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Unread 05-08-2013, 08:34 AM   #1
brycez28
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Top end speed

I recently bought a 1960 willys jeep frame with suspension, axles, and tires. I'm looking to put a 340 buick in it, with a TH400 transmission (Jegs sells an adapter). The jeep has Dana 44 rear axle and Dana 25 front. Are the axle ratios going to be the same or would there normally be a gear change in the transfer case that would allow different gear ratio in the axles? The previous owner thought that it had 5.38 gears, I haven't had a chance yet to verify. Summitracing has a bunch different ratio ring and pinion sets for the Dana 44, but I only seem to be able to find 4.88 gears for the Dana 25? I'm trying to figure out if I can switch the ring and pinions for a lower ratio (summitracing has 3.07 gears for the Dana 44), or if I need different axles.

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Unread 05-10-2013, 06:25 AM   #2
brycez28
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Quote:
Originally Posted by brycez28 View Post
I recently bought a 1960 willys jeep frame with suspension, axles, and tires. I'm looking to put a 340 buick in it, with a TH400 transmission (Jegs sells an adapter). The jeep has Dana 44 rear axle and Dana 25 front. Are the axle ratios going to be the same or would there normally be a gear change in the transfer case that would allow different gear ratio in the axles? The previous owner thought that it had 5.38 gears, I haven't had a chance yet to verify. Summitracing has a bunch different ratio ring and pinion sets for the Dana 44, but I only seem to be able to find 4.88 gears for the Dana 25? I'm trying to figure out if I can switch the ring and pinions for a lower ratio (summitracing has 3.07 gears for the Dana 44), or if I need different axles.
I guess I will break my question down. Since it has different axles, are the gear ratios going to be different, or will they still be the same?
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Unread 05-10-2013, 08:27 AM   #3
222Doc
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the gear ratio in the rear axle and the front must be the same is the same size tires are used. The Tbox high gear 1:1, from there it goes lower. If its going to be a high speed Jeep,1/4 miles lets say. ditch the tbox and the front axle. gear ratio in the axles on road is related to tire size and torque. off road its all about reduction.
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Unread 05-10-2013, 08:40 AM   #4
brycez28
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the gear ratio in the rear axle and the front must be the same is the same size tires are used. The Tbox high gear 1:1, from there it goes lower. If its going to be a high speed Jeep,1/4 miles lets say. ditch the tbox and the front axle. gear ratio in the axles on road is related to tire size and torque. off road its all about reduction.
Thanks! I'm just looking to use it mostly on road, with the occasional off-road excursion. But I would like to be able to cruise at 70-75 mph without running the engine RPMs high and having to fill up the gas tank every 50 miles.
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Unread 05-10-2013, 03:10 PM   #5
ratmonkey
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i think you'd be best served just using the frame for it's VIN and title and buying new axles, suspension, etc, etc... if you want to drive it on the highway and wheel on weekends with good final drive ratios for the two. reconsider that th400, you want an overdrive transmission...
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Unread 05-10-2013, 03:12 PM   #6
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Still running the D18 t case? If so, you might want to look into a warn/Saturn overdrive unit
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Unread 05-10-2013, 09:41 PM   #7
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The Dana/Spicer 25 gears are 5.38, 4.88, 4.27, and 4.09's. Some sites will not show the 4.09's but they do exist-just rare. The 5.38's and 4.27's were both stock gearing and easy to find, while the 4.88's are going to be from the GPW/MB's. The 4.88 ratio was also an option with the V6 CJ's but I believe all those used D27's rather than the 25.

I think the D18 will be the desired Tcase because you are going to have a very short rear driveshaft with the TH400 (too short in my opinion) and the D18 will give the best driveshaft angle. The D18 is also the only one you will get an overdrive for without further lengthening the already too long drivetrain. The gearing for the D18 in a 60 should be the 2.46:1 version but you could go with a TeraLow 3.15:1 set if you do want to get it into the rocks.

With a 340, either the 4.27' or 4.88's would work well with the overdrive. If you still had the fhead, best to stick with the 5.38's. With a little common sense, the overdrive will be fine behind the 340-pretty tough unit for such a small package.
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Unread 05-10-2013, 10:07 PM   #8
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And, I might add-buy a rebuilt Warn overdrive from Herm rather than a new Saturn from AA. The Warn shift forks don't break, the AA ones do.
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Unread 05-11-2013, 09:02 AM   #9
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OK, I'm going to pee on the parade here a bit.

first, 75MPH in an early CJ is simply a dangerous endeavor. The short wheelbase and high CG will not allow any emergency maneuvers at that speed. Loose a tire, Deflect off a chunk of road debris, or try to whip around a muffler lying in the road will probably land you upside down a road speeds. If you are set on this, then this is my advise (for what it is worth)....

You will need to do some careful measuring. A V8 coupled to an automatic transmission in an ECJ is going to be long. I would double check all my measurements to include the grill support to insure you're going to get everything to fit without having a three inch rear driveline. Remember, any lift will rapidly throw a short driveline at an angle that will vibrate or destroy it. The nice thing about the D18 is the rear output comes out low.

