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Transmission conversion for overdrive what to do?

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chuck1006

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Have a 1959 100-6 BN6 that came with an non overdrive tranny and an overdrive out of the car. I know I would need a different tranny output shaft to fit the overdrive. Is it better to replace the shaft or buy a overdrive tranny or trade what I have for one? I have been driving it for a while now with no noise in any gear. The overdrive seems good (turns easily) but I have no way to bench test it.
Thanks for any advice. /ubbthreads/images/graemlins/crazyeyes.gif
Chuck
 
Chuck , thats a hard one. To fit the overdrive will require obtaining and installing a different main shaft.Basically the tranny must come all apart to do this. Trying to judge the condition of an overdrive without the ability to test it operationally is virtually impossible. If you could make a swap that might be the best way to go.---FWIW---Keoke
 
Yeh, that's probably the best way to go. I will start checking around for someone who would like to swap or sell an OD transmission. Maybe someone who wants to switch to non overdrive to set up for racing. I think most racers don't have overdrive. Anyone know?For now though it drives fine and has been great to drive here in Phoenix the past week with sunshine and in the 70's.
 
Re: Transmission conversion for overdrive what to

Chuck: You did not mention what what ratio your dif is. I have a non overdrive 100 vintage race car with a 4.11 dif and am having a seperate dif with a 3.54 ratio put togather for use at higher speed tracks. This is an experiment based in part on how the 100S was run. My car which I have owned for two seasons has been a race car for 10 or 15 years and seems to be built to an M spec but has seen a lot of changes over the years. If your concern is performance related maybe a change in ratio would do the trick. My change is a work inprocess so I am unsure if it will be a sucess. So this is just food for thought. jtb
 
Re: Transmission conversion for overdrive what to

Hi John,
Thanks for the input. I don't know the true ratio of the diff. When I redid my Healey, the only thing I didn't take apart was the rear end. I guess I should remove the cover and count gears to find out. As I said, my Healey came with a non overdrive transmission and a separate overdrive off the car. I bought it from a guy who said he got it from his old neighbors widow. I posted before that my speedo is a 1020 and isn't correct for the cable turn from my tranny. I checked the turns from the tranny and they are at 1603 per mile. I am not sure if this is due to the tranny or dif or combination. When I checked the turns on the overdrive cable output, it was at a ratio difference to the tranny that would indicate the speedo calibration would be correct for the overdrive. As I said, it runs fine today so maybe I should just get a gear conversion to make the speeodometer correct and live with the higher rpms at highway speed. Or maybe do a Smittys 5 speed conversion and sell my transmission and overdrive. Since I am using my Healey for a driver, maybe staying original isn't that important to me. Your thoughts?
Thanks,
Chuck
 
Re: Transmission conversion for overdrive what to

Well Chuck, if originality is not your end goal I would highly recommend a five speed conversion over the old Moss box/overdrive. Smitty has a very good kit available.--FWIW---Keoke------Chuck there should be a metal tag on the Diff that tells what the rear end ratio is.
 
Re: Transmission conversion for overdrive what to

Yes Scott, that is true .However if he waits till the tranny breaks its value will be less and will not help with the purchase of the conversion.Plus lowering the freeway engine revs can save wear and tear on the Mill and the cockpit will also be a bit cooler no pump you know. /ubbthreads/images/graemlins/cool.gif---Keoke
 
Re: Transmission conversion for overdrive what to

[ QUOTE ]
Well Chuck, if originality is not your end goal I would highly recommend a five speed conversion over the old Moss box/overdrive. Smitty has a very good kit available.--FWIW---Keoke------Chuck there should be a metal tag on the Diff that tells what the rear end ratio is.

[/ QUOTE ]
I have heard that you can't always go by the tag because over the years the gears may have been changed out. Seems like there must be a way to count spindle turns per wheel turns and calculate the ratio. Anyone know?
 
Re: Transmission conversion for overdrive what to

[ QUOTE ]
If it aint broke, don't fix it.
And you save money too.

SB

[/ QUOTE ]

Scott,
That would be good now since most of my driving is around town but I eventually plan on doing longer road trips. Spending hours on the highway with higher rpm's would certainly wear on the engine more.
 
Re: Transmission conversion for overdrive what to

[ QUOTE ]
[ QUOTE ]
Well Chuck, if originality is not your end goal I would highly recommend a five speed conversion over the old Moss box/overdrive. Smitty has a very good kit available.--FWIW---Keoke------Chuck there should be a metal tag on the Diff that tells what the rear end ratio is.

[/ QUOTE ]
I have heard that you can't always go by the tag because over the years the gears may have been changed out. Seems like there must be a way to count spindle turns per wheel turns and calculate the ratio. Anyone know?

[/ QUOTE ] I doubt that very many diffs have been changed out Nasty Job.---Keoke
 
Re: Transmission conversion for overdrive what to

These are not Moss transmissions. Those were installed on Jaguars. These are BMC transmission.
There is no metal tag, but the ratio is stamped as a fraction on the center section boss near one of the mounting bolt holes. Like 43/11 or 41/10. I just swapped mine out this weekend.
 
Re: Transmission conversion for overdrive what to

I have two side shift trannys w/ OD sitting waiting for rebuilding. But after dealing with over the road shippers I'm not sure that its worth the effort.

SB
 
Re: Transmission conversion for overdrive what to

[ QUOTE ]
I have two side shift trannys w/ OD sitting waiting for rebuilding. But after dealing with over the road shippers I'm not sure that its worth the effort.

SB

[/ QUOTE ]

Thanks Scott,
I do have the overdrive and it seems to be good although I have no way to bench test. The selinoid operates and it turns freely. I only need an overdrive transmission to go with it.
 
Re: Transmission conversion for overdrive what to

[ QUOTE ]
Seems like there must be a way to count spindle turns per wheel turns and calculate the ratio. Anyone know?

[/ QUOTE ]

Jack up one rear wheel, and turn until the valve is at the bottom.

Put a chalk mark on the drive shaft so that you can see when it has done a full revolution.

Turn the roadwheel one full rotation and count the number of revolutions the shaft makes. (should be around 2 - you'll have to estimate whether it's 1.9 or 2.1)

Double this figure. (ie something around 4)

The ratio of your diff is then 4:1 (or whatever number you have found).

The reason for doubling it is that the shaft has only gone round enough times for 1 wheel, the doublng accounts for the other wheel.
Don't jack up both wheels, as when you turn one, the other will rotate the opposite direction, and the shaft will stay still.
 
Re: Transmission conversion for overdrive what to

[ QUOTE ]
I have two side shift trannys w/ OD sitting waiting for rebuilding. But after dealing with over the road shippers I'm not sure that its worth the effort.

SB

[/ QUOTE ]

Hi Scott, here's a thought, pack up the transmission/overdrive units (don't forget to drain all oil out first) then ship via greyhound bus (their service is called GPX for Greyhound Package Express). It's cheaper and faster than truck freight. You will have to take to the bus station though. I've done this in the past and they are very helpful. On second thought it may be too heavy, give them a call first. Like I said, just a thought.
 
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