Torque tube overdrive project finishes up.

JimShelly

Member
It is time to bring everyone who is interested up to speed on my lovely project. I’ll confess, I wondered if we would ever get this right, BUT in the end I have a car again. With an overdrive. I’ve put on less than 200 miles and I still have tweeking to do, but the overdrive works well. Gearvendors says don’t engage the unit under 30mph as there won’t be enough pump pressure, and by 30mph this car is definitely in 3rd, so in effect I now have a 4th gear. It does change the character of the car.

By the end of 2021 I’d solved all the engineering issues and driven the car on the road, but with horrible vibrations. This is what we did in January and February: We left the tranny and clutch alone, but pulled the rear end out of the car and unbolted the overdrive unit from the middle of the torque tube. The front part of the torque tube and the internal driveshaft from the OD to the torque ball comes apart easily. However, the rear shaft from the pinion gear was another matter.
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I couldn’t imagine getting the torque tube itself out of the rear end after 81 years. We cut an access hole in the top of the tube, then measured where the pin lived and drilled a half inch hole on either side of the tube so we were able to punch the pin out of the driveshaft. We had an advantage in that we’d cut the tube itself to put in the OD unit, but I suppose this would work on an intact torque tube as well. It was not a tapered pin.
The driveshaft was stuck fast and we had to heat it up thru our access hole, then drove it off the pinion gear shaft with an air chisel. We then took both shafts to Long Island Driveshaft where they promised to reweld the ends and make them true (proving that vendors will lie to you on purpose.) The professionally straightened rear shaft still had 12 thou run out over a 10-inch length, so we took it off and tried again. No luck.
By this time the rear driveshaft end was pretty beat so I sourced a used driveshaft from Dave Tacheny in Minnesota, had it shipped, and went to Nassau Driveshaft in Merrick. They did quite a good job of cutting that shaft to length and welding on both the Buick ends and the splined adaptors for the overdrive. My dial indicator setup now indicated about 4-5 thousandths runout on both shafts. We reassembled with these driveshafts and shimmed the mounting flanges we’d welded onto the torque tube to get everything as straight as possible. I set up the Torque ball shims so the front driveshaft fell slowly to the floor when released and ever since reassembly, I’ve been playing with the Torque assembly mounts to center the driveshaft.

This whole process had taken a month during which time the car had been sitting in the corner of the shop. Rather than put dollies under the rear end and maneuver it over to a lift, we left it jacked up and installed the rear end as it sat. That made for a day of crawling around on the floor which really tired me out, but the job was done. I started up, checked my brakes, eased out of the shop and set off down the road. This photo at the bay is 5 miles into my test drive.
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The vibration is lots less and I think I can work on centering the driveshaft so I feel less. As above, I now have a 4 speed car. I put on some 100 miles and shipped the car home to NJ. When I went for a brief drive around Robbinsville I heard the “scary noise”. It was hard to identify and I returned to Florida not knowing what was really going on. Nervous.

But, thinking about it, I’ve replaced the transmission input shaft pilot bearing with a pilot bushing, and my press fit was too tight. That is wearing in. I’ve put in a new pressure plate and flywheel from a 94 Jeep Cherokee. I’ve added the overdrive with all the alignment troubles that made, and I had the rear diff apart trying to find the pin fastening the rear axle to the pinion bearing, so I’ve reset the gear lash back there. I’ve pulled the flywheel, heated the ring gear until it dropped off, turned it around and dropped it back on the flywheel so the worn teeth would not slip on the starter Bendix drive. I’ve put in rebuilt rear lever arm shocks, and re-gasketed the exhaust manifold and downpipe. There were lots of things we’d done which might make noises.

On my next trip north I drove the car as much as I could, heard the noise several times, convinced myself it was coming from the transmission / clutch area and that some wearing in was going on. I also must continue aligning the whole drivetrain with the torque ball mounts. However, the worst is behind me and I’ll start some of the other projects I’d like to do before June when Great Race sets off from Warwick RI heading for Fargo ND for another 2500 mile drive. It ought to be a little cooler than last summer in Texas.

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It sounds like youv'e done some "suffering for your art", but with gratifying results. Great car. Once you've had overdrive, you always want it. I'm modifying a "no sane man would ever bother with that one, it's a parts car" 40 Special using an inferior GM brand power team and rear axle assembly. (250 Chev 6, 200 4R trans, 81 Caprice 2.73 rear axle) Not the correct way to get overdrive, I know, but I had the parts. Jonathan W on You Tube adapted a T5 trans to a straight 8 Buick, also to get the overdrive, also in an (alas!) incorrect manner.
 
Jim, after reading your tales you went through a lot for that overdrive. Does the engine have enough low end power to push the car along at driving speed at the lower RPM?
 
I had a look at the torque/engine speed, and engine speed/car speed graphs for the 248 and 320 in my 40 Shop Manual. Both engines make max torque a 2,000 rpm. I don't know which engine Jim has, but the 248 puts out 203 ft/lbs and the 320 puts out 269 at 2000. The 248, depending on axle ratio and tire size, is turning about 2520 at 60 mph. (Lowest figure of the possibilities, if I read my tiny graph right. Others run as fast as 3120 at 60.) It seems to me that the overdrive would have to have a pretty radical reduction ratio to get the engine below its max torque figure at 60 mph. I make bold to hazard a guess that the OD will drop engine speed by 200-300 rpm. So Jim should be fine for torque to cruise with the OD Make sense at all?
 
