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MG Midget and Sprite Technical - Rear suspension upgrades eg mini dampers

Having recently upgraded the front end of my Sprite IV with Frontline arms 11/16" ARB and 340lb -1" springs, that are a quantum leap forward, I thought I'd revisit the rear suspension.
1000 miles ago I fitted new MGOC standard rear springs with yellow poly bushes and a home brewed tubular damper setup, using standard Mini front dampers fitted to the check strap mounts and the reversed and inverted damper mounting plates.
At the top mount I fitted the dampers inboard of the inner check strap bracket using long bolts and spacers where tha check straps would have been. This required quite long spacers at the lower end between the mounting brackets and the damper eye.
Now having consulted my copy of M&AHS High Performance Manual the photos appear to show the lower mount directly adjacent to the damper which suggests the damper mounts will fit between the two check strap brackets. Is that the case?

I'd like to just fit and forget the Frontline kit which uses posh adjustables, but having just paid for the front end...

I find that under spirited cornering on less than smooth surfaces, the rear tends to sort of hop sideways. Is that a feature of cheap dampers, lack of a Panhard rod, poorly tempered springs ??? On fast dry roundabouts the car will oversteer eventually. Wheels and tyres are also on the shopping list, presently new 145/13 Avon CR322 (22lb F and 24lb R) on 3.5" rims.
The car overall handles much better than before the Frontline suspension was fitted. To the level where I can see the point of extra power, where before I thought a more or less std 1275 seemed plenty thank you very much. If I can settle on a setup for the rear, then I can move forward on the hp front.

Mark
M Crossley

Hey mark

Id say try the panhard rod and wheels 1st, and go from there....with your current rearend mods most likely thats all you will need or want... the only other thing would be control arms, like on the 1/4 eliptic suspension set-up. I dont have tube shocks on the rear yet, but ally wheels and and a panhard rod completely changed the rear suspension to the max in a good way, just make sure your panhard rod is paralle to the axle and the ground. even upgrading wheels from the 3 piece welded wheel (rostyle) is a huge improvement.

Not being a wheelman, are your wheels wire? if not Id look to 4.5 to 6 inch wide wheels 3.5 seems a bit thin...mine are 5.5 perfect in my opinion

Prop
Prop and The Black Hole

Mark,

I just got some Mini dampers also for my '74 midget. I found them to be, well, quite "mini". At the top, I mounted mine between the two brackets attached to the body, where the check strap bolt used to be. But, the mounting loop on the shock is so small, I had to fill the space with about 6 flat washers to prevent it from bending the brackets in when tightening. One potential problem is that the upper tube, which is mainly a dust cover, I think, might hit the body where it passes by that bracket. So, I put the washers on that side so the tube clears. Hope this makes sense, I'm not at home and am trying to remember and will be glad to post pictures later. This puts the lower mount right next to the spring plate. Depending on the spring plate you have (original or custom) you might have the same problem with the shock tube hitting the bracket so you may need to put some washers or spacer there also. My concern is that this particular shock (standard Mini front), mounted in this way, is almost completely extended when the car is just sitting. This gives a lot of compression length, but very little extension. (I'm in the process of making a simple bracket that will bolt to the spring plate and move the lower shock mount up a couple of inches to even out the compression/extension to see how that will work before spending more money on different shocks.) Since the check strap is removed, the shock is essentially the check strap. This seems like it would be bad, but, as far as I know, no modern car has rebound check straps - I guess the shock is it. (Does anyone with tube shocks have the check strap installed, also?) There may well be some sort of check built into modern suspensions, but I just haven't seen any straps! Is this bad? Are shocks designed to limit the suspension in extension? Moss sells a kit designed to mount just like we have done (268-288) but it's quite expensive - about $100/shock. Those shocks have no dust shield on the top, which does away with the clearance problem. I guess that is not needed and not a critical part of the shock. In fact, I saw information on a forum somewhere that instructed you to cut off the upper tube for clearance (related to MGB, I think, but same idea). Sorry for the long post, but one more tidbit- since we are putting non-standard shocks on the car, it's a challenge to find one that fits. Most of the time when shopping, you are asked for the make, model, year of vehicle but that won't work for us. Monroe has a nice informational sheet that has the specs for hundreds of shocks. Unfortunately, its organized by model, but we don't know the model, so you'll have to search through the paper to find a shock with the specs you want. Its here: http://www.monroe.com/catalog/documents/08_MountingLengthSheet.pdf

OK, enough for now.

Jack
Jack Orkin

Jack,
I have mini front shocks (Monroes) on the rear of my car. You may find that you can get around the problem of them being fully extended at rest by inverting the spring plates - you will need to swap them over from side to side to achieve this. The shocks need to operate on both compression and extension without "bottoming out" or you will get horrible bangs and clonks from the back suspension. Takes a bit of setting up but it is a cheap conversion and works well once you get it right.

Guy
Guy Weller

Thanks, Guy. I suppose you are talking "old" mini, right? Do you happen to know the model of the shock? Monroe only lists the "new" Mini in their online catalog, and those are struts. I got my shocks from Mini Mania (US) but don't think they were Monroes. Actually, I think they were a European brand. Just wonder if our shocks are the same. And, yes, it might just be easier to flip the spring plates so maybe this weekend...

Jack
Jack Orkin

Yes, proper mini shocks - not the BMW! I have no idea of the Monroe part number, they were a NOS item from e-bay. But I presume that any sold for that purpose would be to the same dimensional specifications. i.e the same compressed and extended dimensions. The quality of the seals and oil may differ.

