is wrong, on some jeeps and some setups it is when not if, but that's not every single case!!
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Old 07-23-2007, 11:45 PM   #9
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truss that dana 35 and you should be OK. of course you can still break it but just take it easy and dont bounce the jeep.
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Old 07-23-2007, 11:47 PM   #10
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Well mine will be on 31's maybe up to 32's some day but all my trails will be light to moderate. and i do need to get a locker but my part guy is on vacation this week.
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Old 07-24-2007, 12:18 AM   #11
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I planned on a truss already. I want it to be as strong as I can get it becuase I dont really want to do an axle swap right now. I know a guy who ran 35's on the 35 kit and he hasnt had any problems at all. He is just careful not to bounce it but I knew that from watchin others break shafts that way. Its hard sometimes havin a stick and all not to bounce it a tid before I get the clutch in but Im doin pretty well at avoiding it. I ran 33's on a stock D35 for 2 years on my ZJ without breaking anyhting and I wheeled the piss out of it. SO I think I can do this, I jsut wasnt sure if anyone had any experience here with it. Thanks for the replys though.
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Old 07-24-2007, 06:41 AM   #12
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Guys have varying degrees of success with the 35c in the rear of Jeeps, some hold up for years crawiling on the rocks, and I have seen them break driving through a mud puddle in a parking lot (actually happened). If you have a light/steady right foot, you should be okay for the immediate future, but you should start saving for that axle swap now, as the clock is ticking...
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Old 07-24-2007, 07:44 AM   #13
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Thats probably what I'll do. Dana 60 sounds like a good swap to me!
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Old 07-24-2007, 07:50 AM   #14
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Thats probably what I'll do. Dana 60 sounds like a good swap to me!
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Old 07-24-2007, 07:59 AM   #15
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Hmmm...Then when the time comes I'll sell my super 35 kit and gears and get a little of my $$ back to put into the new axle. Oh the possibilities. I think Im gonna do the D60 with an OX locker and Rockcrusher or the cast iron diff guards and 4.88's to match the front again.
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Old 07-24-2007, 08:11 AM   #16
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Hmmm...Then when the time comes I'll sell my super 35 kit and gears and get a little of my $$ back to put into the new axle. Oh the possibilities. I think Im gonna do the D60 with an OX locker and Rockcrusher or the cast iron diff guards and 4.88's to match the front again.
THAT'S what I'm talkin' 'bout!!!!
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Old 07-24-2007, 08:37 AM   #17
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Everyone I've know with 35's and the Super 35 kit do fine. I plan to do the Super 35 with my 33's and maybe trussing as well. Like they said, don't bounce it. I never understood how some guys think it's so cool and is the best way to get over something. Of course, you find them later on the trail with a log strapped to the side of their jeep. Of course, now you can get the floating axles for the 35 and they are supposed to be stronger also. Plus, you don't loose your wheel.
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Old 07-24-2007, 10:05 AM   #18
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the super 35 should hold okay. your at the upper end with the 35's/detroit and the 4.88's though, thus if debating between hitting the gas one more time or getting winched, go the winch route.
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Old 07-24-2007, 10:20 AM   #19
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Guys have varying degrees of success with the 35c in the rear of Jeeps, some hold up for years crawiling on the rocks, and I have seen them break driving through a mud puddle in a parking lot (actually happened). If you have a light/steady right foot, you should be okay for the immediate future, but you should start saving for that axle swap now, as the clock is ticking...
he doesn't have a 35c he has a super 35.My own experience has been blowing a spider gear through the front case of a gm 12 bolt open on bfg a/t 35's on the street. The more extreme you go the more extreme your breakage. But evenJerry Bransford has said good things about the super 35.
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Old 07-24-2007, 10:49 AM   #20
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he doesn't have a 35c he has a super 35.My own experience has been blowing a spider gear through the front case of a gm 12 bolt open on bfg a/t 35's on the street. The more extreme you go the more extreme your breakage. But evenJerry Bransford has said good things about the super 35.
I understand that the c-clips are eliminated with the Super 35 clip, but the "c" in 35c stands for custom, not c-clip, so technically he still has a 35c. I also know that alloy shafts are stronger than stock, but I also know that I have see the Super 35 kits fall apart with 33" tires on them (not so much fall apart as break under stress, but you get the idea). If trussed, this axle lasts longer because the housing flexes less, but this will more than likely still be the weak point in the driveline. As stated above, he should be fine, but if it were me, I would start saving for an axle swap.
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Old 07-24-2007, 03:21 PM   #21
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Normally, I don't recommend any upgrade on a Dana 35 short of throwing it away but since you already have a Super 35 with a Detroit, I also recommend using the truss on the Dana 35.
The real problem with the Dana 35 isn't it's gear strength but the weakness of the center section and the tubes. When these parts flex it puts pressure on all the internals of the diff as well as very possible ring and pinion interference. Spider gears are a very common failure on Dana 35's and flex is the major cause.
Another reason to be gentle with the 35" tires is the 4.88 gearing. The front Dana 30 pinion is really small with 4.88's and is a definite weak link. 2 guys I run with have lost 4.88 Dana 30 R&P's in the last 4 months. 1 guy had 33's, the other had 35's and both were 4 cyls.
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Old 07-25-2007, 07:40 AM   #22
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Thanks for all the suggestions guys. I think if I were to be careful it would hold. I deff. dont let my Jeep bounce at all. As soon as I feel it start to get bouncy I hit the clutch and brake. Now as far as the gears go thats my speculation. Since I bought it with the gears and locker in I never really knew what ratio it had since the guy didnt do it (the owner before him did). But at 70 mph on the highway Im at 3100 rpm's. I know for 33's to be back to about stock they need 4.11 gears I believe or maybe its 4.56. Either way, that seemed like too high rpm's to be running even 4.56 gears and 33's. What does that sound like to you guys? I dont wnat to spend much more money on this axle since I am gonna do a swap anyway probabaly next summer or this winter. The truss I can just build myself. It seems like I should be alright for a while though.
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Old 07-25-2007, 10:08 AM   #23
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I am going to wade in here with a first post but not to comment on the Super 35.....that has been beat to death.

