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85 auto to 04 LS6/6 speed, another LS swap (PIC HEAVY!)
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So, the story starts with my 85 automatic that I had almost completely gone through and restored/modified. My dad gave it to me in 2007 for my 30th birthday since he had bought a C5 and let this one sit for a few years, and it was almost ruined with 117k miles, flat-spotted tires and chrome-flaking ZR1 knockoff wheels, faded paint with yellow fiberglass showing, rotten interior, leaking windows and targa top, half dead digital dash, non functional radio, and not having been driven in 4 or 5 years. He knew it was one of my favorite cars as a teenager and knew he didn't want to fix it up himself.
By 2010, I replaced basically the entire interior, installed a custom stereo, replaced or repaired all the electronics, tuned up the engine and removed the emissions, installed a custom exhaust/headers, painted the car, installed ground effects and custom wheels, custom lighting, did a lot of part replacement and maintenance, etc. I was content to daily drive the car like this for a couple years without issue, although ultimately I planned to swap in an LS motor if the original iron head L98 ever died.
In April 2012 I got my chance. I was accelerating to pass a slow moving dump truck on an on-ramp and as the car shifted from redline in 2nd to 3rd, there was a huge grinding noise and the car temporarily lost speed and the engine
freewheeled as though I were in neutral. I limped it home shifting really odd and making a loud clicking noise in 1st gear. I could have gotten a used stock trans or even bought a rebuilt/upgraded one to get back on the road quickly,
but I never liked the fact that it was auto, I never liked the way it shifted, and I didn't really want to put any more money into the L98 setup. So, it was time for the LS swap to begin.
So we'll pick up here, with me pulling out the original engine.
Here's the LS6 engine I started with, from an 04 Corvette Z06, 405hp/400tq. I kind of pieced this together from lots of separate parts bought in advance of the project. The engine has a lot of powdercoated accessories etc. already and has been rebuilt as well. It has an aggressive street camshaft, valvesprings and pushrods. Here I had installed a cable driven throttle body, although later I decided to revert back to the C5 drive by wire throttle setup that originally came on the engine.
I wanted to run a manual transmission, so of course that means I needed a T56. There are newer manual trans options for LS engines, but they are harder to get and even more expensive, and parts may be less common for them. A used T56 can go for anywhere from 1500-2000 depending on how lucky you are and how far away it is located, and often they are 80-120k miles and probably kind of beat up internally since I doubt most LS1 camaro drivers only drive grandma to church and the grocery store on sundays.
I lucked upon a guy right here on CF by the name of Mike85TPI who would custom build a T56 with upgrades for not much more so of course that is the route I went, because I like knowing what I have. Mike built me a custom trans with some upgrades using parts from a c5 corvette and a camaro, and helped me find a stock bellhousing and hardware for it too.
I bought a new LS7 flywheel and clutch set from a vendor on LS1tech.
Apparently the T56 slave cylinders are suspect so of course I went with a new one. I also went with a stainless remote bleed line for the clutch fluid and a heat rejection sleeve for it, since overheating clutch fluid is supposedly a problem with this trans.
I bought used clutch and brake pedals and swapped them in, which was a HUGE pain and probably one of the most difficult parts of the swap. See that big aluminum bar in the back of the pic? See those two bolts way up in there behind the dash? Yeah, those hold the clutch pedal in place, and human hands are NOT meant to go up in there, even laying on your back with the seat out of the car.
The clutch pedal had the rod that pushes the master cylinder worn almost in half, which is apparently a common c4 issue. So, I just removed that rod entirely and welded a bolt in it's place, then used a sandroll to grind the bolt diameter down slightly so that the master cylinder fit it properly.
I had to buy a custom fitting to connect the slave and SS clutch hose, and another to connect the hose to a stock 85 clutch master cyl that I bought new. I also had to buy the 'spacer" between the firewall and slave cylinder, which seems like a questionable design to me...I guess GM just used some off the shelf master cylinder from some other car application and had to doctor it up to fit the corvette, thus the spacer.
Since I wanted to use drive by wire throttle control/throttle body on the LS6 engine, I needed a drive by wire gas pedal, so I bought one from a C5 corvette. But it didn't have a way to bolt to the C4 firewall, it wasn't quite the right shape or length, and the pedal "pad" didn't match the C4 pedals either, so I set about customizing it. Here's the stock C4 pedal. It mounts to the firewall using a special bracket.
