Home > General > How can a RR in PARK and Handbrake on roll down a hill? |
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PaulTyrer Member Since: 22 Jul 2013 Location: Devizes, Wiltshire Posts: 1254 |
My thoughts exactly, although with it being a 17 year old car it must be a P38, but if it was in park it should have held. Perhaps it was a weak or faulty gearbox linkage? |
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10th Aug 2017 11:26pm |
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Joe90 Member Since: 29 Apr 2010 Location: Hampshire Posts: 6409 |
and who turns their wheels to the kerb when they park on a hill these days? (I know it was in a driveway but still...) .
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11th Aug 2017 7:30am |
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Andy-B Member Since: 23 Mar 2017 Location: Todmorden Posts: 21 |
If the transfer box was in neutral then it would just rely on the handbrake alone.
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11th Aug 2017 1:15pm |
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Sandyt Member Since: 07 Nov 2013 Location: Wraysbury Windsor Posts: 2265 |
P38 could well have been manual |
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11th Aug 2017 4:18pm |
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UK Marine Member Since: 22 Jul 2016 Location: Durham, County Durham UK Posts: 830 |
The handbrake on the P38a acts on all 4 wheels as it's a drum attached to the transfer box, so considered very safe. The transfer box will only go into neutral if you take out a fuse and follow specific instructions regarding ignition key position etc, so really odd that it managed to roll away on its own... ______________________________
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11th Aug 2017 4:44pm |
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sako243 Member Since: 26 Dec 2013 Location: Wales Posts: 610 |
The handbrake setup is I think like that on a Defender. Therefore it can act on four wheels, or three, or two, or one. By acting on the prop with open diffs it is relying on the wheels having traction. If they start rolling then all bets are pretty much off. Ed |
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11th Aug 2017 5:40pm |
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Joe90 Member Since: 29 Apr 2010 Location: Hampshire Posts: 6409 |
@Sandyt
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11th Aug 2017 5:40pm |
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UK Marine Member Since: 22 Jul 2016 Location: Durham, County Durham UK Posts: 830 |
Unless he was doing work on the transfer box and had it electronically in neutral then I can't see it as there is no centre diff lock on a P38a. It uses a viscous coupling to lock when needed and obviously only when under motion when the engine is running. ______________________________
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11th Aug 2017 5:45pm |
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mzplcg Member Since: 26 May 2010 Location: Warwickshire. England. The Commonwealth. Posts: 4029 |
A P38 transmission has no locking diffs at all, only a viscous coupling in the transfer box. It has a transmission brake which acts on the rear prop shaft. So, if a rear driveshaft spline were to fail and allow the wheel to become disconnected from the drive then all wheels become free. This is the exact reason you never jack anything with a transmission brake unless the wheels are chocked, and it's why defenders, Disco 1 and 2 come with a chock as part of the jacking kit. It's also why transmission brakes are a really bad idea. One brake acting for all 4 wheels is a single point of failure with several scenarios for failure to happen.
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11th Aug 2017 8:16pm |
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RR2008HSE Member Since: 06 Jan 2013 Location: British Columbia Posts: 2932 |
We had a scare a few years ago while off-road in. One man's very young son got back in his Disco 3 (LR3 around here) at the top of a mountain. He managed the get the thing started before Dad got to him. Like the FFRR, it only needs to be put in gear and the parking brake will release automatically. Fortunately. All ended well. |
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12th Aug 2017 11:52pm |
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bishbosh10 Member Since: 25 Apr 2013 Location: North Somerset Posts: 344 |
I understand that the bits in the innards of an auto box associated with park are made of chocolate and you should never rely on park to hold the vehicle at any point. Always use the handbrake. Bish.
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18th Aug 2017 1:08pm |
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rodp Member Since: 09 Apr 2017 Location: The Black Country Posts: 318 |
In fact, for the application originally intended a transmission brake is a very good idea. The chances of a drive shaft spline breaking or an half shaft breaking whilst parked are slim to nil, the loading compared to being under power is extremely low. What you do gain is a handbrake well up out of the mud and water so it is almost always in a nice clean working condition. If you off road regularly you'll find drum brakes always full of mud, but the transmission brake is nearly always clean (ish), and it operates on all four wheels which, as you may know, is critical in some off road situations. I trialed for years (full modified) and can't remember a transmission brake ever failing when parked. |
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18th Aug 2017 3:12pm |
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JarrahJack Member Since: 27 Apr 2012 Location: Perth Posts: 23 |
Such a sad story.
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19th Aug 2017 1:55am |
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anorakmark Member Since: 18 Jan 2014 Location: Chatham Kent Posts: 121 |
A very sad story indeed
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17th Oct 2017 2:57am |
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