1800: Lowering RPM on 1800E with automatic transmission

[142 Guy]

Just about anything is doable; however

Whilst changing to an AW70/71 would not be difficult in the OP's P1800

the 'not be difficult' part - maybe not so much.

The AW 70/71 were fitted to the tipped over, over head cam redblock engines. Even if the bolt holes and mounting circle for a B20 bell housing matched up with the tipped over AW 70/71 bell housing, you would still be into sectioning the bell housing, rotating the mounting flange and welding it back together to get the transmission to sit with its correct orientation. If the bolt circle / mounting holes do not match up then you are faced with fabricating an adapter flange, sectioning the bell housing and welding on the adapter flange in the correct orientation. You then still have the question of the attachment of the transmission to the engine.

Its probably doable. Its not going to be a primarily exchange parts and bolt in like most M41 conversions so the 'not be difficult' will depend on your fabrication and design skills or willing to set up a printing press to produce money to have a fabricator do it for you . The AW 70/71 OD ratio of 0.69:1 and a 3.9:1 final drive would make for much more relaxed highway cruising. But, the slightest headwind or hill will force a downshift because US spec B20F engines are not exactly power houses.

It might be easier to transplant the AW 70/71 with the B230 attached rather than try and graft it on to the B20. I have seen an Amazon with a B230FT installed in it so it is probably doable in the 1800. An 1800ES with an AW 71 and a B230 FT would not suffer from headwind problems.

With a 3.9: 1 rear end and the BW 35 transmission, the reported 3000 RPM at 90 km/hr would seem to be correct. If the noise is excessive, I might be first inclined to investigate some noise abatement before embarking on the transmission changeout exercise.

[Othen]

Originally Posted by 142 Guy

Just about anything is doable; however



the 'not be difficult' part - maybe not so much.

The AW 70/71 were fitted to the tipped over, over head cam redblock engines. Even if the bolt holes and mounting circle for a B20 bell housing matched up with the tipped over AW 70/71 bell housing, you would still be into sectioning the bell housing, rotating the mounting flange and welding it back together to get the transmission to sit with its correct orientation. If the bolt circle / mounting holes do not match up then you are faced with fabricating an adapter flange, sectioning the bell housing and welding on the adapter flange in the correct orientation. You then still have the question of the attachment of the transmission to the engine.

Its probably doable. Its not going to be a primarily exchange parts and bolt in like most M41 conversions so the 'not be difficult' will depend on your fabrication and design skills or willing to set up a printing press to produce money to have a fabricator do it for you . The AW 70/71 OD ratio of 0.69:1 and a 3.9:1 final drive would make for much more relaxed highway cruising. But, the slightest headwind or hill will force a downshift because US spec B20F engines are not exactly power houses.

It might be easier to transplant the AW 70/71 with the B230 attached rather than try and graft it on to the B20. I have seen an Amazon with a B230FT installed in it so it is probably doable in the 1800. An 1800ES with an AW 71 and a B230 FT would not suffer from headwind problems.

With a 3.9: 1 rear end and the BW 35 transmission, the reported 3000 RPM at 90 km/hr would seem to be correct. If the noise is excessive, I might be first inclined to investigate some noise abatement before embarking on the transmission changeout exercise.

Maybe you are right. I have not done this swap and I don't know of anyone that has with a B18 or B20 motor. My logic was that the OP has a BW35 auto box, which as far as I know is a one for one swap for the BW55 fitted in my 244 (with a B21a motor). Furthermore I also know that the AW70 was also fitted to the 240 with B21 and B23 motors (from 1984 if I remember correctly) and that changing a BW55 (and therefore I'm guessing a BW55) for a AW 70 (or 71) is not a specially hard job (not quite a straight swap, but only changes to the external components) with a 240.

Now, did Mr Volvo fit a different bell housing to the B18/20 (to the B21/23) because it is on a slant? I don't know. If Mr Volvo did then would the AW70/71 gearbox fit onto the B35's bell housing - and if so what would be the situation with the torque converter, flex plate and starter? I don't know the answer to any of these, but the B20 was also fitted to early 200 series motor cars, so I'd be surprised if a combination of Volvo and Warner parts didn't already exist (the B20/BW35 combination must have been used is early 200s). The Volvo green book covering 240 series auto transmissions (TP30868/ 2; reprint w/o changes) covers the BW55, AW70 and AW71 all in the same book, and implies they are physically very similar (although it doesn't explicitly say any are interchangeable).

