Amazon - J Type Overdrive

[skysurfer]

I have a '69 Amazon retro fitted with a B18B engine, P1800 gearshift and D-type overdrive. The car was originally a B20B model but has been changed for historic rallying which only recognises the B18 unit. I have acquired a good B20B engine for rebuild but understand that this was only mated to the J-type overdrive unit. Is it possible to just remove the existing B18 drivetrain with D-type and replace with a B20 drivetrain with J-type without any further modifications ? I am aware that the B20 overdrive is wired up differently.

[Derek UK]

Answer to probably what you are asking. Just swap the B18 for the B20. Bonus is you'll be able to easily fit an alternator if you currently have an early B18 block without the alternator bracket boss on the block.
Using a B20 drive train will mean adapting to cable clutch etc. Too much effort for the end result.

[Army]

I done a bit of loose reading of this subject and understand that the M41 gearbox (that's the 4 speed M40 with the overdrive) will bolt up nicely onto either the B18 or the B20 engines. So (in case it isn't clear) the engine swap is all that is needed for fitment.

I'm not 100% certain about the relative strengths of the D type overdrive vs J type overdrive but I understand there are harder to find connecting parts for the J type : M40/41 gearbox interface.

The other thing that may or may not be of interest is the final drive ration on the differential. The overdrive gearing is one heck of a large step for either engine to make. The B18 in particular can struggle with a 4.10 final drive ratio which is commonly fitted to 1960s Volvos that were non factory overdrive vehicles. So a check of the existing final drive ratio might be of interest as well...

[swedishandgerman]

You can use a j-type with a b18 or a d-type with a b20, despite neither ever having been produced like that.

The j-type can be run on d-type wiring including relay, but can be run with no relay. A d-type has to have a relay. However, in Amazon, they were always built with relay even when they went across to j-type.

Personally, I wouldn’t change from a d-type to a j-type despite it apparently being stronger. A j-type engages and disengages smoother, but a d-type is slightly higher geared giving better cruising, but only marginally.

When I’m back in front of my computer I will share with you some instructions to include a relay that disengages the overdrive when you knock it out of 4th.

As above, the b20 had cable operated clutch

[swedishandgerman]

Attached are the instructions for fitting a 240 overdrive relay and a momentary switch. Works great with a j-type which engages and disengages so smoothly.

[Volvorama]

From numerous conversions over the years I reckon the older D type is a better unit to have for the reasons already stated. I've also had fewer failed Ds than Js although that doesn't account for mileage or engine power.
Please note though that the gearbox that has a J attached cannot be fitted with a D. Different splines etc. as I recall. Also most Js will have the larger output flange that doesn't fit the Amazon prop and the D flange does not fit either.

[skysurfer]

Many thanks for your very helpful replies gentlemen. It seems to me that the best option is to remove the B18, replace with the rebuilt B20 unit and leave the existing gearbox and D-type overdrive (which are both working fine) alone. I can use the money saved by building the B20 as a fast road engine with a hotter cam etc. My car already has an alternator, cable clutch (and dual circuit brakes) so the switchover sounds as if it should be fairly straightforward. I did read that the J-type was the stronger unit, but my car has been used for serious rallying in the past and the D-type seems to have held up well, although it does jerk a little when switched on/off. I guess this is why the J-type is the smoother unit........

[tdz840]

[QUOTE=skysurfer ....although it does jerk a little when switched on/off. I guess this is why the J-type is the smoother unit........[/QUOTE]

Using the clutch when activating/deactivating the O/D helps engagement. Doesnt need a full clutch movement just a small dip of the clutch👍
Russ

[Ron Kwas]

ss;

In addition to good info given by all, you may want to look at my notes on the subject, especially the "Unwanted Reactivation" improvement with the 240 sequencing relay, on the SW-EM.com, Tech Articles page.

I would also recommend clutching into and out of OD...yes, it is a wet conical clutch inside the unit, so not absolutely necessary, but my position is that anything I can do to diminish shock loads on the drivetrain is a good thing, and at no cost, so I will do it...

Cheers