240 General: New (to me) 1980 Volvo 244

[Othen]

Originally Posted by john.wigley

Glad you had a good day, Alan.

You said:

"I had a look at a AW71 gearbox whilst we were in Worcester, it looks more or less like it would fit and seemed to have the same 4 hole output flange, so perhaps that will be next year's project. My concern is the gearing, in a 740 the engine turns over at 2400 RPM at 70, so the gearing is 56% higher than the BW55 that is fitted. The RB only produced 100 HP when it was new, and probably a few have bolted over the past 40 years, so I don't know that it will produce enough torque at 2400 RPM to be in top gear at 70 MPH. The answer we discussed might be to get some more torque - which might lead to a twin Weber carburettor conversion... but then where would I stop. I need to think about this one over the winter."

I don't know how easy it would be, or if it is even feasible, but might an alternative solution be to change the rear axle reduction ratio? Reference to Mr. Haynes' book of words suggests that there are five, ranging from 3.54 to 4.30, or 3.15 to 3.91, to 1, depending on type.

Out of interest, our last 740s, both '87 2.3 FI autos, turned over at an indicated 2,700 RPM at 60 MPH (a needle's width over 3000 at 70), so it may not be as far out as you think.

If your rear axle is also showing it's age, might this be worth looking into as an alternative to extracting more power from the engine. Perhaps you could even do both?!

Regards, John.

Thank you for that John,

All I can conclude at the moment is that I have to do some more research and think about this one a bit. The engine speed at 70MPH I got from the chap selling the wheels (who had also just sold the AW71 gearbox) - I should be ale to find out how the AW71 and BW55 are geared internally from the Volvo green book and compare them.

My feeling is that if the internal gearing really is 56% higher then the humble B21a motor will not cope with that, and would probably be running in third to achieve 70MPH (so there would be no gain). If that is the case you are right, I would either need more torque or lower final gearing. On a bike that is trivial of course, us bikers change gearbox and rear wheel sprockets to fine tune the overall gearing frequently, but I'm not sure I'd see the value in changing the rear axle (which works just as it should) to make this work.

As you know, I'm planning to keep the RB as a long term project car, so I'm certainly not ruling out the AW71 gearbox swap, but it may need to be part of a package of changes to make it work. I was certainly not planning to make the gearbox change until after 1 April when the RB will be safely registered as an historic car, so I have plenty of time to research and think about this issue.

The good news is that I was really impressed with the RB as it is (I'm even getting used to the buzzy 3 speeder gearbox). I thought the performance and fuel consumption were both excellent for a 40 year old car. It is a bit underpowered for its weight (nothing much wrong, even when it was new 100 HP to shift a ton and a half was not much by today's standards) - so I would not be agin some improvements to the engine.

Bob and I did have a really nice day. Thank you.

Alan

[Othen]

John,

I've just found the internal gearing in the green book. 3rd gear in the BW55 is 1:1, top (4th or overdrive) in the AW71 is 0.69:1, so to compare it as I did above that makes the gearbox 44% higher geared. This takes no account of rear drive ratios of course, which are different between the 240 and 740 (see below).

So, a 0.69:1 increase would mean the RB would be turning 2590 RPM at 70 MPH (assuming the torque converter is running at 1:1 in both cases). The gamble would be whether the B21a would be producing enough torque at 2590 RPM for both torque converter to be running at 1:1, and whether the gearbox would change into top (the maximum 3-4 shift speed for the AW71 is 70 MPH at a 75% throttle opening).

The B21a motor was used with both 3.54 and 3.73:1 final drive ratios (I don't know which I have, I'll try to find out tomorrow), the AW71 had a 3.73 or 3.91 final drive ratio, but I'm still not convinced a B21a will be making enough torque to cruise comfortably at 70 MPH in top without the torque converter running at less than 1:1 (which would lead to pretty poor fuel consumption).

What do you think? More work required on this one?

Alan

[Laird Scooby]

Originally Posted by Othen

Thank you for that John,

All I can conclude at the moment is that I have to do some more research and think about this one a bit. The engine speed at 70MPH I got from the chap selling the wheels (who had also just sold the AW71 gearbox) - I should be ale to find out how the AW71 and BW55 are geared internally from the Volvo green book and compare them.

My feeling is that if the internal gearing really is 56% higher then the humble B21a motor will not cope with that, and would probably be running in third to achieve 70MPH (so there would be no gain). If that is the case you are right, I would either need more torque or lower final gearing. On a bike that is trivial of course, us bikers change gearbox and rear wheel sprockets to fine tune the overall gearing frequently, but I'm not sure I'd see the value in changing the rear axle (which works just as it should) to make this work.

