M47 onto B20

morwenna240 · Jan 16th, 2021, 17:47

Has anybody done this? I see Tinus sells an adaptor. Get rid of foolish overdrive!

142 Guy · Jan 17th, 2021, 18:02

I haven't tried it; but, you might want to do a little research on the M47. It does not get a lot of 'internet love' in terms of durability. If you do proceed with the conversion, try to get the later M47, I believe designated as M47II which has a revised oil filler hole to reduce the risk of the transmission being underfilled causing bearing failure.

The M41, M46 and M47 are all getting long in the tooth and replacement parts are getting harder to source and when available, seemingly more expensive. If you are wedded to the idea of ditching the separate OD unit, conversion to a T9 transmission might be a better path. The T9 is not so rare on your side of the Atlantic so sourcing and more importantly repair parts are less of an issue. The T9 being designed for use on smaller engine cars than the T5 has a better range of ratios.

Amazon Cars offers the bits for conversion - nothing is cheap.

https://amazoncars.co.uk/part.asp?cI...e9+Gearbox+kit

Unless your have a late 140, the shifter is not coming up in the right place; but, that would be a problem even with an M47 in an early 140.

morwenna240 · Jan 17th, 2021, 18:46

Thank you. I'll ask Rob. The idea is not to have two gearboxes, the rearmost of which having a poor rep. The car will be daily driver, this means towing a boat on continent (no, i didn't vote for brexit!), so i want RELIABILITY. Mmm, always thought m47 good box, had two, no probs. No? Will get more opinions, TT also do T9 thing. Y'health.

Burdekin · Jan 17th, 2021, 18:49

The MX5 5 speed was a lovely box as well, but you’d need to sort the conversion.

I know a guy up here with a M41 from a Amazon, spoke with him on the phone a couple of times. He’s a old boy, a nice guy into his cars but buying from him might be hard work. I couldn’t nail down a price with him and just gave up in the end. If you fancy giving him a try PM me and I’ll give you his number. He is west of Aberdeen. A B20 will sit on 5000rpm all day long so the overdrive is just a nice way to reduce the revs a bit and the noise in the cabin. There’s a couple of places in England that will overhaul the overdrive and gearbox for you. Think these are the folks that did my OD https://www.overdrive-repairs.co.uk/...?cat=Overdrive

morwenna240 · Jan 17th, 2021, 19:56

Mmm, maybe i shouldn't over think it too much. I have an M41 with D-type o/d. An i do want to keep the long gearshift, 142. I'm just slightly worried the d-type won't be up to 100 horse ish while towing. Don't have to engage it all the time, i suppose, an towing being limited to 60, according to the letter. Tend to go on the spirit, me.

Burdekin · Jan 17th, 2021, 20:11

Asked some of the Amazon guys and a bit of a mixed answer with regards to the D type. One said he’s towed no bother and another said the D type might be over-geared and would just tow in fourth. Do you tow the boat over from the U.K. or just to the boat ramp when you are over in Europe? Is it a big boat or just a runabout?

142 Guy · Jan 17th, 2021, 22:52

My 1971 142 E has the later J overdrive so I can't comment on the reliability of the D type. My J has 120,000 + miles on it and as long as the oil level is good and I clean the filters when I do the infrequent fluid changes operation has been trouble free.

If you have an M41 with a D type OD that must be from a 140 fitted with a B18 or from an Amazon or a P1800? I have this very fuzzy recollection that the OD ratio on the B18 D units was different than the B20 J units - 0.79 on the J and 0.76 on the D. I can confirm that the J on my car is 0.79; but, can't confirm the 0.76 for the D. It is a little odd that the B18 with less torque would have a lower OD ratio than a B20.

I used to tow catamaran sailboats behind my car(s) when I raced them. Not particularly heavy; but, they were the legal limit for width in North America (8 feet) and with the trampoline installed they did present a fair amount of air drag. Neither my 142 (B20E) or 1979 242 GT could realistically pull the cat at 100 km/hr in OD. I had a 1987 745 turbo which had no problem pulling the cat in OD. Unless you have a small lightweight aluminum fishing boat I don't think towing it at highway speeds in OD is realistic, particularly if the D type OD has the 0.76 ratio.

