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Trevor Barnard
United Kingdom
39 Posts |
 Posted - 18/08/2007 : 17:07:16
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| I'm in the process of rebuilding my PA. Are the front wheels supposed to "lean out". Nothing is out of place that I can see and Blower doesn't say anything about the set up. All help gratefully received! |
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Peter Scott
United Kingdom
1240 Posts |
Posted - 18/08/2007 : 18:46:51
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Trevor
Welcome to the forum.
Page 483 in Blower gives the 'Service Data' for a PA. The Camber angle (degree to which the front wheel leans out) is the 'Steering knuckle' angle ie 9 degrees less the 'King pin' angle ie 6.5 degrees which gives 2.5 degrees.
In other words the king pin leans inwards 6.5 degrees but this is more than offset by the stub axle (steering knuckle) which leans out 9 degrees.
The same page also gives you the 'Castor angle' at 8.5 degrees which is the angle at which the king pin leans backwards.
I hope this helps.
Peter |
Edited by - Peter Scott on 18/08/2007 18:47:18 |
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Trevor Barnard
United Kingdom
39 Posts |
Posted - 18/08/2007 : 18:51:18
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Thanks Peter. I had been looking in the wrong part of the book! Looking at other PAs, they appear to be upright. Are people spacing the king pin in some way?
Thanks for the welcome by the way! |
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Peter Scott
United Kingdom
1240 Posts |
Posted - 18/08/2007 : 20:35:15
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Trevor
If you stand directly in front of a PA you can clearly see the camber angle of the front wheels. I have not seen one which does not have the front wheels cambered.
Don't try to make a judgement from a photograph.
Hope the rebuild is going well.
Peter |
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David Allison
United Kingdom
665 Posts |
Posted - 23/08/2007 : 15:24:17
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Most standard cars built before the 1950s and fitted with cart springs are positive camber - that is the tops of the front wheels incline outwards.
The earlier the car the more pronounced the camber angle appears (this is mostly due to the larger wheel sizes and narrow tyre widths), with the introduction of independant suspension it was found that negative camber improved roadholding and steering feel.
Thus modern high performance cars can have anything up to 2.5 degrees of negative camber and racing cars up to 7 degrees.
Many modern specials built on cart sprung axles have used negative camber - but this is really only suitable for track work and the wider dunlop racing tyres.
It makes the steering very heavy and normally results in hub and stub axle damage.
Our own N type special had negative camber for a season - but my sister never got on with it at all and we have reverted to the original HN Charles set up.
The most important thing to do is put the axle on the right way around (J type owners beware), with the front axle on backwards the steering is quite alarming.
All of the camber castor and king pin inclination (KPI), information is in Blower and I have straightened and reset a number of front axles for all models with a great deal of successs - however do not attempt this yourself unless you really understand heat treatment of metals (I am a Blacksmith - that does not mean I shoe horses).
Once heated and straightened the axle must be normalised and de-stressed - something I need my wife tells me
Once the axle is straight and everything is pointing the right way, it is important to set up the axles castor.
Wedges between the top of the spring pads and the underside of the axle create the castor - this allows the car to steer straight and also to self centre.
Again the great bible Blower has this information - although I think it is right that some P types had no wedge at all?
If in doubt ask someone using a car - My dad is my personal font of useful info - but I guess I was born lucky!
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Mike
United Kingdom
229 Posts |
Posted - 23/08/2007 : 15:31:14
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David,
In this politically correct world you cannot call yourself a "Blacksmith" as it might offend someone, so I think a Hot Iron Smith or Horse Shoe Smith should be the new buzz word!
And I always thought it was your father that repaired my axle!
M ELLIS |
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David Allison
United Kingdom
665 Posts |
Posted - 23/08/2007 : 16:56:50
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Mike - he did actually do your axle himself - using my set up bench plus large bore gas and torch.
He is a very clever chap
I normally do the really mangled ones that require serious heat treatment with him - this is because this type of damage needs more than one pair of hands.
I earn my pennies making lifting equipment for pallet loading - hence my companies workshop has suitable facilities.
I am not suggesting the keen amatuer can not do this kind of work - indeed if I can do it anyone can. All you have to do is read the right books and preferably get taught by someone who knows.
My father made sure my apprenticeship was expansive and tried to make sure I would enjoy learning as long as I enjoyed living! |
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phil
United Kingdom
149 Posts |
Posted - 24/08/2007 : 09:08:11
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Hi all. This post has got me concerned for my PB. As I look from the front of the vehicle, the front left wheel is verticle and the right wheel looks like the top is leaning out far to much. I noticed a comment about the correct way round for the front axle. Does this apply to the P type? There where no shims when it was dimantled. So, should I just shim
out the left wheel that is dead verticle, or remove axle and reverse it?
Any help would be greatly appreciated.
Thank you everyone. This really is a top forum. |
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David Allison
United Kingdom
665 Posts |
Posted - 24/08/2007 : 09:47:32
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Phil
It does sound very much like you need to carefully check the steering geometry - if indeed you do have one wheel negative and one positive camber, the front axle might be bent. |
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Trevor Barnard
United Kingdom
39 Posts |
Posted - 24/08/2007 : 10:02:26
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| And I was worried about both of mine leaning out!!! |
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Peter Scott
United Kingdom
1240 Posts |
Posted - 24/08/2007 : 11:39:44
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Phil
The 2.5 dgree wedge placed between the spring and the axle, on a P, increases the castor angle. It has no impact on the camber. For the camber to be correct you need the axle to be straight, or rather the angles to be correct. Plus the king pin bushes and axle eyes need to be in OK condition. A worn axle eye will reduce the camber angle.
As David said, you need your axle to be checked for geometry and the kingpin eyes to checked for wear by someone with the necessary equipment. To do that you will need to strip the axle so you can fit new kingpins and bushes when it is reassembled.
I went through that process about eigteen months ago. I ended up fitting new springs as well, which significantly increased the castor angle so I had to reverse the wedges to reduce the castor angle to the correct value. Springs when loaded are supposed to be flat but most new ones are not.
Peter |
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phil
United Kingdom
149 Posts |
Posted - 24/08/2007 : 15:28:21
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| I rushed to my workshop this morning and started to measure everything. one side of the car is an inch 1/2 shorter. The axle is indeed poorly. it appears that the axle has been 'fettled' before and i am wondering if it will be repairable (aimed at david allison). what a good start to the weekend. have a good one everyone. |
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Peter Scott
United Kingdom
1240 Posts |
Posted - 24/08/2007 : 21:16:46
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Phil
When you first buy a MMM car, it is very easy to get disheartened by some problem or other, which seems to be overwhelming. But there always is an expert out there somewhere who can solve the problem for you. You just need to find one. And this forum is an excellent way of finding one.
If you want to cheer yourself up, go out for a run. Even if your front wheels are a little 'off' they are fantastic cars to drive and are guaranteed to put a smile on your face.
Peter |
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Trevor Barnard
United Kingdom
39 Posts |
Posted - 24/08/2007 : 22:53:26
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| I fully agree with Peter. I've owned my PA for 20 years and for the first 10 I smiled every time I used it. Unfortunately I have left it sat in the garage for the last 10 years! Time to bring back that smile. |
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Bob Stringfield
United Kingdom
854 Posts |
Posted - 25/08/2007 : 13:19:19
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| I second that. PA0603/ APP 186 is just as much fun as BEV 307 was in 1961. |
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