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Midget and Sprite General
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Thread: Severe judder from rear under 'hard' acceleration.
Posted 19 June 2017 at 14:24:27 UK time
J Gibson, Northumberland, United Kingdom

Hi all - long time since I was in here. Hope all of you are well

My IOW Frogeye was built using a '64 Midget. It has a Ford Type 9 5 speed box. Under hard (hey it's all relative yeah?) acceleration in 1st gear (which is too low a ratio for the car really), and sometimes in 2nd, I get an alarming severe vibration or juddering from the back axle area. This has gradually got worse. At first when it wasn't as bad I thought it might be a bit of clutch slip, and I suppose it still might be even though the clutch (a Peter May item) hasn't that many miles on it, but as it has got worse it definitely seems to be from the rear. Under gentle acceleration and in higher gears there's no problem.

Anybody had anything like this before, and what was the problem? It'll be in for MOT soon so I'll have it looked at then, but just angling for any pointers in the meantime. Cheers, Jordan.

Posted 19 June 2017 at 14:52:01 UK time
Nigel Atkins, Northampton, UK

Hi Jordon,
as is well known I'm not mechanical or technical so these are just my first thoughts as such a person -

rear spring/axle locators - U bolts, suspension pads - you'd also notice the effect of these on handling/holding during spirited driving - might just be a spanner up job perhaps, maybe, possibly

u-joint(s), prop - going or loose - again you'd probably notice something whilst driving though

axle, diff, halfshafts - worth checking oil level or leaks and damage/wear

I'm not sure about this one but brake(s) catching/holding - one side perhaps

clutch - fluid change, air, slave/master, clutch itself - you could perhaps try a load test up a steep hill - again I'd have thought you'd noticed at other times too such as trouble getting into first/reverse/second

That's me out of ideas and a very wide range too so not much help. Perhaps more info and checks after better advice than mine would pin the problem down.

cheers, Nigel

ETA: something with wheels/tyres perhaps(?)

Posted 19 June 2017 at 14:58:26 UK time
Nigel Atkins, Northampton, UK

ETA: clutch release arm bent, joints ovaled

release bearing problem

When my clutch fell apart I'd had both clutch slipping and not releasing at the same time.

Posted 19 June 2017 at 15:17:47 UK time
Malcolm Le Chevalier, Pershore, Worcs, UK

Simple things first, make sure the axle U bolts are cranked up good and tight. It is maybe that the axle is poorly held and moving about under high torque.

Ten minute job with a ratchet and deep socket (1/2" or 9/16")

Posted 19 June 2017 at 15:37:40 UK time
Nigel Atkins, Northampton, UK

9/16"

It breaks my general rule of what don't need a 7/16" spanner/socket usually needs a 1/2" - of course other sizes are often need so keep the tool boxes nearby.

Posted 19 June 2017 at 15:46:54 UK time
AdrianR, Bucks, UK

Alternative theory, check your exhaust is well secured and not rattling against anything. The torque of the engine twists it under load which acts along the pipe and onto the silencers.

Posted 19 June 2017 at 15:51:11 UK time
Nigel Atkins, Northampton, UK

This raises a good point point, is the judder vibration something you hear or something you feel (and perhaps hear)?

Posted 19 June 2017 at 16:36:36 UK time
MG Moneypit, Cheshire, United Kingdom

Is the gearbox rubber mounting up to the job? I have often thought that the simple single mounting we all use must be only marginal when controlling the torque from a tuned engine. The standard A series gearbox is very well controlled but when we convert to type 9 we throw away all that and substitute a sierra rear gearbox rubber mount which to me doesn't seem adequate.

IIRC, the Sierra uses a split propshaft with the front part supported thus adding to the rigidity of gearbox support.

Just a thought.

Rob

Posted 19 June 2017 at 16:39:15 UK time
J Gibson, Northumberland, United Kingdom

Thanks folks. It's definitely felt rather than just heard. It's most unpleasant.

Being an IOW it doesn't have conventional rear suspension so there are no u-bolts or springs - it's Flexiride suspension, trailer-style. Not sure I've knowingly experienced axle tramp, but it puts me in mind of what I expect that to be like. Shall ask the garage to check it over.

Prop/UJ might be a good call also.

Cheers.

Posted 19 June 2017 at 19:01:48 UK time
GuyW, UK

Hi Jordan. It's good to hear from you again!
If your 'flexiride' units are the same as the original 'Indespension' trailer type ones, then l wonder if it is the rubber inserts that are breaking up. When Indespension were first available you could buy the rubber inserts for refurbishing tired units. I don't know if that is still the case. They were supposed to provide suspension and self-damping on a trailer which then didn't need shock absorbers. lf the rubber inserts are tired then l suspect that could axle tramp.

Posted 19 June 2017 at 21:32:40 UK time
Nigel Atkins, Northampton, UK

Good call Guy, I'd put a small bet on that too.

Sorry I'd totally forgot the IOW Frogeyes have different suspension and ruled the (standard Spridget) suspension being a possibility as you'd soon notice and be able to test it if it was that bad.

A member of our club had a IOW Frogeye but I only saw on it the road or parked up.

Let us know how you get on.

Posted 19 June 2017 at 21:42:25 UK time
David Billington, Wiltshire, United Kingdom

Guy,

How were you supposed to install the new rubber inserts as my understanding was they were cooled in liquid nitrogen to shrink them then inserted into the fixed chassis part prior to inserting the shaft connected to the suspension arm and then allowing everything to normalise for use.

