Sharp Motorsports 4600 Class Early Bronco

[markatherton]

koh

awesome write up...

 

[Yeller]

You'll be fine with 1350 ujoints as long as you can get enough angle. 1350's are what we ran in our 4400 car without any issues. they even survived twisting off a few pinions landing under power, shouldn't have that problem with a 60. I'm a fan of gearing the axles, the car will handle better, the added torque load to the chassis can make some funky handling, and the 33:1 will be far more capable than you think, and you are on the right track, anything past 50:1 is a waste of effort, (both of my rigs are 42:1) also remember your racing the crawling will be slow but not like out for a trail ride slow, less gearing will be your friend and be easier on your axles. Once you've done this a while you'll go on a trail ride and be wondering what is taking everyone so long...LOL

The only way I'd consider keeping the 4.10's is if you add a LOT more power and can keep the weight down. Weight kills performance so be mindful of every nut and bolt you add and strip out everything not required.

 

[LSharpNM]

You'll be fine with 1350 ujoints as long as you can get enough angle. 1350's are what we ran in our 4400 car without any issues. they even survived twisting off a few pinions landing under power, shouldn't have that problem with a 60. I'm a fan of gearing the axles, the car will handle better, the added torque load to the chassis can make some funky handling, and the 33:1 will be far more capable than you think, and you are on the right track, anything past 50:1 is a waste of effort, (both of my rigs are 42:1) also remember your racing the crawling will be slow but not like out for a trail ride slow, less gearing will be your friend and be easier on your axles. Once you've done this a while you'll go on a trail ride and be wondering what is taking everyone so long...LOL

The only way I'd consider keeping the 4.10's is if you add a LOT more power and can keep the weight down. Weight kills performance so be mindful of every nut and bolt you add and strip out everything not required.

Yeah, I am sure 1350s would be plenty strong, I am just worried about the crazy driveshaft angles this thing is going to have, and 1410s have a larger operating angle. Again, this is going to come down to seeing what things are looking like further on in the build.

I agree with you on getting the gear reduction as close to the wheel as possible to minimize stress on upstream components and minimize the effects of torque twist. As I said, I am an automatic newbie, and all my experience is recreational wheeling, so maybe I need to change my mindset when looking at things from a racing perspective. I know you have been an advocate of relatively high gearing with an automatic, but 33:1 just seems miserable to me and hard on the tranny for serious rocks. So Yeller, if this were your build, how would you gear it? Just put in 5.38s and call it good?

My main reference points are my father's LJ with a crawl ratio of 35:1 (4.0L, 42RLE stock converter, 2.71 Tcase, 4.56 axles, 35" tires) and my buddy's buggy with a crawl ratio of 51:1 (6.0L (LQ9), TH400 2000RPM stall converter, 3.8 Tcase, 5.38 axles, 40" tires). My father's LJ doesn't seem great in the rocks, and the buggy feels perfect to me. If you convert the crawl ratio of the buggy for 35" tires, it would be equivalent to 44:1.
Another reference point is the stock class Saavy LJ that dominated EMC in its inaugural year which was running 51:1 with a 4.7L stroker. They were running 6.00:1 axle gears (9" front and rear) with a 3.0 Atlas. The thing is the .69:1 overdrive in the 42RLE goes a long way towards offsetting the deep axle gears at speed (equivalent to 4.10 without overdrive).

 

[LSharpNM]

Before tearing down The Bronco, I wanted to get a baseline weight and CG height. The roll cage tubing size is determined by the rig's overall weight per the Ultra4 rules and I wanted to make a better educated guess on my CG height for designing my 3 link geometry. I started looking at corner scales, and good god they're expensive Fortunately I have a buddy at work who used to be into auto-cross and had some old school hydraulic corner scales. They are kind of neat; the cylinder area is exactly 1 sq.in. so the pressure reading is also the weight.

Here are what the scales look like:

Getting the corner weights:

To get the CG height, I raised the front end as high as I could with the jack stands I had, and used the change in weight on the rear axle (65 Lbs.) along with the difference in hub height (7 21/32") to calculate it.

I ended up with a CG height of 18.15" above the axle center line, so 31.65" above ground level when you add the 13.5" rolling radius of the tires (235/75R15s). For a sanity check, I calculated the static tipping point angle for it to go over backwards and came up with 70.64º, so the CG height seems reasonable. The weight distribution came out to 56.2% front and 43.8% rear.

Pretty nose heavy for the desert, but I frankly am not sure what kind of weigh distribution would be ideal for KOH. I know a slight rearward bias is ideal for desert racing, and a front bias is preferable for crawling, so maybe shoot for 50/50? ?:?