You can see the C5 pedal here for comparison.
I cut the bracket off the C4 pedal, and ground down some of the plastic casting to allow me to use it to make a custom mount for the C5 pedal so that it could bolt easily to the C4 firewall in the stock position.
I took the C5 pedal pad off the C5 pedal.
And took the C4 pedal pad off the C4 pedal.
Comparison of the C4 and C5 pedal bracket ends where the pedal pads mount.
I opened up the hole in the C5...
And put the C4 pad onto the C5 pedal.
Here's a piece of sheet metal I cut to serve as a go-between from the C5 pedal mounting holes/bracket and the C4 firewall plastic bracket. I welded a couple bolts in from the backside to serve as studs on which to mount the C5 pedal.
Here's the C4 mounting "bracket" modified a bit.
And here is how they fit together to make an adapter.
Here's the bare C4 firewall where the pedal should go.
I was posting on another internet forum that I was going to do the swap and a guy sent me a message saying that he had some parts that would help me. Turns out he was "jeffvette" from this forum and he already had an LS converted C4 that he was reverting back to <some other older engine> and wanted to sell me the custom mounts etc. he used. Of course I jumped right on the deal. We had some issues with him taking a few months to deliver the parts, but eventually he did give me everything and it helped me a lot.
Included were motor mount adapter plates (they have "vetteworks" stickers on them) which allowed use of the stock C4 motor mounts on the LS engine, I just had to slightly notch the motor mount stands where the motor mounts fit into on the stock subframe about 1/8 of an inch, since the LS is a wider angle block than the SBC and the mounts wouldn't QUITE sit down in there like they were supposed to without removing a little material from the subframe stands.
Also among these parts was a custom T56-to-c4 cbeam adapter that he custom built as well as a stock cbeam with the front holes slotted a bit to mate up with the adapter. He also supplied a custom driveshaft with upgraded spicer ujoints to mate to a D44 rear diff.
Since my auto came with a D36, I knew I needed to upgrade anyway, and the new driveshaft required it (I believe). So I bought a used D44 from a guy on the forum parting out an 88. It had the 3.07 gear which is probably too long for the T56 but for now I left it alone, after cleaning it out and changing in new gear oil and LSD additive. Maybe one day I will change the gear to something more aggressive.
While they were out I had new matching spicer ujoints installed in the rear halfshafts.
And while I had the rear suspension apart I replaced the worn original bushings with these.
I finally dropped the engine in, and then raised the transmission in place for a test fit.
I could tell then that as suspected, the heater core box would have to be cut out and re-fiberglassed to clear the passenger rear ignition coil (the head and valve cover actually cleared, slightly, but not enough for comfort). So, I went ahead and modified that with the engine out of the way. I basically took the piece I cut out and flipped it inside out, then reattached it and glassed over the whole thing.
While the engine was out I also wanted to find a way to attach the stock a/c compressor to the new engine and have it align with the engine's belt drive. The alternative would have been to use a stock LS low-mount compressor and bracket/belt setup, but that would have required more extensive changes to the C4's front subframe, and expensive custom made lines and fittings. So, I rigged up the accessory drive using some extra pullies and spacers, to accomodate the stock 85 compressor.
So here's the stock compressor mounted on the engine. I ground a relief in the pulley to allow easier access to a bolt which basically goes through the compressor and directly into the passenger cylinder head without any sort of bracket.
I customized another bolt and cut up a smog pump bracket from an rx7 to make the upper mounting bracket for the compressor which also serves as the main belt tensioner since the LS auto-tensioner had to be removed to make room for the compressor.
Here's a picture showing the alignment of the compressor with the stock LS auto-tensioner mocked up in it's original place, to show how closely it matches.
Then all I had to do was rig up the idler pulleys. I used a cut-down piston wristpin from a grenaded daewoo engine I replaced for my sister in law as a spacer for this pulley, which is just the idler from the LS stock tensioner removed from it's tensioner bracket, and bolted to one of the stock waterpump mounting ears that the tensioner used to bolt to.
I had to FORCE the cbeam and driveshaft into place...I thought I was going to break the car doing so. Not enough room to get the cbeam between the diff, trans, and tunnel. But, it was that way with the stock trans/cbeam/driveshaft too...kind of a bad design IMO.
So, everything looks good on the engine in terms of clearance at this point.
