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Wilburn
02-03-08, 10:19 PM
Hi,

I have a Dax de-dion with limited slip differential.

I am fed up with the banging that happens when I do a 'brisk' start from traffic lights in 1st gear. The back wheels bang as the power is transferred from wheel to wheel with the limited slip - rather than just normal wheel spin.

What would a powerlock differential do? Would this make the 2 back wheels spin as normal, resulting in the standard squealing of rubber with the Cobra fish-tailing it away from the lights?

TINKA
02-03-08, 11:17 PM
I think you will find a power lock and a limited slip diff are one in the same thing. It sounds like your diff is faulty to me. You will probably have to take it out to repair it and if you donít fancy doing it your self then I would recommend you getting in touch with Russell Ram try sending him a PM :D

ldtopham
03-03-08, 06:22 AM
If both wheels do 'lock' I would first check the halfshaft UJ's for wear before pulling the diff. Have a good nosey at both ends before getting the spanners out;) As Tinka says P/L and LSD are the same thing. If you're not sure what you have, jack the rear and rotating one wheel should result in the other following the same direction.

Impulsebooks
03-03-08, 07:13 AM
Limited slip is just that... it allows limited wheel spin. My cob has powerlock diff and if I really go for it and dump the clutch, both wheels will spin together leaving two black lines. I prefer to save tyres though.

Powerlock will not allow one wheel to spin alone, so when pulling right out of a junction for instance you won't have the driver's side rear wheel letting go. The other wheel stops it spinning. Some will say they don't like powerlock diffs, something to do with cornering, but I love mine. It really works to get the power down and only lets the wheels go if pushed really hard at pull away.

As for the banging... this is nothing to do with using limited slip or power lock. It could be your suspension set up. It sounds to me like your wheels are jumping up and down in the well as they turn (slipping and gripping) They try to hold the ground but can't so they spin. When they spin so fast they oscillitate up and down causing the springs and shocks to make the noise you are hearing. To check this, have someone outside the car watch the wheels as you pull away hard. They should see the up and down movement of the wheels.

Of course you could have a problem in your prop. My old capri used to make the same kind of noise. Used to be the centre bearing bouncing around. But most cobs have a single part prop, so I doubt this is your problem. If there was a porblem in the diff itself, I should think you would hear something all the time not just at pull away.

conrod
03-03-08, 10:48 AM
Paul,

Have you checked the halfshaft nuts/studs at the diff end for tightness? On the Dax De Dion, the studs on the outside (Ford six-stud side) of the CV adaptor plates have a habit of working themselves loose. The main problem is that you can't get a socket over them to torque them up - you can only use an open-ended spanner.

However, following a recommendation by Peter Walker at Dax, I've now fitted M10 K-nuts in place of the nyloc nuts. These have smaller heads, enabling you to use a socket and a torque wrench on them to tweak them up to 34 lb ft.

You'll probably find (as I did) that when you undo the nuts, they stay put and the stud itself unscrews (this is what happens once the threadlok joint has broken). You'll then have to put the stud in a vice to remove the nyloc nut. You can do each stud one by one without removing the halfshafts. I didn't bother with stud/threadlok on reassembly, as there's so much grease in the CV joints it would have been a waste of time. But they seem to be staying tight now!

You can get them from Raceparts, Merlin etc.

Hope this helps.

Wilburn
03-03-08, 10:55 AM
Hi Alan,

Thanks, I will check that out tonight.

I am also going to slightly increase the damper setting at the back as this should then eliminate the rear wheels banging under hard 1st gear acceleration.

Also, my differential is an open diff and not a limited slip! :eek:

conrod
03-03-08, 11:17 AM
Also, my differential is an open diff and not a limited slip! :eek:

Paul - in which case I would thoroughly recommend a Power Lock, suitably re-rated. A bit of a pricey upgrade though ....... ;)

wilf
03-03-08, 12:41 PM
Sounds like axle tramp to me, and I guess it is well known around here that I don't recommend lsd for a road car. Track car, definitely. Road car, just makes them potentially lethal. JMHO is all.

Neil O
03-03-08, 01:01 PM
Sounds like axle tramp to me, and I guess it is well known around here that I don't recommend lsd for a road car. Track car, definitely. Road car, just makes them potentially lethal. JMHO is all.