Anyone want to take a guess at what it weighs as pictured? ;D

 

[landshark99]

3675 lbs

 

[Yeller]

3450 is my guess

I’d do the gears and run the stock case. Next would be the trans gear set or atlas. Even with replacement gears the weak link is still the tcase. The trick to running the taller gears is to drive with both feet and modulate speed with both feet, takes practice to not over apply the brakes and throttle but it works very well. You’ll appreciate the taller gearing bumping ledges

I’d also shoot for 50/50 split. You’ll be close by the time you put your spares in the back.

 

[toddz69]

3800 lb?

Todd Z.

 

[LSharpNM]

Yeller was the closest, it came out to 3,330Lbs.

Doing some really rough ballpark estimates for weight I am going to add, I am thinking maybe around 4,200Lbs race weight. 1.75 OD tube is permissible for vehicle weights up to 4,400Lbs, but I think I might be cutting that close, so I might just step up to 2" tube so I don't have to stress as much whether I'll be over weight or not.

 

[Yeller]

Winner winner

Remember light is king. Put weight were needed to be robust, grams make ounces and ounces make pounds.

 

[LSharpNM]

So I am getting ready to pull the body, but I've noticed most people do some kind of bracing in the door openings. I have never had a Bronco body off a chassis before, but I can see how it would be pretty flimsy without some kind of support.

Does anyone have any input whether the existing cage should be enough to support it, or if I should get busy welding up some bracing? It seems to me the cage should be sufficient, but I don't want to make that assumption and throw the body out of whack.

 

[landshark99]

So I am getting ready to pull the body, but I've noticed most people do some kind of bracing in the door openings. I have never had a Bronco body off a chassis before, but I can see how it would be pretty flimsy without some kind of support.

Does anyone have any input whether the existing cage should be enough to support it, or if I should get busy welding up some bracing? It seems to me the cage should be sufficient, but I don't want to make that assumption and throw the body out of whack.

I would absolutely brace across the top of the door openings, also i would brace from the firewall to the core support if you intend to keep the front clip. a single round or square stock will work on the openings. I also braced across the tailgate area - but since you aren't running one then it may not make much of a difference but the tailgate opening tends to spread apart

 

[landshark99]

Also, do not lift by the front core support - it will taco...

 

[LSharpNM]

I would absolutely brace across the top of the door openings, also i would brace from the firewall to the core support if you intend to keep the front clip. a single round or square stock will work on the openings. I also braced across the tailgate area - but since you aren't running one then it may not make much of a difference but the tailgate opening tends to spread apart

Also, do not lift by the front core support - it will taco...

View attachment 514309

Thanks for the input and the pictures. I was planning to lift it at the rockers (which I am planning to cut off and replace with rectangular tube anyway) with my lift.

 

[LSharpNM]

Got some progress done this weekend, but it has been cold and my shop is currently unheated and uninsulated which cuts down on my motivation (My damn beer froze the other day )

I've been trying to get the body stripped down so I can pull it off the frame and make repairs, but it had been a mess of broken/rusty J-clips and other piddly crap. The dash is blocked from coming out by the cage, and many of the cage bolts are inaccessible from the bottom without pulling more crap out of the way. The inner fenders and wheel tubs are in worse shape than I thought; tweaked, lots of cracks and torn metal, and big sections that were torched out (the upper corners of the inner fenders where all Broncos rust). I think I am probably going to have to replace all these parts with new sheet metal. The fiberglass fenders are pretty rough (which I already knew) and I am not sure if they'll be worth saving since I know nothing about fiberglass repair. I have another set of steel fenders that are a little rough too, but at least they don't have torn out bolt holes. I think I'll throw the fenders on a scale to get an idea if the fiberglass fenders are light enough to justify the hassle since I would rather have dented steel fenders than broken fiberglass when they get damaged from racing.

I ended up getting tired of working on that since it was kind of a PIA to do some of that stuff by myself and it wasn't going to smoothly. I decided to start working on the front axle instead and I got it all stripped and the old leaf perches ground off.

I had broken the driver's side stub on my last outing and it was stuck in the spindle. I had to whip out the grinder with a cut off wheel and was able to cut off just enough of the part sticking out of the wheel-side of the spindle to get the rest of the shaft out. Obviously, the hub was toast too, but I have drive flanges that I will be using (I was already running one on the passenger side, but kept a hub on the driver's side since the diff was welded).

