Vacuum Modulator Swap

Time to replace the old vacuum modulator in the hope that it is the culprit causing hard shifts from 1-2 and 2-3. The modulator is at the back of the trans on the passenger side. It’s in a tight spot – crowded by the exhaust pipe (pink on the right side of the photo) which I’m not going to try and remove.

This is the view of the modulator from behind the rear cross member. The screw holding it in place is on the top side.

The only access to the screw holding the modulator in place is with a couple of extensions plus a wobble extension and a 1/2″ short socket.

Got ‘er out. Trans oil dripped out of the opening after I removed the modulator. It lost about a 1/2 cup of oil at most.

New vacuum modulator from Rock Auto. Much smaller than the original. I’ve primed and painted the modulator bracket and screw.

The new modulator being smaller allowed me to get my hand up enough to get the bracket screw started. It was then easy to tighten using my ratchet and extensions from behind the rear cross member. I put a bit of blue loctite on the screw.

All I needed to do then was cut the elbow off the new connecting hose and slip it in place.

Test drive as soon as I can to check it out 🙂

Trans troubles

I broke the original trans cable when removing it from the manifold bracket. I picked up a new cable from CarQuest and even though it didn’t match the old cable I was assured that it was correct for my year and model. In truth it was not. The old cable had a tension spring that was needed when setting the TV cable to WOT. The new cable slipped in an out easily on the bracket and I couldn’t be sure that I had the correct cable length setting. I found an exact replica of the original on the Northern Corvette website. So I ordered it and got to work putting it in place.

The cable is located behind the two trans cooling pipes. and also behind the exhaust pipe. Ideally you would remove the two pipes and the exhaust. Not going to happen on an engine with 144k kms on it. So I had to get my fingers in with a small 1/4″ drive 10mm socket and remove the old cable. Getting the new cable in place was a bit of a bear as I was working by feel alone. There is also a rubber gasket that needs to fit on the cable end and it of course doesn’t want to stay on the end. But I got it in place after a couple of hours of fiddling.

In order to get the new cable on the carb linkage it’s necessary to remove the TV cable bracket at the rear of the manifold. Other than that it was a breeze to set as per the service manual.

The TV cable has a push up/press down lock. With it in the up position I rotated the carb linkage to WOT which pulled the cable out of the lock at the bracket (I held the coke butterfly open while doing this) and then pressed down on the TV cable lock to set the cable length.

Took it for a test drive and all is good. Passing gear works nicely and I don’t have any fear of trans damage due to an incorrect TV cable setting.

I didn’t clear up another problem that has developed. Shifts from 1-2 and from 2-3 are very harsh. The service manual trouble shooting guide for AT shows that the vacuum modulator is the most likely culprit. Rock Auto has the best price at $58 plus shipping – beats the local parts shops by at least $20. So that’s the next job and it will not be fun getting at it as it is once again tucked behind the exhaust pipe and the rear crossmember is also in the way.

Shaking out the bugs from a car that sat for 20 years!

Power window fix?

The drivers door window stopped working for some reason. So was it the motor or switch. In one case I had to remove the door panel and cover and the other I needed to remove the seat so I could take off the console side panel to get at the switch. A 50/50 chance that I didn’t want to take and end up doing both.

Fortunately there is a connector for the power windows under the dash

The following photos are poor – apologies. I ran a lead from the + battery terminal and connected it to the shaft of a one time screwdriver that I had shaped into an awl. I touched each side of the power window motor lead and the window went up and down OK. So I only had to remove and replace the kick panel to check the motor out.

So the problem was in the switch – if it was getting power. I removed the seat and console side panel. I then removed three screws on the left side of the console cover. I used a block of wood to prop up the panel a bit to make it easier to get at the switch. I didn’t want to remove the whole cover if possible.

I could just get at the screws holding the switch. Unfortunately the rear screw boss broke off – I must have over tightened the screw when I last had the console apart. Bummer.

