The GMT400 thread (88-98 GM full-size trucks)

In reply to Cousin_Eddie (Forum Supporter) :

I will be in DFW in December for work.  Can you hold them until then?  That'd be huge!  Thanks for answering this question.  
 

Next question my OBS is a 91 TBI 305.  A 350 seems to be pricey.  A good better 350 like a Camaro or Vette L98 seems expensive too.  A Vortec 350 even more expensive.  You know what's cheaper a 5.3 LS engine.  The swap seems pretty straight forward and my wiring harness is in sad shape anyway.  So will the 5.3 work with my 4 spd auto or do I really need a 2WD 4L60E?  My truck could be a 700R4 or a 4L60 from what I've read.  I know I will need mounts and exhaust work plus wiring, but I can do that.  

In reply to AnthonyGS (Forum Supporter) :

I think there is one bolt difference in the bellhousing, and it can be left out.  The only other complicating factors I could think of are maybe needing a different flexplate, or a spacer for it, and some way to get the TV cable to work.  I am sure both of those have already been figured out by the aftermarket.

In reply to eastsideTim :

I've seen the spacer and flex plate you mention.  I was wondering about the kick down cable though.  I'm leaning towards a budget 5.3 swap and adding an electronically controlled trans later.  The 5.3 in my wife's Tahoe really does well.  An older version in my OBS would be awesome.  

In reply to AnthonyGS (Forum Supporter) :

From what I remember Patrick telling me, there is no difference between a 700r4 and 4L60(non-E), GM just changed the name.

In reply to Pete Gossett (Forum Supporter) :

That is my understanding too.

What does everyone like for rear shocks for these? The, I'm guessing, stock with coil helpers on my half ton are getting tired.

Air shocks maybe? It's a work truck and I put 1100 pounds in it often

In reply to Antihero :

If it has coil helpers, they aren't stock.

I have stock replacement Bilsteins that work well on my K1500. Honorable mention goes to AC Delco replacements which I had on my C1500. They ride better but I found to be too soft for heavy loads; not sure if they are still cheap but they used to be. Had KYBs, Monroe heavy duty, and Gabriels on various other trucks and all were either very soft or started leaking within 10k miles. Of those cheap non-Delco options, if I had to pick one it would be the Monroe HDs.

I don't really like any of the all-in-one air shocks I've tried - they generally seem to have poor damping and the bag part only lasted a year or two before leaking. There are other separate bag options that work better and last longer, or get one of the tall elastomer bump stops out of a newer GMT800 truck to help increase the rate as it compresses. I was happiest with a stiffer set of leaf springs (got mine from SD Truck Springs I think) combined with the elastomer bump stops.

Yes, I have spent way too much money trying different things on my GMT400s.

gearheadE30 said:

In reply to Antihero :

If it has coil helpers, they aren't stock.

I have stock replacement Bilsteins that work well on my K1500. Honorable mention goes to AC Delco replacements which I had on my C1500. They ride better but I found to be too soft for heavy loads; not sure if they are still cheap but they used to be. Had KYBs, Monroe heavy duty, and Gabriels on various other trucks and all were either very soft or started leaking within 10k miles. Of those cheap non-Delco options, if I had to pick one it would be the Monroe HDs.

I don't really like any of the all-in-one air shocks I've tried - they generally seem to have poor damping and the bag part only lasted a year or two before leaking. There are other separate bag options that work better and last longer, or get one of the tall elastomer bump stops out of a newer GMT800 truck to help increase the rate as it compresses. I was happiest with a stiffer set of leaf springs (got mine from SD Truck Springs I think) combined with the elastomer bump stops.

Yes, I have spent way too much money trying different things on my GMT400s.

Interesting, I think RockAuto told me it was stock.

I probably should stick to shocks with helpers though.

In reply to Antihero :

Like gearheadE30, I have Bilsteins and stock springs on my K1500.  Handles half ton loads and more (like a yard of top soil or even a yard of stone) just fine. Squats a little, but still likely legal in NC (heh). Bilsteins provide great control.  And if I wanted it stiffer in the back, I too would go with new springs.

I once added shocks with helper coils to a 3/4 ton Suburban. Resulted in sudden oversteer once a specific lateral g value was reached. Air shocks will do the same thing when pumped up a lot.

In reply to AnthonyGS (Forum Supporter) :

You would also need a fuel pump because the tbi system runs about 15 psi. I would hypothesize that a fuel tank and pump from a later vortec gmt400 would bolt up and work because those ran up around 45-55 psi but I cant say for sure that it would be that straight forward. 

Another possible issue would be the ac compressor. They are mounted at the bottom on the 5.3. That may have clearance issues.

In reply to gearheadmb :

You are 100% on all counts.  Conversion brackets and fuel pumps using the Vette filter/regulator seem to be the way to go.

