Santa (technically, my sister’s boyfriend) brought me a lovely gift this Christmas: a carb rebuild kit for my spare Thermoquad including all of the gasketry, springs, and other small parts needed to overhaul the mechanical bits. Introduced by Chrysler in 1969, the Thermoquad is a four-barrel carburetor designed with two small primary and two large secondary bores. At idle or cruise, the primary bores supply fuel to the engine in small amounts for efficiency, and under load or acceleration the secondary bores open up to dump fuel into the engine, adding power. It’s built around a phenolic resin chamber sandwiched with two aluminum plates, which was supposed to keep the temperature of the upper bowl 20˚ lower than standard metal carburetors of its day–because vapor lock was standard equipment on a 440 big block. So I’m going to have to study up on this Malaise-era marvel of engineering.
My engine, near as I can figure, is a 1979. As the 70’s wore on and emissions standards got stricter, engine displacement decreased and smog equipment strangled engines. IH trucks weren’t as strictly governed as passenger vehicles of the era (trucks over a certain weight and load limit were exempt from CAFE regulations, hence IHC advertising the Scout as the XLC in 1975 onwards) but smog equipment was still added to pass emissions tests, and the carbs got more complicated as the decade drew to a close. The Thermoquad sprouted all sorts of ports and valves and complicated linkages to govern choke, temperature, airflow and throttle, and the result is a lump of metal that looks like C-3PO screwed a pinball machine.
I’ve got three Thermoquads in my collection. The first is the one that came on Peer Pressure, which I had overhauled by my friend Rodney a few months after I got the truck. Tracing the serial number (9128S), it was originally made for a ’79 IHC 345ci engine with an automatic transmission. Rodney is a gearhead of the first order (he has a slingshot dragster parked in his driveway) and no stranger to carburetors. He made it sing, but that was eight years ago.
The second is a spare I picked up from a fellow north of Baltimore. This too is a 9128S. It’s the spitting image of the one on Peer Pressure, minus the funky extra linkage on the throttle arm to the left. It’s also the rebuild candidate and the one I’ll be working with here.
The third is a spare I picked up from my friend Jason, who converted his Traveler over to fuel injection two years ago. Tracing the serial number (9203S), it was originally made for a ’79-80 IHC 345ci California smogged engine with an automatic transmission. The top of the air horn at the fuel inlet is different, and there is one vent tube where my other carbs have two. It’s also super crispy and in need of a major wash. It will be my bench reference and possibly a source of spare parts.
The first order of business is to arm myself with knowledge. I downloaded a series of getting-to-know-you videos from YouTube where a gentleman steps through the features of the TQ, and another where he goes through the steps of rebuilding one. I’ve got the original ’72 Chrysler TQ service manual, an updated ’82 Federal Mogul manual, and the Dave Emanuel bible.
The first order of business is to clean them both, which will require a bucket of Simple Green and a couple cans of carb cleaner, which I’ll pick up this weekend. Then it’s on to the teardown.
I thought I might get out and shoot a couple of pictures of the Scout with the changing leaves in the background before they all got blown away. It was a good thing I did, because they all got blown away today.
Wow, it’s been several months since I’ve updated here. There really hasn’t been much to add; Peer Pressure has been running reliably and well all summer and I haven’t had a whole lot of time to make any upgrades or do any serious work. About all I’ve done is add a bicycle quick release to the underside of the rear seat. I broke down last weekend and put the hardtop on, which was hard because it was 80˚ on both days. Today was 60˚, and there’s nothing more uncomfortable than wrestling a 300-lb. pile of metal in the middle of November.
I am looking at one of the Champion aluminum radiators to replace the original one I’ve got; the outlet on the filler neck to the overflow tank came to me disconnected where the copper had been brazed. Mr. Scout has one in Chewbacca and says it works great. I may also buy a rebuild kit for my spare Thermoquad and tackle that inside over the winter months. (I’ve been saying that for three years now…)
I really don’t have much to update here. Peer Pressure has been getting regular exercise each weekend and running like a champ, if not a little rich. I had 20 free minutes last weekend and was able to get a bunch of vise grips on the seat belt bolts in the bed so that I could loosen and spin them 180˚ so that they’d be easier for Finn to grab. I did loosen the bolts on the Tuffy console to shift it forward but it didn’t budge. The bolts are long enough that there’s no adjustment possible, so I’m going to need to drill three new holes in the bottom of the console to get it to move. This will allow for the rear seat to fold and tumble easily.