I agree, axle tramp.
Agreeing with Wilf, always difficult to admit to.;)

Try different tyre pressures and damper settings to make the best of what you have before paying out for expensive mods.

dingocooke
03-03-08, 01:25 PM
I read the symptoms and just thought, fairly common behaviour of an LSD equipped car when given loads of gas off the line (back end jumping up and down as well spinning up both wheels), are you 100% sure you dont have a LSD in your car????

Wilburn
03-03-08, 01:27 PM
Dave Brookes told me this afternoon that mine is just normal open diff and not a power lock/limited slip.

dingocooke
03-03-08, 01:33 PM
Dave Brookes told me this afternoon that mine is just normal open diff and not a power lock/limited slip.

OK ignore me then!!!

Neil O
03-03-08, 02:15 PM
OK ignore me then!!!

Can I ignore you too? :p

dingocooke
03-03-08, 02:40 PM
Can I ignore you too? :p

I was hoping :p

Neil O
03-03-08, 04:01 PM
I was hoping :p

Consider it done.........





Doh! :mrgreen:

Wilburn
03-03-08, 07:12 PM
Right, I have been under the back of my Cobra and checked all bolt are tight.

The 6 bolts on each drive shaft to dax spacer then onto diff are tight as I lockwired the little b45t**ds a few weeks ago :-)

I have adjusted the dampers from 9 clicks (approx one complete rotation) to 12 clicks.

If it stops snowing in a bit I'll take it for a test blast. i.e. a 1st gear standing start full throttle blast.

Lets hope it's cured the banging of the wheels when its trying to grip.

I also did this as quoted by member Russel_ram on 16th Jan 2003 and I can indeed confirm that my Cobra DOES NOT have a LSD differential.

.................................................. ..................................

Jack up the car so both rear wheels are of the ground - handbrake off, in gear, can you turn a wheel easily - NO = LSD.

Alternatively (but the same thing really), both wheels off ground as above, in gear, turn one wheel (does it rotate easily?) - does the opposite wheel turn in the opposite direction, YES = non LSD.

Russ

Easiest, but not realiable, does it have a nice, finned, aluminium cover instead of a rusty black steel one - yes = probably LSD.
.................................................. ..................................

Wilburn
03-03-08, 07:54 PM
Ok, I have been out twice just now in Cobra.

Originally the back dampers were set to 9 clicks.

-I moved them to 12 clicks and went out in Cobra.
It made no difference as far as I could see, the back wheels still banged violently under hard acceleration in 1st gear from stand still.


-I then moved them to 21 clicks and tried again.
The back wheels do not bang anywhere near as violently as before but they still bang, or rather bump.

I will try to go out again tomorrow with the rear dampers set to maybe 27 clicks to see if that cures the banging/bumping, however I am concerned that if it does, will the substantially increased rear dampening make the car skitty, especially over bumpy roads?

Happy Jim
03-03-08, 08:21 PM
I will try to go out again tomorrow with the rear dampers set to maybe 27 clicks to see if that cures the banging/bumping, however I am concerned that if it does, will the substantially increased rear dampening make the car skitty, especially over bumpy roads?

You should set your dampers for the amount of damping you need for driving, not to mask another problem. But to answer your question, Yes, if you firm up the dampers too much you will lose tyre contact more regularly (as well as lose your fillings).

If you are suffering from Axle tramp they you'll need to start wielding your spanners...

Jim


Edit :- Axle Tramp definition - : A form of wheel hop that occurs on cars with live axles, caused by the axle repeatedly rotating slightly with the wheels and then springing back.

Clarkson
03-03-08, 08:26 PM
Ok, I have been out twice just now in Cobra.

Originally the back dampers were set to 9 clicks.

-I moved them to 12 clicks and went out in Cobra.
It made no difference as far as I could see, the back wheels still banged violently under hard acceleration in 1st gear from stand still.


-I then moved them to 21 clicks and tried again.
The back wheels do not bang anywhere near as violently as before but they still bang, or rather bump.

I will try to go out again tomorrow with the rear dampers set to maybe 27 clicks to see if that cures the banging/bumping, however I am concerned that if it does, will the substantially increased rear dampening make the car skitty, especially over bumpy roads?

