Aurgathor is correct the gear difference is so the front with pull the rear, helps keep you going straight on slippery surfaces, gives you more control when you gun it.

 

If this is really the case why did my bronco come with 3.50 rear and 3.54 front.

I have found this for you.
Have you ever heard that the gear ratio in the front of a four wheel drive has to be higher (lower numerically) so that the front wheels will pull more? Over the years there have been many different ratio combinations used in four wheel drive vehicles but never so that the front will pull more. Gear manufactures use different ratios for many different reasons. Some of those reasons are; gears strength, gear life, gear noise (or lack of it), geometric constraints, or simply because of the tooling that they have available. I have seen Ford use a 3.50 ratio in the rear and a 3.54 ratio in the front, and I have also seen them use a 4.11 in the rear and a 4.09 in the front. I have found that as long as the front and rear ratios are within 1% that the vehicle works just fine on the road, and can even be as different as 2% and work just fine off-road with no side effects.

Here is the whole artical. http://www.wagoneers.com/JEEPS/tech/GEARING/myths.html

 

Are you sure your Bronco doesn't have 3.50 gears front and back on your 78 Bronco?
My 79 has 3.50 gears front and rear, so I was just asking, but I've usually only seen the front ratios a little smaller(numatically) then the rear ratio.

 

I am positive that is the way they are. They were also the same on my cousins Bronco before he changed them.

 

I understand an engine needs to run in a certain Rpm range. But it a way it seem u would get better mpg in the lower RMP range

 

Of course this difference will exist across the gear ratios. The two axles (front and rear) were manufactured by two different companies. Spicer/Dana and the company that manufactures the 8.8" rear axle for Ford each designed axle assemblies. Ford engineers made the decision to use two axles from different manufacturers and picked two assemblies that, with a part-time 4WD system, would work "well enough". This is the PRIMARY reason Ford so vehemently discouraged their buyers from using these 4WD systems on dry, hard pavement. The slight discrepancy has the potential to stretch or even snap the chain in the transfer case (the weakest link in the driveline by far). With nearly a full 7 rpm difference in engine speed in top gear to maintain a given speed for each axle assembly, the rpm differential is capable of breaking things on dry pavement where wheel slippage is far less likely. (Wheel slippage is what the engineers were counting on in this situation so that the system would still work without stretching or breaking things). I sincerely doubt ANY engineer worth his/her salt would opt for this when they had had the 9" out back originally which could be geared at 3.50 to exactly match the D44 which has a 3.50 gear ratio available for it as well. So why change a good thing? Simple, Ford dropped the 9" from their entire model line in favor of the 8.8. So the engineers did what they could and got close.

Notice that current model Ford 4WD vehicles use axles of the same design by the same manufacturer so that this discrepancy doesn't exist. With the advent of the "front" 8.8 axle assembly, the D44 has gone by the wayside. Now you don't have the problem of different manufacturers equipment being slightly different and the worry about this discrepancy. Everything evolves. The Ford part-time 4WD system has done this as well.

While I agree that it was wise to set things up so that when the 4WD IS engaged the axle used in front has a ratio that pulls slightly, I sincerely doubt that the engineers at Ford chose this as their preferred option. I would want to hear an answer on this question from an actual Ford tech or someone connected on the inside because I just have a hard time believing that the gearing was chosen first then the axle assemblies. The supply-and-demand and cost-effectiveness situation would seem to be a greater dictator of what axles were used when you consider how many units The Ford Motor Co. would have been buying over the period of time that these vehicles were produced.

Just my ramblings folks...take 'em for what they are worth. It really boils down to the simple fact that the reason for it isn't all that important but that it does exist and when you go looking to re-gear you should be aware of it so it doesn't confuse your research while you are considering what equipment to purchase.

 

Thanks Chris. My 96 Bronco is also 3.50 in the rear and 3.54 in the front. This would make the front wheels turn slightly slower then the rear wheels, thus blowing Aurgathor and Bossind's theory out of the water.

 

You have 3.55s in the rear, fords 8.8 didn't come with 3.50. Ford also does not have a 4.11 ratio since the death of the 9".

 

Again ford doesn't have a 3.50 ratio after the 79 bronco you have 3.55s in the rear. Guess the theory stands!

 

Here are your axle codes, notice no 3.50 ratio. I Also have a 96 bronco and it came with 3.55s in the rear and 3.54s in the front.