Now that I know there's enough room, I need to mount my oil pressure sending unit. I'm reusing the stock one from the C4 engine so that my stock dash gauge will read normally. It will not even know that it isn't the stock engine. So I had to buy an adapter fitting to go into the LS block, and then a 45* fitting to angle the sending unit to clear the LS intake.
To keep the stock oil temp gauge working I retained that sensor from the original engine and then installed it on the new engine. The LS car engines without oil coolers have a bypass fitting on the oil pan just above the filter that is perfect for this, in fact the casting is already there, you just have to drill out the hole and tap it.
To keep the stock coolant temp gauge functional, I modified the stock temp sensor from the old engine to fit the passenger side head of the LS motor which had an unused port. I had to grind the sensor down and re-tap the threads.
Once the engine and trans were hooked up in the car I noted that the front of the oil pan just touched the engine subframe, and I decided to notch it out although it probably wouldn't have damaged anything to leave it as-is. So I jacked up the motor and removed the motor mounts to give me enough room to get in there without removing the engine. Some of the other motor mounts available that set the engine back a couple extra inches near the firewall would probably have removed the need to do this, but I'd rather have extra room in the back to work and plumb stuff, personally.
For the fuel system, I went with a stock c5 corvette fuel filter. This converts the supply and return in the C4 to a single supply for the LS engine, since the LS fuel rail does not use a regulator or return line. The c5 filter has the regulator built in. As you can see I've installed two custom fittings on the fuel filter. I put it in the stock location.
Here are the stock fuel lines on the C4.
Now add adapter fittings...
Here's the hookup at the engine made using -6an stainless hose and custom fittings.
I tied it to the brake lines running down to the bottom of the car and wrapped the brake and fuel line with fiberglass header wrap to keep some of the heat out of them.
And a new walbro 255 fuel pump to feed the new engine.
For the coolant system, I took some advice from chaos' LS swap thread, and bought the dayco heater core hoses.
The C4 heater core pipes had ends that stuck out and would interfere with the install, so I had to remove the pipe set and cut down the ends.
As you can see, the heater core hoses rub on this metal frame, so I decided to notch it out which gave me plenty of room. I wrapped the one hose with a bit of leftover fiberglass header wrap, to protect it from heat as it passed nearby to the header. As you can see I also broke off one of my a/c hard lines from the compressor flange while trying to bend and tweak them slightly for clearance, which I later had to have welded back on.
A stock 98-02 camaro upper radiator hose fit the engine and radiator perfectly. I used a stock C5 lower radiator hose, cut down slightly, and it fit perfectly.
As you can see, the hose is really close to rubbing on this metal frame, so I put a plastic boot around the hose to protect it.
The LS engine uses a "steam vent" from the engine which used to go to a fitting on the LS radiator, which the C4 radiator does not have. Rather than screw around with adapter fittings etc. for the radiator hose, I just tapped the top of the water pump and routed the steam hose there.
I reused the original C4 air filter, and made a bridge to the LS throttle body using some 4" silicone coupler cut in half and some dryer hose clamps. The LS 5 wire MAF is in the middle.
The power steering was actually easy to hook up. The C5 power steering high pressure line will screw right into the C4 rack with only slight bending and proper positioning, and then you have the low pressure line which just clamps on to the reservoir and rack with 3/8 hose and clamps.
Here's a shot of the clearance between the crank pulley and the subframe...JUST enough to get a belt on and off the crank pulley if needed.
For exhaust, I already had a 92-96 style magnaflow full system which I kept in place.
I went with the Melrose C4/LS swap headers, ceramic coated, purchased via Jody at Vettaid.
The headers went in and fit perfectly, although there is a bolt on each frame rail that comes REALLY close to hitting the headers, and if I had it to do over again I'd probably remove or grind down those bolts. But then there was a major problem...I could not install the drivers side oxygen sensor, and the passenger side was SUPER close to the transmission. It seemed like the bungs had been placed in the wrong spot.
After several groups of emailed pictures, emails and calls back and forth among myself, Jody, and Dave @ Melrose, it seemed that at some point Melrose's original design for the headers was changed and the sensor bungs were placed in the wrong position. Jody told me to send the headers back to Melrose for another set which would hopefully have the sensor bungs in the correct spot. I talked them into shipping me a set of replacements along with a return label for the originals with the defective bung location.