It might have something to do with that 470lbft torque!;)

BLOKE
03-03-08, 08:32 PM
Hi Wilf, I was just about to reply when I read your post, and it's exactly what I was going to say, yes it will be axle tramp, (somones guna say it aint got an axle) and you will pobably be able to eliminate with suspention/shock settings.
I also agree that a slipper can be lethal on a car such as a Cobra,it trys to drive the car in a straight line, particularly in wet conditions.
Regards Frank Dowsett. BLOKE

dave
03-03-08, 08:35 PM
Hi Paul.
The finned rear cover rule only applies to the earlier (JX6) type diffs, All the XJ40 (De Dion) diffs have an alloy cover.;)

Wilburn
03-03-08, 10:24 PM
"wielding your spanners"

What exactly do I need to do with my spanners?




You should set your dampers for the amount of damping you need for driving, not to mask another problem. But to answer your question, Yes, if you firm up the dampers too much you will lose tyre contact more regularly (as well as lose your fillings).

If you are suffering from Axle tramp they you'll need to start wielding your spanners...

Jim


Edit :- Axle Tramp definition - : A form of wheel hop that occurs on cars with live axles, caused by the axle repeatedly rotating slightly with the wheels and then springing back.

mylesdw
04-03-08, 02:19 AM
Sounds like a combination of damper/spring/tyre pressure. Worth checking that the links that hold the De-Dion beam are all in good order. You can't really have axle tramp (as defined above) on a car where the diff is bolted to the chassis.

Wilburn
04-03-08, 07:42 AM
I am going to keep playing with the rear dampers settings.

What should I do with the rear spring and tyre pressures, increase or decrease them.

Tyres at back are 18" Toyo proxies which are and 295 wide with 18psi in them.


Sounds like a combination of damper/spring/tyre pressure. Worth checking that the links that hold the De-Dion beam are all in good order. You can't really have axle tramp (as defined above) on a car where the diff is bolted to the chassis.

FatBoy
04-03-08, 07:50 AM
I'm not familiar with the De Dion setup, but does the half-shaft still make up the top suspension link? If so, each side of the suspension can try to "walk" forward under hard acceleration i.e. the wheel rolls forward within the wheelarch as the entire suspension twists around teh half-shaft. The tyre then breaks traction and the suspension springs back to its original position ready to start the process again and again, hence the axle tramp and banging.
One way to address this is to fit a Watts linkage to the top of the hub carriers. This allows the wheel to travel vertically under normal suspension movement, but is prevented from moving fore or aft.

Paul

Neil O
04-03-08, 08:15 AM
Try raising the rear tyre pressures. Try a large amount to see if there is any difference. If it is better, then you may be able to soften the damper settings a bit.

Remember, only alter one thing at a time mate, else you won't know what change is working.;)

Wilburn
04-03-08, 08:30 AM
ok, I have just increased rear dampers to 30 clicks, I will go for a test drive in a short while.

If that fails I will increase tyre pressures to see what happens.

JamesP
04-03-08, 08:49 AM
Dave
"The finned rear cover rule only applies to the earlier (JX6) type diffs, All the XJ40 (De Dion) diffs have an alloy cover"

Not always (I hope) I have an LSD from an early XJ40 with a finned cover for my De Dion

James

dave
04-03-08, 10:24 AM
Dave
"The finned rear cover rule only applies to the earlier (JX6) type diffs, All the XJ40 (De Dion) diffs have an alloy cover"

Not always (I hope) I have an LSD from an early XJ40 with a finned cover for my De Dion

James

Hi James.
that's what i just said diddle I? Finned covers are always alloy:D;)

JamesP
04-03-08, 11:51 AM
Oops - my miss

Wilburn
04-03-08, 02:04 PM
Well I checked my tyre pressures, they were all at 15psi .... ooops.

I put them to 19psi

Tested car, with correct(ish) tyre pressures and back dampers at 30 clicks - no different (but lighter steering :) )

I then increased rear tyres to 22psi - still no different.

I then increased rear dampers to 55 clicks (which feels like thats around the maximum) - a very hard skittish ride but the back wheels still bang under hard acceleration in 1st gear.

