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Old 07-02-2014, 07:01 PM   #1
CorkOrangutan
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Default Overdrive Modification for close ratio

So I was talking to my neighbor who drives a triumph tr4 and found out that they also have a Laycock de Normanville overdrive, just like the 240. I also learned that the triumph has a different setup to allow the overdrive to turn on in 2nd, 3rd and 4th, giving you a close ratio seven speed sorta...
Basically I'm tired of my 242 having that big ratio gap between 2nd and 3rd, you wind it all the way up in 2nd through the corner and then 3rd is too high and 2nd is too low and uuuuuuhhhhhhh I'm slowww...
Question now is, would disabling the 4th gear sensor in our overdrives be a very bad idea? It would destroy it in reverse I know, but would the torque from 2nd be too much? Don't really need it between 1st and 2nd, but would be awesome to fill that gap in 2nd to 3rd. Also does anyone know the actual gear ratio the overdrive gives?
Thanks for any help, on the surface it sounds like it would be awesome. My volvo has a 8 speed close ratio gearbox! Because racing!
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Old 07-02-2014, 07:22 PM   #2
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Originally Posted by CorkOrangutan View Post
So I was talking to my neighbor who drives a triumph tr4 and found out that they also have a Laycock de Normanville overdrive, just like the 240. I also learned that the triumph has a different setup to allow the overdrive to turn on in 2nd, 3rd and 4th, giving you a close ratio seven speed sorta...
Basically I'm tired of my 242 having that big ratio gap between 2nd and 3rd, you wind it all the way up in 2nd through the corner and then 3rd is too high and 2nd is too low and uuuuuuhhhhhhh I'm slowww...
Question now is, would disabling the 4th gear sensor in our overdrives be a very bad idea? It would destroy it in reverse I know, but would the torque from 2nd be too much? Don't really need it between 1st and 2nd, but would be awesome to fill that gap in 2nd to 3rd. Also does anyone know the actual gear ratio the overdrive gives?
Thanks for any help, on the surface it sounds like it would be awesome. My volvo has a 8 speed close ratio gearbox! Because racing!
Except its still weak, it still is slow shifting, Because not racing..
A T5 with a decent set of ratio is better, because racing.
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Old 07-02-2014, 07:29 PM   #3
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Yes the lower gears will kill it.

.79 iirc.
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Old 07-02-2014, 08:14 PM   #4
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Except its still weak, it still is slow shifting, Because not racing..
A T5 with a decent set of ratio is better, because racing.
This, or just about any trans with more reasonable gearing.
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Old 07-02-2014, 09:18 PM   #5
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Yeah obviously a T5 or something would be awesomer but I'm poor, soo... But yeah I figured the lower gears would be the death of it. As for being slow shifting, yes it would be, but in theory could still be kinda nice. Ah well, thought of this today in the canyons and knew it was kinda a long shot. Being that I hate having to use the od for 5th, just thinking of doing that every gear and then switching it off every other gear made me second guess myself. But then again, crappy "FREE" 8 speed, lots of money and time T5 or just normal "already there" 4ish(fine 5.) speed. Kinda sounds like something I'd see in the 24 Hours of Lemons
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Old 07-02-2014, 10:08 PM   #6
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More info about the 4th gear bypass/8 speed M-46 mod:

The hydraulic pressure in the M46 O/D unit gets up to about 400 psi when its operating. The pump is driven off of the tailshaft which turns faster as the car's speed increases. Its actually pretty hard to generate enough hydraulic pressure in 1st and Reverse because the road speed is so low. So unless you have brand new seals or something its unlikely that you would be able to engage O/D in Reverse, or 1st gear.

3rd with the O/D engaged is going to give you nearly the same gear ratio as 4th, which is 1:1. I did the math once and it came out to .98:1 or something so close its not going to matter.

The biggest benefit I saw to having the switch bypassed was in 2nd gear. Because the O/D functions like an automatic transmission, you don't need the clutch to shift into it. Depending on rear end gearing and tire size, this might mean you can do 0-60 with only one clutched shift. Which would knock some time off of you're 0-60, if you're into that kind of thing. I did it with a 3.54:1 rear end and 225/55R16s.
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Old 07-02-2014, 11:48 PM   #7
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Back in the day I drove a Mack Semi with a Mack 10 speed transmission. It was possible to shift gears while going in reverse. So like 10 speeds forward and 5 speeds reverse.
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Old 07-03-2014, 12:36 AM   #8
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Quote:
More info about the 4th gear bypass/8 speed M-46 mod:

The hydraulic pressure in the M46 O/D unit gets up to about 400 psi when its operating. The pump is driven off of the tailshaft which turns faster as the car's speed increases. Its actually pretty hard to generate enough hydraulic pressure in 1st and Reverse because the road speed is so low. So unless you have brand new seals or something its unlikely that you would be able to engage O/D in Reverse, or 1st gear.

