rear subframe replacement

[john ward]

My son's 1990 Mini needs the rear subframe changing. He's away at university, so Dad has to do it! I have the car up on ramps at the front, and on axle stands at the back, ready to start.

I assume some of you have done this before, so before I do start to take it to bits, just a couple of questions -

are there any good tips going?
any problems I should be aware of?
the best place to buy the new subframe?
would you use a new one, or is second-hand fine?
anything I have to change at the same time?

and finally - how long should it take? I want it back on the road before the end of November. But I guess that's down to me!

Thank you.

John.

[Cooperman]

Hi John,

It's not too difficult if all the bolts come out easily. The biggest problem is often the bolts at the front end which go into trapped nuts at the rear ends of the sills. If these bolts shear off you can often get the stubs out, after finally removing the sub-frame, by welding nuts onto the stubs. This heats up the stubs and they usually then unscrew. If not, you have to cut away part of the sill to get inside and weld in new nuts, then weld repair patches into the sills and re-paint the area. That's not easy. My advice is to soak the bolts in releasing fluid for a couple of days first.
I would always fit a new sub-frame complete with new trailing arm brackets. I always get mine from Mini Spares a the quality is then guaranteed. Never bother with second-hand ones. If the trailing arm bushes are at all worn, this is the time to re-bush them. You need a long 13/16" reamer to ream out the outer bushes, and take care when installing the needle-roller inner bushes that you don't damage them. Build up the complete sub-frame before reinstalling and give it a whole load of Wayoyl into all the 'nooks and crannies' It's good to change the mounting bracket rubber bushes too. Use all new bolts, making sure that you fill the holes in end of the sill with Waxoyl and copper grease when installing (see my recent 'Maintenance Tip......').
It's also worth checking the wheel cylinders whilst the hydraulics are disconnected.Keep the main hydraulic line clean and plug the end when you disconnect it to retain as much fluid as possible.
To disconnect the top of the LH damper you have to remove the fuel tank. Drain the tank and do this first.
It's difficult to know where to stop as you then start wondering whether to change the rear dampers whilst the tank is out of the car, etc, etc.
The only other point I would make is that often new rear sub-frames give the rear wheels a bit of positive camber due to manufacturing tolerances which spoils the handling somewhat. To correct this is another topic, so come back on here once it's fitted and I, or someone else, will tell you how to measure and correct (if necessary) the camber settings. It's very easy - all you need is access to a MIG welder and a steel ruler.
Good luck with this 'little' job.

I hoope this helps,

Peter

[john ward]

Thank you for taking the time to write all that Peter. I will digest it later, along with the Haynes service manual and the Haynes restoration manual - can't have too much information! Initially I will WD40 all nuts and bolts this evening, ready for the weekend. The car itself has less than 50000 genuine miles on it, we know the first and only owner before we got it. The engine is absolutely fine (I've done anything that needed doing) and John Jnr has taken the car to Uni at Newcastle upon Tyne and back a couple of times. The rear subframe is the only problem, although I will take on board all your comments about replacing bushes etc, and actually already planned to replace the wheel brake cylinders as I think they may be leaking.

I'll let you know how it's going, and come back on if I have any problems.

Thanks again.

John.

[Cooperman]

John,

WD40 is not the best penetrant fluid. I would get one of the special fluids sold by the motor factors which penetrates much better. To get onto those bolts you really need a 3/8" square-drive 1/2" socket on a 5" bar. Do it gently at first and see if you can just get the bolts to move a bit. If you have compressed air, use a air gun on a low torque setting, that's what I do, it usually works fine.

[Mr Edd]

I would buy a non genuine frame(I have found there just as good as genuine apart from a few sharp edges), and if you have time and a mig welder go round and seam weld all the joints, before rust proofing. I did this on mine and it is ok 4.5 years later with no sign of problems.

I would also change the flexible brake hoses for ease. Also make sure the handbrake cable is ok and the quadrants are moving freely. As for the radius arms i normally repair if necessary.

I always change the knuckle joints and all the bushes as they aren’t expensive and its easy to do.

As for replacing other parts have a look and if the look like they are going change as you have got it apart anyway.

Before you finish it is worth measuring from front wheel rim to back wheel rim to see if the car is still straight. Just make sure the front wheels are straight before you do it. If there is a problem you can put some spacers between on the front mount of the rear subframe and the heel board.

As far a time goes it normally a weekend job depending on coffee requirements