I first bench tested the switch and it showed that it was working. So I just plugged it back in the the circuit and darned if it didn’t work OK. So I added a blob of epoxy to the remains of the rear screw boss and put it all back together. I’ve ordered a new console cover and when it comes in I’ll overhaul the switch before reinstalling it – many of the switches on early vehicles are purely mechanical and can, with care, be disassembled, cleaned and put back in the car.

This is the passenger switch that I replaced earlier. I opened it up by carefully bending out the pot metal tabs just enough to wiggle out the bottom plate. I cleaned the contacts and put a new piece of plastic in place (the plastic keeps dust and dirt that gets by the switch toggle from getting into the switch contacts). Once done I reassembled it and bent back the tabs. The tabs being pot metal will likely break off if I try to open it up again. Still I should be able to use some epoxy to hold the switch together next time.

AC woes

This is about the AC on my ’66 Studebaker, but much will apply to the Chevy systems.

My AC started to squeal when it was engaged and then stop when to compressor cycle stopped. That was bad enough, then the compressor started to cycle on and off rapidly. I have a period evaporator in the car with a modern Sanden compressor with R134A.

The Sanden website suggested that the problem might be in the evaporator temperature control switch (This switch isn’t part of the Chevy’s system). Fortunately I have another switch available. Unfortunately it didn’t make any difference.

Going over the wiring I realized that the power to the compressor passed through the low pressure safety switch located at the top of the dryer. When I jumped the safety switch connectors the problem of the off/on cycling went away. I won’t bother to replace the switch as I will need to empty the system of gas and do a recharge. I’ll do that a bit later. I’ll watch the system and if the cooling drops off I’ll check the system to make sure there is enough gas in the works.

The squealing problem is still present. I installed a 12 volt relay temporarily in the system to see if the compressor clutch was not getting its full 12 volts. That wasn’t a problem. I happened to run a feeler gauge between the clutch face and the body. What came out was a thin coating of grease – the upper photo shows the grease on the feelers and the middle with the feelers cleaned. The bottom is a shot of a cotton rag I was able to stuff between the clutch face and body. There shouldn’t be any grease in that area at all. On the next test drive the squeal was present, but the tone had changed and it wasn’t as consistent as before. I’m thinking I’m on to something here. I’ve sent away for a tool kit to remove the clutch from the compressor so I can check out the situation inside. Might be a compressor seal leak. We’ll see after I get the kit and pull things apart.

Dizzy woes

Second rotor destroyed as well as the dist. cap button – one on left has had it’s tip cut off by the rotor and the one on the right is a new one.

The old capacitor setup doesn’t accept the new capacitor with the pin connector.

So I needed to buy the complete harness that has the capacitor integrated in it. Hopefully it will stop the damage to the rotor (by eliminating the sparking between the cap button and the rotor connector).

All back in place. I didn’t have any new special contact grease to put under the electronic module, but there was just enough of the old stuff to smear around 🙂

As to the engine miss. I have done everything I can think of to be rid of the problem, but it still persists. The engine has 144,000 KMs and without hardened valve seats I can only assume that there is a burnt valve in one cylinder. I am replacing this engine so I won’t bother to do a valve job as it is still driveable and ‘good enough’ for local driving. If I do go on a road trip I will add some lead substitute so another valve doesn’t burn.

Checking for an air leak

I used a common propane torch to flow gas around each manifold inlet runner. Unfortunately I couldn’t detect any change in the engine idle at any point.

What I did discover was the cause of the engine shake at idle. At some point when i was swapping out the spark plugs and the spark plug wires I must have broken off the vacuum line to the heater controls.

This added a wee bit of air to the back side of the intake manifold and must have caused what I understand is called a “lean air misfire” in one of the rear cylinders. Once I fabricated a temporary fix the engine idled much better. The vacuum fitting is available for CDN$5.95

Now to get back to some nice summer driving 🙂

Chasing the misfire

Setting the lifters hot is messy and even with rags on the exhaust manifold I was getting spillover onto the floor. So I took and old valve cover and cut the top off. More at the top than the bottom.

Fits like a charm. Just enough room for the rocker clips to miss the top edge of the valve cover. I ran a rag across the exhaust manifold in case of splatter, but since I wasn’t revving the engine all the oil stayed in the valve cover.

