21 replies to this topic

[splintercat]

No doubt  I will get this all wrong,  but,  if you don't ask etc etc............................

 

My latest Mot was just done and passed easy apart from an added verbal advisory that.......there was a tiny spot of rust appearing on my rear subframe.....i have for ages now been toying with the idea of fittting a rear beam axle/ rear beam frame....  so could be an opportunity for me to play 

 

   1     don't really know the difference there between beam axle or just rear beam     or in fact if that is the correct terminology even?

 

                                                         2    I want to go lighter just because I do,    and have read all the pro's and con's with doing this sort of mod however...... I just want to know if anyone knows if either of our favourite magazines ever did an article on ......rear beams? or there are any  on this forum.

 

                                                         3     Somewhere in my little brain I saw an old article on a guy who, rather than buy a KAD/ Johnspeed/ mini spares/ Huddersfield spares   rear beam, he actually modified a standard rear subframe by basically cutting the back end off of it and strengthened it by welding in fillet webs/strenghtening plates.

 

                                                       4     Would appreciate some views on this idea particuarly any references to old articles about modifying a standard frame.

 

                                                      5    winter is nearly here and I desperately need a project to keep me busy busy......

 

 

Sorry bout the spelling.......Splintercat. ps Will  have to go down the coilover route to fascilitate this?

 

pps............now I am informed that I should have said.......Rear coilover lightweight modifyed subframe 

Edited by splintercat, 16 November 2017 - 08:05 PM.

[nicklouse]

Ok basics. Cutting the subframe down leaves you with a rubber mounted flexy thing pivoting on some rubbers. Waste of time and effort when you then have to add lots of brackets to thin metal sheet.

So a rear beam does away with the trailing arms unsuitable for road use.

So you then have the beam with trailing arms and coil overs. Which is what most people use.

First issue. Coil overs. You restrict the use of the car to really only two people and next to no luggage unless you are happy swapping springs out if you want to put some weight in the back.
Second. Coil overs need to be made with the shafts offset so they give clearance as the rear of the car was not designed to take springs. You will need the S type rear drums.
Third the weight will be transferred through the shock mount pin. I will bend. New stub axel or rear arms will be needed.
4 the arch mount was not designed to take the load.

I made(had one made) one to my own specs that removed most of these issues.

[Retroman]

A beam axle is literally and a one piece axle like on an escort, not really an option for a road Mini.

 

The front section of the subframe can be used perfectly well.

But as pointed out by NICKLOUSE above you have rubber bushes on each end, they can be left, or changed to poly or alloy bushes. The actual crossmember must also have extra brackets welded on to stop them moving, other wise they just pivot on the mounts. The brackets can be bolted through the floor under the backseat, and seat pan, 2 top, 2 bottom and use big penny washers inside, preferably welded on. The subframe also needs the ends welding where its cut and or a plate welding on.

 

The beauty of using a cut down subframe;

It fits and carries the radius arms

Has the clearance for any exhaust

Allows the handbrake to be used as standard too.

Standard brake pipe / bais valve also fit

You already have it,

Its a good starting point but needs some work.

 

Option 2 is a fabricated cross beam for coilovers

I have made them from 4 inch alloy c section and 3/4 inch box section both very successfully they ran with standard radius arm pins and no issues, but not carrying any rear passengers. Speedex and Maguire used to do them and box section radius arms too (1/2 the weight).

 

And lastly its a big one...as NICKLOUSE said... the shocker top mount was not designed to take the weight so must be in very good order and have a box section across between the 2 tops and at least 2 fabricated brackets up to the top of the back seat panel, preferably as a K frame to transfer stress diagonally.

 

If you are unduelly worried about bending the 3/8 pins KAD do 1/2in ones, which need rose-jointed coilovers.

 

[splintercat]

A beam axle is literally and a one piece axle like on an escort, not really an option for a road Mini.

 

The front section of the subframe can be used perfectly well.

But as pointed out by NICKLOUSE above you have rubber bushes on each end, they can be left, or changed to poly or alloy bushes. The actual crossmember must also have extra brackets welded on to stop them moving, other wise they just pivot on the mounts. The brackets can be bolted through the floor under the backseat, and seat pan, 2 top, 2 bottom and use big penny washers inside, preferably welded on. The subframe also needs the ends welding where its cut and or a plate welding on.

 

The beauty of using a cut down subframe;

It fits and carries the radius arms

Has the clearance for any exhaust

Allows the handbrake to be used as standard too.

Standard brake pipe / bais valve also fit

You already have it,

Its a good starting point but needs some work.

 

Option 2 is a fabricated cross beam for coilovers

I have made them from 4 inch alloy c section and 3/4 inch box section both very successfully they ran with standard radius arm pins and no issues, but not carrying any rear passengers. Speedex and Maguire used to do them and box section radius arms too (1/2 the weight).

 

And lastly its a big one...as NICKLOUSE said... the shocker top mount was not designed to take the weight so must be in very good order and have a box section across between the 2 tops and at least 2 fabricated brackets up to the top of the back seat panel, preferably as a K frame to transfer stress diagonally.

 

If you are unduelly worried about bending the 3/8 pins KAD do 1/2in ones, which need rose-jointed coilovers.

 

 

[splintercat]

A beam axle is literally and a one piece axle like on an escort, not really an option for a road Mini.

 

The front section of the subframe can be used perfectly well.