Here is a photo of a AW71L auto box from the bell housing end - is it very different from the BW35 (I don't know the answer)?



... and from the prop shaft end:



I'd be a little bit surprised if someone out there hasn't tried this swap, and I'd be amazed if their efforts were not recorded somewhere on the internet.

I can't remember whether the OP's motor car has carburettors or einspritzen, but if it is injected it probably would be powerful enough (about 120HP?) to take advantage of the overdrive with a 3.9:1 axle.

You may well know much more than do I of this situation - my experience is with 240 autos and P1800/P120 manual transmissions, so you may well be right. I was just answering the OP's question about the possibility of fitting a 4 speeder; my gut feeling is that it would be entirely possible to fit later series Warner transmissions (with some combination of Volvo and Warner parts).

This is probably mostly an aside because I doubt the OP is going to take his motor car in this direction. I think he will probably just fix all the other things that need it, and get used to the 1970's driving experience - one manifestation of which is the 3 speeder auto not having sufficient span of ratios to allow for relaxed highway cruising.

Interesting discussion though.

Alan

[volvobysea]

I have been following this thread with interest having a p1800 with a BW35 gearbox.
Only having 3 gears is limiting and the modern automatic boxes fitted with overdrive would give a less noisy car at motorway speeds. Personally I don't see the point of changing to a modern box as the high revving engine is part of the originality. The change to a manual version would make more sense to me but it depends on how far you would want to go as I think the manual rear end had a ratio of 4.3 compared to 3.9 auto. Also I think the m41 overdrive gearbox gives a better driving experience having driven both versions.

If you take a look at this website that deals with the recoditioning of BW gearboxes. (borgwarnertransmissionspecialist.com) you can visually see there are some differences between the BW35 and the AW71L bell housings.

Gavin

[grumpydad]

Hi
the Volvo had a Dana diff in it
so https://www.dana.com/company/
ask them for a higher ratio
if you can find some one with a bit of interest you will get all the info you need
I recon diff swap about £600 labour

hope that helps

[Derek UK]

Google this - Volvo 1800ES conversion to aw70/71

Dutch friend got an adaptor plate from someone in the USA and changed out the BW35 on his American market Amazon Combi with B18, Technically it wasn't very difficult but he was plagued with resonance type vibrations. He changed wheels and tyres had the prop critically balanced rebuilt the rear axle to no avail. Swapped the BW35 back in and all was well. He never did find out what the problem was. He knows his Amazons inside out and has had them for years so he doubt if he missed anything during this time. Sold the car to a friend and still looks after it for him. Don't know if he still has the AW70 and adaptor plate up there in Zaandam.

[142 Guy]

I have not done it, so no first hand experience. However, I did briefly contemplate the B230 FT transplant into my 142 (easier for us on this side of the Atlantic because the steering shaft does not get in the way of the turbo).

The first question is always do you put the engine in as Volvo intended (at an angle) and deal with the hardware interference issues on the right side of the engine or do you fit the engine straight up and down and deal with the tilted transmission problem (and on the 140 the intake manifold and the brake booster trying to occupy the same real estate). If you fit the engine straight up and down and you use original the M46 or AW 71 you need to rotate the bell housing (or the transmission) to get it back to the correct position (shifter 'up' on an M46). I can't remember whether its easier to rotate the transmission on the bellhousing or the bellhousing on the engine.

This guy did an interesting install in his 1800. A B230FT with an M410 and M410 bell housing.

https://volvo1800pictures.com/0_car_...67_94_2645.php

It looks like the M410 bell housing pretty much matches up to the back of the B230 FT. He does not describe any fit modifications (other than clutch actuation). The thing is the 410 bell housing matches up with the B230 FT once the B 230 FT is rotated to the up right position. In its ' correct' position the bolt holes would not match up. By extension, I think that means that an AW 71 which matches up to the B230 FT in its 'correct position' will be tilted if it can bolt up to the back of a straight up and down B20. However, if an M410 (and by extension an M41 or BW 35) can be relatively easily fitted to the back of a vertical B230 FT it does seem that with some modification to the front of the AW 71 bell housing ( building tabs with weld fill to allow hole relocation to facilitate rotation) it should fit the back of the B20. Flywheels and coupling remain to be determined.