When I first fitted them I didn't invert the spring plates and they kept bottoming out in compression. Inverting the plates cured that although they occasionally clonk on full extension if I go too fast and actually get airborne. But the forces on the shock are far less than when bottoming out and it doesn't seem to have done any harm. They have been on there for many thousands of miles, much iof it on quite uneven minor roads.
Guy Weller

Out of curiosity, what is the travel of the mini front damper?. It's mounted a bit inboard of the hub, on the upper link, and I might have though a longer travel damper would be better. I used Vauxhall Chevette front dampers on the back of my frogeye, and took the opportunity to increase the suspension travel, they're pin mounts at the top so not as easy to mount though.

IIRC the mini front suspension has no check strap, that function being performed by the damper as is often the case.

BTW I often wonder why some BMC cars used telescopics on the back and others lever arm dampers. My old A40 Farina had telescopics on the back as standard. The Morris Minor had levers on the standard cars but telescopics on the van and pick-up IIRC. Maybe a case of load capacity?.
David Billington

David - re damper travel. If you really need to know I can measure mine, but it involves at least releasing one end and at the moment its thunder and lightening outside so I'm not doing it! Well not today anyway.

I have just been trawling through old e-mails as, about this time last year Nick Veuger and I exchanged e-mails on just this topic. He was installing mini shocks and was having trouble with them bottoming out. I know I measured mine at the time but just cannot now find the relevant e-mail!

Guy
Guy Weller

On my garage wall I have written 2 numbers in paint. They have been there since 1985, a long time ago.

I wrote them there when I was measuring up to do exactly the same conversion all those years ago.

The 2 figures are 13 inches and 5.5 inches.

I think this is 13 for full droop (onto the checkstrap) and 5.5 up onto the bumpstop. What I can not remember is if that was with the bottom bracket reversed or not. I am 90% certain it was with the bracket in the normal place.

Now I have modified my car to rear disks I can not use the shockers in that manner and have fitted them as designed by other companies at 45 degrees, At the moment I am less than impressed. :-(
Robert (Bob) Midget Turbo

Bob,
Those sound about right, and the difference in that case of 7.5" would give the required overall travel of the telescopic damper. The 5.5 to the bump stop will vary from car to car depending on model and even more so on how tired your springs are.

I think that I found that the damper needs to be pretty well at the mid-point of its stroke, or slightly extended by about 1" from this, with the car at rest and driver seated. The main thing seems to be to make sure that there is slightly more compression still available in the unit from this start position than the air space before the rubber bump stop hits the bump pad. Bottoming out on the damper instead of the bump stop is fierce and not to be recommended!

I think the main difficulty is finding a unit that is short enough when fully compressed. The mini ones do work but reversing the bottom plate to lower the eye point does help, especially if your springs are a bit tired.
Guy Weller

M Crossley,

Today I've visited this site for the first time in a year, with the sole intention of witnessing the benefits of a Panhard Rod I installed several months ago. I think almost all your trouble described is from sideways movement of your axle - just what a Panhard Rod eliminates. I thought a little jiggly wiggly sensation that drove me crazy was the old stock rear dampers, but as I had a PR lying around, I put this on. ... a wonderful difference... the annoying little movement gone, oversteer reduced, and generally the car felt safer and more modern. Excellent money spent.
Steve (Georgia)

Well, if anyone is still interested, I just finished remounting my shocks so they would be closer to midpoint of travel with the car sitting normally.
The Mini shocks I got from Mini Mania are Boge units, model 27-030-9. They were about $37 USD each. Their size is approximately 8.5" compressed and 13" extended. You can see from the before and after picture that I had them mounted on an aftermarket bracket and in top hole they were almost extended. I could have swapped and flipped those, but I would have to use the top hole to keep the shock tube from hitting the bracket, or use a spacer, or cut the bracket, which I didn't want to do. But, I decided just to go back to the original bracket which I estimate raised the shock up about 1.5". I'll give this a try and see how things work and hopefully I won't hear any "bangs or clonks"! Thanks!

Jack


Jack Orkin

Nice Jack, Vary nice....What did you ever do with your engine?

Prop
Props Black Hole

Jack,
Apart from the Drive-it test the thing to do is measure the height between the top of the bump-stop rubber and the tower that it meets with on full suspension compression. And compare that with the available travel on the damper by removing the bottom damper bolt and compressing it upwards. It needs to have slightly more travel available that the measured distance for the bump-stop.
Alternatively just drive it and see if it clonks - you will soon know!

Guy
Guy Weller

the front shock from a Mini is quite short...in fact possibly the shortest tube shock aviliable and has ring mounts top and bottom. The only other shock that might be considered is from a Chrysler small car circa 1971 or so.

the travel on this piece is only about 3 ".

There is not much room for packaging in the rear of a Spridget. Thus the short shock.

BUtttt....using that shock which was designed for the front of a car and putting it on the back might be a problem and has to be oriented in angularity especially if it is NON adjstable in bump or droop. Top mounting on the check strap brackets are not my idea of good bracketry.

I noticed one post that "car skittered" in sweeping corners. Either the shockz were down on the bump rubbers, topped out, or was too stiff in rebound.

Short answer?? For a street car and light track use use the lever shocks and use a heavier weight hydraulic oil......30w motorcycle shock oil mebbe and play with the valving on the removable valve.
M. Who

I think for now I'll try the drive it test! I've been under the rear end too much lately, having just redone the spring bushings and fooling with the shocks and my neck is sore! As far as suspension measurements, would it matter if the measurement is taken with the car on the ground or with a jack under the diff? It seems like it would be about the same, but I may not be thinking clearly.

Prop, as far as the engine, I talked to the guy that built it and he said that as long as its running OK, enjoy the weather and pull it this winter. So, that's the plan. Then, I'll let you know how much trouble it is to pull the engine itself without the Datsun transmission!

Jack
Jack Orkin

This thread was discussed between 20/08/2009 and 25/08/2009

MG Midget and Sprite Technical index

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