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O/D Gear Box Or Not
- Thread starter WJM
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SilentUnicorn
Yoda
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WJM, general opinion is that it is worth it.
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JamesWilson
Yoda
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[ QUOTE ]
Does it cut the revs down by much. Is it worth it.
[/ QUOTE ]
The overdrive will reduce revs by about 20%. This makes longer journeys much more comfortable. I suspect that the economics of swapping out a good non-O/D transmission doesn't re-pay the cost in terms of fuel savings unless you do a lot of mileage, but the benefits lie in useability.
Ratios: 4 speed
Overdrive Top (where fitted): 0.820
Top: 1.000
Third o/d (where fitted): 1.133
Third: 1.382
Second: 2.2167
First: 3.333
Reverse: 3.095
Does it cut the revs down by much. Is it worth it.
[/ QUOTE ]
The overdrive will reduce revs by about 20%. This makes longer journeys much more comfortable. I suspect that the economics of swapping out a good non-O/D transmission doesn't re-pay the cost in terms of fuel savings unless you do a lot of mileage, but the benefits lie in useability.
Ratios: 4 speed
Overdrive Top (where fitted): 0.820
Top: 1.000
Third o/d (where fitted): 1.133
Third: 1.382
Second: 2.2167
First: 3.333
Reverse: 3.095
Nunyas
Yoda
Offline
I find it kind of interesting that the ODs kick in in 3rd gear. It kind of converts your 4speed into a 6speed... where you end up with a new gear between 3 and 4 and then a gear above 4. Sounds more fun to have than a regular 5-speed box to me... /ubbthreads/images/graemlins/smile.gif
mgbmedic
Jedi Trainee
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i'd love to have O/d in both my Bs but I balked at the prices for new/rebuilt(Moss) and even the used prices locally are steep(about $750) and no guarantee that they'll work. I've got a O/D tranny from a 63 BJ7 Healey, wish it would fit...hmm, actually, I have a whole Healey drive train...hmm, no way, An MGB/GT with a Healey guts? How absurd. Good luck and fill us in on the details, I could use the guidance if and when I tackle that project.
Steve_S
Yoda
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"An MGB/GT with a Healey guts?"
It's called MGC!!! /ubbthreads/images/graemlins/wink.gif
John, the overdrive is more of a luxury than a necessity. It wil lower your revs on the highway making the car run a bit smoother and less noisy. Keep in mind that the MGB is a bit underpowered overall, so that top gear with the OD on will not give very good acceleration. It's best used as a highway cruising gear.
Third gear with OD is very useful for canyon driving, overtaking or just when you're stuck at a certain speed where 3rd is too low but 4th is too high. I use 3rd OD almost as much as 4th OD. However that said, I have driven my "other" MGB for 16 years with no OD and have never had a problem.
In a GT, OD is almost a must because the GT cabin can be quite noisy at higher revs.
It's called MGC!!! /ubbthreads/images/graemlins/wink.gif
John, the overdrive is more of a luxury than a necessity. It wil lower your revs on the highway making the car run a bit smoother and less noisy. Keep in mind that the MGB is a bit underpowered overall, so that top gear with the OD on will not give very good acceleration. It's best used as a highway cruising gear.
Third gear with OD is very useful for canyon driving, overtaking or just when you're stuck at a certain speed where 3rd is too low but 4th is too high. I use 3rd OD almost as much as 4th OD. However that said, I have driven my "other" MGB for 16 years with no OD and have never had a problem.
In a GT, OD is almost a must because the GT cabin can be quite noisy at higher revs.
JamesWilson
Yoda
Offline
[ QUOTE ]
.... So you have a second 3rd gear and a 5th gear am I on the right track. I tought that it was a 5th gear only.
[/ QUOTE ]
The overdrive is a unit that fits between the transmission and driveshaft/differential. It doesn't change the number of "gears" you have, but alters the ratios of 3rd and 4th somewhat.
You then get 6 possible ratios from the four speed transmission.
As the table shown earlier reveals the difference between 3rd O/D at 1.13 and 4th at 1 is small.