So fitting might not be as onerous as I first thought; but, I am not so sure its moved to ''not be difficult' category .

[Othen]

What an interesting (if somewhat academic because I don't think any of the correspondents intends to swap a BW35 for a AW71 gearbox) discussion this is.

I read (in Wikipedia) that the very early (so must be 1974/75) 200 series had a B20 motor, similar to the OPs, and also that all models were available as automatics (that would have been a BW35, again the same as the OP). I have never seen (to the best of my knowledge) a 200 with a B20 motor, it would appear that Mr Volvo changed to the B21 in 1976. The slant four B21 continued with the same BW35 transmission, and later the BW55 (which I understand is identical externally) until the AW70/71 in 1984.

Where is this line of thought going: I'm still convinced it ought to be possible to bolt a BW35/55 to the back of either an upright B20 or slanting B21 motor using only combinations standard parts that either Mr Volvo or Mr Warner produced in the mid-1970s (as we know both happened in production cars). We also know that the next step to fit a AW70/71 to the back of a B21 motor is fairly trivial.

I'm not sure this line of argument of mine has moved a B20/AW71 conversion from the 'quite challenging engineering' to the 'easy fit' realm or not; it might still be quite difficult to source the correct combination of Volvo and Warner standard parts. Whether we call it an easy or challenging task doesn't really matter in that no one reading this column intends to have a go :-).

As has been said in the posts above, the 3 speeder auto is just part of the 1970's motoring experience. I hope the OP comes to enjoy that in his P1800 motor car.

Interesting discussion.

Alan

PS. See my later post below for a more enlightened view :-).

[Othen]

Originally Posted by Derek UK

Google this - Volvo 1800ES conversion to aw70/71

Dutch friend got an adaptor plate from someone in the USA and changed out the BW35 on his American market Amazon Combi with B18, Technically it wasn't very difficult but he was plagued with resonance type vibrations. He changed wheels and tyres had the prop critically balanced rebuilt the rear axle to no avail. Swapped the BW35 back in and all was well. He never did find out what the problem was. He knows his Amazons inside out and has had them for years so he doubt if he missed anything during this time. Sold the car to a friend and still looks after it for him. Don't know if he still has the AW70 and adaptor plate up there in Zaandam.

That is a very interesting story - thank you. So we know someone has done this previously (I'd have been surprised if that was not the case).

Alan

PS. See the post below!

[Othen]

The internet is such a wonderful place.

I followed Derek's advice and googled 'Volvo 1800ES conversion to aw70/71' and found this absolute gem:

https://www.v1800reg.org/pages/AW70%20CONV.PDF

Not only has exactly the swap the OP was asking about been done previously, but the correspondent has detailed the entire process from research to driving the converted motor car.

It would seem that everyone was right about bolting an AW71 auto box (with a bell housing designed for a slant 4 motor) to an upright B20:

- the bolt pattern is identical, so the gearbox will bolt on, but would be inclined at an angle. This would work as such, but might lead to reliability problems in the longer term.

- the above may be fixed with a pretty simple adaptor plate. It would be something of a miracle if any of the batch that were produced 25 years ago were still available, but getting one CNC cut from the drawings would not be difficult or particularly expensive.

I think the lovely article in the link probably brings this answer to the OP's question to a very comprehensive conclusion. It has been an interesting (and fun) discussion and again shows the value of this excellent forum.

Good fortune OP. Now you have all the information why not find an AW71 auto box (pretty common and not expensive), have an adaptor plate manufactured and document the conversion to your motor car with some words and pictures in these pages?

Alan

[hertugweile]

First of all, thank you to all participants for your valuable inputs.

Regarding originality, I just want to mention that I strive to keep the car as original as possible, but open for some modifications, as long as they are reversible.

As mentioned earlier, I have some other work on the car that has higher priority at the moment - but promise, I'll document the process, if I decide for a swap.