It sounds like youv'e done some "suffering for your art", but with gratifying results. Great car. Once you've had overdrive, you always want it. I'm modifying a "no sane man would ever bother with that one, it's a parts car" 40 Special using an inferior GM brand power team and rear axle assembly. (250 Chev 6, 200 4R trans, 81 Caprice 2.73 rear axle) Not the correct way to get overdrive, I know, but I had the parts. Jonathan W on You Tube adapted a T5 trans to a straight 8 Buick, also to get the overdrive, also in an (alas!) incorrect manner.

Can you explain the incorrect manner? I have seen Jonathan's video. Perhaps i missed something?

Ben
 
"Incorrect manner" is just my nod to the superior attitude of those who say of anything done to a car that changes the way it came from the factory, that it is not "correct". I believe the air in the tires may be replaced with non-factory air, and still pass muster, but that's about it. I saw a beautiful (but improved) 40 Buick on YT. It was followed by a comment that they didn't use clear coat paint when it was first built, and in his opinion, it was a basket case. I think Jonathan did, and does, a great job.
 
When engine HP/TQ is measured on a Dynamometer, it is measured at Wide Open Throttle. Those are the figures you see published for a particular engine. If an engine is rated at X amount of torque at an RPM, it doesn't mean the engine makes that amount of torque whenever it is at that RPM. The Dynamometer water brake applies a huge load to the engine as it hits WOT, and then power is measured as the engine RPM increases in the range selected. My engine builder told me that a Dyno stresses the engine more than anything you can do to it on the street/track.

This was my 470 on the Dyno in August of 2012. Listen to the motor as it strains against the water brake.


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I was just reading, in the Feb. 2011 issue of Street Rodder, about a Chrysler powered 34 Ford that set the Bonneville speed record for its class at 301 mph. The horsepower was estimated at about 4000, the owner saying he wouldn't run it on a dynamometer because something really bad would happen. I didn't know what he expected to break - the engine or the dynamometer. Now I have a better idea about that - not the dynamometer.
 
"Incorrect manner" is just my nod to the superior attitude of those who say of anything done to a car that changes the way it came from the factory, that it is not "correct". I believe the air in the tires may be replaced with non-factory air, and still pass muster, but that's about it. I saw a beautiful (but improved) 40 Buick on YT. It was followed by a comment that they didn't use clear coat paint when it was first built, and in his opinion, it was a basket case. I think Jonathan did, and does, a great job.

Gotcha! I agree. I have not been to his channel recently,

Ben
 
Jim, after reading your tales you went through a lot for that overdrive. Does the engine have enough low end power to push the car along at driving speed at the lower RPM?
So far I've not had a problem. It works just like a 4th gear. When I start to lug the motor, I switch the OD off and drop into 3rd in the transmission. And bear in mind this car is probably turning 4000 rpm to do 60 without the OD. I must really fit a tach to check that some day but that's my estimate. The OD lowers engine 23% which is still cranking.
 
I had a look at the torque/engine speed, and engine speed/car speed graphs for the 248 and 320 in my 40 Shop Manual. Both engines make max torque a 2,000 rpm. I don't know which engine Jim has, but the 248 puts out 203 ft/lbs and the 320 puts out 269 at 2000. The 248, depending on axle ratio and tire size, is turning about 2520 at 60 mph. (Lowest figure of the possibilities, if I read my tiny graph right. Others run as fast as 3120 at 60.) It seems to me that the overdrive would have to have a pretty radical reduction ratio to get the engine below its max torque figure at 60 mph. I make bold to hazard a guess that the OD will drop engine speed by 200-300 rpm. So Jim should be fine for torque to cruise with the OD Make sense at all?
Stray Tate: That's interesting information, thank you. This motor howls at 60mph in 3rd gear, hence my 'seat of the pants' rpm estimate of 4000. The OD gives a 23% reduction thereof, meaning even if those numbers are right, I'm still taching 1940rpm, pretty close to the max torque number. I'm definitely going to have to fit an electronic tach later this month when I'm back to the car and driving. I'll get a definitive RMP and get back to you.. This is my Buick at the Beach photo which I see didn't make it into my original post. Jim
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Just for comparison. My 1950 standard transmission equipped car came with 4.1/1 gears. I swapped them out for 3.36/1. The RPM dropped approximately 650 per the tach.. The engine has ample torque. BUT, I lost low and slow performance one will still have with the overdrive. An overdrive is more versatile at about ten times the cost. ENJOY the drive.

Ben
 
I entered a TSD rally last Sunday and drove 110 miles to and from it. The rally itself was another 95 miles long, so I got in a 200 mile day.
The overdrive acts like a 4th gear. I shift through 3, then clutch in, power on to the OD, clutch out for the 4th. It is great. I'm still chasing centering the torque ball to further limit vibration, otherwise everything seems to be going well.
Jim
 
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