Gearing question

[dommo2007]

Can anyone reccomend a good site(or a good thread on here...I searched, but I didnt really find the answer I am looking for) that would explain the basics of regearing axles? I understand that when you slap on bigger tires, you loose both MPG and top end. If I started with 3.73(I think, but I have to double check that) and, after lift and all that jazz, went up to 35" tires, what would I want to re gear it to in order to acheive a half way decent gas mileage? I will be wheeling it when ever I get a chance, but I have to drive it to and from work everyday, so I am not as concerned with making a bazillion horsepower, just so that I will be able to drive on the freeway with out some Kia running me over...haha. Anyways, any help is great.

Oh yeah, also, other than being detrimental to the center of gravity(not to mention just plain lame), are there any MAJOR down sides to haveing a body lift in addition to a suspension lift? I.e. on another truck I had, which I bought with a body lift, it situated the radiator all funky and instantly overheated, whereas without the BL the radiator would get plenty of air flow. Am I going to have any of the same issues with a 95 Bronco?

Thanks

 

[Seabronc]

There are several sites that have calculators which you may have already found. You don't necessarily have to lose mileage when re-gearing as long as you gear to the same engine RPM at your normal cruise speed. The other thing you will probably but not necessarily need to do is to recalibrate the speedometer. Depending on the year of your truck, that is either done via a speedo gear change or a recalibrate of the computer. The Bronco engine is designed to run between 2000 and 3500 RPM for best economy or power, in the lower 2000s for economy and upper 3000s for best power. Jeff's Bronco Graveyard catalog has several charts and gives the formulas necessary to calculate the changes. Also, you need to decide where you waht the truck to do most of it's operation, that makes a big difference in the gearing selection. If it is primarily a road machine then the gearing will most likely be a little less aggressive than if it is to be an off road trail machine or a rock crawler where you want higher RPMs at a low speed in order to get the engine into it's operating range. If you have overdrive then you can go a little more aggressive with the gears while maintaining a decent cruise RPM.

I think I have the charts in picture form and will try to post them later.

Good luck,

>-

 

[dommo2007]

Well, the Bronco will PRIMARILY be used for driving me to and from work. Not a real long drive by any stretch, but about half is highway, half city driving. I take her up in the mountians, mudding, what have you, when ever I get a chance...not so often right now, as I need new tires. I still want to be able to pull my butt out of a decent mud hole, but I am also trying to improve fuel economy. Yeah, she will see the dirt, but she aint no compition rock crawler by any means. I have a wish list to help the mileage issue, and gearing isnt necessarily on the top of that list, but it is one of the issues I am taking into consideration. I figure with the other lifted trucks/suv's I have owned, I will be in the market for gears between 4.10 and 4.56. Sound about right? I just figured I would ask, since I dont know how much difference there is between re-gearing my Bronco, and when I re geared my old Cherokee for instance.

As to where the Bronco engine should be operating...I dont have a tach in my truck, so I really couldnt tell you. It does have overdrive if that helps provide more info. I figure the low 2k-high 3k is right about where I am at most of the time, but I really wouldnt be able to tell an exact number, stock gears or otherwise.

I suppose this is pretty lazy on my part, since all I want is an answer of what other people are running, how its working for them, etc. Just that with all my trucks, this one included, I have come to admit that re gearing, being the actual install or just deciding which gears to use, is several levels over my head. I try to leave it to people that get paid WAYYY too much...lol.

Thanks for mentioning JBG...I have ordered a few things from them, but I never noticed the gearing charts. I am going to check that out.

Ok, one last thing(and yes, this will make me sound fairly newb-ish, but thats ok with me): with the last truck I had that had an OD tranny(a 04 Dodge Dakota) I got MUCH better gas mileage by running with the OD off in the city, only turning it on when I was driving on the highway(or times when I would be going over about 45-50 for extended periods of time). I have tried this with my Bronco, but havent noticed much difference in gas usuage...a little bit better acceleration with it off though, so I generally run with it in OD. Is there any reason I shouldnt do this(wear issues, etc.) and should I be getting noticably better mileage in the city with it off?