So a week later a set of replacements show up, but Melrose sent me 350 headers, not LS1 headers. More calls, emails, and pictures ensue. I use the return label to send the 350 headers back to Melrose, and again ask for a replacement set of LS headers. A week later another replacement set shows up, and they are LS1 headers, yay. But they have the sensor bungs in the same positions on the sides of the pipes, boo. More emails, pictures, and calls. Dave at Melrose gave me the option to wait a couple weeks for a "new batch" of headers to come back from the ceramic coater, which "should" have the bungs in the right position.
Two weeks later Dave calls me to let me know that he just picked them up and they are all wrong as well. HE quotes me 4-6 weeks for building a new set of headers with the bungs in the correct place, ceramic coating, and shipping. I tell him to just send me a set of bungs and plugs (for the old bungs) and I'll weld them on myself in the right spot, so that's what we do.
I had to cut a small notch out of the rear of the passenger side header to clear the coolant temp sensor I modified and installed there earlier.
I finally get the headers installed and fitting properly, and connected to the magnaflow exhaust after cutting off one front flange and modifying the pipes slightly.
Here's what I wound up with for the shifter. I had cut an extra large hole to accomodate the trans and the CAGS solenoid sticking out of the side. You can also see the wiring harness plug that used to go to the auto trans shifter.
After trimming the inside console plastic...
I initially bought an aftermarket short shifter the same as what Mike85TPI used on his swap, but as it turned out the base of the shifter stuck up too far and hit the 84-89 style shifter plate/bezel trim and couldn't be used without a more major modification to the shifter area that I didn't want to make. I also really didn't want a short shifter since I hate notchy shifts.
So I bought a couple of stock 98-02 camaro shifters for 20 bucks off LS1tech and experimented with them. I needed the shifter offset to the rear and the left to place it in the middle of the shift gate of my 84-89 console plate. To accomplish this, I cut the shifter in half near it's base just above the pivot point while leaving enough height so that I could move the shifter into all gears and not hit the transmission, and welded on a metal bracket to offset the handle, then welded the handle back onto the bracket. Here's what I wound up with, and believe it or not, it fits the car like it was made for it, sits exactly in the middle of the gate, and shifts perfectly, and it feels better to me than that short shifter did.
I did notice that it was a little flexible going into reverse, so I later welded a long bolt between the shift stick and the base/pivot point as a gusset for strength so that my welded-in bracket wouldn't flex anymore, and it worked great.
In order to get power through the ignition switch circuit, I had to jumper these wires in the old auto shifter plug.
I also noticed that with the cable removed that used to go between the shifter and steering column, I had issues with the ignition switch locking in place and not letting me take the key out, because of the automatic safety stuff. So I had to find the mechanism that the shift cable used to move, hold it closed and verify that the ignition switched worked freely at all times, then I just tacked a bolt in place on the column to hold it there.
I used the stock clutch interlock switch on the clutch pedal and ran my ignition circuit wires through it, so that you have to push the clutch pedal to start the car.
The yellow wire is the one I interrupted with the switch to accomplish this.
So by now you're probably wondering how I handled one of the most difficult parts of such a swap...the wiring. I could have bought a used stock harness from a corvette or camaro and used it as the basis to run the engine, and have to sort out which wires were not needed for an emissions-stripped LS engine, then figure out which wires were needed to interface with various parts of the car in order for everything to work, for about $250-400 or so. Or I could have even bought a standardized aftermarket "painless" wiring harness to suit LS engines and used that with the swap for 450-500. I was capable of either of those options, but I run a full time shop working on cars for other people and the last thing I want to have to do at the end of a 10-12 hour day is to try and do major wiring work on my own project for free. So, I was trying to be lazy about it and throw money at the project to save time, and I decided to have a harness custom built for my car by a corvette specialist who had done this before in the hopes of minimizing the time required from me.
I had of course read the LS1 C4 swap article published some years ago, and in it the harness work was done by Current Performance and I seem to recall that it was said to be basically "plug and play" with a few connections made to the interior of the car. I sent an email explaining to them what I was looking to do and was quoted a couple of months and about a grand to build a similar harness. The response was none too descriptive and didn't inspire my confidence, so I went shopping around elsewhere.
I stumbled upon Vettaid, who claimed to do the same work and be a corvette specialist, so I thought, "here is my ticket". I sent a similar email stating my project specs and intentions, and my wish for as much of a plug and play harness as possible, requiring as little intervention from me as possible. HE asked that I call him to further explain the project, although I thought that I had gone into great detail as to the specs of the swap.