As someone previously noted they find it quicker and easier to engage the O/D rather than shift; and there may be times when the slight difference in 3 O/D and 4th is useful too.
The main impact is to reduce the top gear available from 1 to .8. That's where the greater benefits are seen- for traveling in top gear at lower revs more economically and comfortably.
Its possible to have transmissions designed to more effectively use the O/D with a greater gap between 3 and 4 that 3 O/D might then fill, but I can't recall seeing that.
An overdrive gives 6 forward gear ratios, but its mostly useful on 4th rather than 3rd.
.... So you have a second 3rd gear and a 5th gear am I on the right track. I tought that it was a 5th gear only.
[/ QUOTE ]
The overdrive is a unit that fits between the transmission and driveshaft/differential. It doesn't change the number of "gears" you have, but alters the ratios of 3rd and 4th somewhat.
You then get 6 possible ratios from the four speed transmission.
As the table shown earlier reveals the difference between 3rd O/D at 1.13 and 4th at 1 is small.
As someone previously noted they find it quicker and easier to engage the O/D rather than shift; and there may be times when the slight difference in 3 O/D and 4th is useful too.
The main impact is to reduce the top gear available from 1 to .8. That's where the greater benefits are seen- for traveling in top gear at lower revs more economically and comfortably.
Its possible to have transmissions designed to more effectively use the O/D with a greater gap between 3 and 4 that 3 O/D might then fill, but I can't recall seeing that.
An overdrive gives 6 forward gear ratios, but its mostly useful on 4th rather than 3rd.
I have overdrive...that is the coolest part of it, being able to say it does. /ubbthreads/images/graemlins/cool.gif
Most of my driving with the B is local and I don't really need it, but like others have said, I use it more in 3rd gear than I do in 4th. One the highways, the OD is great for speeds over 50 MPH or on long coasts below 50, but most of my use is in 3rd gear at between 35-40 MPH on surburban streets. Shifting back and forth between 3rd and OD 3rd is easy and smooth and doesn't dog the engine quite as much as 4th does.
Just my humble opinion...It isn't worth it, but I would not buy another one without OD /ubbthreads/images/graemlins/crazyeyes.gif
Bruce /ubbthreads/images/graemlins/driving.gif
Most of my driving with the B is local and I don't really need it, but like others have said, I use it more in 3rd gear than I do in 4th. One the highways, the OD is great for speeds over 50 MPH or on long coasts below 50, but most of my use is in 3rd gear at between 35-40 MPH on surburban streets. Shifting back and forth between 3rd and OD 3rd is easy and smooth and doesn't dog the engine quite as much as 4th does.
Just my humble opinion...It isn't worth it, but I would not buy another one without OD /ubbthreads/images/graemlins/crazyeyes.gif
Bruce /ubbthreads/images/graemlins/driving.gif
CraigFL
Jedi Trainee
Offline
I just put my O/D in and it's great! I can cruise at 65mph and under 3000 RPM.
I bought a complete O/D transmission but since I knew my transmission was good, I exhanged only the parts necessary plus installed new gaskets/seals on the O/D unit.
It should also be noted that not all MGB O/Ds work in 3rd gear too. Some years have the lockout mechanism(that activates the switch) tapered so that you can only engage in 4th gear. You would need to change this part in the remote shifter mechanism if you wanted operation in both 4th and 3rd gear.
I bought a complete O/D transmission but since I knew my transmission was good, I exhanged only the parts necessary plus installed new gaskets/seals on the O/D unit.
It should also be noted that not all MGB O/Ds work in 3rd gear too. Some years have the lockout mechanism(that activates the switch) tapered so that you can only engage in 4th gear. You would need to change this part in the remote shifter mechanism if you wanted operation in both 4th and 3rd gear.
Steve_S
Yoda
Offline
What, a healey engine in a B? I doubt it could be done. The MGC engine was very similar to the Healey unit but in order to fit it into an MGB chassis, the entire front suspension had to be changed to a torsion bar setup. This allowed the oil pan to use the space where the MGB front crossmember would normally sit. I suppose it would be possible to fit one, but honestly I'd just buy an MGC since it would be far easier and probably much cheaper!