Hmm.....now I'm wondering if I stay away from overloads.

I wouldn't say it's understeer but it drives like a truck.

Of course trying to make a 1997 4wd truck with a lumber rack handle better with less oversteer is the most GRM thing ever too

In reply to gearheadmb :

Yeah, the AC compressor wants to occupy the same space as the frame rail on the passenger side. Not that big a deal, the aftermarket has numerous solutions for conversion brackets. 

For the fuel pump, grab one out of the 96+ Vortec trucks, it's a cheap drop in solution. Corvette filter/FPR is only necessary if you get a donor motor with a returnless fuel rail, most of the early gen III truck motors were return-style.

Completely forgot about the fuel pump.  For my S10, I just went with an aftermarket 255 LPH pump, and installed it in the stock sender assembly.  I replumbed most of the fuel system, but that was due to space constraints in the smaller chassis.  My 92 S10 4.3 TBI and the 2001 GMC Sierra I pulled the LQ4 from even have the same part number for the fuel filter.

Fresh detail, paint correction and ceramic.

Anyone got a good source for the sport mirrors or even the newer medium mirrors that are actually good quality and don't shake?

Getting a random number 6 cyl misfire code and a Bank 2 number 1 O2 sensor slow response code. Replaced the spark plugs and wires and still getting both codes so I'm assuming they are connected somehow. Spark plugs and wires were ancient so that was a good thing anyway.

But took a look at the O2 sensor and apparently they decided to put it in the worst place ever. Also apparently it's something like a 21.5mm because it's not a 7/8ths, not a 22mm either. It's also horrifically seized up, so what should be an easy job is apparently gonna be annoying. A couple runs of MAAP torch and wd40 has resulted in nothing, so yay.

It was supposed to be a 5 min easy job dammit

No real updates on the big diesel. I did finally change the fuel filter and oil, and cleaned it inside and out for the first time since I've owned it. Running well at 220k miles.

Have always wanted a crew cab long bed DRW gmt400... with the denali Escalade front end. 
 

this one popped up on fb market place a few months ago so I finally bought it  in December so I can save it. At one time it was loved,  it it's been neglected and El cheapod for a while. 
 

the good. It's solid, it runs, everything works. it had good parts used in the conversion. 
caddy tails, Sir micheals roll pan, milled alcoas, has a working us gear /Doug Nash overdrive, shaved handles all around with 60lb solenoids, static drop with helper bags amd cnotch etc. 

the bad:it was a WT so no power windows or mirrors and had some kind of bucket seats bolted to bench seat frame in the front. It was painted red correctly but the red is sheedlingclear and then black was added later when it was denali clip converted. 
 

what I've done so far to it. 
 

pulled yard and yards of old unused wiring out of it, including some lamp cord being used as wiring for god knows what. once upon a time it had a quarter shell and power tonneau, both now gone. It had a busted trailer brake module in it I removed and some other ghetto fab stuff I undid and redid right, like using a real gmt 400 fog switch instead of lighted rocker etc. 

I adapted the aftermarket bucket seats to OEM power bucket bases in the front, bought a used denali console and painted it SEM light neutral like the gmt800 Escalades with plans to later repaint the rest of the plastics the same color, added Escalade surround and cluster and the autodim compass/temp mirror and visors (re-covered) from a local denali,  double din conversion with Xm dvd and front and rear cameras, upgraded the speakers from 5.25 coax to morel 6.5 components, and hope to finish pulling old wiring and put in new carpet. Amd ditched the gmt900 style tow mirrors for some power heated standard gmt400 mirrors. On a tuck this size they look sport enough and the visibility is honestly almost as good. 
 

oh, amd added a repop batwing caddy air cleaner to get rid of the open element filter someone added at some point. 

thats a sweet one, can't wait to follow your progress on it. start a thread!

The longdiesel continues to serve well when called upon. I recently replaced the cracked tail lights with some LED-flavored Amazon specials. I really like them since they look sort of OEM+.

Shortly after that, another crew cab (without a frame) popped up 45 minutes from my house on Marketplace, so I grabbed that to swap some of the nicer parts onto mine.

I've not had the time nor assitance to swap much onto mine so far, but I did get the seats out of the donor and cleaned them up. First step was to remove the absolutely roached front seat from mine and scrub the floor.

New one cleaned and installed:

Despite the lack of headrests, its a much nicer place to be. I need to swap many more parts from the donor as time allows.

Prepping mine for sale, did an ugly patch job on the worst fender so the flares have something to attach to.

Anyone put a 4L80 where a 4L60 was?

Found a 4L80 that appears to have been rebuilt at the junkyard. Truck is a '98, so is my K1500.

I'm thinking my transfer case probably has a smaller input? Driveshafts different length? I know there's a tune and minor wiring repinning needed.