So last year a buddy who is a lot smarter than I am helped me swap a GM TBI (’90s-era from a junkyard) on my swapped-in AMC 360 V-8 in my ’80 CJ-7 (it replaced a worn out 304ci). It runs really well, but the throttle is too touchy. I’m using the gas pedal assembly that came with the Jeep and it’s got a fiberglass tub. We mated the cable to the TBI throttle arm on the driver side (hope that’s what it’s called). It is extremely hard to feather the gas for smooth acceleration, especially off-road. We made it out to Moab for EJS 2013. My first time in Moab, and while I loved the fuel injection at altitude and on the steep hill climbs, I hated not being able to give a small amount of throttle smoothly. It requires so much force to get the pedal to move that when it finally does give, the pedal goes way farther down than I want it to and my CJ-7 jerks forward. I don’t even know where to begin. Do I need an aftermarket pedal assembly? Do I need to modify the pedal assembly I have? Can I get different load-rated springs for the arm on the TBI?
Initially I thought that you probably had the throttle cable going to the wrong hole on the throttle body, but after looking at your picture and my two Jeeps with Howell fuel injection (which is a slightly modified version of the GM TBI you have), I can see that that is not the problem (see image above). So here is the next step. First I’d pull out the throttle cable and give it a good cleaning. I suspect that junk between the cable and cable housing is causing your touchy throttle issue, and with a little cleaning the problem will be resolved. It should slide in and out with almost no resistance. Give that a try, and if it does not help there is one more thing you can try. Move the engine-side mount for the throttle cable housing to adjust the position of the gas pedal inside the Jeep. Try moving the mounting point of the throttle cable under the hood up and slightly towards the front of the Jeep so that the butterflies are open fully when the gas pedal is just about to hit the floorboard.
’Nother GM Small Block Swap?
I own an ’84 CJ-7, Howell injected 4.2L backed by a TF999, Dana 300, AMC 20 rear with Auburn Pro Series limited slip, Dana 30 front with Detroit Truetrac, MileMarker hubs, 3.73 gears, and custom driveshafts (double cardan rear). I have a ’68 Chevy 307ci short block that was removed from a Chevelle in 1968. It has less than 500 miles on the clock and has been in the crate ever since. I intend to freshen it up, add a mild RV cam, and transfer over the Howell TBI. The TF999 is stock with less than 10K since a rebuild. Is it feasible (or smart) to adapt the GM engine to it given the other drivetrain components already installed? The CJ is currently set up with a serpentine belt system with a Jeep Air aftermarket A/C which has to be figured into the installation. Does anyone have a kit or a comprehensive list of parts needed to make this installation idiot-proof? Also, what is the least painless exhaust treatment? Stock cast iron manifolds, block hugger shorty headers maybe? I’m not a fan of fender well headers. Your sage advice would be a life-saver on this project.
Yucca Valley, CA
Mike, this sounds like a cool swap for sure. I’d say the TF999 would be up to the task of handling that GM 307, and there is an adapter from Advance Adapters (PN 716131-A, $489.28) to mate an old-school small-block Chevy V-8 to an AMC six-cylinder (or V-8) TF999. As an alternative you could go to a GM TH400 or TH350 and adapt the Dana 300 to it (with the adapter costing about $500), but I don’t think there is much benefit in strength to doing this if your TF999 is healthy and since you already own it. Also, the GM tranny pan will interfere with the front driveshaft. You will also need motor mounts to convert to the GM engine, the exhaust (as you point out) will need work, you may need new driveshafts and a Chevy conversion V-8 radiator because the hose outlet/inlet are on opposite corners. I also searched and found over 40 different shorty headers on summitracing.com that seem to fit a 307ci in a ’68 Chevelle. One set has to work for your conversion. The only real complications that I see are the following: First, your serpentine beltdrive on the 258ci and A/C compressor means you’ll need to figure out serpentine accessories drives for the older GM V-8 and a mount that will work with your A/C compressor. Summitracing.com lists at least a few serpentine drive belt kits that should work with a GM 307ci V-8. Second, the Howell on your 258ci is probably a throttle body from a 4.3L V-6 rather than a small GM V-8, so it may not move enough fuel and air to keep the 307ci happy, especially with an RV cam. I am sure Howell would be happy to tell you if it will work, or if you will need to upgrade to the GM V-8 throttle body.
Verne Is a Neanderthal
Hey, how’s it going? Just wanted to drop you a line and say how much I enjoy your work. I’m looking forward to seeing the tranny swap in your Shrink Ray TJ. I did want to mention in the Grand Cherokee “How To Build It”article you list the ’93 as the only ZJ with the AX15 when that was an option through 1995. I don’t mean to come off as a stickler I just wanted to give you a heads up. My previous Jeep was a ’95 ZJ with the AX15, and it was a hoot. Have a nice day and keep up the good work.
Thanks for the kind words, and also thanks for the info. Honestly, I have never seen any ZJ with a manual, and for a long time I doubted their existence altogether, as I had only heard rumors of them. One rumor had it that some police departments had ZJs with V-8s and five-speeds, which seemed off, since all I know is that the cops generally like autos -- and donuts). Anyway, it’s good to know they were available up until 1995 in ZJs.
Someone once said, “To err is human,” and based on my prominent brow ridges, large cranial size, love of rocks, dirt, hand tools, and meat roasted over a fire, I may just be at least part Neanderthal. It’s not a big deal, momma still loves me, but it also might mean I make errors more often. Luckily, I am happy to learn about anything Jeep -- from the comfort of my cave -like office -- even if it means I am occasionally wrong.
Also, the tranny swap in Shrinky is under way, and I can’t wait to get it finished so I can see how nice that deep first gear is on the trail. Keep your eyes peeled for the tech on the swap.
Drum to Disc Never Dies
Hello. First off, keep up the good work. I’ve been reading Jpfor about a year now, and I think you guys are doing a smashing job! The only thing I would like to see more of is more coverage and tech articles on the CJ-2A and CJ-3A. One question that I have is what would be the easiest way to swap the drum brakes over to disk brakes? Can I use my existing hub/spindle? What caliper bracket could I use? Thanks and keep the shiny side up.
Man I wish we had more flattie tech, too. Oh boy, time to start looking for a new project. Of course lots of the tech in this issue also applies to early CJs including -2- and -3as.
Believe it or not, a long time ago I wrote an article called “Drum to Disc” about putting disc brakes on my CJ-3A. It was back in the 00s, in other words, way back when. The pictures are in black and white, but they still work for showing people how to swap to much better brakes on Dana 25s, 27s, and early Dana 30 front axles. So you could track down a November, 2001 copy of Jpand check out the article, or you can check it out at fourwheeler.com/how-to/93298-drum-to-disc-brake-upgrade/. Now you can track down all the parts for the brakes I talked about in the article like caliper mounting brackets from a ’73-’91 1⁄2-ton GM 4x4, ’71-’78 1⁄2-ton GM 4x4 front calipers (and pads), Rotors from a ’77-’78 CJ (the ones that are 11⁄8-inch thick), 10 longer wheel studs (we used Dorman PN 610106), and spend some time figuring this conversion out. Alternatively, you can get a disc brake conversion kit and new brake master cylinder from Herm the Overdrive Guy (http://hermtheoverdriveguy.com).
Got a tech question you’re just itching to get answered? Send it on in to Jp Magazine, Your Jeep, 831 S. Douglas St., El Segundo, CA 90245, or e-mail it to email@example.com.