Rear bumper question

Hey there -

I'm still new to the Jeep world and was hoping to get some help. Back in the 70's the PO did an engine swap to a 72 Ford 302 with a 2-barrel carb. The T90, D18, and axels are stock (41 & 25) with open 5.38's. Based on a few outings of combined trail and backroad use (~45 mph max) I'm averaging 7 mpg. With a 10-11 gallon tank, that leaves me less than an 80 mile range to empty. I do not have an overdrive, and will be looking into getting one in the future.

So far I have been carrying two jerry cans in the back, along with my spare and tools, leaving no room for the rear seat. I have been looking into purchasing a rear bumper that can hold my 2 jerry cans and spare, so I can actually bring my family along with me and have a reasonable range before running dry (~140 - 160 miles). One can and a spare mounted to the rear just won't give me the range I'm looking for.

I can flat tow with my Ranger (4.0 SOHC), but feel unsafe doing so in the hills/mountains. Plus I am concerned about leaving the Ranger parked at a trailhead for a few days. I do not have a vehicle that is capable of pulling the Jeep on a trailer. Ultimately I think the overdrive will help the most, as I believe my mpg is much better on the trail than trying to keep up with highway speeds (no gas guage; 10 gallons in, 70 miles later it ran out of gas).

I know many of you fab your own bumpers, but I lack the tools necessary. Most all the bumpers I have seen advertised are for the 55-up CJ5, or are listed as "pre-76 CJ." Are the mounting points for the rear bumper similar for the flatfenders as they are for the 55-76 CJ? Would a "pre-76 CJ" bumper work? :?

 

Another option would be to put in a rear 15 gal tank. I don;t know if that works on a flattie though. If your frame rails are narrower than an ECJ it might be a tough fit. I wouldn't expect an OD to give you much more in the way of mileage, especially on the trail. It sure is nice though, having all those extra gears.

 

rear tank as Posi states or even another underseat tank on the pass side as well
course, the tool box would have to go...

 

Grt_Ape,
I know you said that you don’t have the tools to fab a bumper but you might want to look into how much it would cost at a local shop to remount the hardware of a bumper to match your Jeeps bumper mount points. Then you have the bumper you want with the tire carrier, gas racks and trail racks, instead of finding something that is “kinda” what you want.
As what Posimoto was saying the idea of a rear tank, I have a buddy up in Durham, near Chico, that has a custom fab shop and he has made a few 20+ gal tanks for Flatties and they work great. I took my 76 CJ5 to him and he did work for top-notch work for good price. He saved me money even with having to go back and forth from southern Monterey. I would be happy to send you his name and # if you want.
Douglas

 

Thanks for all the replys -

The 7mpg was combined 1/2 trail and 1/2 hwy use. I thought that was horrible, as the 302 is running only 2-barrels. My 289 Mustang got 22 mpg on 2-barrels. I have replaced the plugs, wires, cap, & rotor. The points & condenser checked out ok, but were not replaced. Timing is also within spec.

dereamy - Small world ...I lived out on Oro Chico Hwy in Durham for 18 years. My parents are still there. I would love the contact info for your friend.

Boyink - Great link...I'll look into their setup.

 

Look for a hole in the power valve if you're running a 2100. That will dump gas into the bores all the time, and could be responsible for the poor mileage. Usually drivability suffers, but maybe not in this case.

You can test it by closing the idle jets all the way - if the engine keeps running at idle, you likely have a hole in the PV.

JMO - jerry cans are very 'Jeep', but I think mounting them on your vehicle is unsafe and wouldn't carry one except in an emergency. Check into the dual tank option - under the back floor or under the seat, as Jim suggested.

 

Grt_Ape,
I sent you a PM with his contact info. This is a small world, good luck with what you have to do.
Douglas

 

A four barrel quadrejet would get you better mileage but, suck on the trails.