You have stated that you turn 3100 rpm at 70 mph and that is too much engine speed. My question is - Why do you think that 3100 is too much?

Your engine is a modern 7 main bearing design with factory ratings of 190 hp@ 4600rpm, 235lbft @ 3200rpm, redline 5300rpm. It is fully capable of running 4000 rpm all day long without failure. 3100 rpm will not harm your engine in the short run.

No what about fuel economy....

Brake Specific Fuel Consumption is a measure of the efficiency of an engine and is simply the amount of fuel burned per hp produced. Torque produced by the engine is directly related to the volumetric efficiency of the engine. Putting this together, you see that the engine operates most efficiently at the peak of the torque curve. It will burn less fuel per HP produced at peak torque.

The HP your engine produces is defined by this mathmatical equeation:

Engine HP = Torque X Engine RPM/5252

From this you see that as engine rpm increases so does horsepower. There is obviously an upper limit to this, but for the rpm range we are discussing it is true. We also know that it takes fuel to make horsepower, but at the peak of the torque curve, it takes less fuel burn per horsepower than at any place else on the curve.

How can you measure all of this theoretical BS in your Jeep? One simple way is with a vacuum gauge. Engine manifold vacuum is directly related to throttle postion and fuel burn. Simply stated, the higher your indicated manifold vacuum, the better the fuel mileage.

Now back to the gears. What is the purpose of gearing in the rear end? They are simply a way to multiply the torque produced by the engine. If your engine makes 200 ft-lbs of torque and you have 4.00 gears in the rear end, you have 800 ft-lbs of torque at the rear tires to move the Jeep. That is assuming the transmission selected for a 1:1 ratio, which it will not be if in overdrive. It will be less, .78 for a 5 speed and .68 for an auto (I think these are correct).

Depending on weight and drag produce by the body at a given speed, your rear gearing will require a certain throttle opening to maintain speed on level ground. Changing the rear gears changes this relationship and may result in less throttle opening, higher manifold vacuum, and reduced fuel consumption.

