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Thoughts on Drive Shaft Thiccness? (diameter)

VolvoScout

VolvoScout

Member
Joined
Jun 4, 2012
Location
Upstate, NY
What are the advantages and/or disadvantages of the larger (thicker) driveshafts on later 240s vs the smaller (thinner) driveshafts on the early 240s?
I've noticed that the later driveshafts are definitely heavier; does the driveshaft weight have a significant effect on power to the wheels?
I am assuming it was for durability, but why did Volvo go to a thicker driveshaft?

I have a larger drive shaft that came out of a '93 and wondering if it's worth swapping the thinner driveshaft out of my '82...
 
If you wanted to go with that option, you would have to swap the output flange on trans and the flange on rear end. So it's not really a direct swap. But not hard to source those parts.
 
white855T said:
If you wanted to go with that option, you would have to swap the output flange on trans and the flange on rear end. So it's not really a direct swap. But not hard to source those parts.
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I just oversized the holes slightly to use the bigger driveshaft. No issues
 
VolvoScout said:
What are the advantages and/or disadvantages of the larger (thicker) driveshafts on later 240s vs the smaller (thinner) driveshafts on the early 240s?
I've noticed that the later driveshafts are definitely heavier; does the driveshaft weight have a significant effect on power to the wheels?
I am assuming it was for durability, but why did Volvo go to a thicker driveshaft?

I have a larger drive shaft that came out of a '93 and wondering if it's worth swapping the thinner driveshaft out of my '82...
Click to expand...
I have never seen the small diameter tube 240 drive shaft fail. The change more likely had to do with reducing vibration. The larger diameter tube is much stiffer both in twist and bending. That skinny shaft is like powering the car with a piece of PVC pipe.
 
Rob Prince broke a skinny drive shaft in torsion. The later larger style is stronger.

The turbo cars got the thicker driveshaft with a built-in dampener.
 
blkaplan said:
Rob Prince broke a skinny drive shaft in torsion. The later larger style is stronger.

The turbo cars got the thicker driveshaft with a built-in dampener.
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I meant stock I have never seen the skinny shaft break. It was only used in the 105 hp NA 240. There is no way I would want to run the skinny shaft period, let alone with a modified redblock or engine swap in front of it. Volvo realized how weak the design was when they were designing the Turbo 240s.
 
2manyturbos said:
I meant stock I have never seen the skinny shaft break. It was only used in the 105 hp NA 240. There is no way I would want to run the skinny shaft period, let alone with a modified redblock or engine swap in front of it. Volvo realized how weak the design was when they were designing the Turbo 240s.
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Yes, they would be good enough on a stock b21 turd with skinny 14" tires.
 
VolvoScout said:
At what horse power/torque would it be recommended to switch from the smaller to the larger drive shaft?
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I can give you an assumption. Volvo decided it was a good idea to upgrade before they introduced the Turbo 240 which only made 132 HP. So, that skinny shaft was probably at its limit with the NA 105 hp engine. As soon as the shaft starts to twist much disaster is looming.
 
hiperfauto said:
Volvo used the larger shaft when they went to fuel injection on the B20s. They made ~130hp.
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They may have, yet, weren't consistent. A 78 B21 K-jet wagon with M46 I bought for parts ran the skinny drive shaft. My 79 B21 K-jet 242 also had the skinny drive shaft in it.

Then, Volvo went the opposite direction again. The 1982 B21 K-jet 245 with M46 I parted out had the large shaft just like the one that came in the Turbo 240. I'm guessing the change likely occurred in 1981 when the Turbo was introduced. Everything after 1982 that I have seen has/had a variant of the larger diameter drive shaft in it.
 
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Volvo lowered the compression ratio after '71 so the engines didn't make as much power. They probably switched back to the smaller shaft when that happened pinching pennies wherever they can.
 
hiperfauto said:
Volvo lowered the compression ratio after '71 so the engines didn't make as much power. They probably switched back to the smaller shaft when that happened.
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Damn bean counters. I read somewhere way back about how much money Ford supposedly saved by using only 4 lug nuts on the 6 cylinder Mustangs vs. 5 lug nuts on the V8 cars from 1964 through 1966. It was significant. All Mustang owners hate that decision.
 
It's not necessarily torque capacity that informs driveshaft diameter. A larger diameter driveshaft has a higher critical speed. Critical speed being the rpm at which it wants to whip itself into the shape of a jump rope. A car with more power can go faster, needs a bigger shaft.
 
i run a stock 88 245 driveshaft with a 1310 yoke welded to it behind my ls swapped 242 and have had no issues. on my turbo ls 244 i was running a 2 1/4 one piece driveshaft with 1310 u joints with no issues. i think with the later bigger shaft you will be fine with however much power you can throw at it with a redblock as long as the rest of the drivetrain is in good mechanical order.
 
I have a stock/modified for T56 slip yoke at front in a turbo LS combo that hasn't given up yet. It's just got new stock u joints with a hd center support bearing. Car is in sig, 1982 also.
 
244tiCanuck said:
It's not necessarily torque capacity that informs driveshaft diameter. A larger diameter driveshaft has a higher critical speed. Critical speed being the rpm at which it wants to whip itself into the shape of a jump rope. A car with more power can go faster, needs a bigger shaft.
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Drive shaft length also affects critical speed. There's a reason Volvo uses 2 piece drive shafts.
 
hiperfauto said:
Volvo lowered the compression ratio after '71 so the engines didn't make as much power. They probably switched back to the smaller shaft when that happened pinching pennies wherever they can.
Click to expand...
B20E 1800s still got the 1310 driveshafts.

But the 1972 1800E I got from the US with a B20F got the 1140 driveshafts.

73-74 164s over here got 1310 / 1310 driveshafts, as did B20B and B20E 140s.

B20A 140s got the 1140 /1140 and sometimes the 1140 /1310 combo.

A 78 model 244 which I parted has 1140 driveshafts behind its B21A and M45. The 242GT (B23E) had 1310s front and rear.

Many years ago, I ran a shortened HT Holden 2-inch diameter single-piece tailshaft in my former 144, behind the Celica 5 speed. Under bump, the tailshaft sometimes used to rub on the seam in the transmission tunnel under the rear passenger seat. Ah, the follies of youth....
 
My '80 wagon has a combo shaft. Center and front are 1100 series, rear is 1310. With a weird size increase half way down the rear shaft.

I recently saw an '82 with an all small shaft.

My '73 144E has a small shaft.

Also interesting is the dampers that got put on some M40 gearboxes. The output shaft flange is much larger.
 
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