How to Repair Other Common Corvair Engine Issues

The Corvair Powerglide automatic transmission remains one of most stable and resiliant transmissions Chevrolet made. The following troubleshooting techniques apply to all models from 1960-69. Amazingly, the Corvair air cooled engine seldom overheats or above 400F. The two issues covered in this discussion cover common issues with the automatic transmissions and engine overheating. Usually these occur after a car has been idle for many, many years.

Powerglide Modulator

The modulator, should it fail, can cause problems with shifting and if the small rubber connector tube is clogged, contribute to idle problems. The device contains a diaphragm and valve. If your engine is hot and you cannot obtain a reading when checking the PG fluid level when the engine is running ( it reads empty on stick), the modulator may be the issue as it is allowing the fluid out of its area. Loss of tranny fluid without locating the leak may indicate a ruptured diaphragm. This allows the oil to be drawn into the intake manifold causing excessive white smoke. If there is no smoke, check the rear axle lubricant as tranny oil can enter if the pinion shaft seal is worn or bad.


This is a 2-3” diameter like vacuum mushroom looking thing that is installed in a less than 30 min (with the right tools) in the side of the automatic transmission. Access is difficult so jack up the car and remove the rear right tire. It is located in a recessed area and using the special tool from Clark’s Corvair makes it easy. Odds are nothing has ever been done to it so prior to loosening, spray some lubricant to loosen it. Remove the short rubber tube, verify it is not clogged etc. Verify that the tubing attached to the rubber tube remains solid with no holes etc.


After a few torques, remove it. There is a small valve in the hole, if it sticks or binds while in the bore hole (it does not turn freely), remove it and inspect for roughness. Use a fine slipstone to polish roughness out by rubbing the valve on the stone. Rotate the valve as it is moved across the stone surface. Insert it and make sure it freely turns. Part of the valve is actually sharp and square, leave these areas alone.


If this valve does not need smoothing, leave alone and install a new modulator with the gasket centered on the threads. Carefully thread the unit back on with the special tool or Water Pump pliers.


To test the modulator before removal:

Attach a vacuum gauge to the lower end of the modulator hose and start engine. At idle speed, the gauge should read within 1 inch. If the reading is not this, something is blocking the tube. Open the throttle and there should be a quick drop in vacuum, if there is none or a delayed drop, the restriction is internal within the vacuum line somewhere.


If both readings are OK, the oil pressure at idle with fluid level full and engine hot should read as follows with modulator hose connected:


In Neutral\Drive:         47-57 psi


If there is no oil pressure, there is a broke front pump drive shaft, or shaft disengaged from the front pump drive hub. If there is low oil pressure, it may be caused by a dislodged plug from the front of the hollow front pump drive shaft.


You are done.


Normal shifting during driving (assuming no issues) should occur at 11 mph and at 44 mph, ± 3 mph. Going 45 mph and more and a downshift to L (low) will not cause the PG to shift. When the speed drops below 45 mph while still in L, the downshift will occur.


NEVER shift from D to R while moving, doing so will damage the PG.


You can push start your PG at 18mph.


If you are going 41 mph or less and you floor thru Detent with the accelerator, the PG will shift into Low and up shift at 44 mph or so.


Detent = is pressing or pulling through a definite resistance.


Additional problems


If your engine starts while the car in any of the gears (the car should start only in N):


1. Loosen the mounting screws and move the switch housing forward or rearward until the starter operates in only Neutral. Tighten screws and retest. Verify the backups also work.


2. Make sure the selector lever is D and check. Rotate the throttle lever clockwise. The hole in the large arm must be below the oil pan rail and measure 3\8”. If the hole is above the pan rail, the cable ball end did not enter the slotted lever and must be reinstalled.


If your shifting is rough or too early or late, your Governor may be defective or

improper Throttle Valve (TV) pressure may be the cause. To check the TV:

1. Attach a 0-100 psi gauge to the TV test port on tranny (this will hard to locate). It is at the 8 o’clock position.

2. Disconnect the accel rod from the tranny throttle lever.

3. Raise the rear wheels 5” off the ground.

4. Start engine and idle.

5. Disconnect throttle rod from crossshaft  and modulator hose from Balance Tube.

6. Slowly pull rod toward the rear of car. Pressure should be 40 psi to the Detent position and be 52-54psi through Detent position. If lower than 52 psi, low pressure is causing it to shift early, if more than 54 psi, excessive pressure causes it to shift later.