He told me he could do what I wanted and deliver a harness to me in 3-4 weeks which would be accompanied by a set of instructions and labels for each wire that required manual connection to the car by me, so I committed to the build. He also told me that he could supply me with the tach adapter to drive the stock dash gauges, but he "wasn't sure" about the need for a speedometer adapter (later, my own research indicated that this was an absolute requirement as the signals are completely different).
Even though his website quoted C4 LSx custom harnesses built to order for (at the time) $650, and still as low as $685 as of today, he quoted me $850 for the harness via phone. Now I am pretty sure that the tach adapter box from dakota which he supplied was included in that price, which would have accounted for about $80-100 of that discrepancy depending on how much he is marking it up. The rest, I am unsure about. I thought that perhaps I was getting some custom harness built a few notches above a standard conversion harness per my request, so I was fine with that, if it saved me the time of tracing down wires and reading wiring diagrams. I also paid him an extra $50 for a TCM (throttle control module) cable to go between the C5 gas pedal and the C5 TCM that I had to buy separately, and $20 more for a custom bracket that he told me he makes to mount the C5 TCM in the C4 dash where the old C4 PCM used to go. This was June 19, 2012.
I continue to supply Jody/Vettaid with the technical info he requests immediately, and at times I kind of wonder if he knows as much about C4's as he claims, since he's asking me stuff about the car that a specialist should already know. But, I chalk it up to the differences between years and models being many, and give him the details he asks about. Sometimes I would send emails with my own technical questions and they would get answered with one or two lines that didn't really answer my questions, other times they would not get a response at all. Weeks go by, the original early august deadline passes, I request more info, he gives me a new deadline of labor day, that deadline passes with no word and again I have to keep after him. I finally received the harness Sep 13. The custom TCM bracket I paid extra for was not in the box, so when I contacted him to ask why, he says that he forgot about it, he thinks he has some being made up, and will send me one whenever he gets them. To my knowledge, I have never received that bracket yet.
The harness itself appeared to be expertly manufactured, and I was very pleased with the quality of the wiring, connections, and plugs. Most of the engine-side plugs were labeled nicely.
I did notice that both front oxygen sensor plugs were different than the sensors I bought. I bought new upstream bosch oxygen sensors for a 2004 corvette Z06 based on application data from autozone.com and bosch's own website, and I had specified in the harness order that the engine was a 2004 corvette engine. The harness came with flat plugs for the sensors, while the sensors themselves had square plugs. I wound up changing the oxygen sensors to match the plugs.
Also, the plug for the reverse light switch did not match, even though I bought a new reverse light switch for a 1998 camaro and I specified in the harness order that the transmission would be a 98-02 camaro T56. So, I had to pay like 12 bucks to a seller on ebay for the proper plug, and cut/solder it onto the Vettaid harness. In this pic, the plug is the one that came on the vettaid harness, the right sensor is the new 98-02 camaro sensor (which application charts list as the correct GM backup switch for most RWD car transmissions back to the mid 80's, so it would seem to be a common/standardized plug although Vettaid claims never to have seen it), and the top sensor is the one that came spare with my transmission and is most likely from a C5 corvette, although I did not try to use it because I couldn't identify it (and neither could he).
During the phone conversation and ordering process, I had asked about the T56's CAGS and reverse lockout solenoids, and he indicated to me that "I think most people just eliminate them". When it came time to get my swap working, I found it impossible to shift into reverse because the solenoid was not being actuated my the PCM...because THERE WAS NO WIRING PRESENT IN THE HARNESS TO OPERATE THE SOLENOID. As I later found out, the PCM MUST control the solenoid in order to shift into reverse AT ALL. I didn't know this going into the swap, but it seems to me that a corvette wiring specialist should have known about this and been able to not only advise me about it, but put the provision into the custom harness. So, again, here I am paying 12 dollars extra to an ebay harness connector seller for the correct plug for the reverse lockout solenoid, another 4 dollars for a PCM pin to put into the blank hole in the PCM plug, and running new wires in my new $850 custom built harness between the lockout solenoid on the shifter and the PCM so that I can shift my car into reverse. Brilliant, more of my time wasted. (I found this out near the end of the wiring and swap work, and by this time I think I was so tired of it that I did not even take a pic of running the extra wires and connector.)