1975 GMC Suburban
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This is my parts-hauler and our general family vehicle. It's got the room to haul all of us plus our gear. It's also more manly than a weenie 4-door mid-size car. This page is just an attempt to document what I've done to it - because as anyone who knows me will attest - I can never leave things the way I found them and I've always got a plan to improve things in some way. Sometimes I actually manage to improve things somewhat.


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  • Basic Specs:
    • 350 cid V8 engine
    • 4bbl carb
    • TH400 transmission
    • 12-bolt rear axle w/4.11 ratio

  • Factory options:
    • Power Steering
    • Power Brakes
    • Front and Rear Air Conditioning (Non-functional due to leaky coolant lines to the rear AC unit)
    • Oil Cooler (Currently disconnected - the factory adaptor places the oil filter too close to the drivers side header collector)
    • Cruise Control
    • Full Instrumentation (minus tachometer)
    • Power Operated Rear Window

  • Options and Custom Modifications I have added and/or am in the process of adding:
    • TH700R4 Overdrive Transmission w/Lockup Torque Converter
    • Factory Tachometer
    • Headers w/ 3" Collectors
    • Dual Exhaust w/ "H-Pipe" Crossover
    • Holley 600 CFM carb
    • Edelbrock Performer Intake Manifold (w/EGR)
    • Vacuum Gauge
    • Transmission Temperature Gauge

  • Future Options and Modifications (aka, wishful thinking):
    • 3-point Retractable Front Seat Belts
    • Rear Window Defogger
    • Power Windows
    • Power Door Locks
    • Posi-traction Rear Axle
    • 93 Amp alternator
    • Remote Oil Filter & re-hookup Oil Cooler
    • Fix AC
    • Fix Cruise Control
    • New Window and Door Seals
    • Delay Wipers


Related Pages

As individual parts of this page get too long, I move them off to separate pages to keep things more manageable. Here's the current list of the separate pages.



Here's a photo of my spiffy new manifold I got on eBay and installed a while back. I even stayed emissions-legal and went with an EGR manifold.

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After many miles of service, the motor developed a rod knock, but I caught it early and stopped driving the truck. Rebuild time! It needed a rebuild pretty badly, so of course I captured it in graphic and descriptive form for all to see - check out the page with all the gory details of the rebuild. At the end is a really good section on the process I went through to get the engine tuned properly after I installed it - very good reading for someone attempting this for the first time - like I did here. :-)

After running the truck for a while (about 15,000-20,000 miles) after the rebuild, it started running really bad, so I dove in for a basic tune-up and to fix the problem. Spraying some carb cleaner around the intake manifold revealed a intake gasket leak in the area where the #1 and #3 intake runners went into the drivers side head. Time for an intake gasket replacement! So, I popped the manifold off, cleaned it up, and installed a new spacer under the carb to prevent heat transfer. At least I got a chance to see how the intake valley area had fared after running the engine for a while - pretty well apparently.

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After the rebuild I had a pretty greasy engine compartment, and I eventually traced the mysterious oil leak down to a missing bolt. Go figure. Easy fix, but everything is pretty darned greasy now - which is a bummer because I spent so much time cleaning stuff before putting the motor back into the truck.

After the truck sat for a while to replace the trans (see below) the carb was gummed up and in dire need of a rebuild, and I didn't have time to do it. So, I paid a local carb shop $400 to rebuild it - and "wow!" is all I can say. The truck runs damned near perfectly now - the only complaint I have is on initial cold startup it wants to stall the very first time you put it into gear. As soon as it gets into gear once, it settles down and does fine. The idle is perfect, power is good, my wife's only comment after test driving it was "it didn't try to stall when I came up to a stop sign". I'll take that as a good sign. The shop that did the work was Carburetor Connection in Kirkland, WA and they'll be getting plenty of repeat business from me in the future. It was expensive, but the results speak for themselves. I would have spent weeks messing around with the carb and never gotten it to run that good.