7. Pressure in Low should be 66-77 psi. Pressure in N or R is 0.

8. To adjust the TV pressure, remove tranny oil pan. Using an allen wrench, hold the Throttle Valve plunger as you turn the jam nut CCW 1 full turn to raise TV pressure 3 psi. One full turn CW will lower it 3 psi. To change only 1 psi, move to the flat area of jam.

You may have a defective Governor.


Check tranny oil after engine has run 15 min and is running. If the oil is more than 1\2” above the FULL mark, drain excessive amount to avoid oil foaming and other problems


Engine Overheating

The main cause for this is debris clogging up the cylinder fins which are vital for proper cooling. If your engine top shroud or oil is hot to touch after running for 5-10 minutes you might want to “de-flash” your engine. Corvair engines do not normally run so hot that the

top engine shroud is too hot to touch, warm yes, but not hot. The oil from the stick should not be hot either. If it pings, smokes, the passages are blocked. Clean the Oil Cooler, fan, remove the top engine shroud if you need by removing the carbs and alternator. Spray compressed air in from the bottom and see what comes flying out of the fan area. Once you do, you'll probably see that you need to pull the lower shrouds to clean it properly. This is especially the case if the vehicle has been parked for a period of time. Cleaning the fins out is VERY important and easy to do.  Slow timing may also cause engine overheating as does running too lean in the carbs.


Shine a light under the car so that you can see what needs to be de-flashed. Use a cheap keyhole saw from the local home depot or tool store to insert between the fins to punch out debris or excess metal. If the exhaust manifolds are still on, they block the light from below and limit how far the blade can go thru the head, but you can still do the job with them on.



Corvair engine with no top shroud: Note the finned cylinders and spark plugs. Debris stuck between fins causes overheating.
Corvair engine with no top shroud: Note the finned cylinders and spark plugs. Debris stuck between fins causes overheating.
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Comments 56 comments

Sexy jonty profile image

Sexy jonty 7 years ago from India

Very well written hub .....

very much informative ......

Thank you very much for your great hub, for good advice, good wishes and support. Thanks for sharing your experience with all of us.

bubba 6 years ago

hi perrya. do you have any lit. with photos on how to remove the insides of a good trans. (broken case), and replace in a good case? for a 65 PG. thanks

perrya profile image

perrya 6 years ago Author

Sorry, no. Never had that issue!

onicroster profile image

onicroster 6 years ago from New York

hey, thanks really helped me out on way to home. just saw an old lady messing up with her car. I helped her out...thanks to you :-)

perrya profile image

perrya 6 years ago Author

Very cool

kyle 6 years ago

why dont u just heliarc the case did that on oweer boger worked fine

perrya profile image

perrya 6 years ago Author

have no idea what you are referring to.

car scratch repair 6 years ago

I have a problem with my engine overheating. I try to keep the fan as cool as possible but still having problems. Any other ideas?

perrya profile image

perrya 6 years ago Author

Hmmm, because the engine is air cooled, de-flashing the fins usually solves the issue. How hot is your engine running?

hank 6 years ago

65 powerglide stuck in 1st and rev. Cannot upshift while driving. Any thoughts?


perrya profile image

perrya 6 years ago Author

Check for a broken E clip, which is inside the tranny. Pieces of it may be jamming things up. Remove the oil pan and then the valve body to find the pieces. A broken E clip (cheap part)usually keeps the tranny in low.

Danny 6 years ago

My corvair starts right up with no problems stays running in nuetral fine. when i put into reverse or drive though it bogs out. I try for about 15 minutes and then it works but it seems to hesitate and even die sometimes at stop signs right when i start to hit the gas? After its been driven for 15 minutes or so it runs great with no problems. Any ideas?

perrya profile image

perrya 6 years ago Author

well, many things may cause some of the issues: dirty carbs and ventura jets inside them, does not take much.The carb airflow is not synched, carbs are not adjusted to spec, vacuum leaks. Automatics are much more difficult than a stick.

usedmotor 6 years ago

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transmission slippage 6 years ago

This is so real! The details are awesome. it is so rare to see writers putting his head on his piece in an internet page accessible to people without charge.

