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Old 2nd February 2010, 10:01   #1
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Default Unable to achieve engine braking

Hi all,

I have just picked up a 4WD invader. The only issue I find in this vehicle is the crawling speed is high when it comes to heavy decline stretch.

Would be great if some one can help me understand, if I could add a additional low gear? Does the transfer case will have space for that? Or the next option would be to change the existing low gear. And what would be the ratio?

Thanks & Regards
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Old 2nd February 2010, 16:12   #2
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Default Go for lower diff ratio

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Originally Posted by robinson.s View Post
Hi all,

I have just picked up a 4WD invader. The only issue I find in this vehicle is the crawling speed is high when it comes to heavy decline stretch.

Would be great if some one can help me understand, if I could add a additional low gear? Does the transfer case will have space for that? Or the next option would be to change the existing low gear. And what would be the ratio?

Thanks & Regards
Robinson.s,
Were you in 4wd low 1st gear while desending? If yes then speeds must be manageable enough. The problem with present engines are they are rev friendly and attain higher rpms easily.

Adding a further lower ratio is painful and expensive. Low ratio on a M&M is 2.46:1. If you feel you need more torque while climbing and slow desent, go for 4.27 or even 4.5 diff ratio on both ends. This should slow down things considerably. This is a much easier option.

DO not open your transfer case for this.

If you are still not satisfied drive a gypsy on a steep slope, you will like M&M instantly
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Old 2nd February 2010, 16:24   #3
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You sure about not using brakes/clutch while descending?

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Originally Posted by vinod_nookala View Post
... go for 4.27 or even 4.5 diff ratio on both ends. This should slow down things considerably.
Yes, both ends is the operative word, hence emphasizing it again.

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If you are still not satisfied drive a gypsy on a steep slope, you will like M&M instantly
100% Agree. And after you have liked the MM, drive my Gypsy to fall in love with the crawling speed of a Gypsy all over again..
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Old 2nd February 2010, 16:37   #4
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Diesels do not have good engine braking ability. Therefore on steep slope, you need to keep tapping brakes lightly otherwise it will revv away to glory.
I have seen that while descending very steep slopes on 1st low, if I do not keep tapping brakes, the engine happily revvs close to 4500rpm
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Old 2nd February 2010, 16:42   #5
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Originally Posted by tsk1979 View Post
Diesels do not have good engine braking ability.
. You sure..? I thought the diesel's are good at that..

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Therefore on steep slope, you need to keep tapping brakes lightly otherwise it will revv away to glory.
I have seen that while descending very steep slopes on 1st low, if I do not keep tapping brakes, the engine happily revvs close to 4500rpm
Don't know much about Safari, but MM's can be practically left alone on a descent in 1st Low without a driver on a steep slope.. Have seen this myself many times over..
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Old 2nd February 2010, 17:07   #6
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Even the safari low ratio is very very low, much lower as compared to gypsy.
However, when you descend a very long incline, the rpm starts increasing.
Thats why many trucks have special jake brakes, because unlike petrol vehicles, leaving a truck in first gear on a sharp incline is not enough.
Engine braking - Wikipedia, the free encyclopedia
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Old 2nd February 2010, 17:33   #7
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adding a bit to that, there is a transfer case with 2.48 ratio in Low mode

Spike
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Old 2nd February 2010, 17:38   #8
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Quote:
Originally Posted by tsk1979 View Post
Even the safari low ratio is very very low, much lower as compared to gypsy.
However, when you descend a very long incline, the rpm starts increasing...
On the Pearl Valley OTR, I did a rather long and steep descend on 1st low and there was no need for me to use the brakes. I reckon Vijay (Star_Aqua) was spotting for me that time.

For those who attended that OTR, is was the last slope, after which we had the snacks before our return back to the briefing spot and then off to lunch.
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Old 2nd February 2010, 17:50   #9
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Guys, Common rail diesel engines don't give engine braking like the old school engines. Something about ECU trying to act smart. So diesel Jeeps give very good engine braking while common rail Safari/Scorpio won't.
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Old 2nd February 2010, 17:58   #10
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Its not just the Crdi engine Samu san. Even old tech Diesel engines lack engine braking (retardation when foot is lifted off the throttle) because Diesels do not have a throttle plate.

In petrol engines engine braking is caused by the vacuum buildup when throttle plate is closed creating a vacuum in the manifold.
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Old 2nd February 2010, 18:04   #11
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Then why is my diesel Jeep having such good engine braking? I rarely use brakes.
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Old 2nd February 2010, 18:28   #12
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Quote:
Originally Posted by Samurai View Post
Then why is my diesel Jeep having such good engine braking? I rarely use brakes.
Sharat, I am (remotely) thinking engine braking and crawling are 2 different things and the statement 'diesels are bad at engine braking' holds good. The crawling in diesel is possible because it has a bad engine braking AKA it can never go to a zero RPM because its a diesel. But in a petrol the engine cant hold on to its RPM and you cant crawl, it would sputter to a halt @ zero RPM's. Let me know if the above theory helps?
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Old 2nd February 2010, 18:41   #13
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Maybe you're right, might be the case with new gen Diesels. The last Diesel i have driven was our Qualis and yes it does have engine braking, but not as much as a Petrol car.
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Old 2nd February 2010, 18:54   #14
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Santosh, I am under the impression that crawling only refers to climbing, where you do have to press the A-pedal.

Regarding engine braking, try this experiment. While driving down the slope in a road, press the A-pedal and accelerate, and then let go the A-pedal. Will the vehicle retard suddenly or continue in the same speed?
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Old 2nd February 2010, 19:02   #15
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Quote:
Originally Posted by Samurai View Post
Regarding engine braking, try this experiment. While driving down the slope in a road, press the A-pedal and accelerate, and then let go the A-pedal. Will the vehicle retard suddenly or continue in the same speed?
Sharat, I am thinking a petrol engine will retard more (loose RPM quicker) than a diesel. Why dont we bring torque into the discussion. Does the inherent nature of diesels having higher Torque makes it lazy to loose RPMs' and thus inhibit engine braking; a petrol has lot lesser torque to shed...
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