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MG Midget and Sprite Technical - Bushes

Ok so the dampers are off ready for V&C Engineering.
In the removal process the trunnion bushes look a bit knackered.
Normally they'd just be replaced with new rubber ones but from comments on here, it seems new rubber ones don't last. The current ones are 20+ years old.
The black polybushes from the likes of MGOC (https://www.ebay.co.uk/itm/254135726123) seem reasonably priced but do they last and is the ride noticeably harsher after fitting them?
Thanks.

Jeremy MkIII

Hi,

Not sure how much help I can be here.

Before I restored mine three years ago I’d never driven a Midget so can’t tell how much fitting Super Pro poly bushes changed the handling of the car.

What I can say is that I was surprised how planted the car felt for its age compared to driving modern cars.

Wouldn’t say the drive was harsh in any way. Very positive in fact.

Wouldn’t fit rubber bushes when these wear out. Hoping that will be a long way off.

Hope that helps.

James
James Paul

I fitted blue Super Pro bushes during restoration. Compared to the previously tired rubber bushes, the ride was better, sharper and more enjoyable. I was advised not or fit the harder bushes as they would give a much harsher ride, and that these were more for track cars.
Philip Sellen

Jeremy
I'm intending to change my trunnion bushes also and made a note a while back to use blue poly ones, like Philip. You'd think the poly would wear better than the rubber we seem to get now.
Bill B

James, Philip, Bill,
thanks for your replies and experiences, think I'll give the polybushes a try and see what they're like.
Upper trunnions are not the most difficult to replace if it turns out the ride is too harsh for my liking!
Jeremy MkIII

When I Polybushed my car, many years and many k miles ago, I fitted blue all round. Since then the only ones I have replaced are the rear links. They are easy to do. I probably need to check others by now.
At the time there were red, yellow and blue options in 3 grades of hardness. Blue softest but firmer than rubber. The other 2 for fast road and track though I can't now remember which was which. Given that other thread on British roads, then blue would be plenty firm enough!

Colour coding may still apply although my suspicion is that cheap copy versions were being introduced which used colour for it's chav factor rather than an engineering specification.
GuyW

Thanks Guy,
did you notice a difference in ride harshness?
Similar to these?

Jeremy MkIII

I know long term memory lasts better,😁 but this was a very, very long time ago Jeremey! And anyway surely most choosing to switch to Polybushes would be replacing old rubber ones, knackered and probably softened with age and contaminants. And that's just the bushes! So not a good basis for comparison. I just know that I was happy with them and they have lasted extremely well.
GuyW

Oh ok, thanks Guy, I've ordered a set so we'll see how they turn out. The current ones are fraying at the edges so the new replacements should be better!
Jeremy MkIII

On the upside, spring's approaching.

Bushes will soon be growing. 😁😁.


Now where's that rubber tree?


anamnesis

Actually Anam, that's the germ of an idea.
Not growing a tree but 3D printing. Is it possible to print polyurethane?
Anyone here familiar with 3D printing?
Jeremy MkIII

3D printing TPU (Thermoplastic Polyurethane) is quite possible and I've done it a number of times. You need a printer capable of using flexible filaments but it is done with Bowden extruders although other types can give better results AFAIK. IIRC both my printers cost around £160 new about 5-6 years ago so not the cheapest but nearer the bottom of the range. Something like the suspension bushes should print well as it's fairly squat and flexing of the printed object shouldn't be any issue. I did wonder about printing steering rack gaiters but the shape would flex too much and require a printer that can print a support structure, I have seem similar items 3D printed.
David Billington

Something like this David?
https://www.thingiverse.com/thing:7248431
Maybe slightly offset to give a bit of negative camber?
Do you know if there is there a 3D for dummies guide or is youtube your friend t learn about it?
Jeremy MkIII

Jeremy,

I'm by no means proficient at 3D modelling but a tophat bush is quite basic. The software I use is FreeCAD for the modelling and Cura for the slicing, both are Linux/Mac/Windows. I get what I need done and refer to online FreeCAD tutorials as required, plenty on Youtube, some of the stuff they show just loses me as it seems to go so quickly and some of the techniques they use, constraints I'm not familiar with. The most advanced thing I've done so far was modelling some mallet handles requiring lofting for the elliptical handle section and conical transitions from round to elliptical at the head end.