Nissan Frontier 6 years ago

This is such a great help buddy. Thank you so much for reminding everyone here that it is not always about changing units every time but exerting effort to maintain the cars they own.

There are plenty of ways to save and this one will serve that purpose big time.


claysclan1 6 years ago

In September of 2010 I had a family emergency, since I do not like to fly, I drove my 1968 Corvair Monza two door from Huntington Beach to Columbus Ohio in three days with know problems. I did have Greg Peterson give it the once over before my trip out of Long Beach California. The car now has 112,000 miles and I will be driving it back to California soon, The car is not restored but solid being from California, This should answer all question about reliabilty. I did finally replace the harmonic balance in Nov of 2010 in Ohio

Transolution 5 years ago

Great detailed HUB. It's obvious you know what your talking about when it comes to the Corvair. Might have to come back with some questions for you when I have them.

perrya profile image

perrya 5 years ago Author

I agree with Danny, except minor things. my 67 Corvair coupe, 4 spd runs like new, it only has 56K on it.

Chris Watkins 5 years ago

great blog thanks!!!!

frankh 5 years ago

My girlfriend has a 64 convertible that has a horrible squeeling noise coming from the torque converter area. I am not familiar with the corvair automatic transmission and was looking for some ideas.

perrya profile image

perrya 5 years ago Author

Squeeling? sounds like the fan belt. What are the other symptoms when driving and shifting?

frankh 5 years ago

I took the fan belt off of the car to rule out the cooling fan,idler pulley and the generator. Started the car and narrowed down the noise to somewhere near the torque converter/flywheel area. Is there some sort of cooling fan inside the bell housing?

perrya profile image

perrya 5 years ago Author

No, maybe some of the teeth in the converter are missing. Maybe the bands in the AT need repaired or adjusted. Does it shift fine?

frankh 5 years ago

She drove it approx. 20 miles with the squeeling, said that it drove fine and shifted like normal, just the noise. I haven't driven the car since. Have been a little worried that it may cause expensive damage.

frankh 5 years ago

I will keep looking into the problem, thank you very much for your ideas.

terry 5 years ago

i have a 64 corvair monza 900 coupe with the automatic sound like my starter is not engauging half the time or teeth are broke...does this model have a regular flywheel or is it a ring gear weled on the torque converter?pics of the torque converter would help if you could find some...thank

Steve 5 years ago

I have a 63 Monza 900 Convertible. What and where are these oil ballasts I've heard of? I'd like to check if I have them, and if they have fluid in them...

perrya profile image

perrya 5 years ago Author

well, in a 65+, they are in each corner of the fender, behind tail lights and headlights. They DO make a big difference in stability on roads at higher speeds.

ri 5 years ago

My 400 trans is only working in reverse do I need to replace trans mission or vacuum modulator..... It also goes like 5 mph in drive

DonV 4 years ago

I have just checked the vacume advance on my 64 corvair. It takes aalot of ahnd pressure to move the old one. The engine has two vacume tubes on each carb. with the vacume tube going to only one(other one has been capped off). I checked for amount of vacume from just the one carb and even when the engine is reved up there is very little vacume. Do I need to run more tubing to both carbs for more vacume then to the vacume advance?

Mark 4 years ago

Hello! I have a '63 Monza 900. It's been a great car. My question is about the throttle linkage that runs underneath the car from the accelerator back. About halfway back, there is a small linkaga that hold together two parts of the shaft. After 48 years, that finally decided to pop apart on my car. Are there any cheap fixes that I can do to avoid a towing bill up to my corvair guy? He's about a half-hour away from where I live. p.s. Where is Santa Rosa?

perrya profile image

perrya 4 years ago Author

My 67 has a different linkage, so i am not sure.

