Lessons Learned While Servicing a C4

[Mark E.]

I wanted to share a couple of lessons learned while servicing my C4 which may be helpful to other C4 newbies. During the past weeks, I've been servicing the new-to-me 1993 with 16,000 miles:

Changed fluids: Engine oil, coolant, brake, clutch, transmission, rear axle. Straight forward, but learn how to purge air from the cooling system.

Changed filters: Oil filter, air filter, fuel filter, A.I.R. pump filter. The AIR pump filter was gone with only a few foam remnants remaining around the pump's inlet. I didn't realize a cone-shaped foam filter should be over the inlet until I did some research. I'm now noticing that every C4 with an electric AIR pump (LT1, LT4, LT5) I've seen since is also missing this filter. They apparently disintegrate over time. One of the few sources (maybe only) is Corvette Central which I believe they fabricate in-house.

Repaired two Bose amplifiers (shipped to Doctor Don's here in Texas). R&R super easy.

Replaced clutch slave cylinder (leaking). Huge problem with this... see below.

Repaired right headlamp motor gears. The actual gears were okay, but the three plastic spacers in the motor's gear housing had turned to dust. About 3 hours for a first-timer.

Replaced the fuel sending unit. The fuel gauge is now somewhat accurate! Super easy job... comes out from fuel filler hole on top of tank.


Surprise news (to me anyway)- All of these service items, except two, were very easy to perform. In fact easier than the majority of cars I've worked on, and certainly easier than my C3 (try replacing the fuel sending unit or speaker on a 1970).

The two pain-in-the-arse exceptions:

- Bleeding the clutch: Quick and easy, right? Wrong. I couldn't bleed the air out of the system. I spent over an hour bleeding fluid, yet massive amounts of air continued to come out of this short line. I even acquired an adapter for my Motive Power Bleeder, yet more air kept coming out with no improvement. A few days later (with an immobile C4 in my garage) I found a post on the CF forum by a gentleman who said bleeding the clutch is simple: Close the bleeder valve then rapidly push the clutch pedal up and down for a couple of minutes using your hand. He also said it's only necessary to depress the clutch its first 2 inches of travel. This sounded crazy (and the service manual doesn't mention any of this) but since I was desperate, I tried it. AND IT WORKED! A perfectly bled system in two minutes without getting under the car.

- Flushing the cooling system: I followed the service manual procedure- remove knock sensors (where block drain plugs are on other Chevys), remove petcock, drain fluid, flush with water, fill system, run to temperature, let cool, drain. Repeat this process until water comes out clear. It also says "NOTICE: Do Not use chemical flush." Easy enough process but after EIGHT cycles of doing this, the water coming out was still brownish in color. And looking into the surge tank I could see it was coated in a brownish/reddish film that wasn't flushing out. I was getting tired of crawling under the car to remove/install knock sensors.

So I tried something new: "Simple Green Pro HD". Simple Green's website recommends it as an acid free, water based product safe for all cooling systems. It's not an acid so my thinking is it would be safe to use even though Chevy says don't use a "chemical flush". I tried it, and it did not help- the brownish/reddish film was still there.

So I tried another product: "Evapo-Rust Thermocure Coolant System Rust Remover". It claims to be a "water-based solution that is easy-to-use on automotive cooling systems. It is non-corrosive and non-flammable...". This product worked GREAT! After a single draining, the inside of the surge tank looked absolutely clean with no film or residue. Water flushed out clear after this.

Figuring out how to bleed the clutch and flush the cooling system took more time than all the other service items combined. But it's done and the 40th Anniversary is running awesome.

Comments and suggestions welcomed.

[Patrick H.]

Re: Lessons Learned While Servicing a C4

I used Evapo-Rust and a modified water pump on the 63 to remove corrosion. Fill block, put a hose between water pump and intake, and use a drill to circulate the Evapo-Rust.
I suspect that someone had used only water in the system, and it was not kind to any of it.
It did work well, so it's nice to know they make a version just for cooling systems.

[David H.]

Re: Lessons Learned While Servicing a C4

Mark

Thanks for Evapo-Rust Coolant System idea.

Dave

[Kent S.]

Re: Lessons Learned While Servicing a C4

I've used Evapo-Rust to clean many rusty small parts -great product! Didn't realize they made a product for cooling systems so thanks.

[Terry M.]

Re: Lessons Learned While Servicing a C4

Thank you Mark. This information may apply to more vehicles than Corvettes and other generations of Corvette. Excellent post.

[Duke W.]

Re: Lessons Learned While Servicing a C4

- Bleeding the clutch: Quick and easy, right? Wrong. I couldn't bleed the air out of the system. I spent over an hour bleeding fluid, yet massive amounts of air continued to come out of this short line. I even acquired an adapter for my Motive Power Bleeder, yet more air kept coming out with no improvement. A few days later (with an immobile C4 in my garage) I found a post on the CF forum by a gentleman who said bleeding the clutch is simple: Close the bleeder valve then rapidly push the clutch pedal up and down for a couple of minutes using your hand. He also said it's only necessary to depress the clutch its first 2 inches of travel. This sounded crazy (and the service manual doesn't mention any of this) but since I was desperate, I tried it. AND IT WORKED! A perfectly bled system in two minutes without getting under the car.




Figuring out how to bleed the clutch and flush the cooling system took more time than all the other service items combined. But it's done and the 40th Anniversary is running awesome.
.

Bleeding the clutch system on my '88 MBZ 190E 2.6 special order five-speed manual transmission, I had always worked in the conventional way - working the bleed valves on the brake calipers and clutch slave while a helper worked the pedals. Both the brake system and clutch release system share the same reservoir.

