CorvetteForum - Chevrolet Corvette Forum Discussion - C3 Tech/Performance

water pump vs. heater hose ques.

jgill — Wed, 03 Jun 2026 12:32:34 GMT

switching over to a serpentine system for my C3. this is a long style pump with only one screw in outlet at the top. nothing down low for the normal heater hose hook up. is it ok to use this top outlet for the heater hose?

Advise for a new bee '74 swap

Grateful Dad — Wed, 03 Jun 2026 02:49:08 GMT

Hello

I got my first Corvette this past fall and immediately started tearing into the project. I am at the point where I want to get the engine & transmission mounted to the frame now that the transmission is mounted to the engine. I would like to make sure I am doing the drive line angle correctly, and I am attaching are some pictures of the measurement I took. I have zeroed out my gauge on the side of the frame, then took measurements on the transmission, drive shaft and pinion. Right now, the assembly is still on the hoist. there is one bolt thru the crossmember into the isolator to hold position. My assumption is that if this is right, I will need to find/fab engine mounts to fit the space I have to the frame arms. I initially bought ICT billet 1/2" "stock location" plates but I think they are the too thick and not long enough to push the engine back to where it should be. if you have any recommendations I would appreciate it. also I am not sure about the spacing on the driveshaft to transmission seal, I am including a picture of this too.

a few details, I am working on a 1974 frame, the engine is a LS2 from a 2006 Corvette. the transmission oil a T-56 Magnum. the oil pan is a holley 302 low profile and it currently clears the rack & pinion with no problem.

Another concern is the heater hose outlets and positioning. I know the t-56 is larger them most transmissions and I know I will have to cut an opening around the shifter, but I am hoping that by positioning everything correctly I can minimize the amount of tunnel work I will have to do to clear. any help or advice is welcome.

Attached Images

posi clutch type

GTR1999 — Wed, 03 Jun 2026 01:23:44 GMT

I am starting on a 74 diff and found all the posi clutches broken.

I posted this info on a FB group I belong to and I'm sure some of you are part of that group as well.

The clutches used from late 1971-79, sold over the counter, and still sold today, were slotted or the term I coined years ago, "Snowflakes"

This type of clutch was an attempt to stop posi chattering, which is very common with spring loaded posi's.

While the slotted clutches are available today it makes no sense at all to use a known weaker part. The price probably isn't a factor. If you are rebuilding your differential and posi, use the better parts. Don't be dumb or cheap, it's your car. If you are getting a posi built, ask what is being used.

Fiber clutches are the latest, not the greatest, revision. It does resolve posi chatter but at the expense of constantly smudging clutches.

What is this connector

mbuescher — Wed, 03 Jun 2026 00:38:27 GMT

1975 Center Console Wiring, wondering what this connects to??

Any Help would be appreciated,

Thanks in Advance.

Re-Gluing Detached Side Marker Lens

C8H18 — Tue, 02 Jun 2026 20:12:14 GMT

A while back my left rear side marker lens fell off - the rubbery yellowish glue must have dried out. I now have a used replacement assembly and it's lens seems snug and tight. But I checked the other side markers and Yep - the right rear is also very lose and about to fall off. So I need to glue at least that one (heck maybe I should pry them all off and re-glue!)

I was going to re-glue with some clear silicone household caulk...? Unless anyone has a better suggestion...

Thanks,

PS the pic below shows the previous one (now missing lens) and the new-used - some slightly differences in casting details (no "SAE AP70"). Is one of them a repro vs an original?

Power Steering Pump Rebuild - What's Involved?

Stephen Irons — Tue, 02 Jun 2026 19:17:12 GMT

I have been aware that the P/S pump on our '78 has been making a few squealing/groaning noises on occasions when "under load" and warm. During our recent 1385 mile trip to the south of France in 30+ degree C heat it was doing so quite a lot! I also get the impression sometimes that the P?S is not giving me the assistance that it maybe should be.

I'm now wondering if maybe a rebuild or replacement of the pump is on the cards. But a few questions first:
Is it likely that the pump would in fact not be actually pumping enough to give it's full potential?
Would a rebuild with a "normal" kit solve that?
How doable is a rebuild - will I need a puller, or can I leave the pulley on thge shaft and just remove that whole part?
Or, is a new pump a better idea in any event?

I should say that I have eliminated the belts as the origin of the noise and, I am not thinking at all about installing a Borganson system.

Any thoughts and/or suggestions most welcome!😄

Shock valving selections for C3s, for newbies to experts

leigh1322 — Tue, 02 Jun 2026 17:50:22 GMT

I was going thru this thought process for my own car, so I thought I would document it for others.
There is a lot in here.

How to choose a shock for a C3 (or) how to adjust shock valving, and why

There are so many different brands and types of shocks available for our cars. It is very difficult to know which one to choose or why? What the advantages of one type of shock valving are vs another? What can an adjustable shock do for the driver? Besides cost more?

Shock types by valving style

� Non adjustables: Ride oriented (or) handling oriented

� Single Adjustables: Rebound only adjustable (or) adjusts both rebound and compression together

� Double Adjustables: Compression and Rebound are adjusted separately

That is five valving styles. They each have their own advantages.

