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MG Midget and Sprite Technical - Frontline RTL problems - Advice needed.

Hi Guy's

I bought stinker (it has a name), a new front and rear suspension, frontline polybushes throughout, stiffer sway bar, tube shock conversion front (already came with a spax rear), 2" lower front springs, 1.5" lower rears and an RTL from Frontline.

Now the fitting was simple for all parts of the kit if time consuming and the front end is just fantastic. Turns in beautifully, sits flat and grips hard. The rear....... I dont seem to have any rear suspension movement other that in the tyre sidewalls. Needless to say this is not to plan. The car rides like a goat cart at the back (when I can persuade it out of the drive but thats another story) and It seems that my RTL is locked solid?

Now when I installed this thing I followed the instructions very carefully. But when it came to the phrase "NOTE: When adjusting the tie bars it is very important not to pre load the RTL" and then "Each rod end should have a minimum of 6 full threads in the rod end." Hmmm....

So I dont see how other than ensuring that there are "a minimum of 6 full threads..." I can be sure I have not pre-loaded my RTL. Anyhow realising this I settled on compliance and making sure the connecting rods were able to rotate freely before I tightened the locking nuts. My reasoning being that if they could rotate freely they couldnt be too pre-loaded.

So the question is......... can anyone here see the mistake I may have made? Has anyone here experienced the same problems with an RTL? Has anyone here ever had any experience with an RTL?

Cheers, Jeff.

Picture is Stinker returning from a recent jolly.


J M Mitting

My understanding is the rear does best with the lever shocks, the tubes take some setting up and isnt very noticable improvment ....ive seen otheres say installing the tubes upside down helps a lot

Good luck

Prop
and and the Blackhole Midget

Jeff

As per the instructions, have you checked that the central pivot point does not lock up against the main bracket ?.

Dave
Dave Barrow

Thanks Prop, Dave,

I hadn't heard those thoughts on the performance of the RTL before Prop. However this car has had tubes shocks from long before I bought it and its not going back to levers while I own it so I'll need to find a solution as is. Given the way the poor old thing used to move sideways during hard cornering it cant help but be an improvement in lateral axle location, it just needs to move up and down now.

Dave, yes as per instruction the central pivot point shows no sign of binding or catching on the main bracket, dammed if I know whats going on. I'll try to get under it again today and see if a light comes on for me.

Thanks for your input guys, anybody else?

J M Mitting

I've had an RTL on my car for many years, and the improvement over a Panhard Rod was noticeable and welcome. I also use FL rear teles.

The RTL should not add to the rear suspension 'stiffness' - if it does, it means it's binding somewhere; for the moment, I'd disconnect it at both ends (tie them up), and adjust rear dampers for minimum resistance, and gradually work up from there. I think my dampers are around 1/3 of clicks up from minimum.

Then you should check the RTL by push/pull on one linkage to see how much resistance to movement there is: should be easily moved by hand. If not, remove it (4 bolts) and place on the bench. Then slacken each pivot bolt in turn and check rods for easy movement. This will identify the bind and you can easly fix. (Watch out for trapped boots, too.)

BTW - the 2 main pivots (for the rockers) should have spacing washers each side of the spherical bearing - without this, they will certainly bind.

I recently re-furbed my RTL, replacing one spherical bearing and 3 boots - I was going to post a pic, but it's on one of my other machines... (trying Ununtu on this one...)

A
Anthony Cutler

Thanks Anthony, that sounds like the plan. I'll let you know how it turns out.


Cheers
J M Mitting

I am curious not having heard of the RTL previously. I am familiar with panhard rod and also Watts linkage..

Its not obvious from the frontline site how this functions exactly - and consequently why its better than a watts or panhard rod..

- from what I gather the RTL connects to the Axle at either side and then to some sort of pivot arrangement in the middle of the vehicle on a bracket. Can anyone explain
John Barber

Mumford link (aka RTL) originally developed by M for Malloc sports-racer with solid axle at time when the competition was using independent rear.

It improved on the Watt link by having an adjustable roll-centre height that could be lower than the Watt's (normally axle cntre-line) whilst not reducing ground clearance and impinge into air-stream; also roll-centre rises/falls with the body.

Watt link is an improvement on the Panhard rod, which has 2 asymmetric pivot points (one attached to the body, one to axle) such that the roll centre is variable (height and side-side) depending on suspension height and load/roll.

Panhard fine on racers with limited suspension movement, but a compromise for road cars.

The RTL geometry has consistent roll-centre and allows some sideways movement but always in conjunction with controlled roll - feels very natural and stable. Have a play with the FL demonstrator - they often take an RTL hooked up to an axle such that you can investigate the body movement by moving the plate that would normally be attached to the body.

On one of my other machines I have a short article that I can post, if you'd like.

A
Anthony Cutler

Im sorry.... I mis understood the term RTL, so my comment was out of place....personally i have a panhard rod and love it

Prop
Prop and the Blackhole Midget

Hi i went from panhard to rlt and the difference was very noticeble the rear was a lot more err ?? supple but the side ways axle to body location is still evident .
Darren 2litre frogeye

I installed an RTL to my Sprite IV as the last suspension upgrade step, after already fitting Frontline front arms and dampers lower front springs and A/R bar.

