getting ready to buy a 1980 dl with a 4 speed [non] overdrive. will it be ok at highway speeds over 60 or will it be like a normal 5 speed riding in 4th gear needing to upshift to that last gear.. meaning that the enging will be at high rpm... reason why im asking is that a friend of mine had a 3 speed volvo with no 4th gear and couldnt travel on the highway because of high enging reving...

Overdrive cuts down significantly on engine noise, but it does not improve gas mileage much (1 or 2 mpg at most in my experience) and the engine doesn't care whether it is turning 2,500 in overdrive or 3,000+ in 4th gear.

With a 3.91 rear end, you will probably spin 3,200-3,300 at 65 mph and 3,500 at 70 mph. Noisy but not a big deal.

Uncle Keith,

1980 Volvo 240 (2 or 4 door)?

Yeah, the K-jet or early carburetor exhaust manifold can really give you a howl at around 3300-3700 RPM in any 1976 to 1981 or so B21 Volvo versus the faster flowing, more evenly piped manifold in the late B23/B230 with the LH-Jetronic fuel injection.

You could swap out the first version B21F manifold with a B230 manifold like from a 1991 240. If your current model has EGR (exhaust gas recirculation) with a pipe coming from the rear of the manifold, you may want to:
- Assess whether the new, faster flow stock B230 manifold from a 240 B230 with EGR will drop in to your EGR equipped 1980 240 B21F. (I'm assuming you have Bosch K-jetronic injection in your 1980 240).
- If not in CA-state, you may be able to remove the EGR system as Bosch K-jet and the ignition system operate independently of it and install a non-EGR fast flow OEM stock B230 manifold from a late model Bosch LH-Jetronic B230 engine. Newer is better.

Sound deadening along the firewall interior. Some mat stuff that can take the high temps of summer on the North American market passenger side as the area gets hot from a hot ground under the car and the heat coming from the exhaust.

It'll add some vibration if missing, yet you want that exhaust header pipe secured to the bracket that is part of the support assembly secured to the lower right bell housing bolts. You want that support as it is a safety issue, it protect the utterly weakest exhaust piping connection on the Volvo 240 where the header pipe secures to the catalytic convertor.

You will want to verify oxygen sensor operation. Most that have K-jet on a 240 ignore this most critical sensor. Verify operation and renew if at fault. Review the archives for this procedure. The K-jet system uses a single-wire Bosch oxygen sensor.

Inspect the motor and transmission mounts and replace. Harder B21F motor mounts, like people like me that install the real diesel 240 mounts, turns into more vibration through the unibody and into the passenger compartment. So, use the softer Volvo OEM motor mounts if you have to replace these.

All the while, you can consider:
- A taller final drive ratio by swapping gears in that Dayna differential or the entire differential with a quality used model of a taller gearing. (Some folks disdain the taller gearing as you have slightly less torque in lower gears. I say P'shaw on them as this is a normally aspired B21F in a Volvo 240.)
- Or, as many do, locate a quality used M46 transmission with all the works from the bell housing (and all in it including clutch assembly and flywheel), the entire drive shaft, and transmission support member. Inspect the Dayna model on the donor car for ratio in that donor car differential or if it is a limited slip or locking differential.

Hope that helps.

Questions.

Well Duffed and Buttermilked.

Yes---and yes. you will be able to cruise the highways ok - noisy but ok. And yes that it will be like driving a 5-speed in 4th. The 1980 240 model (I drive an '80 245 w/four speed plus o'drive--the M46 transmission) came with a 3.91 rear axle ratio in either version. For many years the 122 and 140 models carried a 4.10 -- with some models as low as 4.56. If you like it--buy the car and then keep your eyes open for a donor car with O'drive. Everything on a 240 M45 to M46 conversion is straightforward and things fit all through the model years -- especially if you're working on an older model like the '80. -- Dave

I took a 76 240 from Tulsa,OK to Baraboo, WI in a day and the back the next. It cruised at about 75-80 just fine but anything over 70 killed the gas mileage (I think it was about 22 mpg). It also takes a while to get over 70.

Even with the windows closed, it was loud.

you'll be turning 3,000rpm @ 55mph and it just keeps climbing after that. I try to keep highway driving to short trips and not go over the speed limit.

~Mike

Respectfully disagree with your post. 3,000 is not going to do any harm to the engine, nor would 3,500 or even 4,000 rpm. He can drive the car all day at those speeds with no ill effects. It will be loud though.

The overdrive on my M46 stopped working over 10 years ago. My mechanic looked into it and told me that I needed a new solenoid and some other OD service (car had over 200k at the time). I decided not to bother with the expense. I have a 3.31 rear end in my car, so the revs are lower, but I drive at 75-80 mph in 4th gear on a regular basis. That is about 3700-4000 rpm. Been doing it for over 150,000 miles and the engine runs just fine. My gas mileage is only a couple mpg lower than it was when the OD worked. Biggest difference is the engine noise in the cabin. I just turn the radio up.