cowgirl79 4 years ago

I have a 61 Monza 900 (auto)- replaced the points 2 days after I bought it, ran fine for a few weeks, fuel pump killed over, replaced it. NOW, it runs fine for about 15-20 minutes and chokes out. Idles fine in neutral, but as soon as I put it in gear, it starts knocking really bad and has no power. If I leave it in neutral, and rev the engine a few times, then put it back in gear, it will creep along then suddenly it runs ok for a few minutes longer. Thinking distributor...??? It almost seems like it kicks itself out of timing, but I am not sure. Any ideas??

perrya profile image

perrya 4 years ago Author

You may have multiple issues with the knocking. This is one of those things where you need to fix one thing, and see if it fixes the issue. It may need a new distributor as you said.

cowgirl79 4 years ago

Multiple issues? I was afraid of that! Guess I will start replacing parts until it runs right, hopefully I can figure it out soon. Thanks so much!

perrya profile image

perrya 4 years ago Author

Good luck!

donnie 4 years ago

65 corvair that has high oil pressure and blows filter apart

rare69 4 years ago

'66 PG increases RPM when Low is selected . The throttle lever rotates clockwise to push the accelerator lever up to a high idle speed.

linkage adjusted by manual from gas pedal to carbs with no difference. cannot downshift in drive at WOT.

Had this car 30+ years always same symptoms.

Richard Cook 4 years ago

Just started working on 65 Corvair Monza. Compression is #1 146,#2 157,#3 170,#4 160,#5 165, #6 170. Book says 120-130 is normal what do my reading tell you??

perrya profile image

perrya 4 years ago Author

Low compression either from valves or rings. You can do the test wet and dry. Check the lbs. dry and then give a little shot of oil in the plug hole and check the lbs. If the pressure goes up wet, then the rings are losing the pressure. If the pressure is the same wet or dry, then it's a good chance that it needs a valve job.

Richard Cook 4 years ago

Thanks for the input but I still don't understand the readings. The only spec I have found says compression should be between 120 and 130. If this is true how can my reading even be achieved??

perrya profile image

perrya 4 years ago Author

High compression is usually caused by either excessive carbon build up, excessive fuel being injected or oil\coolant getting in. The corvair should have a reading of 130 psi

Richard Cook 4 years ago

1965 Corvair Monza vacuum leak. Is it possible to have an intake manifold leak with the manifold/head being common and comparession reading of 150# on all cylinders? I was wrong on my first set of readings. All plugs burning clean on one head/manifold all plugs burning dark on other head/manifold. Is there a separat seal between the head surface and the common intake surface?

perrya profile image

perrya 4 years ago Author

burning dark? oily dark or sooty dark?

Richard Cook 4 years ago

No oil. They are dry but obviously not firing as they do on the other head.

perrya profile image

perrya 4 years ago Author

Other that plugs being dry, black, are they burning fine? Maybe you need to reset timing? plug wires? I don't know what has already been done.

Richard R. Cook 4 years ago

I've covered all those bases so wondering if vacuum leak in the intake portion of head could cause poor fuel supply to that bank, not allowing the 1,3,5 cylinders to fire fully. This problem is effecting the one bank only and uniformly. Can I get the good 150 reading on these cylinders and have a vacuum leak in the intake portion of the head/manifold? I know what a correctly firing plug looks like, grey or light brown. Engine misses and backfires under any load (acceleration). I've worked on my cars for years but have no experience with the Corvair engine.

perrya profile image

perrya 4 years ago Author

So u did all the usual tuneup things, new coil? fuel pump still good? A vacuum leak would cause a bad fuel-air ratio.

thomas 4 years ago

Powerglide leaks oil sometimes all oil, sometime a little bit of oil and sometime no oil leak????

Wayne H 2 years ago

how do you go about changing "O" seal in the Throttle valve on a 66 corvair monza

perrya profile image

perrya 2 years ago Author

Sorry, no, but I have the shop manuals

Steve 2 years ago

My PG in my 66 Vair does not shift int second. Have driven it up to 52 mph with no shift. Any Ideas?

disgrig 20 months ago

My '62 Corvair Monza automatic shifts hard (jerks) when shifting from neutral into Drive and also when coming to stop/downshifting. Any ideas on what to start with?


perrya profile image

perrya 20 months ago Author

Many shifting issues are tied to internal issues because AT trannys have bands that overtime may become damaged or worn.

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