I adjusted each valve to zero lash and then added one quarter turn. I’m not sure if any of the lifters are collapsed so I didn’t want to tighten too far. The valves are nice a quiet, but the misfire is still there!!!

Next I will test for an air leak at the intake base runners.

I’ve had the valve covers off three or four times at least and it is a real pain getting the short bolts in place on the bottom edge with the reinforcement arms. I don’t like the long T screws used by some rodders, but I can appreciate the ease. So I made up some long replacements using stainless bolts. I ran an nut up the thread ends and tightened it a bit. I also use shake-free lock nuts.

Now it’s a lot easier to get the valve cover tied down. The only place it didn’t work was under the AC compressor bracket. I still have to use a short bolt there. I don’t use a ratchet on the bolts. I only tighten them as much as I can by hand using a socket with a screwdriver handle. Works super so far.

When I’m satisfied with that all’s well with the lifters I can always take the time to put back the short bolts.

Doors and lifters…

Back working on the doors trying to get them to close nice and the windows to seal better by adjusting the glass position. This is the right door and it is working quite well. I have it apart to compare to the left door which doesn’t close any where near as nicely.

The top shot is of the left door and the bottom the right. As you can see the door glass fits further back on the right door which helps a lot with proper fitment. There is no way I can move the glass any further back on the left door. This leaves me with a small gap at the top of the door that I can’t adjust out. In the end I had to used a length of 1/4″ foam tape on the top of the window gasket ( the section on the removable roof panel) to seal it enough to eliminate most of the wind noise. Not a good situation, but what can you do!

Back to trying to find the source of the engine miss. It is an even miss that is constant at all speeds. A mechanic told me it is likely a cylinder that is misfiring. Easiest way to identify the cylinder is to use a hand held unit like the one above to check the temperature of each exhaust point. I did this and #2 cylinder’s temperature was well under that of the other cylinders. The plugs above are the #2 plug on the left and a good used plug on the right. The #2 is full of carbon is oily. and doesn’t seem to be firing.

I replaced the plug with a good one , but no difference.

Time to check the lifter settings. I have set them cold, but this time I’ll try a hot setting. The clips along the top are something I have kept over the years from back in the ’70s when I had a 427 C2 and I needed to set the solid lifters on a hot running engine. They stop oil spurting out of the holes in the rockers. The rag along the bottom was an attempt to keep oil off the hot manifolds.

I suspect bad lifters so I just set the #2 lifters to zero lash. That got the cylinder working again, but I still have the persistent miss!

Driving season!

Time to drive the ’79 🙂 Not too much to report on bugs. Still working on the engine misfire. Trying Sea Foam products to see if it is a sticking valve. No luck so far. Car still pulling slightly to the right on hard braking. It may be that the left front pads and rotor are not contacting fully. Otherwise all’s pretty much OK. I do expect that the rear wheel bearing will need attention down the road. I’m waiting on a donor 350 engine to build next winter. I have all the gear to overhaul the AC and am looking forward to having that running. Still have issues with the drivers door. There is too much play in the window even with the new outside seal, etc. But for now I’ll just enjoy some driving.

Cheap vs good, but not best

After checking to make sure that the car had not skipped a link on the timing chain – it hadn’t – I took off the dist cap to be sure the rotor was pointing where it should and I was surprised to find that the centre contact was partially burned off! It was an economy rotor. The dark grey unit is the better quality unit (all CarQuest brands) They seem Identical.

There is a difference in the colour of the contacts. Not sure what the difference is. The old one looks to be bronze, but the new one???

I decided to replace the cap as well. The contact plates seem to be bronze where the old cap had Aluminum or stainless?

The plug posts are obviously the same as the undersides.

These are the centre contact electrodes the one on the right is the old one and it has a groove in it where the rotor contact strip was cutting its way through. Also, again brass vs aluminum or stainless.

On a good note, Carquest is refunding me for the rotor. I’m not going to gripe about the cap as I’ll keep it for a backup (that I should never need given the miles the Chevy will travel).