Basic Shock Selection & Valving Critique

� OEM ACDelco shocks – ACDelcos. Part number matched. These were valved precisely for your Corvette, your year, with your options. And will likely will produce the best OEM style ride over any aftermarket shock. But realize that if you change any springs, sway bar or bushing you can upset that balance. And realize they were designed to fit your car with 1960s slide-rule technology. Technology has come a long way in shock valving since then. We can do better with more modern offerings. We can improve either ride, or handling, or both.

� Aftermarket Generic Ride Oriented shocks -I will dump all dump all the inexpensive non-adjustable part store brands in here in one lump. KYB, Gabriel, Monroe, etc. etc. These are designed to be kinda close to factory shocks ride quality. But they are also designed to fit as many cars as possible under each part number. They are absolutely not specific for a light weight C3. And a C3 has different motion ratio for the rear shocks and rear springs, and those rear shocks need to control a much lighter IRS suspension vs a solid axle. So none of these generic shocks will be exactly “on-point”, unless they are designed and valved for a C3 only. I doubt many shock manufactures do that, it would drive their costs up. They may be kinda close, but If they also fit other cars, they will most likely be too stiff, and make the car ride more firm than necessary. This is a case of you get what you pay for. If you just cruise around, and very infrequently push the car hard in corners, these may be all the shock you need.

� Aftermarket Handling Oriented Shocks – Bilstein, QA1, etc. Non-adjustable. These suppliers have tried to bias their shock valving toward the handling side of the equation, without killing the ride. For a decent ride/handling compromise. They do not ride overly firm, and the handling will be more controlled with minimal oscillating. Just cruising around the street you may not notice any difference at all in the ride vs the store brand shocks. But if you throw the car around a bit in twisty roads, even a novice driver should notice there is more car control. The car is just difficult to get upset, it always feels under control. These would be my go-to shock recommendation for people who like to really drive their sports cars a little harder. This valving compromise is sensitive enough, that the rear shock valving must be pretty specific for a C3 IRS.

One strong caveat: If you change the spring rates from stock, you will change the required valving balance. FI: A stronger rear spring rate is a common upgrade. When you increase a spring rate, you must lessen the compression valving, or the ride will suffer. And you must also stiffen the rebound damping or the car may pogo / oscilate. Yes, the rebound needs to be stiffer to control the stiffer spring, but not the compression. With a stock shock and a stiffer than stock spring, the car may exhibit both undesireable features at once. FI: Ride oriented shocks and the gymkhana / F41 springs would be an example. Both Bilstein and QA1 offer two valving choices for our cars. Bilstein offers a B6 and a B8 version.For Bilstein the “lowering springs” comments means for slightly stiffer springs. Van Steel has 2 C3 specific custom valving options on the non-adjustable QA1s, one for ride, and one for handling. The fiberglass rear spring options are almost all stiffer than stock, so you should select the handling/sport/lowering valving option for those springs.

� Single and Double Adjustable Shocks – They give you the opportunity to user adjust between smooth ride valving, a good ride/handling compromise, and extreme handling only valving, with a quick adjustment. For many users, that would be enough reason to buy them, and try them. These shocks are the main reason for this discussion. Some SA are rebound-only adjustable, like Koni and Ridetech. Some SA adjust both valves at once like some QA1 shocks. Others are Double Adjustable, like, QA1, Viking, Koni, Penske, JRI and others. With DA you can change both the compression and rebound separately. What can these type of shocks do for you? How can you determine if they are worth it?

For many C3 drivers, this is all the information they need.

But some will want more information. That is what this write-up is truly about, adjustable shocks. What can adjustable shocks do for you? What will you feel?

I ran adjustable shocks (Konis) for 30 years of autocross into the Pro-Solo level. I was nationally competitive too. But with shock valving, I mostly just experimented and used the manufacturer’s supplied guidelines. That and with a lot of testing, I slowly learned about shock tuning, and what stiffnes I liked, and when. But I never really knew how to explain “why” I liked “A” vs “B” until more recently.

Almost done with my 76 restomod

Corvettedave02 — Tue, 02 Jun 2026 16:04:50 GMT

I haven�t posted much lately but do read through the forums. Regardless I thought I would post the near completion of my �forever project�. I got it tuned by Rich on Fastmanefi.com. He did a great job! I had a faulty fuel pressure regulator which wouldn�t hold pressure. I�m replacing it along with new lines on the intake this week. I�ll finalize the tune with Rich after. Will be working out the bugs for awhile I�m sure.

