Evening gentlemen,
I recently picked up my 1995 Corvette from the shop, I am currently trying to do everything I can to make it pro charger ready along the way I experienced some issues, I recently got it back with a brand new suspension including coil-overs, no issues there. It is an A4 with an 2000 stall and a transcooler kit that goes throughout the car. So I did do a Dana 44 Swap upgrading to new 3,73s , I I actually found a unused Hyper tech power programmer 3 for my car and did have the "performance" tune and adjusted the speedo successfully as well as set the limit to 186 and the tire height accordingly as well as set fans to turn on at 180f instead of 185f, other options I left stock. Anywho, just about 1k miles on the new mods and I decided to see if it was ready for some actual driving. I got up around 120 once and the car seemed like it hit a limiter which with the dana 36 and the 2.59s I hit way faster. It would not go past 120 which confused me, I heard a loud vibration/humming coming from the back end of the car (which I had heard before at way lower highway speeds as I had assumed the new dif was breaking in) . The car still drove okay but it seemed to start lagging and not accelerating as it should. I slowed down and cruised over to the gas station a few miles down the highway. When I got out what I'm thinking is a completely other issue as smoke starts coming from the top of the hood and a large amount of coolant splashes out onto the ground.underneath the car, the low coolant light then came on and I went home. The car never overheated and the check engine light did not go on. I don't know if I blew a hose a water pump or something worse and in regards to the car not going past 118-120 I set everything with the hyper tech back to stock except for the gear change. It goes in the shop tomorrow but with all the shortages it's hard to get the car prioritized to get worked on so trying to gauge what's wrong with it beforehand helps, Thanks for any advice!

 

Water pumps have a weep hole at the bottom. When the pump goes water will pour out that hole. The way these cars are designed with the opti/distributor directly under the water pump that failure usually causes a problem with the opti. Most likely the cause of your loss of power. 95 had an improved opti that vented and didn't get ruined as often as the earlier ones, but they can still be ruined. I'm guessing your spirited run was too much on the aged water pump. So at minimum you will need a water pump, new thermostat and the coolant system flushed. Bearing contaminants in the cooling system can shorten the life of a new water pump, so be sure to have it flushed.

 

The diff humming: since you brought up break it, you need to talk to the person who set it up.
cooling : check coolant level cold, then drive it again. See if it happens again watching digital temp from dic. If it goes over 230 rolling or starts smoking time to park it. Make sure no debris is blocking air flow to radiator. Corvettes are somewhat vacuum cleaners sucking up litter bug waste on the roadway.
The 120 mph wall must something in the calibration. Mechanically, it should run over 140

 

This is what I figured, I was able to find an MSD kit on eBay and I'm getting it flatbed over to where I can get a further look at it.
I'm confused by your first sentence, you think the differential is broken? Is the humming not normal? The digital temp showed it around 203 when I pulled in last night, haven't tried yet as the low coolant light is on. The 120 limit has me confused and I since went back to the stock options with the exception of the speedometer recalibration so I'm yet to see if that fixed it, but you are right I've done over 140 with the stock dana 36 and 2.59s.

 

I can't speak from experience on the quality of an MSD opti if that's what you're referring to, but I've seen several posts complain about them. I wouldn't rush to get rid of your original. It may just need a good cleaning. Don't let the mechanic take it. Original optis are often more desirable and people will pay more for a used original than any of the lesser quality new ones available today.
Once you get it sorted out mechanically it sounds like you might need to check your u-joints and the fit of the D44 swap. That humming and vibration is probably due to something not being 100% balanced or lined up back there.

 

Interesting, so in regards to eventually procharging it you think my original opti spark would be able to handle it? I was referring to MSD I had not heard neither good nor bad things about it but thats good to know that their system is junk, the U-joints being out of place sounds like a lot easier of a fix.

 

I don't want to sound like an opti expert. I just read on here and see lots of people complain about pretty much all the aftermarket ones, except the stock ones rebuilt. All of the timing is done in the computer, so this isn't like an old distributor where MSD built a superior unit with magnetic pick ups. Even with procharging it, all your timing is done through your tune. The opti only installs one way. You cannot advance or retard the timing by installing the opti on a different tooth like you can regular distributors.
Might be as simple as unbolting your drive shaft from the yoke and rotating it 180 degrees and installing it that way. I would make sure all your u joints are thoroughly lubed too. A long time ago I installed a new u joint and didn't know about lubbing it. Had a very bad experience with that and had to get a new u joint...I was young.

 

I try to restate this.
the diff doesn't have a " break in" period. Talk to whomever put it together or sold it to you about the humming, before doing more than a visual look over, especially if you paid for d44 to be installed.
The 120 wall there is a 30% rpm difference betweenthe 2.59 and 3.73. Tach signal is not going to match transmission table in the calibration. . You need either a tuner.to reprogram car or install a speedometer converter module so pcm is seeing correct speed.
if cooling system was over filled it can burp excess coolant making alot of smoke and not necessarily having a problem. Making sure coolant level is correct before another test drive verifies there's is a problem. If you have access to a cooling system pressure tester, pressure test should identify source of leak if present.

 

The coolant leak is the rear crossover pipe which is a pain to get to but simple fix.