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Old 21st September 2010, 12:35   #1
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Default Tall reverse gear in SUVs and MUVs... Why?

My observation based on Scorpio and Safari. I think other MUV/SUV kind of vehicles, and maybe even cars may have same issue.
The reverse gear is rather tall.
For example, if you engage reverse gear, release clutch completely, and let your vehicle putter in reverse at idle, the speed is pretty fast for control.
Ideally, the reverse gear should give you low speed. So when you reverse out of a garage or something, you do not need to keep pressing clutch to control speed.
This leads to another problem. When reversing up a slope, there is not enough torque in reverse gear, which leads to half clutching.
Not a good thing.
If mfrs gave a much shorter reverse gear, it would do the following
1. Give lower speed, which is a good thing. Most of us do not like to drive high speed on reverse gear
2. Reversing up slope would be possible without burning clutch. Very useful in steep slopes.

So why tall reverse gear, any logic?
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Old 21st September 2010, 12:41   #2
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Spot on, Tsk ! I have been having exactly the same thoughts while reversing my Scorpio out of my garage.

And yes, I have struggled while reversing up an incline near Mangalore.

Wish the manufacturers did something about this.
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Old 21st September 2010, 13:04   #3
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@tsk,
Your safari's reverse is taller than the first but shorter than second?
Or even taller than second?

Does your owner manual mention the ratios?
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Old 21st September 2010, 13:10   #4
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Its shorter than 2nd, but taller than first. At a lot of places where are inclines which are tough even in 1st gear. So a taller gear for reverse usually means clutch abuse. I have 4x4, so I wriggle out of such situations with 4L. Since I encounter such situations on hilly dirt tracks and like, its not an issue.
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Old 21st September 2010, 13:13   #5
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yes TSK - even i find this to be true. if i release the clutch fully while in reverse and my foot is off the accelerator, my Scorp moves along on account of its own torque - but it moves quite fast. However if I am in 1st gear moving forward with my foot off the accelerator, it goes much much more slowly - just chugs along in fact.

this used not to be the case in the old Amby and Fiat - and in my old Mahindra CJ 500 and in the MM540 too. There one could release the clutch fully keep ones foot off the accelerator and move slowly back in reverse.

Indeed, if I remember right, there were times in the 1970's when my dad used to reverse the old Amby and Fiat up particular slopes which were a bit too steep and difficult to manage even in 1st gear while facing forward!


Quote:
Originally Posted by tsk1979 View Post
My observation based on Scorpio and Safari. I think other MUV/SUV kind of vehicles, and maybe even cars may have same issue.
The reverse gear is rather tall.
For example, if you engage reverse gear, release clutch completely, and let your vehicle putter in reverse at idle, the speed is pretty fast for control.
Ideally, the reverse gear should give you low speed. So when you reverse out of a garage or something, you do not need to keep pressing clutch to control speed.
This leads to another problem. When reversing up a slope, there is not enough torque in reverse gear, which leads to half clutching.
Not a good thing.
If mfrs gave a much shorter reverse gear, it would do the following
1. Give lower speed, which is a good thing. Most of us do not like to drive high speed on reverse gear
2. Reversing up slope would be possible without burning clutch. Very useful in steep slopes.

So why tall reverse gear, any logic?
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Old 21st September 2010, 13:31   #6
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http://www.safaridicor.com/buzz/Tata...TT_Dicor_S.pdf

According to this, the reverse gear is 3.75, 1st is 4.1 and FD is 4.1.

So the overall ratio for revers is 15.37 where as 1st is 16.81. There's an 8.5% diff.

Shan2nu
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Old 21st September 2010, 14:01   #7
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Originally Posted by tsk1979 View Post
So why tall reverse gear, any logic?
Quote:
Originally Posted by tsk1979 View Post
Its shorter than 2nd, but taller than first.
This is just me thinking - the highest ratio available in a gearbox is related to the largest & smallest gears you can accomodate within it. So 1st is usually the tallest. The forward gears are all constantly in-mesh, but reverse isn't - the gap for the idler is probably why reverse is slightly lower than 1st.
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Old 21st September 2010, 14:04   #8
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Interestingly I was thinking about the same problem!! It gets more pronounced for me as I use the MM540 and the Safari interchangeably on almost a daily basis. There's one that moves so slow in reverse you could step out and walk along while the other one zips.

For a typical SUV, I guess something like the 540 is more appropriate which has a short Reverse.