Posted 19 June 2017 at 22:00:30 UK time
Nigel Atkins, Northampton, UK

Like ARB drop links I think you have to buy the whole units rather than just the rubber bits.

And if the new units are anything like new ARB drop links the rubber bits will be crap and fail in a few years rather than decades.

Posted 19 June 2017 at 22:41:07 UK time
GuyW, UK

I doubt that nowadays one could get the rubber inserts anyway. But David I do know that they were available in the earliest versions of the Indespension units. They were oval in section and were inserted into the corners between the inner and an outer square section tubes which were assembled at 45 degs relative to each other.

Possibly the method only worked on the shorter, light duty units and that the larger ones needed to be cooled as you say. I really don't know. I built a number of small trailers in the late '60s using those units. I do know that if you overloaded them the inner section of the suspension unit could be forced round past the rubbers and rest in the next corner with drastically lowered suspension. They could be corrected with use of a long scaffold pole as a lever but once it had happened, it was prone to repeat performances.

Posted 20 June 2017 at 06:08:09 UK time
J Gibson, Northumberland, United Kingdom

I've been trying not to consider duff flexiride units as a possibility, even though the suspicion has been nagging away in the background. I noticed tonight there's a bit of a rubbery squeak too from the back when pulling away gently, which makes the nagging more insistent...

Having spent a goodly chunk of cash on getting the whole rear end rebuilt not so very many miles ago the thought of having to do much of that again so soon fair makes the blood run cold.

Posted 20 June 2017 at 17:26:27 UK time
Rob Armstrong, North Yorkshire, United Kingdom

Sounds very much like tramp to me. Mine did it a lot till I fitted an anti tramp bar.

Posted 21 June 2017 at 01:25:52 UK time
William Revit, Tasmania

Sounds a bit like gearbox mounting to me or the exhaust(or tailshaft) hitting the floor under load
The torque is multiplied in lower gears giving more load on things like mountings etc
It won't be the clutch as that is more likely to play up in the higher gears
willy

Posted 21 June 2017 at 09:16:41 UK time
J.N. Williams, Surrey, United Kingdom

Hi Jordan,

Sorry to hear about your problem. I've got a similar IOW Frogeye (no 143, so quite early) with type 9 gearbox and Flexirides, and had problems with the rear suspension: the Flexirides seemed OK.

I had the rear suspension bushes replaced (some were quite knackered - 6 per car from Ford Cortina Mk3 (1970-76) rear suspension bush, upper arm front, part ref no. 1481424, available from South Wales Props (www.southwalesprops.co.uk) under EM1492 (can be pressed in with vice and socket). I also replaced the rear shockers with Spax adjustable shock absorbers Mini, rear, standard size on mine (top fitting is a spike and nut). I know that these changed on Frogeyes over time. This sorted it out, but I now have a bit of a squeak from the rear - Flexirides?

To find all this, I e-mailed Keith Brading who has files on all his IOW Frogs, and he was very helpful in sending me the original spec. If you do find out any availability on Flexirides, please let me know.

Good luck
Nick Williams

Posted 23 June 2017 at 06:50:09 UK time
A de Best, Holland

Hi Jordan, good to hear your still enjoying your Frog!

Posted 23 June 2017 at 13:35:50 UK time
J Gibson, Northumberland, United Kingdom

Arie, my man! :high-five: Hope you're well mate :)

Nick thanks for all that. I've been down all those roads, new bushes and shocks etc.

The Flexiride units are still available I think, from Peak Dynamics (was Peak Trailers). They still offer the same kind of unit so once I get the measurements I'll enquire if they still carry them. Hopefully the splined shaft is the same as it used to be, else new suspension arms will need fabricating too. Yikes.

Guy you are right they do a light duty flexiride unit that you can swap the rubbers out of, but the heavier duty units are permanently bonded - http://tinyurl.com/y8tkvx25


I haven't had chance to get under it yet for a poke around, so it might be something less daunting than feared...

Posted 23 June 2017 at 19:12:35 UK time
GuyW, UK

The R-flex Insert range are pretty well identical to the Indespension Units I used half a century ago! And it looks like they have considerably developed the technology with the fully bonded versions. The early versions claimed to be self damping so no shock absorbers were needed, and I see that the damping characteristic is referred to for the later versions too. So Jordan, does your car have normal shock absorbers fitted? I suspect that the damping from the Flexiride units isn't up to decent road performance on a car so it will have both. If so what state are your shock absorbers in? If there is any slack in their operation, or an initial easy or soft movement then that could certainly cause axle tramp.

Guy
Still at Riding Mill?

Posted 24 June 2017 at 19:24:36 UK time
J Gibson, Northumberland, United Kingdom

Guy it has a reasonably fresh pair of KYB Mini dampers fitted. Think of the indepension unit as equivalent to a quarter-elliptic leaf spring. The trailing arm is more rigid than a spring though so you don't need a top link to keep it all located, you can just hang the axle off the two arms. It still needs to be damped though just like a conventional spring. Attached is a fairly terrible sketch I made years ago apropos the mounting of the dampers on mine and another (modified) car. I've omitted the axle which hangs on brackets under the lower damper bracket. The two upper tubes to the top of the damper are fixed and part of the spaceframe chassis. The indepension unit is bolted to the bulkhead behind the seats.

Image

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