As you know, I'm planning to keep the RB as a long term project car, so I'm certainly not ruling out the AW71 gearbox swap, but it may need to be part of a package of changes to make it work. I was certainly not planning to make the gearbox change until after 1 April when the RB will be safely registered as an historic car, so I have plenty of time to research and think about this issue.

The good news is that I was really impressed with the RB as it is (I'm even getting used to the buzzy 3 speeder gearbox). I thought the performance and fuel consumption were both excellent for a 40 year old car. It is a bit underpowered for its weight (nothing much wrong, even when it was new 100 HP to shift a ton and a half was not much by today's standards) - so I would not be agin some improvements to the engine.

Bob and I did have a really nice day. Thank you.

Alan

I'd hazard a guess you have the 3.54:1 diff in the RB Alan because in 3rd in mine, it's also doing ~3750rpm and that's on 195/65/15 tyres and a 3.54:1 diff. Originally it was a 3.91:1 diff but when that went, i had to change the back axle and luckily found a 3.54:1 back axle.

I'd question the up-change speed as it's difficult to judge 3/4 throttle, i know 2nd is good for 85-90mph and never fully explored 3rd or 4th yet.

However, at 70mph which is where you seem most concerned with, it's more about keeping it rolling than getting it rolling. If you treat 4th in the AW71 as an overdrive (you can let the box do it all or use the button on the side of the gear lever) then it shouldn't be a problem. Even if you have to knock the overdrive off on a long motorway hill then back on after, you've not really lost anything and youll be gaining on the flat and downhill.

Might still be a good idea to boost the output slightly with a twin choke Weber and 4 branch manifold etc but i'd say try the AW71 box first before you start on the engine.

Glad you had a good trip and the economy is pretty good too!

[john.wigley]

Sound logic, Alan. While I think that a 4-speed 'box could benefit the RB in terms of refinement, economy and potentially performance, I would have to defer to 'L.S.'s encyclopaedic knowledge of such matters. However, If the RB were mine, I think I would still explore all possibilities. The mods that you envisage would do the car no harm, while also being fully reversible should they not be successful or you wish to revert to standard specification in future for any reason.

Regards, John.

[Othen]

Many thanks for your thoughts Dave and John,

The good news from today’s trip was that the RB is much better on a longer run than I had expected it to be, normally I only use the car for short, local trips - but it was more in its element today. The conclusion being: there is no rush to change things: the engine, drivetrain and chassis are all very good indeed.

My way is to plan things carefully (years of military training and experience I suppose), so I’m happy to make sure everything is likely to work before making any more changes. I have the winter to think about whether or not to do the AW71 gearbox change. If the BW55 had a fault I’d certainly change it in April, but it doesn’t...

I quite like the look of the new wheels, which is good. I’m looking forward to getting them sorted over the next few weeks. I’m still not quite sure what I’m going to do with them, perhaps just store them so I have a spare set of nice, period wheels in 10 years time when the Virgo wheels need changing?

Bob really enjoyed our road trip today - as did I.

Alan

[Othen]

PS. Chaps, I’m still feeling rather smug about the RB’s performance today, and in particular the fuel consumption, I thought that very nearly 30 MPG was very good indeed. I’ve only owned the RB since February, and when I think back to all the little things that were wrong with it when I bought the car I am really pleased with myself.

[Dippydog]

I think you have every right to feel smug over the fuel consumption.It is pretty impressive and I'd say down to your due diligence and care that it's been achievable.
Out of interest[probably more aimed at L.S.]what controls the gear changes on the two different gearboxes? I know for instance that the 3 speed on Senator A was by a take off pipe from the inlet manifold[so my manifold depression]where the later 4 speeders on the Senator B was electronic.

[Laird Scooby]

Originally Posted by Othen

PS. Chaps, I’m still feeling rather smug about the RB’s performance today, and in particular the fuel consumption, I thought that very nearly 30 MPG was very good indeed. I’ve only owned the RB since February, and when I think back to all the little things that were wrong with it when I bought the car I am really pleased with myself.

You've come a very long way with the RB in a relatively short time Alan and you have every right to feel justifiably proud (and smug!) with the progress you've made.

Originally Posted by Dippydog

Out of interest[probably more aimed at L.S.]what controls the gear changes on the two different gearboxes? I know for instance that the 3 speed on Senator A was by a take off pipe from the inlet manifold[so my manifold depression]where the later 4 speeders on the Senator B was electronic.