While the rear axle should be fine, the front simply won't take any abuse from the 8 and live long. I know you're wanting to use it as a road toy, but something to think about. A swap to a later 30 with disks (I'll beat on the brakes in a minute) would be a good move. Which brings me up to the next topic...

Chances are good the gearing will be 4:88 or 5:38. If so, the OD won't be enough to fully utilize the bigger motor. I would be thinking in the 3:54 to 3:73 arena (see above post for the 30 about available gear ratio's). This would drop your RPM's significantly. Since you will be regearing, drop the OD idea. They are good units, but won't take the pounding from the 8 (some will differ, but I have seen my share of broken panetary's), and there is no reason to have one if you do the gearing properly.

Brakes are totally inadequate! An upgrade to Waggy in the rear with either the same or disks up front will be necessary. This includes a dual MC.

The Ross steering will kill you. a swap to a Saginaw (preferably power) box will be needed.

I would price a FULL cage. Tumbling at 70 MPH will require all the protection you can get.

Remember, it isn't how fast it can go, but how safe it will be when something goes wrong.....

Last edited by jeepdaddy2000; 05-11-2013 at 09:04 AM.. Reason: spell check failed me!
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Unread 05-11-2013, 10:20 AM   #10
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Quote:
Originally Posted by jeepdaddy2000 View Post
OK, I'm going to pee on the parade here a bit.

first, 75MPH in an early CJ is simply a dangerous endeavor. The short wheelbase and high CG will not allow any emergency maneuvers at that speed. Loose a tire, Deflect off a chunk of road debris, or try to whip around a muffler lying in the road will probably land you upside down a road speeds. If you are set on this, then this is my advise (for what it is worth)....
I've got to agree with jeepdaddy2000... 75mph in any short wheel base Jeep (early CJ, CJ5, etc.) is dangerous. For me, if I got to cruise at 70-75 mph, I'll come home and get the Honda Accord.
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Unread 05-11-2013, 09:17 PM   #11
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Geeezzzz, I have been driving my 3B at 75 mph for 35 years and have yet to have a problem. There are a lot of factors besides just the Ross box and the 9" brakes in the equation. Springs (and how set up), shocks, and tires are all big elements, not to mention the steering geometry. If you are running big mudders on a super flex suspension with worn bushings with Bubba's steering I suspect you could get into trouble at 45 mph but you can build one capable of staying on the road at 75 mph.

I do think the TH400 is going to cause a severe headache in the rear driveshaft department. And I don't think I would be using the 340-not an engine with a lot of parts availability-and since you are not bolting it into a 225 V6 chassie, you will have to come up with new motor mounts anyway. It would be a near bolt-in for a 225 replacement. I seem to recall one of the "owners" on the 3B Page has one so equiped and that may be worth a gander.
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Unread 05-13-2013, 05:45 AM   #12
brycez28
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Thank you everyone for your thoughts! I was kinda concerned about the transmission length as well. I will think about moving the axles to increase the wheel base, which will give me more transmission room and more stability. As well, I will not be doing a lift on it. I don't have a transmission for it yet, so I'm still considering all my options.

I don't plan on putting a jeep body on it, but have a full body roll cage with a minumal sheet metal body, which should also lower the center of gravity. Please correct me if I'm wrong, but I shouldn't need to upgrade the brakes? Even though I will have more power, I'm not going to be using over sized tires (main reason why brakes would need to be larger) and my total weight at the end should be well below that of the original jeep. The reasons why I want to use this engine are because I already have it, it has about 120 hours on a rebuild, and it is unique. I haven't had any issues finding parts for it.
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Unread 05-13-2013, 07:53 AM   #13
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The 9" brakes will work if all is up to snuff. They are manual adjust and that needs to be done on a regular basis. Since this rig is apparently off-road only you may get by with them but there will not be much there when they get wet. If the use includes on-road miles, I would be replacing them with either 11" drums or discs.

As for the D44 rear axle, I'm going to guess the keys will eventually shear on the 2 piece axles-I have managed that with a stock V6. However, I did run a 2-piece behind a 327 for a couple of years and didn't have a problem.

You may want to look into WI vehicle laws. MT is very loose but I still don't think one could run something on the highway with essentially no body.
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Unread 05-13-2013, 08:33 AM   #14
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Quote:
Originally Posted by brycez28 View Post
I guess I will break my question down. Since it has different axles, are the gear ratios going to be different, or will they still be the same?
Just for future reference it is very rare for a 4x4 vehicle to have the same axles front and rear. Gear ratios have to match because the front and rear output on just about any and all transfer cases is at the same ratio.

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Unread 05-13-2013, 09:40 AM   #15
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My question is does it have to be an automatic? many fine manuals that will allow a bit longer drive shaft.

And the topic of when is a CJ unsafe?
My 5 tracks straight and stops well and as long as I am in the interstate 70 MPH is no problem thanks to overdrive and a 350. and yes If a dog ran in front of it id just have to mash it no evasive manuvers , unless I have a second or two to react. Its not a sportscar . just because it can go that fast doesn't mean you do it . I only come near 70in the long straight parts of the 70 MPH zones.
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