Shifty Business

It's always something. Now, the transmission is going south on me. It makes bad grinding noises that get worse when you put it in gear and the idle drops down so low it almost stalls the motor. Time for an upgrade! I've decided to swap my non-overdrive TH400 transmission for a TH700R4 overdrive transmission. The swap is nearly a bolt-in because the TH700R4 is similar in size to the TH400 and it uses the Chevy bellhousing bolt pattern so it will bolt right up to my existing Chevy 350 engine. I am collecting all of the relevant details for the transmission swap along with figuring out how to build a custom TV cable bracket for the carb and the lockup TCC wiring on separate pages to keep this page from getting too cluttered.

At one point I found and purchased an add-on Doug Nash Overdrive unit with the intention of installing it and getting overdrive that way. I never got around to it, and with the TH700R4 swap, it was no longer needed, so it was sold to help recoup some of the cost of the swap. The pictures I took of the unit, wiring, and paperwork to provide to the buyer are below. It was a neat little unit based on the research I did - pretty durable and commonly used in RV/Motorhome applications, though the competition said it had a habit of running hot under extended load while in overdrive. The descriptions I read also indicated the shift was also comparatively slow - shifting into and out of overdrive was more like shifting a truck transmission. It is essentially a two speed manual transmission (1:1 and overdrive) with an electrically operated shifter mechanism. It was not going to help you win any dragstrip races if you were shifting into and out of overdrive, but then again, that's not what it was designed for, so that's fine. I researched a similar product from Gear Vendors which is intended for fast shifts. That one is basically a small automatic transmission with only two gears - 1:1 and either a 22% overdrive or a 22% underdrive. Much more expensive, but supposedly much better for performance use. Like $2000+ more expensive, IIRC. I bought the TH700R4 used for $350. I guess that makes me a low-budget Car Craft sort of guy. Like every other married gearhead, I tell the wife it's making the best use of what little budget I have so she thinks I'm responsible with money and doesn't cut the parts budget even further, and then I spend lots of time secretly wishing I could spend $200,000+ on my automotive toys and get the stuff I really want...

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I managed to lose my transmission support plate for my floor jack, so after cleaning out the entire garage to try and find it, I finally had to give in and buy a new one. The one I got is TCI part number 896500 and it's called a "transmission cradle" in the tool description. (NOTE: The links to other sites go stale over time, so you may need to search for it yourself on Jegs.com.) Pulling the trans out was fun, in particular I thought the dipstick assembly would come out with the trans - but no such luck. It separated from the trans at the worst possible time - right when I was balancing the trans on the jack - and spouted a geyser of ATF down my driveway. Yuck. Other than that, the old transmission came out with minimal trauma and no loss of any extremities, though I did need a good shower afterwards.

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I found a TH700R4 transmission out of a 1983 Caprice that had all the right mounting provisions to replace my original TH400 with minimal trauma, so I bought it and dove right in. I did some rewiring work on the transmission internals so the TCC would work right in my non-computer-controlled application and figured out how to wire up my own TCC lockup controls. I installed a drain plug into the transmission pan while I was in there along with slapping in a new filter.

While I was at the junkyard hunting down the vacuum switch and wiring for the TCC lockup control, I even scored an overdrive-style shift indicator plate from a later-model Chevy pickup that bolted right in place of my original one. It's the little things like this that make swaps like this "complete" and pretty trick. The font they used on the later model indicators is a bit different, but it's close enough that only someone as nit-picky as me would notice, and it's close enough that even I may stop noticing it after a while.