I have a stock Rubicon with 33 inch tires and a 6 speed. Highway performance is just OK - I downshift on hills when loaded. Mileage dropped from approximately 16 to 14 mpg when I changed to 33 inch tires. This is in 6th gear on the highway so I am obviously operating the engine in at a much less efficient rpm than stock. I am burning more fuel at the same speed.

Doing the math on gear ratios and tire size we find that 5th gear with the 33s and 4.11s is almost exactly the same overall raitio as 6th with 4.88s and 33 inch tires. So I ran a fuel economy test in 5th gear.

At 70 mph in 5th gear I get about 14.5 mpg, which is about .5 mpg better than in 6th. I am obviously lugging a little in 6th and that is not good. I now only use 6th going down hill. You might ask what engine rpm is at 70 in 5th gear?,........

It runs about 3025.....The gas mileage is better than at 2600 in 6th. For me the real advantage is the driveability....it is much better not having to downshift for hills and pulls much better when passing.

In summation:

3100 rpm is not too high, your engine was designed to operate there and is operating near the peak of the torque curve.

Depending on your driving habits and the amount of weight in your Jeep, you may get better fuel economy with the 4.88s than with your stock gears. My guess is it will be better.

I think that 4.88s are the perfect choice for 33 inch tires and a manual transmission. If I had an automatic, I would regear to 5.13s. And my Jeep is my daily driver, not a trailor queen.

Sorry for the long winded response and I hope that some of this makes sense to you. Bottom line is you are fine with the 4.88s. Keep your foot out of the stupid pedal and the S35 should work just fine with the 33s.
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Old 07-25-2007, 10:57 AM   #24
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Hmm. Im glad you know so much because everything you just told me puts me a lot more at ease. It just seemed like a high cruising rpm on the highway but I can understand what your saying. I really appreciate your knowledge because now I dont think I will go with 35's yet. Im sure in the long run they'll get on there after my axle swap but for now 33's seem fine I suppose. They do tuck VERY well with the 4 inches of lift and I think 35's would rub just a smidge. Besides, I have wheeld this thing pretty hard with the 33's and I think the super 35 kit wont have any problem at all holding up to being locked with that tire size. It will make me feel more comfortable knowing I dont have mcuh to worry about as far as breaking shafts or anything.
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Old 07-25-2007, 11:14 AM   #25
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I want to condcut my own Fuel Mileage test using a GPS and a Fuel flow gauge like the ones in airplanes. They read in Gallons per Hour (GPH).

I believe that GPS is much more acurate on speed than any speedometer. Therefore, I can take acurate speed, and a GPH reading from a flowmeter and make a mathmetical calculation to determine exact fuel mileage at different speeds. Then I would repeat this after making configuration changes to the jeep.

However, I am having troubles finding the fuel flow meter. Any suggestions?
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Old 07-25-2007, 11:48 AM   #26
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Wow, thats an awesome idea. Way out of my league though on where to find one of those. Have you tryed doing a google search on them? Other than that I cant really give you any help with that one.
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Old 07-25-2007, 01:19 PM   #27
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I tried that, all i am getting is test stands for use in garages. I may try to find one right out of an old airplane.
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Old 07-25-2007, 01:34 PM   #28
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I want to condcut my own Fuel Mileage test using a GPS and a Fuel flow gauge like the ones in airplanes. They read in Gallons per Hour (GPH).

I believe that GPS is much more acurate on speed than any speedometer. Therefore, I can take acurate speed, and a GPH reading from a flowmeter and make a mathmetical calculation to determine exact fuel mileage at different speeds. Then I would repeat this after making configuration changes to the jeep.

However, I am having troubles finding the fuel flow meter. Any suggestions?
When I did my mileage test, I used a GPS for the mileage, but without a fuel flow meter, I did the next best thing. I used a loop route and came back to the same gas pump with my Jeep parked in the same location relative to the pump. I then filled it as best I could to the same level.

I hoped this would be fairly accurate, but who knows for sure.
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Old 07-25-2007, 03:17 PM   #29
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Oh, the trouble we'll go through to figure out gas mileage...
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Old 07-25-2007, 03:17 PM   #30
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to go back to the original question it i s a VERY bad idea to have 4.56's in the rear and 4.88's in the front if you are gonna be in 4wd, so you shouldnt even do that swap if it was a better axle

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