I plan to put my rear dampers back to 9 clicks tonight and then increase the rear tyre pressures to see what effect that has.

........... its all good fun eh! :)

runt
04-03-08, 02:12 PM
Paul, thats weird; I find you only have a scale of 1-20 on damper adjusters..
What Paul (Kirkham) describes, this was a problem in my days of thrashing my old S Type Jag 420..( wheel moving fore/aft).

Paul.:)

Miket
04-03-08, 03:35 PM
Well I checked my tyre pressures, they were all at 15psi .... ooops.

I put them to 19psi

Tested car, with correct(ish) tyre pressures and back dampers at 30 clicks - no different (but lighter steering :) )

I then increased rear tyres to 22psi - still no different.

I then increased rear dampers to 55 clicks (which feels like thats around the maximum) - a very hard skittish ride but the back wheels still bang under hard acceleration in 1st gear.

I plan to put my rear dampers back to 9 clicks tonight and then increase the rear tyre pressures to see what effect that has.

........... its all good fun eh! :)

Have you got Toyo tyres fitted????? if so, I think you'll find that whatever you do with the damper setting and tyre pressure you won't get rid of the axle tramp in dry weather, the Toyo's grip so well that it's hard (not impossible) to spin them without slipping the clutch first. ;) :D

Mine does it also. ;) :D

Wilburn
04-03-08, 09:19 PM
Hi Miket,

Yes, my tyres are Toyo proxies which are and 295 wide at the back.



Have you got Toyo tyres fitted????? if so, I think you'll find that whatever you do with the damper setting and tyre pressure you won't get rid of the axle tramp in dry weather, the Toyo's grip so well that it's hard (not impossible) to spin them without slipping the clutch first. ;) :D

Mine does it also. ;) :D

wilf
05-03-08, 08:09 AM
There you go - all you need to do is fit some crap tyres and your axle jumping will be a thing of the past..............:mrgreen:

Wilburn
05-03-08, 09:57 AM
I think I have reached a conclusion.

I need 8,000 bhp and 500 wide tyres - but then don't we all :-)

Seriously, I have set the rear dampers back to how they were before I started messing around and put the rear tyres (toyo proxies 18" and 295 wide) to 28psi.

If I do a very 'brisk' standing start in 1st gear, the banging is virtually elminated :-)

If I do a very 'brisk' standing start in 2nd gear, the back end lights up and there is lots of smoke everywhere (with zero hint of banging)

Previously it would not spin the wheels in 2nd from a standing start as there was so much grip (with rear tyres at around 18psi)

So, it looks like its all down to the immense grip of the toyos (with correct tyre pressures).

The toyos say they can handle a max of 50psi, not sure what the max psi should be on a Cobra but I feel maybe 30-32 would be the approx limit before traction becomes severely diminished.

dingocooke
05-03-08, 10:08 AM
LOL great for loooooong wheelspins but you should really be running around 19-20 psi front 20-21 rear IMHO.
High rear tp's will do a few things;
1-Prematurely wear out the middle of the tyre and not the whole tyre; if you ever wondered why higher p's give less grip? The profile is more rounded (ballooned in the centre) so you have much less tyre in contact with the road so less grip, running over pressure for your application is pointless, you may as well fit 205's...
2-The first time youre pressing on a little, you will spin it at speeds that you previosuly found safe; good for the body shop/DB's repair income though...
3-Make the ride a lot harder, which will prematurely wear out the suspension, and make a lot of other parst develop rattles and squeaks!!

Wilburn
05-03-08, 10:19 AM
Yes, I agree 100% with you there!

Pity my tyres were at 15psi (that was because I got lazy with checking them every month)

I intend to run preciesely as you say, around 19-20 psi at the front and a tad more at the back.