But as pointed out by NICKLOUSE above you have rubber bushes on each end, they can be left, or changed to poly or alloy bushes. The actual crossmember must also have extra brackets welded on to stop them moving, other wise they just pivot on the mounts. The brackets can be bolted through the floor under the backseat, and seat pan, 2 top, 2 bottom and use big penny washers inside, preferably welded on. The subframe also needs the ends welding where its cut and or a plate welding on.

 

The beauty of using a cut down subframe;

It fits and carries the radius arms

Has the clearance for any exhaust

Allows the handbrake to be used as standard too.

Standard brake pipe / bais valve also fit

You already have it,

Its a good starting point but needs some work.

 

Option 2 is a fabricated cross beam for coilovers

I have made them from 4 inch alloy c section and 3/4 inch box section both very successfully they ran with standard radius arm pins and no issues, but not carrying any rear passengers. Speedex and Maguire used to do them and box section radius arms too (1/2 the weight).

 

And lastly its a big one...as NICKLOUSE said... the shocker top mount was not designed to take the weight so must be in very good order and have a box section across between the 2 tops and at least 2 fabricated brackets up to the top of the back seat panel, preferably as a K frame to transfer stress diagonally.

 

If you are unduelly worried about bending the 3/8 pins KAD do 1/2in ones, which need rose-jointed coilovers.

 

Thanks for all the info.......think my mate Calver from Mini Mag did an article on making a rear beam out of an old subframe Feb 2010.........gonna read this and then make a decision.........mean Keith is a bit of a legend isn't he so def worth a read. Will hopefully keep you posted and if I do it then Ill make a thread/post it here if I can ................thanks Splintercat

 

 

[nicklouse]

sorry pointless. just make one

 

 

you can easily fit a bit for the handbrake cable.

[CityEPete]

I think those tyres might be below the legal limit :-D

[nicklouse]

still over 5mm of tread.

[splintercat]

sorry pointless. just make one

 

Wow !!      am liking that a lot...........something else to ponder about ? guess Ill be pm ing you bout this if thats ok?

 

 

you can easily fit a bit for the handbrake cable.

 

[nicklouse]

and that was done in 96

[tiger99]

Just curious. Which radius arms are these?

[nicklouse]

Just curious. Which radius arms are these?

go on guess. they are related.

[Icey]

We had a rear-beam and coil-overs. Lasted about a year before I was sick of it.

With so little weight over the rear the car was incredibly twitchy and it was difficult to get the brake balance right.

But the biggest complaint was the coil-overs. We used the offset mounted type and I was never comfortable with the loads it was putting into the wheel wells, I would strongly suggest turreting the rear. And in general non-progressive coil springs are awful compared to cones.

If this is a road car (as in it gets used on the road 99% of the time - fast road is a meaningless marketing term), I would strongly recommend thinking again.

[Cooperman]

If moving to coil springs which can never be as good as the original rubber spring cones, it is vital to have proper and accurately made rising-rate springs which are well-mounted in turrets.

The issue with saving weight at the rear is that the rear is already a bit too light and the weight balance is best improved by removing weight at the front, or if weight is removed from the back an equal amount is removed from the front.

The dampers will need to be softer than with a normal set-up to prevent skittishness on bumps. In general that type of rear axle is best suited to a totally smooth race track where weight saving at the rear is combined with general weight saving.

The other issue with that type of rear end on a road car is the loss of the rear crash resistance (what crash resistance?) caused by the removal of the rear sub-frame which is designed to take some of the crash loads. The position of the petrol tank is less safe with no rear sub-frame as in a rear end shunt the boot floor is even more likely to crush horizontally.

But in the end it is up to the individual owner to decide what he wants from his own car. A classic Mini will never be a fast road car, but can be made slightly less slow. A better way of improving acceleration would be to lighten the flywheel, fit polycarbonate windows and take out any other unnecessary weight.

Nick's beam looks a really good design for competition use when the regulations permit.

[splintercat]

If moving to coil springs which can never be as good as the original rubber spring cones, it is vital to have proper and accurately made rising-rate springs which are well-mounted in turrets.

The issue with saving weight at the rear is that the rear is already a bit too light and the weight balance is best improved by removing weight at the front, or if weight is removed from the back an equal amount is removed from the front.

The dampers will need to be softer than with a normal set-up to prevent skittishness on bumps. In general that type of rear axle is best suited to a totally smooth race track where weight saving at the rear is combined with general weight saving.

The other issue with that type of rear end on a road car is the loss of the rear crash resistance (what crash resistance?) caused by the removal of the rear sub-frame which is designed to take some of the crash loads. The position of the petrol tank is less safe with no rear sub-frame as in a rear end shunt the boot floor is even more likely to crush horizontally.

But in the end it is up to the individual owner to decide what he wants from his own car. A classic Mini will never be a fast road car, but can be made slightly less slow. A better way of improving acceleration would be to lighten the flywheel, fit polycarbonate windows and take out any other unnecessary weight.

Nick's beam looks a really good design for competition use when the regulations permit.

 

 

Still reading the article from 2010 in the Mini Mag as an alternative ........However.head is begining to hurt as there are some serious arguments BOTH for and against even considering a beam. All are relevant, and all are even if some seem to be subjective rather than objective. This in itself is not a bad thing as it shows both depth and passion against perception  based on fact and measurement. Hmmmmmm still reading and enjoying the different points of view .....Thank you all.