Amazon just delivered this huge tome to the house: the International Scout Encyclopedia, co-written by the owner of Super Scout Specialists, the preeminent IH Light Line dealer. I’ve skimmed the first chapter so far, and it’s a trove of amazing pictures, history, and trivia.
I got impatient this afternoon. I had about 1/2 hour of free time, so I looked around the basement for some scrap metal I could use to build a temporary repair for the throttle bracket. Spying a used IKEA drawer rail from Finn’s dresser (a couple of years ago she leaned on the open drawer with enough force to bend the rollers off the rail, so I had to get replacements from the store and fix it), I measured it in place, then took a hacksaw and lopped off about 4″ at the end. After drilling a hole in the middle, I mounted it to the bracket and then mounted the cable bracket to the end–giving me another 2″ of slack in the throttle cable. I fired it up and the clutch acceleration problem is gone. To celebrate, Finn and I loaded it up and drove to the pool, where we swam until darkness, and then we drove home under a sky full of stars.
Later this summer, I’m going to fabricate a cleaner, more permanent solution. But we’re back on the road, and that’s all I care about.
I got the accelerator cable in on Friday, and after breakfast on Saturday morning I went outside to put it in. It’s fairly straightforward and went in without too much hassle, once I realized the loop molded into the cable wasn’t supposed to hook over the top of the bracket, but used to screw in (and provide room for adjustment) on the bracket itself. The cable hooked right up, and in about 10 minutes I was ready to fire it up and go for a test drive. But when I put the clutch in, the engine revved.
It turns out this isn’t an uncommon problem; what happens is that the cable is too tight on the carb, and the clutch linkage at the pedals travels up the firewall right next to the accelerator. When I push the clutch in, it forces the throttle linkage backwards, revving the engine. Problem is, I’ve got no play at all on the bracket. The cable is pushed as far forward (towards the carburetor) as possible; there’s nothing else. The arms on the carb aren’t adjustable, and there’s no other allowance for adjustment in the cable itself.
I looked in the fittings and bracketry that came with my second engine, but there’s no spare there. So I’m going to fabricate a U-shaped piece of metal with two holes. One side will go on the bracket and the other will hold the cable, and I’ll build in room for forward adjustment.
In other news, Finn and I drove to White Marsh to visit a guy who had an original IH Service Manual for sale on Craigslist. I have the new reprints from Super Scout Specialists, and they’re great, but I couldn’t pass this up. It’s softbound but 3-hole punched, so now I’ve got to keep my eye out for a 1 1/2″ red binder to put it in.
In doing the preliminary research on my carburetor, I stumbled upon a 16-part video series detailing the process of rebuilding a Thermoquad, which I downloaded for future reference.
Driving back from a yard sale on Saturday morning, the accelerator pedal dropped to the floor, again. Since I’ve owned Peer Pressure, I’ve had intermittent problems with the throttle cable, which was originally jury-rigged to the engine block with an automatic cable bracket. My friend Alan swapped me that for a manual bracket, but the cable itself was held to the bracket with a rubber-grommeted clip. When the engine heats up, the grommet gets slippery and the cable slips out of it. Usually this is a 5-minute fix, but on Saturday the grommet disintegrated in my hand as I was refastening it. With Finn waiting in the back seat, I jury-rigged the cable with some zip ties and we made it home under our own power.
On the phone with Super Scout Specialists, I learned that I have the wrong cable completely. The one I’m supposed to have is manufactured with a loop that goes around the bracket and held in place by the clip, so I ordered the correct part last night after investigating. I’ll have to carve out time to install it, based on when it gets here.
And I was thrilled last week when Bill Caswell started following me on Instagram!
Also, I haven’t forgotten about this. It’s just that they came out a LOT smaller than I thought they would. I’m going to get a new set ordered in the spring, and then I will send them along to you, friends.