12 Conventional non-Positraction Differential
2.73
16 Conventional non-Positraction Differential
3.73
17 Conventional non-Positraction Differential
3.31
18 Conventional non-Positraction Differential
3.06
19 Conventional non-Positraction Differential
3.55
23 Conventional non-Positraction Differential
3.54
24 Conventional non-Positraction Differential
3.54
25 Conventional non-Positraction Differential
4.10
29 Conventional non-Positraction Differential
3.55
31 Conventional non-Positraction Differential
3.73
32 Conventional non-Positraction Differential
4.10
33 (1992-1998) Conventional non-Positraction Differential
3.54
33 (1999-2002) Conventional non-Positraction Differential
4.30
34 Conventional non-Positraction Differential
3.73
35 Conventional non-Positraction Differential
4.10
36 Conventional non-Positraction Differential
4.56
39 Conventional non-Positraction Differential
3.55
41 Conventional non-Positraction Differential
3.73
42 Conventional non-Positraction Differential
4.10
43 Conventional non-Positraction Differential
4.30
45 Conventional non-Positraction Differential
4.10
46 Conventional non-Positraction Differential
4.56
49 Conventional non-Positraction Differential
3.55
52 Conventional non-Positraction Differential
4.10
56 Conventional non-Positraction Differential
4.10
58 Conventional non-Positraction Differential
4.86
61 Conventional non-Positraction Differential
3.73
62 Conventional non-Positraction Differential
4.10
63 Conventional non-Positraction Differential
4.30
65 Conventional non-Positraction Differential
4.10
66 Conventional non-Positraction Differential
4.56
68 Conventional non-Positraction Differential
4.88
69 Conventional non-Positraction Differential
3.55
72 Conventional non-Positraction Differential
4.63
73 (1996-2000) Conventional non-Positraction Differential
5.13
73 (2002) Conventional non-Positraction Differential
4.30
75 (2002 Motor home - Dana 80) Conventional non-Positraction Differential
Supply Bill of Material Number
75 Conventional non-Positraction Differential
5.38
78 Conventional non-Positraction Differential
4.88
81 Conventional non-Positraction Differential
3.73
82 Conventional non-Positraction Differential
4.10
83 Conventional non-Positraction Differential
4.30
86 Conventional non-Positraction Differential
4.56
88 Conventional non-Positraction Differential
4.88
95 (2002 Motor home - Dana 135) Conventional non-Positraction Differential
Supply Bill of Material Number
95 Conventional non-Positraction Differential
5.38
98 Conventional non-Positraction Differential
4.88
B4 Limited Slip Differential
3.73
B5 Limited Slip Differential
4.10
B9 Limited Slip Differential
3.55
C1 Limited Slip Differential
3.73
C2 Limited Slip Differential
4.10
C3 (1992-1998) Limited Slip Differential
3.54
C3 (1999-2002) Limited Slip Differential
4.30
C4 Limited Slip Differential
3.73
C5 Limited Slip Differential
4.10
C6 Limited Slip Differential
4.56
C9 Limited Slip Differential
3.55
D1 Limited Slip Differential
3.73
D2 Limited Slip Differential
4.10
D3 Limited Slip Differential
4.30
D5 Limited Slip Differential
4.10
D6 Limited Slip Differential
4.56
E1 Limited Slip Differential
3.73
E2 Limited Slip Differential
4.10
E3 Limited Slip Differential
4.30
E6 (1992-1998) Limited Slip Differential
4.10
E6 (1999-2002) Limited Slip Differential
4.56
EW (1992-1999) Limited Slip Differential
4.10
EW (2000-2002) Limited Slip Differential
4.88
F1 Limited Slip Differential
3.73
F2 Limited Slip Differential
4.10
F3 Limited Slip Differential
4.30
F5 Limited Slip Differential
4.10
F6 Limited Slip Differential
4.56
F8 Limited Slip Differential
4.88
G3 Limited Slip Differential
4.30
G5 Limited Slip Differential
5.38
G8 Limited Slip Differential
4.88
GW Limited Slip Differential
4.10
H5 Limited Slip Differential
4.10
H7 Limited Slip Differential
3.31
H8 Limited Slip Differential
3.08
H9 Limited Slip Differential
3.55
K5 Limited Slip Differential
5.38
K8 Limited Slip Differential
4.88
KW Limited Slip Differential
4.10
W5 Limited Slip Differential
4.00

 

3.50s front and back on the 78-79 bronco standard option - I just looked it up. but I didn't think 3.50 was available in a dana 44. Weird.

OH never mind you could get a 3.50 ratio for the dana 44.

 

The problem here is that that Dj300 (who originated this thread) is running an '83 model which still has the 9" out back NOT the 8.8. The 9" has no 3.55 ratio. Never did. The simple truth of the matter here goes back to my last post and that is that this was not a design decision, this was a purchasing decision that the engineers "made work" when Ford opted to drop the 9" from the entire line. The 9" AND the Dana 44 have a 3.50 gear ratio available (and it was done that way on the early models). The 8.8 does not. Therefore when the 9" was dropped, the engineers went back to the drawing board and worked with the closest ratios they could get from the two different manufacturer's axle assemblies. Again, now that the 8.8 is available as a front axle assembly this is what is used so that there is no ratio discrepancy. In short the engineers are not as all-knowing and all commanding as they would have us believe. Sometimes it boils down to what the company decides to buy for them to incorporate into the design.

 

I thought 80 was the last year for the 9" in the bronco.

 

Ok my search shows that 83 was the first year for the 8.8 and 82 was the last year for the 9". Anyone confirm this?

Well Actully DJ300 even states he is running an 8.8 "I'm running 8.8/3.08 L diff."

 

The 0.01 difference itself is small enough to not cause much problems
on a *straight* road, rubber is after all, a little rubbery. The problem is when you need to turn, and that's when the driveline can get under some very serious stress in a short amount of time.


If it were superior to have gears with equal ratios, then how do you explain that aftermarket gears, even in ratios not available as OEM still follow the pattern of the front gear being slightly lower?