About then years ago I had to replace the slave. Now I've got an empty system, so how do I bleed it. I have both the OE service manuals in pdf form and a soft cover Hayes manual based on and English 2.3 four-cylinder, but the clutch release system is basically the same, and it said to connect a hose between the slave bleeder valve and the RH brake caliper valve. Then open the slave bleed valve a half to one turn and "bleed" the RH caliper. This pumps fluid from the bottom and pushes the air up to the top and into the reservoir.

Prior to bleeding the slave I flushed the brake system so the fluid would be fresh. It only took about a half dozen cycles with a helper pushing the brake pedal and me operating the RH caliper to fill the clutch system with fluid.

Duke

[Gary G.]

Re: Lessons Learned While Servicing a C4

One of the lesson learned was the HVAC control unit. I have written a tech article that was shared in the California Chapter news letter. When the buttons no longer want to function it is a simple cleaning of the contacts.

[Mark E.]

Re: Lessons Learned While Servicing a C4

Many clutch master cyls are leaking now. Watch the fluid level, if it goes down, suspect the master cyl. They leak inside the car, behind the carpet, you won't know it unless you look up there from inside the car with the hush panel down.

Thanks for the heads up, Dave. I'll check it out.

Another way to effectively bleed the 89-96 clutch is gravity bleed. Fill the master. Open the bleeder on the sleeve with your drain pan underneath it. Go do something else for awhile, check the pan every now and then. When it is dripping, close the bleeder, and do the pump it up, hold for a minute, release sharply. Shouldn't take more that two cycles. Done.

I tried the two-man method- no go. I tried the gravity method- no go. I tried pressure bleeding- no go. Maybe I didn't give the gravity method enough time, but if pressure bleeding doesn't work it seems gravity wouldn't either. I like the "quickly pump with your hand" method- it's quick, no need to get under the car, and most of all- it works (although I don't really understand why). And I don't understand why bleeding this short, simple system is so difficult to bleed compared to brakes.

[Mark E.]

Re: Lessons Learned While Servicing a C4

One of the lesson learned was the HVAC control unit. I have written a tech article that was shared in the California Chapter news letter. When the buttons no longer want to function it is a simple cleaning of the contacts.

Gary,

Would you share a link to your article? A couple of weeks ago, the "temp down" button stopped working for a few days. I could raise the temperature but not lower it. Then it mysteriously began working again. So something is going on...

[Floyd B.]

Re: Lessons Learned While Servicing a C4

Mark,

Thanks for the post.

>> The AIR pump filter was gone with only a few foam remnants remaining around the pump's inlet. I didn't realize a cone-shaped foam filter should be over the inlet until I did some research. I'm now noticing that every C4 with an electric AIR pump (LT1, LT4, LT5) I've seen since is also missing this filter. They apparently disintegrate over time. One of the few sources (maybe only) is Corvette Central which I believe they fabricate in-house.

Do you know the CC part number for this filter? I'm not able to find it in their online catalog.

[Michael J.]

Re: Lessons Learned While Servicing a C4

You are really brave to tackle a new car like this. I stick to C2s because they are such simple machines, these C4s seem very complex.

[Mark E.]

Re: Lessons Learned While Servicing a C4

Mark,

Thanks for the post.

>> The AIR pump filter was gone with only a few foam remnants remaining around the pump's inlet. I didn't realize a cone-shaped foam filter should be over the inlet until I did some research. I'm now noticing that every C4 with an electric AIR pump (LT1, LT4, LT5) I've seen since is also missing this filter. They apparently disintegrate over time. One of the few sources (maybe only) is Corvette Central which I believe they fabricate in-house.

Do you know the CC part number for this filter? I'm not able to find it in their online catalog.

Corvette Central #304102

[Mark E.]

Re: Lessons Learned While Servicing a C4

You are really brave to tackle a new car like this. I stick to C2s because they are such simple machines, these C4s seem very complex.

Michael,

I thought you had a C6 or C7 ZR1?

[Michael J.]

Re: Lessons Learned While Servicing a C4

I had a C6 ZR1, and traded it in on a C7 ZR1, I also have a C8. But the difference is that I take those cars to a dealer for anything, whereas I do all the work on my C2s myself. I would never try to ever touch the new cars, just too complex and beyond my mechanical skills, so I admire anyone who tackles these new electronic ones, like a C4.

[Mark E.]

Re: Lessons Learned While Servicing a C4

Michael,

Your hesitancy about the complexity of a C4 may be a reason these cars are valued much less than a C1-C3 even though they perform better, are more comfortable, and feature a good air conditioner. (Plus there’s a greater supply of C4s, of course).

The more I learn, the less intimidated I become about servicing these. Build quality and serviceability is higher than older generations. Drive-train mechanicals (basic Chevy), suspension, brakes, lights, etc. are no more difficult. Gauge and control clusters are removed from the front, the fuel pump and sending unit come out from the top, no need to rip the dash out to replace a speaker, and no need to stand on your head to reach the fuse panel. The fuel system is arguably easier too. For example, replacing fuel injectors vs. rebuilding a carburetor.

Then there’s the engine and body management systems and their sensors. A bit intimidating at first but what helps are the thorough shop manuals. They explain diagnostics in detail which removes much of the guess work. Yes, some things are more complex (Opti-Spark and water pump on LT1, starter on LT5, ABS, FX3). But after reading and learning from the manual, tackling even these systems is within the skills of most hands-on owners.

So if you like these cars, I encourage their consideration. Compared to earlier generations, they offer big-block performance at Corolla prices. Want an NCRS ready car? A significant number of low-mileage, original cherries remain out there you can acquire and turn around to be Flight judged. Think about it: For the same price, which requires more skill, time and money to get ready for judging: a #1 C4 or a #4 C2?