 

As far as mileage goes; off-road mileage is really hard to judge. I have gotten anywhere from 1 mpg to 8 or 9 mpg. But think about this; if your first gear ratio is 2.98, your crawl ratio would be 39.4:1. If you swapped to a good 4 speed and got rid of the 5.38s, you could actually have a lower crawl ratio (58 to 75 range) and better gas mileage. Overall, you would have better trail performance due to the lower crawl ratio. Better street performance due to a higher axle ratio (That 302 would actually be more fun to drive). Better highway mileage, and worse trail mileage, but who cares about trail mileage. Cool Eh!

Want to make another win/win/ modification? Throw some fuel injection off of a mustang on top of that 302. Better off-road performance due to running at any angle. Better fuel mileage on the highway.

 

I have virtually the same set-up (except a 289 and an OD) but haven't kept track of mileage (still working on making it streetable). At some point in my Jeep's past they installed a custom tank that goes under both seats! I've never filled it up, but it has gotta be 25 or more gallons.

Have you considered just bolting a couple of jerry can holders to the back of the Jeep? The PO did that on mine (apparently he was paranoid about running out of gas). It would be easy and not as involved as fabbing a rear bumper.

FYI, the best off-road carb behind the 2bbl Ford is a Quadrajet IMHO. I have many, many hard trail miles on a Q-jet and love it. I know of many otehrs with the same opinion. Not as good as fuel injection, but they rock!

 

You could probably get a local shop to make you up a rack for gas cans + tire etc. I made my own it wasen't that bad to do. Get out the card board and make a model of what you want. Then take all the cardboard peices down and have them cut and weld. If they don't have to spend all the time figuring out what you want it will be alot cheaper.

 

Where are you located in central Ca. ?

 

We're located in Merced. Been here for almost 9 years. Previously lived in both Chico and Durham in Nor Cal.

Most trails that I've been on are a ways away...you either tow your rig to the trail or drive an hour or more to get there. The driving part sucks with 40-45 mph top speed and 7mpg. Try doing the speed limit on the hwys around here (65-70) an you'll get run off the road by somebody doing 90. I take my time on the back roads, but 70-77 miles to empty is expensive! La Grange OHV is relatively close, but not very big.

Looks like I may want to spend more time diagnosing the poor mileage problem before bandaiding the issue with more fuel capacity. Right now I'm running a Motorcraft 2100 with the internal vacuum power valve. As mentioned, I believe the power valve may be suspect.

Will let you know what I can dig up.

Thanks again,

Chris

 

Chris, I'll be glad to fab a bumper for you when the time comes. I'm up the road in Antioch. Also, there is a great carburetor rebuild facility near by if your interested. Let me know if I can help. Jeff.

 

Thanks Jeff. I'll keep you in mind when I decide to do a bumper.

My Jeep's PO farmed out most of the modifications he had done over the past 30 years. He wasn't able to answer very many of my questions, as he simply didn't remember.

At one point, he had an underhood fire following a tune-up. I believe he replaced the fuel filter at the carb and didn't tighten the hose clamp securely. The paint on the hood is toast, and he replaced the carb with a remanufactured unit. He melted the wiring inside the alternator, although he apparently didn't know this. He got tired of charing the dead battery all the time and parked it for 5 years. I even found a hose clamp buried in a pile of ash on the intake. Rebuilt the alt, now the battery stays charged. R)

The point is that the carb is practically brand new. It has been sitting for 5 years, so a rebuild may be in order. Some of the old gas may have turned to varnish and gummed things up. She starts fine, idles fine, and drives fine. Just poor mileage at this point.

 

That MPG doesn't seem so far off to me, V8 pushing a jeep down the highway with 5.38's.... if he was doing highway speeds (i will say 60 for a jeep)

60 mph
1:1 final drive ratio
31" tires
boxy jeep

doing the math your taching out at 3499RPM with a V8 running down the road, even with a 2 barrel that will suck some gas.

Though for comparison I run a V8 (355) in a larger YJ with OD, 4.10 gears and 33's with the 700R4 I run 2200RPM and 70 MPH and can get around 18 or so with a 4 barrel... I turn my OD off and I am LUCKY to get 10, I think when I did that with 30" tires I got 7, I have 33's now though