I have recently bought 71 old cutlass supreme. Engine block number is 36M07841. Any help is appreciated, thanks.

 

3= Oldsmobile division of GM
6= 1976 motor
M=Lansing MI (where it was built)
07841= assembly line sequence

 

Many things can change. I bought my 70 with an Olds 260! I currently have a 76 block with 70 heads. What is the big number by 1 and 8 on the cylinder heads?

 

8

 

I bet it is probably untouched inside and still runs very good. The Olds 350 from that era were very durable.

 

Yes the motor is strong but trans is shifting hard. Mechanic friend said I need to check the Diaphragm bell at end of trans. Going to look today.

 

What in hell is a "diaphragm bell". I'm 75 and have never heard of that.

 

I was thinking the same thing. The only "diaphragm" on the trans is inside the vacuum modulator.

 

Gotta be torque converter he's talking about? but thats not at the end unless he thinks the end is the front? What do you check anyway? IDK

 

No man he called back, vacuum modulator. Took some pics of it doesn’t look good at all.


Guy has a liquid seal gasket. But to me this doesn’t look like the on I pulled up online. It’s shifting hard in both speeds.

 

^^^ I'm betting on the diaphragm inside the ATM, as well.

 

Leaking transmission fluid at this location = ruptured ATM diaphragm. Easy fix.

 

Thanks but I don’t know what transmission it is. Crazy I know! I bought it without regards. Great deal couldn’t pass it up!

 

First pic is rear trans seal (driveshaft) The second pic is the speedometer cable. I dont see a pic of the modulator.

 

I realized after a few hours of looking up the transmission parts. They are all fairly inexpensive. Hope this is an easy fix like mentioned. Thanks for all input

 

ATM is a cash machine.

 

Yes, a ruptured vacuum modulator will cause rough and late shifts. I also had that symptom from the governor on my 1970 TH350. It acted like it had a shift kit. I changed the governor and added lighter weights for higher rpm shifts. It shifted like mush at part throttle after that, weird. I used that governor with an adjustable modulator in a 1985 TH350C and it shifts normal. For the leaking rear seal, a tail shaft bushing and new seal should fix it.

 

True enough. I should probably have typed out ATM (Automatic Transmission Modulator), which is how I usually reference the transmission vacuum modulator.

The OP (Jay) stated he didn't know which transmission he had and I can't tell from the picture. With that said, you can identify (to some degree) whether it's the 350 or 400 via location of the ATM.

The first image is the ATM location for the 350 transmission, second picture ATM location of the 400 transmission. Follow the modulator pipe from the engine intake manifold, it traverses downwards alongside the transmission oil filler tube, then snakes rearward towards the back of the transmission until it attaches to the ATM. Review the integrity of the ATM.


350

400

 

Good news and bad, good thing- vacuum modulator is good. Purchased one but 1/2 bolt for clip stripped to hell. Owner previously for whatever reason ran 1/4 rubber tubing all the way to carb!! Hose was dry rotted so I replaced and it shifts perfectly. Bad news is I still have that slight leak at the rear seal. Not tremendously worried, but I will tend to it later. Thanks again for all input and advice— New 71 Olds owner!