LOL great for loooooong wheelspins but you should really be running around 19-20 psi front 20-21 rear IMHO.
High rear tp's will do a few things;
1-Prematurely wear out the middle of the tyre and not the whole tyre; if you ever wondered why higher p's give less grip? The profile is more rounded (ballooned in the centre) so you have much less tyre in contact with the road so less grip, running over pressure for your application is pointless, you may as well fit 205's...
2-The first time youre pressing on a little, you will spin it at speeds that you previosuly found safe; good for the body shop/DB's repair income though...
3-Make the ride a lot harder, which will prematurely wear out the suspension, and make a lot of other parst develop rattles and squeaks!!

dingocooke
05-03-08, 10:26 AM
hehe if you just want to pull the occasional very long very smokey burn out (or video it) a bottle of Domestos is your friend (just wipe any splashes off your body work clothes wheels etc after hehehehe)

Wilburn
05-03-08, 10:54 AM
eh ????? :confused:


hehe if you just want to pull the occasional very long very smokey burn out (or video it) a bottle of Domestos is your friend (just wipe any splashes off your body work clothes wheels etc after hehehehe)

dingocooke
05-03-08, 11:02 AM
stop car get domestos (or cheapo Wilkos bleach) from boot, poor a little (or a lot LOL) onto tarmac, burn out, die laughing/on the smoke drive off, pull over wipe off any bleach, chuckle with friends at video, dont get caught....(drag strips used to use bleach for the warmup burnouts-probably not any more with HSE etc...?)

Wilburn
05-03-08, 11:03 AM
cool :twisted:

wilf
05-03-08, 01:00 PM
Steve - there was me thinking you wanted all that bleach for your hair!

dingocooke
05-03-08, 01:07 PM
Steve - there was me thinking you wanted all that bleach for your hair!


A cap full would do whats left!!! Ahh long flowing hair, such a nice memory...bugger!!

Impulsebooks
06-03-08, 04:18 PM
I then increased rear dampers to 55 clicks (which feels like thats around the maximum) - a very hard skittish ride but the back wheels still bang under hard acceleration in 1st gear.

I plan to put my rear dampers back to 9 clicks tonight and then increase the rear tyre pressures to see what effect that has.

........... its all good fun eh! :)

I am a great believer in "middle for diddle" for my guestimates. So if 55 is max, I would set 27 clicks. Obviously a professional can do better than guess, but one of your posts was very revealing when you said that after the second (or was it third?) adjustment of your dampers t banging was much less. This says to me that you are on the right track, but that dampers are not the entire story. Do you know what your spring ratings are?

Edit: Ooops, just read that you fixed the problem. So I will delete my second para. Still think "middle for diddle" re your dampers though. :)

runt
06-03-08, 04:55 PM
As I mentioned earlier, how come your dampers have a scale of 0- 55; mine only go round to 20..

Paul.:confused:

Wilburn
06-03-08, 04:57 PM
No idea :eek:

They are made by Gaz if that helps?

I know my front dampers are set to absolute minimum.

runt
06-03-08, 05:06 PM
Yep, I've got the Gaz, set mine @ 9 front & rear, as suggested by Prof. Walker, perhaps there different shocks as I have standard chassis (just noticed yours is De Dion).

Paul.

Wilburn
06-03-08, 05:10 PM
Yes, Gary at Dax said on a De Dion set the front to minimum as the front De Dion sorts it all out......some how....no idea how! :eek:


Yep, I've got the Gaz, set mine @ 9 front & rear, as suggested by Prof. Walker, perhaps there different shocks as I have standard chassis (just noticed yours is De Dion).

Paul.

runt
06-03-08, 05:18 PM
They probably are different Gaz, as you say that De Dion is clever stuff; my cousin had to explain how it works about twenty times and then.. I got it!:rolleyes:

Gary is a fount of knowledge too.. but if he ever offers me a lift again, there'll be a space where one second ago there was a runt..;)

dave
06-03-08, 05:19 PM
And the winner of the most confusing avatar image goes to......







.......Nrudliw!8)

Miket
06-03-08, 05:21 PM
And the winner of the most confusing avatar image goes to......







.......Nrudliw!8)

And I thought it was my computer. :confused: ;) :D :D

Wilburn
06-03-08, 05:24 PM
Great, whats the prize?



And the winner of the most confusing avatar image goes to......







.......Nrudliw!8)

runt
06-03-08, 05:28 PM
Thank Christ, thought it was my eyes seeing double, prize is.. a cd of DB singing 'Witch Queen of New Orleans'..:p

wilf
06-03-08, 07:18 PM
That would be better than TonyM singing "The house of the rising bun". :twisted:

Neil O
07-03-08, 08:10 AM
or Antony singing "Postman Pat". ;)