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MG Midget and Sprite Technical - Rear axle out this weekend

So, I mentioned in an earlier thread my plans to change the rear suspension. I went one further and had the whole back axle out and painted it up. See before photo below. After to follow.

I only had 2 problems. 1 I striped the thread on one of my brake pipe unions. That will get fixed this week. The second problem is a bit more worrying...

Essentially, the back axle is now about an inch further to the near side of the car than the off... I can't think how this is possible other than being sold dodgy bent springs on ebay... but they look okay.


Does anyone have any thoughts?




C L Carter

and the after photo


C L Carter

Doesn't that look nice! Is the centre painted or just cleaned up?
Greg H

just cleaned up the diff with Jizer. Its ali so it wont rust!

C L Carter

Most spridgets have the axle offset in the body.
Are you sure it wasn't like this always?
Onno K

No I'm not sure... but theres no way of checking now... I just noticed when I was doing up the wheel nuts that on one side I was nearly scraping the bodywork with my ratchet handle and on the other I was well clear...
C L Carter

crazy thought: one of the springs isn't in backwards, is it?

(I am pretty sure that it would never be able to go together like that, but, you know, just in case...)

Norm
Norm Kerr

I'm going to jack it up again... loosen the u bolts... shake it round a bit... drop it down... roll the car back and forth... then torque up the bolts under compression... see what happens

C L Carter

2 Things mate

Firstly many axles that I have measured are not balanced. If you measure between the spring base/mounting and the brake backplate you will see a small difference. This means that the axle will be slightly off centre.
Secondly the bodywork will also not be central and will again make it appear that one side will be nearer the wheel than the other.

Unless it is a huge problem best not to worry too much and get on with it.

The spring can not be the wrong way around as one end is longer than the other and the effect would be to have the axle askew. :)
Bob Turbo Midget England

Just had a quick and dirty measure of the axle Christian's midget (he left it at my "work" while he waits for pipe bits).
The distance from the tyre to the outer wing is 2cm more on the drivers side.
So something is wonky!
The drivers side wing did have quite a large patch applied, so I wonder if this is contributing to the apparent difference?
Is there some datum that we can measure from on the body?

-- Josh
J Levine

Josh,
this is another subject covered quite recently, search required

I think it included three quater of an inch (20 mm to you youngsters) difference would probably be usual

build and assembly of cars wasn't that accurate back in the day
Nigel Atkins

Josh,

Both sides have been "patched" by PO... but I chatted with him last night and we've ruled out body work as a factor. I think this is a new problem created from the weekend activities.

I might try measuring what Bob has suggested though!
C L Carter

Christian?

You can try measuring a number of dimensions.

Try from the centre of the body to the eges of either wheel arch to check the body work dimensions/accuracy

How could the PO rule out body work? even heritage shells are out by a decent factor as would new cars originally.
Robert (Bob) Midget Turbo

20mm is no problem.
Adding up all of the potential tollerances this does not sound like an impossible number
Onno K

Well, I've started going through old photos, and I'm trying to convince myself it was always like that. I might drive around a bit and see if it sorts itself out a little.

Is there a torque to be doing the U bolts up to? I just went until my bushes began to distort - which isn't very far - see photo


C L Carter

You always distort those bushes (that's why I want to go to the alloy blocks)
There is no number for those bolts but....

to lose will cause rear wheel steering when lifting off

to tight will strip the thread off the U bolts

But bloody tight is the general consensus
Onno K

alloy blocks is a great idea! I'm going to make some now =]
C L Carter

Just buy them from peter may or Dominic
Onno K

torque for the U bolts

if I am not mistaken, they are 3/8-24 UNF, so the recommended torque would be 35 ft lbs (dry) / 20 ft lbs (if liberally dosed with anti-seize)

take a torque wrench to them and you'll be surprised at just how many more turns it takes, to get anywhere near that torque

and, after a few days / weeks of driving around, check and they might just take some more


Norm
Norm Kerr

The u-bolts have lock nuts on them and you are compressing the spring pads ... not stretching the bolts. Torque wrench is useless here.
Trevor Jessie

Drive it.
All you are measuring at the moment is where the bolts have pulled the mounting rubbers as you assembled it. This really doesn't mean much until the suspension has settled down. It needs to be worked for a couple of miles. Then measure as before and see if there is a problem. There is usually a difference as the axle does move about a bit, but 20 mm difference (i.e. axle is moved only 10mm off centre) is no problem at all.

Did you fit the spacer washers beside the front Metalastic bushes? I usually add extra shim washers in there to take up any lateral slack. Using polybushes at the rear will also help reduce axle "lateral shift". Beyond that, you are into the world of modification like Panhard rods etc.

Guy

U-bolt torque is another long fairly recent thread

personally and I also think it was the concenus -

use a spanner and get as tight as possible by hand without overdoing it, tighten each side of the U-bolt evenly before moving on to the next

after driving the car for a bit you'll need to check and probably retighten

at each 6 month service check them but I found on mine after a year they were fully settled and I could no longer nip them up

PS
I think mine were a lot more squashed that in your photo
Nigel Atkins

I agree with trevor, the torque wrench is useless in this application. However I'm keen to know what calculation/tables you got the torque setting from for that thread size, Norm?