I also measured the steering stroke for a ram. With the steering stops where I had them in the beater Bronco II (to keep the 38" XMLs out of the leaf springs) there was almost exactly 7" of steering throw. With the steering stops removed, I got right at 8" with the factory tie rod hitting the factory diff cover. I also measured without a tie rod and got ~9" with the knuckle binding on the "C" in both directions. I am thinking an 8" ram should be the ticket.

I debated stealing the ARB locker out of the EB Dana 44 to run in this axle, but it is a high speed carrier (3.54 gears) and you can't get thick cut legacy HP Dana 44 gears. Additionally, I would have the added expense, complexity, and weight of an onboard air system. I decided to bite the bullet and ordered up a Grizzly Locker to keep things simple, and they supposedly don't get taken out by broken axle shafts like Detroits do. I also bought some 5.38 gears and committed to going no doubler.

 

[BanditBronco]

That's sad when you want to move from pulling the body apart to grinding brackets off the axle haha I am sorry for you!

Are those stock chevy knuckles?

Good call on the grizzly, I have ran one for a year, I replaced an Eaton E locker with it just for simplicity when I went full width and I haven't regretted it. Grizzly front, spool rear is a solid combo.

I would be curious on fender weights as well. You can always just drill new holes to mount the fenders, or don't even use the original mounting points, make your own and use fiberglass body mounts like the ones AutoFab makes, Kartek has a bunch of mounting solutions.

 

[LSharpNM]

That's sad when you want to move from pulling the body apart to grinding brackets off the axle haha I am sorry for you!

Are those stock chevy knuckles?

Good call on the grizzly, I have ran one for a year, I replaced an Eaton E locker with it just for simplicity when I went full width and I haven't regretted it. Grizzly front, spool rear is a solid combo.

I would be curious on fender weights as well. You can always just drill new holes to mount the fenders, or don't even use the original mounting points, make your own and use fiberglass body mounts like the ones AutoFab makes, Kartek has a bunch of mounting solutions.

I know, right! At least the grinder keeps your hands warm

They are F250 knuckles; this is a '78-'79 axle. They use a 5 bolt spindle just like the other Ford stuff, but are already setup for high steer arms, and the tie rod arms are cast higher than the Bronco knuckles.

Good ideas on the fenders, I hadn't really though about those options, and I certainly wouldn't feel bad having to modify the fenders I have.

 

[cofferjl]

I have not been around the KOH races much but I have been around/raced a lot of short course racing and tough truck racing. After reading through your posts I would like to offer some tips that I think may help. I am in no way trying to offend you with any of these tips just trying to help a future fellow racer out.

I think that you should make friends with some fellow racers to help crew for them first that way you will get a better idea of the work that you are up against. Then I think that you should focus on the safety aspects of this build first. Build a good chassis that will last {i.e. a good cage). Then follow Landshark99's suggestion of servicing everything and installing the explorer motor stuff. I wouldn't even worry about a cam right now. Do these things to get you racing as soon as possible. Too many guys start out builds that never get finished because they run out of steam or find other interests or their class gets cancelled before the build gets finished so that they have to start from the beginning again, ask me how I know. ( https://www.ford-trucks.com/forums/1587228-off-road-race-bronco-7.html).

Second you must force yourself to work on your race car. DO NOT stay out of the garage because it is cold/hot. Treat this project as a JOB until it is finished. Stay on one aspect of the project until it is finished, when you jump from one area of work to the next things get missed, bolts don't get tightened, fluid doesn't get added, or parts get ordered twice.

Next do not expect sponsorship from anyone, keep promoting yourself and the build but see any help that comes your way as a bonus. Accept the fact that you will spend far, far more money than any rational person would be able to justify. This is not only a job it is also an addiction.

Lastly, know that when this build is driving, that the job isn't even half finished. Then next comes the repairing, rebuilding, reworking, improving, prepping and racing in a vicious cycle. Also the people in your family will need to accept the fact that your life and possibly theirs is now based around racing. Vacations will be taken traveling to races, birthday parties will be scheduled on non race weekends or celebrated at the race, and holiday's will be hosted at your place so that you will have extra hands to help in the minutes before Thanksgiving dinner, besides you can see the fireworks through the garage door while you are under the race car anyway.

Once again not trying to make you change your mind, just giving you some pointers. I do want to see this build completed because it makes me feel better about my own sickness.(lol) All of the difficulties and sacrifices will be worth the amazing memories you will make with family and friends, that is the ultimate reward you get for being involved in racing.
Also I want to be the first to say. Hello, my name is Cofferjl, I'm an addict and welcome to the club.