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Here are some rare photos of me working on one of my vehicles. I usually take the pictures, and that means almost no pictures of "work in progress". Deb was taking photos of Caitlin, so she snapped a few of my ugly mug under the truck. In these photos I was working on getting the transmission cooler lines hooked up to the transmission, and the combination of things being '"just different enough" between a TH400 and a TH700R4 and me having inadvertently tweaked the lines during some previous work made for a most frustrating experience. I could only fit one hand up to where the lines screwed into the transmission case, and that was only when I was laying a certain way under the truck. Add in that getting a wrench on the fitting was next to impossible and that when you did, you only got 1/4 turn out of it, and well, you get the idea.  Caitlin was within earshot, so I had to watch my mouth. I managed to not teach her any new words, so that's good. But, by the time I was done, I was filthy up to my elbows and the trans cooler lines managed to find enough fluid left to drip onto my chest. I hate transmission fluid. It's times like these that I so want a lift to do work like this in a more comfortable manner...

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While getting the truck started up again after all of the transmission and wiring work, I managed to (once again) prove true two things that are universal when working on cars. 1) It's the little stuff that causes the biggest problems, and 2) If something can go wrong, it will. In the "little stuff" category, everything went perfect until the point I tried to start the truck - the engine turned over fine and seemed like it should start - no luck. After a hour fooling around with it I managed to figure out that I had no spark but that I did have power to the HEI unit. Huh? Then I realized I had forgotten to plug in the little three wire harness that goes from the distributor up to the cap to get power down to the HEI unit and a signal back up to the coil. Doh! In the "anything can go wrong" category, once I got it started I realized it was dribbling fuel from the soft line that runs from the hard line on the frame over to the fuel pump. It turns out that when I was making the final hookup to the new grounding post I installed on the frame, I had to push the fuel line out of the way so I could tighten the mounting bolt. In doing so, the fuel hose was old, hard, and brittle enough to split and cause a leak later on when I started the truck. Another 20 minutes to change that. The morale of this little tale? Double check everything - especially the dumb stuff, and be gentle on old hoses. Acting like a gorilla just breaks things.

I built a custom TV cable bracket with a cruise control cable hookup and it works pretty darned good.

Stuff Left To Do:

  •  Buy required items
    • Low-vacuum switch (for TCC unlock under load)
    • High-vacuum switch (for downhill coast lockup)
    • Trailer brake controller
  •  Wiring
    • Build new O2 sensor wiring harness
    • Build new interior harnesses for gauges, warning lights, switches, etc.
    • Add backup lights to trailer
  •  Install torque converter dust shield
  •  Figure out why I can't get the shifter all the way into 1st gear - adjust, change, or modify parts as needed


Wiring Changes

This section got way too long to be included in this page, to I broke it out into it's own special page. Gauges, TCC lockup wiring, and various other odds and ends are covered there.


Vacuum Lines Galore

I'll also be doing some cleanup on the vacuum lines to help keep things neat. I'm pondering making up some hard lines for various chunks of the vacuum line system and only using regular vacuum hose to bridge the gaps at the ends and to connect to the engine itself. My only problem is figuring out how to make an vacuum-tight T fitting in those hard lines. If I can figure that out, this could be a pretty slick way to handle the vacuum lines. With all the stuff I have, there are a number of vacuum lines already and it's looking kind of messy. It's got power brakes, AC/Heater controls that run on vacuum, a vacuum switch for the AC compressor, one ported and one manifold vacuum switch for the TCC lockup, cruise control that has several vacuum lines running to it, a vacuum gauge, a vacuum port for tuning, the EGR valve, the vacuum advance hookup for the distributor, and the PCV valve. They all require a vacuum line hookup of some kind.


Purchasing Order

This was Car #9. It was bought as a replacement family hauler after the demise of our 1980 Ford Fairmont Station Wagon. This was the first vehicle I bought from a car dealer, and the first one I financed. My first truck and tow-capable vehicle. Later to become my first engine rebuild and transmission swap (as opposed to a straight transmission replacement).

Comments? Kudos? Got some parts you'd like to buy/sell/barter/swap? Nasty comments about my web page so far? You can email Mike or Debbie.

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Page last updated 01/02/2009 01:51:39 PM