I followed the instructions closely. I took the car out and the rear was almost solid. It would oversteer at the drop of a hat even with the dampers wound right off. I persevered with fiddling for a while to no avail. I nearly took it off and chucked it in the bin. In the end I drove down to the Frontline workshop. They put it up on a ramp, checked my work and tweaked the short central link (the one they suggest you don't play with) and extended the long links, whilst the car was on its wheels. Then we went for a road test. Ed adjusted the dampers to his satisfaction then I had a go. Excellent. I appreciate you couldn't just pop over to the shop, but a phone or email might be useful. The chaps there are very helpful.

The end result is very good. Its supple but well controlled. It will hang the tail out round (and round and round)roundabouts, but only if you want and its very user-friendly. Its expensive, but thats another issue altogether.

Mark
M Crossley

Thanks Mark,

Thats excelent advice. It probably should have been my first step but I had never heard of anyone else having this problem and so doubted my own work. Given this I will get on to the frontline guys ASAP.

Cheers, Jeff.
J M Mitting

The design isn't so complicated... I installed mine after re-furb, checking it had free movement before fitting to the car; and that the short central link had plently of free movement before it could clash with the frame (when rear is loaded both sides). Best done with the rear wheels up on large blocks. The long rods should be unloaded with car in 'rest' position, and have equal number of threads engaged on each side.

The short central link should be about as short as you can make it.

Pic of mine during re-furb.

You can see the spacers middle-right, next to bolts; spherical (swivel) joint above-right.

A


Anthony Cutler

Thoughts in this discussion seem to be focused on the RTL binding to produce the excessive rear stiffness but that is not necessarily the case. The RTL may be free to move but if it is set-up so that it gives a roll centre significantly away from that dictated by the cart springs then the result is to effectively lock the suspension movement. I'd have to look up the Mumford geometry details and look at the installation to figure out adjustments or comment further.
David Billington

Anthony,

Your photo shows 3 holes on each side of the RTL body plate in a vertical alignment, are these intended as alternate pivot centres for the rocker links, so allowing for some alteration of the RC.

Jeff,

Has your car been fitted with stiffer spring bushes and axle plates in the past as if so these may be causing an issue. As FL claim the RC is lowered with the RTL then stiffer spring mounts could work against the RTL and prevent it from working as intended. I had a little search and found the RTL installation instructions at Moss http://www.moss-europe.co.uk/graphics/uk/instructions/FLD30931_SEMI_Inst.pdf and felt some of the info a bit dubious, I especially found the comment about the extra stiffness of the suspension after fitting being put down to the gaiters on the rod ends laughable.
David Billington

Hi David,

When I rebuilt the rear end I fitted Poly bushes throughout, they should be a little stiffer. The springs themselves I took apart and fitted strips of galvised steel librally coated in moly grease between the leaves before re-assembling them to act as anti-squeak strips then fitted new bands around the springs. The springs themselves seem fine if a little soft and once re-assembled they still seem fine. I have some free time this afternoon, I'll go and investigate further.
J M Mitting

Jeff,

After discussing a few points with Anthony regarding the RTL, is the stiffness in roll, 2 wheel bump, or both.
David Billington

Right, got 15 minutes to work on it this afternoon. Disconnected one side of the linkage and gave the body a good shove (I'm quite large, me driving a midget is bit like the school bully picking on first graders) and......... Nothing. Still negligible spring movement, no wheel to body movement, nothing, nil, zip, nada. Sooo the stiffness is somewhere else in the system, I'll disconnect the other side and start with the usual suspects. The tube shocks can be disconnected next just in case, then I'll start playing with the spring hangers and the front plates. After that if a solution has not presented itself I may shoot it and put it out of my misery.

Any other suggestions re: fixing the problem are welcomed.

Thanks for all the input so far.
J M Mitting

Well I disconnected the other side of the RTL and the linkages moved freely without binding. So I disconnected the shockies and sure enough there was movement again. Not full movement but movement anyway. I think having the shocks set to about half their damping strength in combination with the stiffnes of new bushings and rebuilt springs was preventing any movement. So I'll re-install the system with the shocks set to their lowest damping rate and all shall be well.

In short no issue with the RTL, all new suspension bushes and shocks combined with owner/operater issues the culprit. A learning experience, I'm sure there'l be many more.
J M Mitting

for road use I've found the dampers (AVO uprights on mine) need to be around 1, 2 or 3 clicks up from softest setting for best all round compromise real world road driving

of course it all a matter of balance, one component to another and front to rear, you also need to factor in settlement and wear of components so a click either way could be useful sometime (possibly far) in the future and altering tyres pressures to suit, blend in with suspension setting will make a difference as will a change of tyre and or size of tyre - personally, for road use, I don't think much wider or lower ratio of sidewall tyres are usefull on a pretty standard road going Spridget even with the FL kit

as you've found the classics ran a lot softer than modern cars especially modern sports cars and if you try to stiffen them up too much for road use you spoil the the balance of the car

generally the rear rear wants to be softer than the front

the lower and stiffer front springs help with the sharpness of turn in but for me personally on the roads I like to drive they sit the car too low

of course different cars, owners and use will want different settings and others will disagree with some or all of my opinions here but I always remember driving a B that had the overall drive and ride spoilt engine and suspension 'improvements' and 'upgrades' so that taught me to be more cautious and selective about going too far away from original design in a standard car for general road use
Nigel Atkins

This thread was discussed between 05/04/2012 and 22/04/2012

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