For modelling a tophat bush I would select the Part workbench in FreeCAD and the 'Create Primitives' tool which will allow you to create the necessary basic shapes. A cylinder for the brim, a truncated cone for the upper hat part, and another cylinder for the centre. The radii and height can be entered, as can the position so the cone can be placed at the brim height, the centre cylinder offset for an eccentric bush if required. Once the brim and upper are created they can be selected in the object tree and using Boolean Union from the Part menu made one object, then selecting that object and then the centre cylinder it can be cut using Boolean Cut to leave a new object with a hole in the centre, your tophat bush. Radii can be added if desired using the Part Fillet menu, select the 2 surfaces you want a radius between and the radius. Once done selecting the final object it can be exported, File Export as an STL file is what I use. It can be done other ways I have imported 2D DXF information such as a section through an object and then revolve it around a centre to create a 3D solid, another way to skin a cat. Being parametric you can adjust size and position of objects by editing the base item in the object tree and it should propagate down through items created from the item, as you could use the Cylinder, Cone tool and edit the position and dimensions after creating a default object.

The STL file is opened in Cura and having selected the 3D printer and filament being used, it has a number of common TPU filaments to chose from as well as Generic TPU. AFAIK the specific TPU settings are what has been contributed by the user community as being found to work best for that product. 100% infill for a solid bush and then perform the slicing which will create the Gcode required to control the printer and then transfer to the printer and print away.

Things have moved on a lot as I asked a neighbour that has a 3D printer to do some for me and he refused as when he got into it maybe 20 years ago you had to play around to find the right settings but with more recent developments and user community feedback the suggested defaults work quite well in my experience so he has asked me to print some items for him. A mate mentioned the first 3D printer they had at British Aerospace IIRC which cost around £250k and the parts had to be handled carefully and weren't really usable but these days a cheap printer and associated software will produce usable parts for a few £100. You then can get into filament selection as he has made some items such as binnacles for his car where they are found to warp in summer heat printed in PLA or similar as they were experiencing 80C is sunshine so he had to switch to a more suitable filament to cope with those temps.
David Billington

i fitted poly bushes all round and the ride improved a lot more planted ,I got sick of the rubber ones becoming a service item changing them every year or so.
mark heyworth

David,
Wow. Thank you for taking the time and trouble to write it all down and explain what's involved. It's far from the straightforward projects shown on some YouTube/Instagram shorts. There's a lot to learn.
Many YouTube videos to watch I think.
I've reread your post a couple of times and apart from showing my total ignorance on the subject, I was thinking it may be slightly easier to make the bushes solid and then drill them out to make them give some negative degree camber. Lots to think about, thanks again,
Jeremy MkIII

Jeremy,

I think you would want to 3D print them with the hole in. I think trying to drill the hole after printing would be frustrating unless you can get them really cold so they lose their compliance but better still maybe to make a round knife cutter and trying that rotating slowly with water as a lube. I've cut plenty of discs and a few other shapes with knife cutters and various sorts of rubber and it works well although nothing with the thickness of a tophat bush. Holding a tophat bush while trying to drill might be a task in itself due to the compliance. Reminds me a bit of trying to sand blast underseal, it doesn't work well due to the compliance of the material meaning it is difficult to abrade away.

I knocked up a quick representation maybe took about 5 minutes, took more time to sort out the screenshots and type this reply , I admit I have done it before. Bush brim is 28mm OD, 5 mm flange height, cone is 20mm OD to 24mm OD and 20mm high, bore 12mm. 2nd image is with the X placement adjusted by 1mm in the original centre cylinder which effects the later boolean cut results.

I admit again I've done this before and when I started it could make my head hurt as often a lot to take in.

I forgot to mention, close the Create Primitive window before doing the boolean operations or they remain greyed, I wondered for a few moments why it wouldn't let me do it, all went smoothly once closed. Using the create cylinder and cone functionality shouldn't have that problem but the sizes and positions need to be changed in the object details once created to change from the default values.





David Billington

Wow again David!
Thanks for that, pretty impressive. Just the small matter of understanding it all now🤔
Take your point about trying to cut a hole in one of them - hadn't considered he possible flexing; bit like trying to cut a neat hole in a jelly.
Have you considered going into business to produce offset negative camber bushes?
Correct me if I've remembered it incorrectly but- didn't you have the original idea/design for making a revised front suspension with vertical telescopic dampers which Frontline have subsequently manufactured?

Right on to YouTube to see what I can learn...



Jeremy MkIII

This thread was discussed between 16/02/2026 and 20/02/2026

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