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MG Midget and Sprite Technical - DIY rear telescopic shock conversion
I have been thinking of converting the rear shocks to telescopic. I have seen the conversion kit sold by Moss etc which puts the shock at an angle. I have also seen the DIY approach See:http://188.8.131.52:76/shocks.htm
I was thinking of attempting the later (and have bought some cheap shocks to try it out).
Does anyone have any comments on this method.
I have heard that it can pull out the attachment to the chassis (where the droop-limiting strap would normally be). I have fitted new assemblies to both sides and have seam welded them in (they are normally spot-welded) so this should solve this.
Any (constructive!) comments would be great!
|I think that your link covers the main concern: the rebound strap structure was not designed to take the loading of a damper, so will likely stress crack over time, like his did. With sufficient welded reinforcement, this should be able to be overcome, if you choose this route.|
There has been a ton of discussion about this over the years, do a search in the archive (the link just below the "bbs" link at the MGE home page). Comments I recall reading in there, when I was considering about this were:
- the lever arm dampers work rather well
- the benefit of telescopic is difficult to justify for a road car
- for racing, in classes that allow this kind of modification, it might have some benefit
- the tele shocks that will fit in the extremely short stroke available under a midget: are they designed and valved for a Midget, or are they some "random" one that just happens to fit?
- if your lever arm dampers are worn out, ANYthing will feel like an improvement.
There certainly are plenty of folks who have done the conversion, and not all of them have changed back (some have), so if you want to try, then go for it, but take careful note of the stress fracture warning in the link that you posted and weld in reinforcements if you do.
i have run for the last three years with mini front shocks on the rear with no problems.
|Tim I think you have taken the right approach to this. |
Wish I'd welded strength into mine before it tore the stressed rebound link frame off the floor too! Extra welding after modification is a pain in the situpon.
Bob's 1500 in that web article is the fuel injected car that appeared in PPC a few years back and it handles very well.
Mine has Mini front shocks on the rear as in the article, and works just fine.
The Spax conversion's geometry doesn't seem to allow any real damping motion as its action is more to rotate than to push in and out (up and downwardly) so I think this is a better way to proceed
|My conversion has been fine now for about 8 years. But there can be an issue with the length of travel of the shocks, especially in relation to bump and hop and your particular ride height. You will likely have to swap and invert the spring plates, but it may still need working out, especially if you have tired leaf springs or a very low car.|
|Guy Oneandahalf Sprites|
I did this conversion about three years ago and have recently changed back to lever arm. I used adjustable mini front dampers and found that the rear axle movement is very restricted, also using the damper as the rebound stop damaged them and they became noisy in operation. I noticed a difference when I fitted the mini dampers because my old lever arm dampers were uprated ones so were far too hard. I now have standard lever arm dampers and very happy with them.
|M J Pearson|
|I ran the Spax adjustable shocks mounted verticaly to some new mounts, They worked very well set on the softest setting. As shown they came up through the floor to give plenty of movement.|
|"the rebound strap structure was not designed to take the loading of a damper, so will likely stress crack over time, like his did"|
If you meant mine, the mountings have been fine. 10,000mls and not a bend bow or buckle on the mountings. But it is a 1500 shell which is strongly reinforced at the rear end. The rebound straps are bolted into the main chassis rails which extend to the bumper. As Big Bill suggests, reinforcement on the earlier shells is necessary but sufficient.
|Um, I am the only one who hasn't read about any stress fractures in that link? The rebound box fell out DURING the conversion, not after it. I'm not saying that reinforcement isn't a wasted effort, just that it wasn't mentioned in the link.|
What I intend to do is something akin to Mr Bintcliffe's idea. Except that's roughly how I'll mount some coil overs, instead of just the tele's.
|I have a RWA and use the strap mountings for the dampers; no problems to date... incl using the dampers on hard setting for competition (and leaving them on same setting for the road).|
I should add that my car was comprehensively and regularly Waxoyled from soon after acquisition in 1977 to around the mid-80s.
|Ive got the Frontline rearkit which already has vertical positioned damper.|
|Arie de Best|
|how much better are the vertical ones? Ive got slanty spax on at the moment, and looks like the work of a couple of hours to swap 'em for more vertically inclined ones.|
I guess the answer to the bottoming out problem is to either find shocks with stops in them or be clever with selection - I've got mini adjustables on the front of mine and the short throw is OK, but looks like it's too small for the back? though maybe it's down to how they're mounted. Certainly I think it's worth a go as the mini adjustables are only 35ish quid each..
|I added a lowered mounting lug on the inverted spring/damper mount plate to prevent 'bottoming'. It only needed to be ~1" lower to avoid the unwelcome crash...|
|Mine look like this.|
|If you can get a shock with an offset upper mount, then at least you can have the upper bushes supported on both sides without the shock leaning inwards towards the bottom.|
Try as far as possibe to have it mounted between the two bits of metal for retaining the check strap as opposed to inboard and hanging on for dear life.
Even some hefty washers will allow the load to be spread, but ideally you want to strengthen all the metal around the attachment point.
|That's a good point from Peter Moore about mounting the shocks in single shear. I wonder how many of those who have had problems have been caused by the additional flexing that a single shear mount will put into a panel that was originally used as part of a double shear mount?|
|Tried the mini front ones for a couple of years but problems with the short stroke and rebound brackets breaking have made me change to mini rear shocks. Same mounting at the bottom but required welding in of small turrets just forward of the bumpstop. Stroke is longer on the mini rears so this has allowed near to standard axle movement. Not tried it out yet so can't comment on how well (or not) it works! |
The problem I had before was that the short stroke meant that either they were bottoming out or the inside rear wheel was lifting off the ground on tight corners as the shock didn't allow the axle enough droop. Obviously only under extreme driving so on the road it didn't show up as much.
Good thing about using Mini front or rear shocks is that you have access to cheap and plentiful standard or uprated adjustable units from a car of similar weight to the Midget.
|I fitted the angled Spax arrangement to mine back in 2000. That's over ten years ago and i've had absolutely no problems and I've found the adjustable dampers a great improvement on the lever arms ones (though I have to say they were pretty U/S when I changed them). Road use only though.|
I am interested by the issue with the shock breaking on full suspension compression. I am guessing that it could be aleviated by lowering the rear suspension?
On full compression the rear suspension is limited by the rubber bump stop. Measure the distance between the two shock mounting points and subtract the clearance between the rubber and the bump stop plate. The chosen shock then needs to have a compressed length slightly less than this calculated clearance. Then you know that the suspension will be stopped by the bump stop and not limited by the shock itself.
If the calculated clearance is to short for your shock, then inverting the lower spring plate will give more tolerance for your chosen shock.
|Guy Oneandahalf Sprites|
|Tim, you could have a look at this thread as well, it gives several different options:|
|Graham P 1330 Frogeye|
This thread was discussed between 20/01/2011 and 26/01/2011
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.