If memory serves the Senator A had the GM180 box, as did the Series 2 SD1s and the Series 1.5 SD1s, of which i owned one. That threw a strange fault where it was changing up much more rapidly than it should have done until i discovered a stray vacuum hose. Reconnected it to the vacant looking stub and hey presto, normal service was resumed!

As far as i've always been aware, the Aisin-Warner boxes don't rely on vacuum to change gears, not on these anyway. Some later versions had electronic control but that was obviously influenced by the fuel/ignition ECUs as well. Not sure if it retarded the ignition timing slightly as the Honda PGM-Fi ECU and EAT ECUs do just before a change up to make it smoother but electronic control is just one more thing to go wrong on a relatively simple auto box.
As i remember it, there is a governor in the AW boxes that alters the hydraulic pressure with engine speed and at certain points triggers an up change or down change, depending on whether the pressure is high or low.

[Othen]

Originally Posted by Laird Scooby

I'd hazard a guess you have the 3.54:1 diff in the RB Alan because in 3rd in mine, it's also doing ~3750rpm and that's on 195/65/15 tyres and a 3.54:1 diff. Originally it was a 3.91:1 diff but when that went, i had to change the back axle and luckily found a 3.54:1 back axle.

I'd question the up-change speed as it's difficult to judge 3/4 throttle, i know 2nd is good for 85-90mph and never fully explored 3rd or 4th yet.

However, at 70mph which is where you seem most concerned with, it's more about keeping it rolling than getting it rolling. If you treat 4th in the AW71 as an overdrive (you can let the box do it all or use the button on the side of the gear lever) then it shouldn't be a problem. Even if you have to knock the overdrive off on a long motorway hill then back on after, you've not really lost anything and youll be gaining on the flat and downhill.

Might still be a good idea to boost the output slightly with a twin choke Weber and 4 branch manifold etc but i'd say try the AW71 box first before you start on the engine.

Glad you had a good trip and the economy is pretty good too!

Good morn Dave,

I'm not sure how I would discover the final drive ratio in my car - short of taking the differential out and counting the teeth - I wonder if there are any markings on the casing that might give me a clue (I'll have a look today - see the PS below).

I suspect you are right about the RB having a 3.53:1 ratio axle, and thank you for the information about your car being at 3750 RPM at 70 MPH in third, that is entirely relevant and probably gives us a good indication for the RB. It is a good thing that I probably have the higher gear ratio.

I understand and agree with your point about treating 4th on the AW71 transmission as an overdrive (regardless of whether the manual override is used) - but what I'm wary of is ending up with something that is less good than the RB now.

Yesterday's trip has shown me that the RB has turned out rather better than I'd hoped: it has a good (although underpowered) motor and a strong drivetrain, it doesn't leak or use any oil and the fuel consumption is remarkable (well, I think so) for a 40 year old car. My concern is that if I don't plan the outcome properly I might end up with a worse car: one for which the transmission is not well suited to the engine, perhaps it leaks oil or has 20 MPG fuel consumption - that is all.

I still think a 4 speed AW71 transmission would be a good place to end up with the RB, but the motor car is a long term keeper (particularly after yesterday's test) so there is no great rush over this. If I change the gearbox I'll have to fit a fluid cooler, and so a radiator from a manual car (no great issue, we discussed this previously), come up with a solution for the prop shaft and the centre bearing support, quite possibly find some more horses for the engine (or fit a 2.3 litre unit) and maybe change the final drive ratio (I think I would have to fit a 3.91:1 rear axle, maybe from a 740). None of those things are huge problems in their own right, but having got the RB running very well indeed I just want to plan the next move carefully, rather than risk ruining a very nice motor car.

We have all winter to think about this one :-)

Alan

PS. To determine the final drive ratio I could just jack up one rear wheel and count the number of revolutions the prop shaft makes for one turn - einfach, nicht nahr?

[Laird Scooby]

The first three ratios are pretty similar on the 4-speed box Alan, 3rd is the same @ 1:1 so there shouldn't be a case of it being less good on economy.

On the 7xx, there is a label on the left hand end of the axle denoting the diff ratio, however over time this label disappears for various reasons. I'm not sure how it's denoted (if at all) on the 2xx so yes, jacking one wheel and counting the turns of the propshaft might be an option. I'd suggest 10 turns of the roadwheel to give you either 35.4 or 37.3 turns of the propshaft as trying to differentiate between 3 1/2 and 3 3/4 turns from one turn of the roadwheel could prove tricky!