76 L82 4-SPEED CAR IOriginally which I bought 36 years ago and used as a daily driver.

Mods
Autofab 4link with 9� and Detroit locker, 35 spline axles
427 sbc. Dart block, AFR heads, pump gas
Fastxfi
Tremec TKX, McLeod dual disc, Mark Williams yoke and 3� chromoly steel driveshaft
Vintage Air
American auto wire upgraded wiring harness, Aurometer gauges, new Speedo and stock tach with a new circuit board
Hydroboost, new stainless lines, front will wood 4 piston calipers, stock e brake.
Lots of paint correction and buffing but the 25 year old paint looks like new overall. A great driver for sure.
New or refurbished entire interior, rebuilt doors, new glass , new everything

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Blueprint engines oil pan and problems with steering cylinder.

stingraymax — Tue, 02 Jun 2026 07:08:13 GMT

Hi, I came across a post but can't find it anymore about Blueprint engines oil pans hitting the c3 steering cylinder. Anybody that has installed a BP engine and came across this problem (I have a '75 with Power steering) ? I would like to know before installing my BP engine if I need to change to another oil pan.

Thanks

Transmission question.

miked123 — Mon, 01 Jun 2026 23:35:29 GMT

Is this transmission fluid a good full synthetic transmission fluid to use even though it says Dexon VI - Mercon LV? for a rebuilt TH400? On the back it does say that this is compatible with all GM Hydra-Matic trannys and I know the TH400's use Dexron VI. Ive done some googling and see that the Mercon LV fluid is NOT the same as Dexron VI. it seems like a lot of fluid I've looked at have been the Dexon VI - Mercon LV.

1. Am I able to use this fluid without any issues? or should I be looking for exclusively Dexron VI?

C3 Headlight Assembly alignment issue

robertea — Mon, 01 Jun 2026 23:12:47 GMT

I started something that I wish I hadn't done on my 69. My headlight assembly is aligned in the opening, but the leading edge was sitting a little low. I figured out the bolt to turn and have raised the front lip a little. It has been this way for years, but I just started messing with it now. It's so much fun lying on the floor at my age trying to get this working and getting up and down 50 times to get different tools.

Now comes the bigger issue. In the full open position the assembly does not open high enough to get the bezel off without damaging the paint. It is at least an 1/8" below the lip of the nose. I have removed the grill so that I have more room to see what is happening and I have disconnected the vacuum canister and I do not see any way to open the assembly any higher. I looked at two different AIM's (69 and 74) and what they show for the adjustment does not agree with my assembly. I have gone to the Service Manual, but I don't see anything in their routine to get the assembly to open wider. I also found a mistake in that document. It's not very often that this car has an issue that I can't fix. Looking for someone that has worked on these things before.

While I am in there I am cleaning and lubricating anything that moves.

rocker arms

DingoDave — Mon, 01 Jun 2026 19:37:33 GMT

Looking to install roller rocker arms on my 75 350, seems everything I've looked at says does not fit. They are ported fulie heads with 3/8 studs. I've been wrenching for a lot of years (retired mechanic) and search results seem to make no sense. Am I missing something? Gen 1 small block. Looking for recommendations without breaking the bank.

Wiring question

C3-LT1 — Mon, 01 Jun 2026 19:10:41 GMT

I am near the end of restoring my 1971 LT1 and have a wiring problem and am definitely not experienced in auto wiring. I am installing a Dewitt's radiator with dual electric fans and converting the headlight and wiper door actuators to electric with Richard454 kits. Based on my rough calculations (correct me if I'm wrong) I will need an alternator around 100-120 amps. The only chrome one I could find that fit a Gen I SBC was 150 amp one wire alternator which is installed.

All new Lectric Limited wiring harnesses will not support that many amps so I need to know how to wire the car and new electrical accessories. I asked Claude and it said to leave the alternator connection from ;the wiring harness unconnected and run a 2 AWG wire directly from the started (positive battery cable) to the alternator and also a 2 AWG wire from the negative battery terminal directly to the engine.

Also connected to the positive battery terminal (starter terminal) run a 4AWG wire to a buss on the firewall from which to run separate circuits wit appropriate fuses and relays for the fans, headlight and wiper door actuators. The wiring could be organized with busses on the firewall so everything is clean, labeled and organized.

My question is if the above is accurate and makes sense and will work, and if so, how do the Lectric Limited harnesses for the rest of the car get power if the harness isn't connected to the alternator?

Thanks so much and if you need more information please ask.

1971 350/270 Vacuum Advance Tube Install Config

C8H18 — Mon, 01 Jun 2026 16:29:31 GMT

I'm figuring out how to get my '71 350/270 engine configuration back to original-ish configuration and recently purchased a vacuum advance tube (3994054) and tube mounting clip (3841096).

Q1: After looking at various pix online of '71 engines the clip doesn't seem to show up very clearly as to where it's located to hold the metal vacuum tube... Does the clip mount under the the intake manifold bolt head on the in front or behind the bimetal choke spring?

Q2: This is what the parts I ordered look like - I notice variances between these and what I see pictured sometimes for '71 - do these look correct for a '71 350/270?

Thanks,

Bad Fuel Gauge or Sending Unit?

durangochad — Mon, 01 Jun 2026 15:51:53 GMT

I bought my 72 LT1 convertible about 6 months ago. At my first fill up, I noticed the tank was almost empty, but the gauge was pegged far right beyond the full mark. Since then, I've seen the gauge never changes. I'm kind of hoping this is a sending unit problem instead of a gauge problem. Does anyone have a suggestion for where I should start given what I'm seeing on the gauge? Appreciate your help.