Lowering RPM on 1800E with automatic transmission
 

I own a 1972 1800E, imported from the US. It's equipped with a 3-speed Borg-Warner automatic transmission... but to be honest; I'm not really satisfied with it (the transmission).

At 90 km/h it runs at about 3000 rpm, but I find a bit on the high side - and makes the car somewhat noisy as well.

Have any of you ever replaced - or considered replacing - the transmission with another (like a 4-speed) or made other modifications, like exchanging the differential with a different gearing ratio (I don't know the gearing ratio of the currently mounted diff)? Any advice to share?

I would check the auto box is setup correctly like kick down cable etc and shift ( does it engauge into gears and line up on display ? ) oil ? , once you have explored that I would then make a choice sell the car and just buy one with a manual gearbox is already installed or go the long and expensive route of converting it …

I have driven a few auto P1800E and also P1800ES models all bar one drove really well strong pulls and not noisey at all ( also check your oil levels are fine with good oil in gearbox -atf - and the rear axle has good diff /gearbox oil ) .
The conversion route your short front prop will marry up all fine , you will need a j type overdrive unit with gearshift , now the important bit as I have done Amazons conversions is the support bracket mounts in a different place plus. A set of manual pedals will be required ie clutch pedal , brake pedal but will slide up in place inside the pedal box all fine married to a clutch cable in your case as late model car .

Your rear axle ratio is fine as it’s a late car with rear disc and pads so the desirable ratio just may be a wee bit different I seem to recall auto cars had a different ratio but still good tho compared to a pre 64 car .

Summary :

If it was me I would , check the car over and double check all is correct
Settings on auto shift
Oil good quality and on the level line both in gearbox and rear axle

Then make a choice if still not good sell the car to buy what you want which is cheaper & quicker or go balls deep to carry out the conversion

Best of luck and keep us updated

Kind regards
Robert.w

I wondering whether you meant change the gearbox to a 4 speed auto, rather than a manual?

I think this would be possible, and probably not particularly difficult (although I don't know anyone that has done it in a P1800). I'm pretty sure your P1800 will have a BW35 transmission, which is pretty much the same as the BW55 in my 244. it isn't too difficult a job to change that to an AW70 or AW71 four-speeder (plus hydraulic overdrive on the AW71). I'm pretty sure the AW70/71 will fit into the same space, it is about 2 1/2" longer, so the propshaft would need shortening and the cooling pipes extending by that amount. There are a few accounts of people doing this conversion with B21 motors - yours will be a B18 but I doubt it would be any more difficult.

Best wishes,

Alan

I would check you have the correct Auto axle ratio , a LOT can be bodged in 50 years .. there will be higher rpm and slippage when you accelerate as the torque converter doesn't have a lock up function which came with the later Asian Warner auto boxes .

Hello Robert.

Thank you for your thoughts. I recently replaced the kick-down cable (it was stuck in kick-down mode when I got it), as well as changed the gearbox oil (the good stuff). The car had not been driven for more than 20 years. Haven't checked the rear axle, but will do so.

I'm not experienced on automatic transmissions, but for now, I'll get some of the guys from the Volvo 1800 Club with a similar model to take it for a test drive and get their opinions.

I won't part with the car at the moment, but will take your suggestion into consideration.

All the best and happy easter,
Anders

Hello Clan and Alan.

Thank you for your comments.

Yes, I meant a 4-speed automatic. Very interesting and was also wondering if a lock-up mechanism was present on the BW35-gearboxes (which, as Clan mentions, there isn't).

I'll focus on getting the car roadworthy for now - need to fix the front crossmember, steering joints, brake lines and I also suspect that the shaft needs balancing, but will keep an eye out for an AW gearbox along the way.

Check your owner's manual. In the specifications you should find a speed versus RPM table for the transmission. That would confirm whether something has been changed or is amiss.

The BW35 is 1:1 in 3rd gear. With a 4.1:1 ratio in the differential that should net you around 87 km/hr at 3000 RPM, consistent with what you report (affected by tire size). Conversion to an M41 with OD and keeping the 4.1 rear end would give you about 108 km/hr at 3000 RPM.

Switching to a 4 speed automatic may or may not improve things. If 4th gear is an overdrive then that should drop the engine RPM under cruise conditions. However, if 4th gear is still a 1:1 all you may have is some slightly improved acceleration by having closer spaced gears.

Edit: looks like the P1800ES cars with BW35 had a 3.9:1 rear end ratio. A 3.9 rear end would give you 91 km/hr at 3000 RPM. So, your numbers may still be correct.

The AW70/71 gearbox does indeed have an overdrive top gear:

https://i.imgur.com/Wtp9hqjh.png

The first three ratios are identical to the BW55 (and therefore probably the BW35, but I don't have direct knowledge of that gearbox). The overdrive ratio is 0.69:1 (and the AW71 also has a hydraulic lock facility), so that would give relaxed cruising - something like 115KPH at 3,000RPM.

I'm not sure there is anything wrong with the OP's set up at the moment (but of course it would be a good idea to check and service everything properly - the most effective procedure is several partial ATF changes over a period of a few months). The gearing sounds about right to me: my 244 (with the very similar BW55 auto box) does about 55MPH (88KPH) at an indicated 3,000RPM with a 3.73:1 rear axle. That does seem very low geared compared with modern motor cars, but was the norm in the 1970s.

I had intended to change the BW55 in my 244 to a AW71L, and had even acquired the gearbox and done some considerable research. It would not have been an especially difficult job (although I decided originality was the best course of action for the RB, and so have recently sold the AW71L auto box).

Whilst changing to an AW70/71 would not be difficult in the OP's P1800, I don't think there is anything wrong that some maintenance wouldn't cure.

:-)

Alan

The 940 4 speed box does make a lot of sense for conversion. If I put my 145 auto back on the road as Auto I will probably go that way. For local driving the gearing is perfectly ok but for long Motorway runs the gearing would be better with a taller top gear

Exactly, that is the AW71L auto box.

:-)