3rd with the O/D engaged is going to give you nearly the same gear ratio as 4th, which is 1:1. I did the math once and it came out to .98:1 or something so close its not going to matter.

The biggest benefit I saw to having the switch bypassed was in 2nd gear. Because the O/D functions like an automatic transmission, you don't need the clutch to shift into it. Depending on rear end gearing and tire size, this might mean you can do 0-60 with only one clutched shift. Which would knock some time off of you're 0-60, if you're into that kind of thing. I did it with a 3.54:1 rear end and 225/55R16s.
Hmm, so you actually did this? How did the OD hold up? That's a lot of helpful info so thank you. I really would only see it being good for staying better in the power band in between 2nd and 3rd, as that's where the annoying big gap in ratios is.
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Old 07-03-2014, 01:07 AM   #9
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Originally Posted by Hoggster View Post
More info about the 4th gear bypass/8 speed M-46 mod:

The hydraulic pressure in the M46 O/D unit gets up to about 400 psi when its operating. The pump is driven off of the tailshaft which turns faster as the car's speed increases. Its actually pretty hard to generate enough hydraulic pressure in 1st and Reverse because the road speed is so low. So unless you have brand new seals or something its unlikely that you would be able to engage O/D in Reverse, or 1st gear.

3rd with the O/D engaged is going to give you nearly the same gear ratio as 4th, which is 1:1. I did the math once and it came out to .98:1 or something so close its not going to matter.

The biggest benefit I saw to having the switch bypassed was in 2nd gear. Because the O/D functions like an automatic transmission, you don't need the clutch to shift into it. Depending on rear end gearing and tire size, this might mean you can do 0-60 with only one clutched shift. Which would knock some time off of you're 0-60, if you're into that kind of thing. I did it with a 3.54:1 rear end and 225/55R16s.
On first and reverse it will go in, it shudders .....I have my overdrive 4th gear bypassed, but I don't use it on any gear lower than 4. You will kill the overdrive. See john v. Post above. Also it is recommended by Volvo to clutch shift into and out of overdrive.

You live 3rd world yet creating 1st world problems....if you don't have $$$ for t5 swap, just go buy a whole 80s mustang 5.0 and not be slow anymore.
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Old 07-04-2014, 09:28 AM   #10
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You dont have the money for a trans swap, do you have the money for another m46 when yours dies?
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Old 07-04-2014, 10:31 AM   #11
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You dont have the money for a trans swap, do you have the money for another m46 when yours dies?
It's not possible to make chicken salad from chicken sh!t.
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Old 07-04-2014, 10:33 AM   #12
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It's not possible to make chicken salad from chicken sh!t.
But this is Tbricks,so they're gonna try.

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Old 07-05-2014, 09:41 AM   #13
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But this is Tbricks,so they're gonna try.

but theyre killing it for us grandpa drivers that dont care about the gearing, and see 2nd gear as just fine for pulling hard up those city hills.



op just swap in a 3.73 or 4.10 rear end and be done with it
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Old 07-05-2014, 11:41 AM   #14
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It's not possible to make chicken salad from chicken sh!t.
Isn't that how they do it at McDonald's?
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Old 07-05-2014, 09:21 PM   #15
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How McDonalds can racecar afford?
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Old 07-05-2014, 09:35 PM   #16
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Oxymoronic.
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Old 07-06-2014, 12:24 PM   #17
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From what I understand if the od is on and you put tranny in reverse bad things happen to your od unit
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Old 07-07-2014, 12:13 PM   #18
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Yeah mine was shorted and it would reverse for about half the driveway then it would bind up.
I had the 4th bypass done for awhile on my old car and I like it. It didn't blow up in the time I did it. I think I will do it to my current m46 for SNG but I have a tko almost ready to go in.
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Old 07-07-2014, 02:03 PM   #19
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^hmm, make the OD that someone could actually use in working condition virtually worthless after the inevitable happens to the rest of the gearbox. Only on TB.

Not enough fluid pressure in 1st and reverse, no help from the sprag clutch in reverse. Engagement in reverse usually ruins the cone clutch, cone clutch thrust bearing, and whatever various metal bits find their way into other parts if it runs that long...
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Old 07-12-2014, 07:19 AM   #20
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I've been screwing around rebuilding an M41 and J type. For the J type I found a great website that's actuly for Triumphs. There I learned the J type on a Triumph only shifts on the 3rd and 4 th gears because it's not as strong as the other OD they used. Anyway I'm setting mine up the way Volvo intended to only shift in 4th gear.
If I was racing or whatever I'd do a 5 speed swap. (if the rules allowed) But I drive like an old gezzer so I ain't to worried about it.
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