 

[LSharpNM]

So I got the steel and fiberglass fenders weighed, and they came out to 14.3 and 10.3 pounds respectively. Now while it may appear that there is a 4 Lbs. difference, it wasn't exactly apples to apples since the steel fender still had the lower supports bolted on, the side-marker housing, bronco script logo, and a fiberglass flare riveted on versus the fiberglass fender which was bare. I am betting the actual weight difference is only a pound or two.

I have not been around the KOH races much but I have been around/raced a lot of short course racing and tough truck racing. After reading through your posts I would like to offer some tips that I think may help. I am in no way trying to offend you with any of these tips just trying to help a future fellow racer out.

I think that you should make friends with some fellow racers to help crew for them first that way you will get a better idea of the work that you are up against. Then I think that you should focus on the safety aspects of this build first. Build a good chassis that will last {i.e. a good cage). Then follow Landshark99's suggestion of servicing everything and installing the explorer motor stuff. I wouldn't even worry about a cam right now. Do these things to get you racing as soon as possible. Too many guys start out builds that never get finished because they run out of steam or find other interests or their class gets cancelled before the build gets finished so that they have to start from the beginning again, ask me how I know. ( https://www.ford-trucks.com/forums/1587228-off-road-race-bronco-7.html).

Second you must force yourself to work on your race car. DO NOT stay out of the garage because it is cold/hot. Treat this project as a JOB until it is finished. Stay on one aspect of the project until it is finished, when you jump from one area of work to the next things get missed, bolts don't get tightened, fluid doesn't get added, or parts get ordered twice.

Next do not expect sponsorship from anyone, keep promoting yourself and the build but see any help that comes your way as a bonus. Accept the fact that you will spend far, far more money than any rational person would be able to justify. This is not only a job it is also an addiction.

Lastly, know that when this build is driving, that the job isn't even half finished. Then next comes the repairing, rebuilding, reworking, improving, prepping and racing in a vicious cycle. Also the people in your family will need to accept the fact that your life and possibly theirs is now based around racing. Vacations will be taken traveling to races, birthday parties will be scheduled on non race weekends or celebrated at the race, and holiday's will be hosted at your place so that you will have extra hands to help in the minutes before Thanksgiving dinner, besides you can see the fireworks through the garage door while you are under the race car anyway.

Once again not trying to make you change your mind, just giving you some pointers. I do want to see this build completed because it makes me feel better about my own sickness.(lol) All of the difficulties and sacrifices will be worth the amazing memories you will make with family and friends, that is the ultimate reward you get for being involved in racing.
Also I want to be the first to say. Hello, my name is Cofferjl, I'm an addict and welcome to the club.

I appreciate the advice, and don't worry, I am under no illusions of grandeur! While I don't have any racing experience yet, I think I have done my homework and have a good idea of what to expect and understand the grind that goes along with building and campaigning a car. I do wish I had had been able to pit for a team prior to starting my effort (planned to last year, but things fell through).

King of the Hammers is a once a year race that is the first race of the Ultra4 series which consists of ~5 races throughout the year (KOH, ~3 regional races, & nationals). Many folks only commit to KOH, which is kind of the boat I am in. There are a few regional races I may try to make after the rig is done, but I have absolutely no interest in the short course races with man-made boulder fields on a dirt track. I figure 1 race a year for sure (KOH) plus maybe one or two others at my discretion. I am not going to be chasing the points championship for the series, or be traveling to go to a race every weekend. I might enter the rig in a local WE Rock event in the Sportsman class from time to time as well or do a NORRA race just for fun (I know it won't fit into any class rules).

 

[cofferjl]

Cool, sounds like you got a plan. I know years ago I said I would just race a few times and still take my other stuff to go on trail rides and things like that. Then it all just kind of snowballed.
I personally don't do any racing that involves major rocks, think more like racetracks like bark river, crandon, etc. I would love to some day run the mint or other desert race but that probably won't happen.
Since you live in NM you might check out the Texas desert racing association. That might be another opportunity for you to race that is reasonably close.

 

[66horse]

Awesome. So much fun. I pitted for Andrew Goodell for a few years when he was running the EMC in a stock class bronco. A little right side seat work as well.

Too far out to fully commit to pitting for you in 14 months but hit me up when it is closer. I am definitely interested.

On the t-shirts. Do it. 3 reasons. (1) People will buy them. (2) Extra incentive for you to stick it through - cannot let the people down that support you. (3) I want one. The logo is cool enough to put on a t-shirt. You could also post a separate thread asking if anyone on here does t-shirt or other type of design work and see if you can work out some sort of minor sponsor deal.

Cheers and good luck!

Steve