Thanks,

Dom

 

[Seabronc]

4.56 would probably work out quite well with cruise control. That would give you 2845 RPM at 65 MPH cruise in 3rd gear and the cruise control would bring it down to around 2270 RPM. The actual numbers for the Bronco engines is 2000 - 3000 as acceptable operating range and 2300 - 2600 as optimum. The formula is MPH(cruise speed) x gear ratio x336 / divided by tire diameter = RPM.

Good luck,

>-

 

[dommo2007]

Well, I dont ave cruise control. Is that something I should think about installing, since although some of my daily commute is highway, if that is gonna cost me an arm and a leg, I dont know if it would be worth it. I tried working the numbers, and, stock, I fall at about 2800rpm for 65 mph. a little high I suppose, but not much. When I did the math for 35"s and 4.56 gears, I would be at about 3100rpm. Is that something that would hurt me much, or would I even notce it with the gas mileage?

 

[Seabronc]

Well, I don't ave cruise control. Is that something I should think about installing, since although some of my daily commute is highway, if that is gonna cost me an arm and a leg, I don't know if it would be worth it. I tried working the numbers, and, stock, I fall at about 2800rpm for 65 mph. a little high I suppose, but not much. When I did the math for 35"s and 4.56 gears, I would be at about 3100rpm. Is that something that would hurt me much, or would I even notice it with the gas mileage?

Sorry, I meant to say Over drive not Cruise Control. It definitely would hurt you in the gas mileage. If you don't have Overdrive and it is to be primarily a street machine I'd go a little less aggressive to 4.11 or less. If that is a stock truck, you probably have 3.55 gears in it.

Just noticed the second question on overheating. I can't see why doing a lift should cause it to overheat unless it changed the relationship of the fan to the radiator. In that case a GOOD electric fan, like a Lincoln Mark VIII fan would solve the problem. Your run of the mill Autozone fans don't pull enough air when needed. As long as you have sufficient air flow over the radiator coils you don't need a fan until the air temperature gets too high to provide much cooling. I use a Mark VIII fan and it almost never comes on in the winter, (only when setting still in traffic for 5+ minutes), and on the hottest days with surface temperatures around 135 degrees it comes on under 35 MPH but the engine never gets more than a few degrees above the temperature I have set the controller up for. Overheating could be caused by a clogged radiator, too small of a radiator, gunk on the metal surfaces of the water jacket, weak water pump, etc.

Good luck,

>-

 

[dommo2007]

Ok, got it...re: the OD not cruise.

Yeah, I havent exactly got the money for all my grand plans for the Bronco, so I have plenty of time to decide exactly whaqt to go with, how much she will be on the street, etc. Like I said, I want to be able to have my cake and eat it too and all that...dunn if it will ever work out real well. I mean, I REALLY want to be able to justify having 38" Boggers, but do I really NEED them, well, probably not.

If I ever throw on a BL, then I will deffinatly check out the fans you were talking about. Just trying to think of these problems, before I blow the truck up driving down the road one day. Probably wont ever go that route, just exploring options and such.

One last random question: I see that alot of people have done a "3G" swap. What the **** is this, and is it something I want to do?

Thanks

 

[dommo2007]

Oh yeah, did the math for RPM with OD, and it came to about 2350 w/ OD, 35"s and 4.56, so that seems more in the realm of the reasonable. From your experience, how much do engine mods, such as after market exhaust, headers, cold air intake, stuff like that...how much does it help the 302 for both mileage and power? Yeah, it'll cost a bit to replace just those for instance, but if I make some decent improvements in both catagories, I suppose it is worth it enough to try to bs my wife that its worth it...lol I never really got into that part of building my truck, not much experience there. Probably should have since my last truck, a Cherokee, had a I-6, but on the other hand, it didnt weigh in at over 6k #.

