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  1. #31
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    1,630
    Quote Originally Posted by petrolhead27 View Post
    Jacked both rear wheels up and when turning one the other turns the same direction but if I hold one still I can still turn the other withe little resistance so I’m guessing the power lock is worn out
    Any noise is a major concern and with it locking up in reverse you have some serious issue which needs investigation. I would not drive the car. If it has lost all PL capability then something has failed. The plates might be totally worn and possible broken parts. The diff drain plug is magnetic so a drain down and inspect what metal is attached to the plug might give you some indication on the state. If not drop the diff cover off.
    Dax 351 Cleveland T5 2.88 PL

  2. #32
    Join Date
    Apr 2012
    Location
    swansea,south wales
    Age
    57
    Posts
    194
    So I found the cause of my locking up on reversing on full lock . It’s the front wheels digging in to the inner wings when on full lock I’m thinking I need to fit steering rack stops. I recognise my PWR loc diff is knackered and I think I shall replace as soon as I can get hold of one I will also take the opportunity to change ratio as well as my revs are up a little high as I’m 3.54 and could benefit from 3.07 or there abouts.thanks for all the helpful replies I’ve got on this thread.

  3. #33
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    1,630
    One point to check is your lock to lock and centralised the rack if you might have more lock on one side.
    Unless you have large tyres up front than is recommended.

  4. #34
    Join Date
    Aug 2007
    Location
    Bournemouth
    Posts
    618
    Quote Originally Posted by petrolhead27 View Post
    So I found the cause of my locking up on reversing on full lock . It’s the front wheels digging in to the inner wings when on full lock I’m thinking I need to fit steering rack stops. I recognise my PWR loc diff is knackered and I think I shall replace as soon as I can get hold of one I will also take the opportunity to change ratio as well as my revs are up a little high as I’m 3.54 and could benefit from 3.07 or there abouts.thanks for all the helpful replies I’ve got on this thread.
    3:54 would be fine with a six speed box perhaps.
    I run a 3:07 lsd with a 5 speed Getrag coupled to a SBC 350. This is fine for me, at motorway speeds the engine isn't straining or over revving at all. I had a 4 speed in it up until early last year, the MPG was amusing!
    For a 5 speed, depending on the top gear final ratio I would say 3:31 or 3:07. Big power engines can go down to 2:88 which will give you very long legs and if you have big power, startling acceleration with less gear changes.
    David.

    Life is driving the Cobra. The rest of the time is just waiting................till I fix it!

    Wessex region caretaker rep.

  5. #35
    Join Date
    Sep 2010
    Location
    Cambridge
    Age
    36
    Posts
    1,227
    Quote Originally Posted by Darnpistonbroke View Post
    3:54 would be fine with a six speed box perhaps.
    I run a 3:07 lsd with a 5 speed Getrag coupled to a SBC 350. This is fine for me, at motorway speeds the engine isn't straining or over revving at all. I had a 4 speed in it up until early last year, the MPG was amusing!
    For a 5 speed, depending on the top gear final ratio I would say 3:31 or 3:07. Big power engines can go down to 2:88 which will give you very long legs and if you have big power, startling acceleration with less gear changes.
    I had 3.54 on my 383 SBC with getrag box, 4th was 1:1 and 5th was 0.8 I believe. To my mind on that gearbox 1st was too short, 2nd was perfect and 3rd tiny bit short, 4th actually a tiny bit too long and ideally 5th would have been a lot longer for cruising only as on fast A and B roads 4th gets you to XXX speed anyway so never use 5th if your in the mood to be on a bit of a mission. If I could make my choice again I would have gone for a longer diff as the 383 with good oomph would have easily coped with it but the neck-snapping 2nd and 3rd gear acceleration might not have been quite so hilarious as it was with the shorter diff

    I think there's a rare short ratio version of that getrag box around where it was used in a BMW (5 series?) rather than the Jag? might have imagined that but have vague recollection when I was in the research phase for my build.

    Dave A

  6. #36
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    1,630
    The other consideration is your tyre diameter which effects the final ratio. I run 235/60 15 on the rear. Going up to 245/60 or 275/60 does change the gearing which you need to consider.

    The link below is a great calculator . You can enter all the ratios and compare with a diff swap at speed or rpm.

    https://www.blocklayer.com/rpm-gear.aspx

    I run a 351 Cleveland with 360 lb torque with a flat power band from 1800-5000rpm

    When you have bags of torque pulling a 2.88 with a 5th of 0.84 is not an issue and it gives you a nice cruising speed with a low rpm 2,250 rpm (72mph for Europe) which also gives you a good pickup not having to change down. It still gives a kick in 5th at these speeds.

    Going to a 3.54 diff @72mph rpm goes up to 2740rpm.

    Going to a 3.54 diff @72mph rpm goes up to 2570rpm with a tyre change to 275/60 r15

    Some gearbox 5ths are 0.67 so you need to work through all your ratio's and tyres to decide on your diff.

    I could not run a gearbox ratio of 0.67 5th , 0.50 6th with a 2.88 as both 5th and 6th would be over geared for motorway speeds in the U.K. 5th would be 1800rpm @72 mph.
    Dax 351 Cleveland T5 2.88 PL

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