If you want to keep the 'period correct' long shift lever then the M47 transmission won't be an option for you without a lot of shift lever re engineering.

morwenna240 · Jan 17th, 2021, 23:44

The boat is a 15 ft wooden (clinker built) open longliner, on steel trailer, boat usually full of camping gear, big canvas tent, etc. All up weight prob 15 cwt.
We drive to south coast ferry, cross channel to France, then wherever, so yes, bit of towing. The 240 torslanda has no prob, one day when feeling in hurry, saw 90. E320 cdi i had before didn't notice it. Mmm, ok guys, i'll fit the m41 an D, c what happens. Yes, 142, told it came from 1800, bought from Triple S. Others have said the o/d fitted cars had lower diff ratio, that being so my 145 would prob not like towing in o/d, which wouldn't really matter as at towing speeds engine won't be screaming.

Underdrive · Jan 18th, 2021, 09:39

Don't forget the rear diff ratio will have an effect on gearing. It will be different depending on whether O/D was fitted new or not.

morwenna240 · Jan 18th, 2021, 11:24

Aye. O/d not fitted at factory. C/swede, do u have the info; do non o/d cars have higher diff ratio?

Jan 16th, 2021, 17:47	#1
morwenna240 Senior Member Last Online: Mar 23rd, 2024 19:59 Join Date: Sep 2019 Location: heptonstall	M47 onto B20 Has anybody done this? I see Tinus sells an adaptor. Get rid of foolish overdrive!

Jan 17th, 2021, 18:49	#4
Burdekin Chief Bodger Last Online: Today 10:28 Join Date: Oct 2009 Location: Aberdeen	The MX5 5 speed was a lovely box as well, but you’d need to sort the conversion. I know a guy up here with a M41 from a Amazon, spoke with him on the phone a couple of times. He’s a old boy, a nice guy into his cars but buying from him might be hard work. I couldn’t nail down a price with him and just gave up in the end. If you fancy giving him a try PM me and I’ll give you his number. He is west of Aberdeen. A B20 will sit on 5000rpm all day long so the overdrive is just a nice way to reduce the revs a bit and the noise in the cabin. There’s a couple of places in England that will overhaul the overdrive and gearbox for you. Think these are the folks that did my OD https://www.overdrive-repairs.co.uk/...?cat=Overdrive __________________ One day I will get rid of all of the rust.

Jan 17th, 2021, 20:11	#6
Burdekin Chief Bodger Last Online: Today 10:28 Join Date: Oct 2009 Location: Aberdeen	Asked some of the Amazon guys and a bit of a mixed answer with regards to the D type. One said he’s towed no bother and another said the D type might be over-geared and would just tow in fourth. Do you tow the boat over from the U.K. or just to the boat ramp when you are over in Europe? Is it a big boat or just a runabout? __________________ One day I will get rid of all of the rust. Last edited by Burdekin; Jan 17th, 2021 at 20:13.

Jan 17th, 2021, 18:02	#2
142 Guy Master Member Last Online: Yesterday 15:52 Join Date: Jul 2020 Location: Saskatchewan, Canada	I haven't tried it; but, you might want to do a little research on the M47. It does not get a lot of 'internet love' in terms of durability. If you do proceed with the conversion, try to get the later M47, I believe designated as M47II which has a revised oil filler hole to reduce the risk of the transmission being underfilled causing bearing failure. The M41, M46 and M47 are all getting long in the tooth and replacement parts are getting harder to source and when available, seemingly more expensive. If you are wedded to the idea of ditching the separate OD unit, conversion to a T9 transmission might be a better path. The T9 is not so rare on your side of the Atlantic so sourcing and more importantly repair parts are less of an issue. The T9 being designed for use on smaller engine cars than the T5 has a better range of ratios. Amazon Cars offers the bits for conversion - nothing is cheap. https://amazoncars.co.uk/part.asp?cI...e9+Gearbox+kit Unless your have a late 140, the shifter is not coming up in the right place; but, that would be a problem even with an M47 in an early 140.