In answer to Guy, Yes, spacer washers and plastic bearing washings - was no slack at all. Also fitted poly's at back. I'm going to drive it a bit and reassess.

In response to Nigel, I could continue squishing these if I wanted to... but it will just splurge out and destroy the pads... I think I'm going to phone the manufacturer and see what they say.

C L Carter

Christain,
I wasn't saying mine were necessarily correct by being squished up more than yours just put the comment out there to see others response

mine just got done squashed some where along the line so had to stick with it to keep as tight as described
Nigel Atkins

Nigel, what I was saying was - i'm not sure if you are meant to keep tightening until the pads are no longer compressible... The nuts aren't coming off as they are under tension of both the pad, spring washer and they also have a nyloc... the question is... will over or undertightening effect performance?
C L Carter

Christian,
Find a nice straight bit of empty road and give it some welly on and off with your hands off the wheel. You'll soon know if they're too loose!
When I've done it I've tightened them up as hard as I can with about a six inch wrench, driven a hundred miles or so, then tightened up again and left them at that. They shouldn't go anywhere.
I also reckon your offset issue might cure itself too with a good drive and a retighten under load.
Matt1275Bucks

I think that tightening the u-bolts to the point of distorting the pads is unnecessary, and a red herring when it comes to the apparent off set of the axle. Do the u bolt nuts up firmly with a standard length of open ended or ring spanner and you won't be far wrong. I am a great believer that the sizing of spanners was evolved to give the correct torque - long before torque wrenches were in common use.
You can always go back over the nuts when things have settled down. And thereafter, check them every few months. If you overtighten at the start you will destroy them and have nothing left in. Reserve !
Guy

Hi

the reason why I brought up the use of a torque wrench (sorry, I should have been more clear) is for Onno's comment that going too far will strip the threads, so, using the torque wrench as a guide, one can see that they can be tightened up a great deal without risking going over that limit

when I was first tightening mine, I was SURE that they were at, or near their limit, but after a quick check with the measuring tool, could see that they were close, but that many, many more turns of the wrench were quite possible without going over, because, as Trevor pointed out, the resin pads are being squished


So, coming back to C L Carter's original question:

over tightening will eventually strip the threads

under tightening (the main concern) will allow the rear axle to squirm around and that will interfere with the handling



Of course, it is fine to just turn and hope, but using a tool designed to monitor what is going on, it takes out some of the guesswork.
For folks who have years of wrenching experience, it sounds like training wheels, or being overly fussy, I guess. But to folks who are doing it for their first time, it is nice to know how to use a tool to help guide the work.

Norm
Norm Kerr

Norm,
I have nothing against the use of a torque wrench. Good advice. But equally just blindly ratcheting away until the wrench clicks will be fine for not stripping the nut threads, but won't tale any account of the degree of distortion of the pads. One needs to keep an eye on them too.
I also suspect that the original rubber pads were harder than the current cheap replacements. Perhaps more akin to yellow polybush in hardness.
Guy

I've gotta be honest, I thought these poly bushes would be harder than they are... I can't see a huge benefit of them over rubber ones other than their improved frictional ones.

Torque wrenches are for the guidance of wise men, and the reliance of fools!
C L Carter

Christian,
I'd have said looking at your photo that you're about right in terms of distortion. Check its all tight on the road, i.e. no rear wheel steer under throttle off- throttle on and you should be good to go. If its a bit wobbly it may just need a little nip up but your pads shouldn't look like they've been squeezed to death.
Matt1275Bucks

Christain,
I don't know how much those pads should be squashed but to get the nuts tight with a ring spanner they did get pretty squashed on mine

you could try Matt's method to ascertain the correct tightness/squash

I'm hoping you'll find out for the correct tension/squash

I'd have thought the clamping needs to be firmer rather than looser(?)

I replaced all round the harder to the touch yellow urethane bushes and pads with the much softer to the touch Super-Flex bushes and pads and much prefer the later
Nigel Atkins

>>> over tightening will eventually strip the threads <<<

Well, this is just a suspicion based on recent experience... There may be another risk in over tightening. I had a break in the main leaf of my RH hand spring in early summer, and noticed on disassembly that the U-bolts had been tightened by POs until the rubbers were completely crushed, and the metal edge of the pad locator bracket was pressing against the top leaf-right where the leaf broke. I wonder if that created a pressure point that eventually caused the crack. See pic below. When I bolted everything back up with a new leaf, I did as Mr. Carter suggested above, and tightened the U-bolts up until the pads were nicely distorted, but not smashed outright. So far, so good.

-:G:-


Gryf Ketcherside

This thread was discussed between 28/11/2011 and 01/12/2011

MG Midget and Sprite Technical index

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