46RH overdrive ratio.

[Headintheclouds]

Just checking figures for 46RH overdrive. 2400 RPM steady level driving. Switch in overdrive - 1850 RPM. This comes out at about 0.77:1 but the overdrive ratio is given as 0.69:1. Switch in lockup and RPM drops to 1650. 2400 to 1650 is a ratio of 0.68:1.

Does the stated ratio include the change due to lockup or is this transmission slipping? What is the ratio due purely to the sun and planet gears in the overdrive?

 

[273]

Just checking figures for 46RH overdrive. 2400 RPM steady level driving. Switch in overdrive - 1850 RPM. This comes out at about 0.77:1 but the overdrive ratio is given as 0.69:1. Switch in lockup and RPM drops to 1650. 2400 to 1650 is a ratio of 0.68:1.

Does the stated ratio include the change due to lockup or is this transmission slipping? What is the ratio due purely to the sun and planet gears in the overdrive?

yes there some converter slippage when not in lockup

 

[Headintheclouds]

I get that but I thought the gear ratio in the overdrive was 0.69:1 and that doesn't seem to be the case. It would be good to have that confirmed and know it's not extra slippage in this transmission.

 

[273]

A 0.01 difference, did you measure your tires precisely with driving weight on them ?

 

[Headintheclouds]

I obviously haven't explained very well. What i'm questioning is whether the gear ratio of the overdrive disregarding lockup should be 0.69:1 or whether the stated figure includes lockup.

 

[MopaR&D]

I obviously haven't explained very well. What i'm questioning is whether the gear ratio of the overdrive disregarding lockup should be 0.69:1 or whether the stated figure includes lockup.

The stated figure is the gear ratio within the transmission itself. It does not take into account slippage because that can change depending on various factors. So to directly answer your question that figure would "include" lockup.

Earlier transmissions don't have lockup converters and came with various torque converters that provided different slippage depending on the engine, final drive ratio and vehicle weight so to state a figure that takes converter slippage into account would be tedious and not helpful.

 

[273]

I obviously haven't explained very well. What i'm questioning is whether the gear ratio of the overdrive disregarding lockup should be 0.69:1 or whether the stated figure includes lockup.

lockup has nothing to do with gear ratio

A torque converter slips so they designed lockup to stop slip while cruising

tires are part of gear ratio 0.01 difference = 26.7" vs 27"

 

[Headintheclouds]

You are absolutely right. Of course lockup doesn't affect the gear ratio. If we ignore lockup in my figures the revs drop from 2400 to 1850 due to the overdrive gear ratio alone. This is about 0.77:1. I thought the gear ratio of the 418RH was 0.69:1. This didn't make sense.

I then calculated the ratio between RPM in top against that with overdrive and lockup and that came out at 0.68:1. This led me to question whether the stated figure wasn't the gear ratio but an overall ratio.

 

[273]

You are absolutely right. Of course lockup doesn't affect the gear ratio. If we ignore lockup in my figures the revs drop from 2400 to 1850 due to the overdrive gear ratio alone. This is about 0.77:1. I thought the gear ratio of the 418RH was 0.69:1. This didn't make sense.

This is without lockup right? so there tq converter slip happening

I then calculated the ratio between RPM in top against that with overdrive and lockup and that came out at 0.68:1. This led me to question whether the stated figure wasn't the gear ratio but an overall ratio.

Once lockup in gages there's a 0.01 difference between the stated and calculated gear ratio right ?
Your question why this difference, my answer probably tire size used in calculation.

Are you using actual measured tire 2x radius (center of axle to ground) or calculated tire size?

0.01 difference = about 5/32 of a inch of radius

 

[Headintheclouds]

The figures I gave are both direct and without lockup. I assumed - perhaps wrongly - that the slippage at 2400RPM would be similar to slippage at 1850 rpm. Both travelling at about 70MPH on light throttle.

 

[273]

Just checking figures for 46RH overdrive. 2400 RPM steady level driving.

3rd ?

Switch in overdrive - 1850 RPM. This comes out at about 0.77:1 but the overdrive ratio is given as 0.69:1.

od no lockup? gear ratio is actually still .69 with 200 rpms of slippage

Switch in lockup and RPM drops to 1650. 2400 to 1650 is a ratio of 0.68:1.

od and lockup? no slippage

Does the stated ratio include the change due to lockup or is this transmission slipping? What is the ratio due purely to the sun and planet gears in the overdrive?

So ultimately there's only a 0.01 gear ratio discrepancy, which is probably the tire size your using not slippage.

Edit* I just realize your not probably using the tires size and gears to figure out od ratio.
see below

 

[273]

Switch in lockup and RPM drops to 1650. 2400 to 1650 is a ratio of 0.68:1.

Just using these numbers 1650/2400 = 0.6875:1 or rounded up 0.69:1 OD ratio

 

[67Dart273]

Differences in tire "stated" size, tach/ speedo innacuracy......................

 

[Headintheclouds]

Let's ignore the lockup.

So 2400RPM. No overdrive. No lockup. Presumably some slippage.
Engage overdrive. Still no lockup. 1850RPM. I assumed much the same slippage.
About 0.77:1
This suggests that either the gear ratio isn't 0.69:1 or that the slippage at 2400 is very different to that at 1850.

 

[Dmopower]

The OD gear ratio is .69. And the slippage changes in each gear, with weight, ect. When locked up it's .69

 

[273]

Let's ignore the lockup.