Jan 17th, 2021, 18:46	#3
morwenna240 Senior Member Last Online: Mar 23rd, 2024 19:59 Join Date: Sep 2019 Location: heptonstall	Thank you. I'll ask Rob. The idea is not to have two gearboxes, the rearmost of which having a poor rep. The car will be daily driver, this means towing a boat on continent (no, i didn't vote for brexit!), so i want RELIABILITY. Mmm, always thought m47 good box, had two, no probs. No? Will get more opinions, TT also do T9 thing. Y'health.

Jan 17th, 2021, 19:56	#5
morwenna240 Senior Member Last Online: Mar 23rd, 2024 19:59 Join Date: Sep 2019 Location: heptonstall	Mmm, maybe i shouldn't over think it too much. I have an M41 with D-type o/d. An i do want to keep the long gearshift, 142. I'm just slightly worried the d-type won't be up to 100 horse ish while towing. Don't have to engage it all the time, i suppose, an towing being limited to 60, according to the letter. Tend to go on the spirit, me.

Jan 17th, 2021, 22:52	#7
142 Guy Master Member Last Online: Yesterday 15:52 Join Date: Jul 2020 Location: Saskatchewan, Canada	My 1971 142 E has the later J overdrive so I can't comment on the reliability of the D type. My J has 120,000 + miles on it and as long as the oil level is good and I clean the filters when I do the infrequent fluid changes operation has been trouble free. If you have an M41 with a D type OD that must be from a 140 fitted with a B18 or from an Amazon or a P1800? I have this very fuzzy recollection that the OD ratio on the B18 D units was different than the B20 J units - 0.79 on the J and 0.76 on the D. I can confirm that the J on my car is 0.79; but, can't confirm the 0.76 for the D. It is a little odd that the B18 with less torque would have a lower OD ratio than a B20. I used to tow catamaran sailboats behind my car(s) when I raced them. Not particularly heavy; but, they were the legal limit for width in North America (8 feet) and with the trampoline installed they did present a fair amount of air drag. Neither my 142 (B20E) or 1979 242 GT could realistically pull the cat at 100 km/hr in OD. I had a 1987 745 turbo which had no problem pulling the cat in OD. Unless you have a small lightweight aluminum fishing boat I don't think towing it at highway speeds in OD is realistic, particularly if the D type OD has the 0.76 ratio. If you want to keep the 'period correct' long shift lever then the M47 transmission won't be an option for you without a lot of shift lever re engineering.

Jan 17th, 2021, 23:44	#8
morwenna240 Senior Member Last Online: Mar 23rd, 2024 19:59 Join Date: Sep 2019 Location: heptonstall	The boat is a 15 ft wooden (clinker built) open longliner, on steel trailer, boat usually full of camping gear, big canvas tent, etc. All up weight prob 15 cwt. We drive to south coast ferry, cross channel to France, then wherever, so yes, bit of towing. The 240 torslanda has no prob, one day when feeling in hurry, saw 90. E320 cdi i had before didn't notice it. Mmm, ok guys, i'll fit the m41 an D, c what happens. Yes, 142, told it came from 1800, bought from Triple S. Others have said the o/d fitted cars had lower diff ratio, that being so my 145 would prob not like towing in o/d, which wouldn't really matter as at towing speeds engine won't be screaming.

Jan 18th, 2021, 09:39	#9
Underdrive Senior Member Last Online: Apr 9th, 2024 10:10 Join Date: Jan 2014 Location: stranraer	Don't forget the rear diff ratio will have an effect on gearing. It will be different depending on whether O/D was fitted new or not.

Jan 18th, 2021, 11:24	#10
morwenna240 Senior Member Last Online: Mar 23rd, 2024 19:59 Join Date: Sep 2019 Location: heptonstall	Aye. O/d not fitted at factory. C/swede, do u have the info; do non o/d cars have higher diff ratio?

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