I don't think its a solvable problem though.

Cheers,
Adi
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Old 21st September 2010, 14:16   #9
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Quote:
Originally Posted by Shan2nu View Post
http://www.safaridicor.com/buzz/Tata...TT_Dicor_S.pdf

According to this, the reverse gear is 3.75, 1st is 4.1 and FD is 4.1.

So the overall ratio for revers is 15.37 where as 1st is 16.81. There's an 8.5% diff.

Shan2nu
Quote:
Originally Posted by im_srini View Post
This is just me thinking - the highest ratio available in a gearbox is related to the largest & smallest gears you can accomodate within it. So 1st is usually the tallest. The forward gears are all constantly in-mesh, but reverse isn't - the gap for the idler is probably why reverse is slightly lower than 1st.
If you look at the spec, reverse gear is taller than the 1st gear. Thats why slopes you can tackle in 1st gear can be too steep for reverse gear
Ideally, I would prefer a reverse gear shorter than 1st gear.
for example if 1st great gives you 8.25kmph at 1000rpm, then reverse gear should give you around 4.125kmph at 1000rpm.
right now, it will give you a higher speed at 1000rpm
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Old 21st September 2010, 14:27   #10
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I do not have any explanation, but I have noticed the same in Baleno also.

During my early days as a Jeeper I was constantly advised by my uncle (guru) to always reverse into steep inclines as Reverse is shorter and provide max torque. We had wriggled ourselves out from many a tricky situations that way. Looks like things have changed!

I have a feeling that this has got something to do with Synchromizer or similar mechanism that allows reverse to get engaged even when the car is rolling.
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Old 21st September 2010, 14:30   #11
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Quote:
Originally Posted by WhiteKnight View Post
I do not have any explanation, but I have noticed the same in Baleno also.

During my early days as a Jeeper I was constantly advised by my uncle (guru) to always reverse into steep inclines as Reverse is shorter and provide max torque. We had wriggled ourselves out from many a tricky situations that way. Looks like things have changed!

I have a feeling that this has got something to do with Synchromizer or similar mechanism that allows reverse to get engaged even when the car is rolling.
?? Reverse engaging when car is rolling?
Do not do so unless you want to wreck the gearbox. you cannot engage reverse when car is rolling. Only forward gears are syncromesh
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Old 21st September 2010, 14:44   #12
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Quote:
Originally Posted by tsk1979 View Post
If you look at the spec, reverse gear is taller than the 1st gear. Thats why slopes you can tackle in 1st gear can be too steep for reverse gear Ideally, I would prefer a reverse gear shorter than 1st gear. for example if 1st great gives you 8.25kmph at 1000rpm, then reverse gear should give you around 4.125kmph at 1000rpm. right now, it will give you a higher speed at 1000rpm
Yes, ideally one would wish reverse to provide a ratio high enough for backing-up speeds to be reasonably low (crawl ?). However to have reverse offer twice the ratio of 1st gear (using your example) the concerned gears have to be that much bigger - implying a larger & heavier transmission casing. And if the gearbox is large enough to accomodate gears for crawling in reverse, one can argue, why not crawl in 1st also ?

Assuming that manufacturers wish to have the smallest & lightest gearbox possible that still provides a reasonable range of ratios, I think compromises are made.

Looking forward to hearing what the "gurus" think...
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Old 21st September 2010, 15:10   #13
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Because first gear is used quite a bit, and a very short 1st gear would mean the need for a 6 speed gearbox for even spread.
As for gbox size, the mfrs can give a reverse gear as short as 1st atleast. why is it taller.
Right now, a 2WD safari cannot be reversed up a steep slope from stand still without either clutch burn, or wheel spin. And I am talking about moderate slopes. If it was as short as first gear we would atleast get some respite
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Old 21st September 2010, 15:18   #14
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Is it because with the reverse gear engaged the vehicle is fwd instead of rwd.
Plus these wheels don't have the engine weight helping them gain traction.
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Old 21st September 2010, 15:26   #15
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Quote:
Originally Posted by tsk1979 View Post
As for gbox size, the mfrs can give a reverse gear as short as 1st atleast. why is it taller.
I'm guessing it's because reverse gears cannot be constantly in-mesh as the forward gears are. The reverse gears are apart & also have to provide enough space between them for accomodating the idler. Hence, for a given gearbox casing size, the reverse gears would be smaller than their 1st gear counterparts (by atleast the height of their gear teeth).
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