So 2400RPM. No overdrive. No lockup. Presumably some slippage.
Engage overdrive. Still no lockup. 1850RP. I assumed much the same slippage.
About 0.77:1

I see what your getting at you think even with slippage it should maintain the same ratio, so slippage in your mind should be a fixed amount, no matter speed rpm power etc... Why would it be ? and obviously it's not.

This suggests that either the gear ratio isn't 0.69:1 or that the slippage at 2400 is very different to that at 1850.

 

[67Dart273]

Well you CAN'T ignore lockup.

 

[Headintheclouds]

I was obviously assuming that the amount of slippage would be similar at a fixed speed and power between 2400RPM without overdrive and 1850RPM with overdrive. It looks as though I must have got this very wrong.

 

[273]

I was obviously assuming that the amount of slippage would be similar at a fixed speed and power between 2400RPM without overdrive and 1850RPM with overdrive. It looks as though I must have got this very wrong.

Gear ratio can't vary so slippage % must, mph speed is the same but power is usually less at these lower rpms especially as they get lower and the speed the fluid coupling in the converter is probably less etc.. these must have an effect.

 

[Headintheclouds]

Thank you for that. Sorry if my lack of understanding is frustrating but I'm finding it hard to work this out.
Please try to be patient.

Amongst other things I'm trying to work out the speeds to switch in overdrive and lockup automatically. In the above example it looks as though switching in overdrive without lockup introduces a load more slip that would generate loads of heat in the transmission fluid and harm gas mileage.

This leads to questions about stall speed and slippage below that speed - and I got some very sarcastic answers when I last asked about that. it's pretty frustrating as we all have to start somewhere. My area of expertise is electrical systems. I have seen what seem to be some very dumb questions asked on forums that I have answered patiently and I think I have really helped people.

 

[273]

Thank you for that. Sorry if my lack of understanding is frustrating but I'm finding it hard to work this out.
Please try to be patient.

It's all good, I was misunderstanding what you were trying to get at, I thought you were stuck on the 0.69 vs 0.68 not converter slippage %'s.

Amongst other things I'm trying to work out the speeds to switch in overdrive and lockup automatically.

I'd start a new thread asking just this.

In the above example it looks as though switching in overdrive without lockup introduces a load more slip that would generate loads of heat in the transmission fluid and harm gas mileage.

I'd leave out this just makes confusion of the question

This leads to questions about stall speed and slippage below that speed - and I got some very sarcastic answers when I last asked about that. it's pretty frustrating as we all have to start somewhere. My area of expertise is electrical systems. I have seen what seem to be some very dumb questions asked on forums that I have answered patiently and I think I have really helped people.

Ask away that's what the forum is for, try not to let some frustrated you from posting.

 

[Headintheclouds]

Thank you for a constructive reply. I think your breakdown aboveshows where part of the problem lies. People seize on a part of what you have written and flame you for it without trying to understand the whole question. What i'm getting into here is quite a complex topic.
If I start a new thread asking about the speeds of operation I'm starting over with all sorts of issues - tires, final drive, torque converter etc. The biggest issue is the latter. I can't work out if I'm switching at the right speed if I don't understand what's happening in terms of slippage.
Obviously at low speeds a torque converter has total slippage. I don't understand how linear this is up until the point when decent power is transmitted. If I have a stock converter with a stall of 2000RPM am I asking for trouble switching in overdrive without lockup if it brings the RPM down below stall speed? Is stall speed even relevant in this case? Any pointers to where I can read up on this and avoid derision on the forum would be welcome. There's plenty out there for those wanting to burn rubber and show off but not so much for those of us who want to cruise peacefully and save gas most of the time but occasionally let rip and fly.

 

[273]

For the od gear, I think your over thinking it, a 1:1 final gear with a 2:45 rear would be the same as a 0.69:1 with 3.55 why would treat shifting much different, when you get up to/near cruising speed shift as long your not lugging the engine should be fine, and when at cruising speed I'd engage lockup, I guess I could be wrong I don't have this setup.

 

[TrailBeast]

Thank you for a constructive reply. I think your breakdown aboveshows where part of the problem lies. People seize on a part of what you have written and flame you for it without trying to understand the whole question. What i'm getting into here is quite a complex topic.
If I start a new thread asking about the speeds of operation I'm starting over with all sorts of issues - tires, final drive, torque converter etc. The biggest issue is the latter. I can't work out if I'm switching at the right speed if I don't understand what's happening in terms of slippage.
Obviously at low speeds a torque converter has total slippage. I don't understand how linear this is up until the point when decent power is transmitted. If I have a stock converter with a stall of 2000RPM am I asking for trouble switching in overdrive without lockup if it brings the RPM down below stall speed? Is stall speed even relevant in this case? Any pointers to where I can read up on this and avoid derision on the forum would be welcome. There's plenty out there for those wanting to burn rubber and show off but not so much for those of us who want to cruise peacefully and save gas most of the time but occasionally let rip and fly.

You are correct in realizing that lower rpm = more slip.
Just a FYI, if your trans was slipping for 10 seconds it would be toast.
It’s not like a clutch, where it’s made to slip on and off through it’s life.
Most don’t realize that, but trans builders do.

 

[Headintheclouds]

I think what I'm getting confused about here is difference between engine RPM and torque converter output RPM and how efficiently the torque converter is working as that changes. For the figures in my example to stack up there must be quite a bit more difference between input / output RPM at 1850RPM than at 2400RPM. Does this make sense and does that necessarily mean it is working less efficiently?