 

[Bebop Man]

Where can I find what the stock gear ratio would be my Bronco. I think it's somewhere in the neighboorhood of 3.54 or so. Maybe 3.73 (based on what I see for RPMs on the tach at highway speeds)

 

[Seabronc]

Where can I find what the stock gear ratio would be my Bronco. I think it's somewhere in the neighboorhood of 3.54 or so. Maybe 3.73 (based on what I see for RPMs on the tach at highway speeds)

If it is a stock never changed rear end, the axle code on the safety compliance sticker can be interpreted. It is also on the differential tag that is attached via one of the cover bolts. You should start you own thread rather than attaching to some one Else's. That way your question won't possibly get lost.

Good luck,

>-

 

[Seabronc]

Oh yeah, did the math for RPM with OD, and it came to about 2350 w/ OD, 35"s and 4.56, so that seems more in the realm of the reasonable. From your experience, how much do engine mods, such as after market exhaust, headers, cold air intake, stuff like that...how much does it help the 302 for both mileage and power? Yeah, it'll cost a bit to replace just those for instance, but if I make some decent improvements in both categories, I suppose it is worth it enough to try to bs my wife that its worth it...lol I never really got into that part of building my truck, not much experience there. Probably should have since my last truck, a Cherokee, had a I-6, but on the other hand, it didnt weigh in at over 6k #.

I'm not a fan of the KN stuff, mainly because if your intake system is functioning properly it gets cold air from outside the truck any way and I don't see the need to spend extra money to get what I already have. Secondly, the stock intake is designed to give the engine warmed air when it it needs it. Replacing the stock intake negates all the stuff that is done to give the engine good cold weather start and run characteristics. My feeling is if the existing intake system isn't running properly, then fix it. If you are modifying the engine to require a larger volume of air then that changes the picture, but then throw away any thoughts about improving gas milage, you are then moving toward a performance engine.

As far as mods go, you can't have your cake and eat it too. Boosting the 302 power generally requires more gas to feed it. However, there are modifications that free up power which can be expended on moving the truck. Minor improvement is gained from the electric fan modification by taking the fan load off the engine. This is good as long as the fan controller is set up properly to only turn the fan on after the engine gets to a set temperature. Like I have stated before, my controller is set between 5 and 10 degrees above the thermostat. As long as my truck is moving fast enough to keep the water temperature below that it will not come on, in the Winter that is most of the time even when setting still, in the Summer on real hot days that is usually around 35 MPH or less.

Just a note on this, my cooling system includes an over sized radiator, you also need to make sure your cooling system is clean, (flush it using a cooling system flush product).

Another mod that will free up power is a full time electric pump that has a controller to vary the flow rate depending on the engine temperature. The power saving is in eliminating the water pump drag on the engine. The benefit of both of these changes would be negated if they are running full blast all the time since the load would be shifted from a mechanical one to an electrical one. Believe me, the alternator can put a big drag on the engine.

Weight reduction is another way to effectively give you more power and at the same time improve gas mileage. I don't have all of these implemented yet but I have a goal of 20+ MPG on this truck. I have started on the weight reduction project, but still have a way to go. I plan to use fiberglass panels in the weight reduction, probably a fiberglass hood and tail gate.

The 3G alternator modification is a very simple one to do but not necessary on a 95 since it already has a 3G. As long as there are no major electrical load changes the alternator in your 95 should be just fine. If you have a 4 hole pattern between the metal ribs, yours is a 135 Amp alternator, if it has 2 holes then it is a 95 Amp alternator. Older trucks like mine definitely need it if they go with a powerful fan like mine, ( the Lincoln Mark VIII fan draws 100 amps on start up and quickly settles down to around 33 Amps), a little too much for the old alternators or a stock 95 Amp 3G.