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SP 250 clutch judder when reversing.

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timmartin
Posts: 65
Joined: Wed Feb 17, 2016 1:37 pm
Location: Berkshire

SP 250 clutch judder when reversing.

Post by timmartin »

When I bought my SP 13 years ago clutch judder used to make smooth starts difficult unless pulling off on tickover.
Some years and more than 10k miles ago I had a Healey BJ8 diafragm clutch fitted. It was made by AP and described by the Healey specialist as “heavy duty”.
The flywheel was lightly skimmed and redowelled to suit.
Judder gone and nice to use - but a new problem has developed.
Starting off forwards is still fine (possibly not perfect) but any sort of clutch slipping in reverse (eg parking or very slow manoeuvring) is really horrible. Very dificult to avoid judders.
I don’t understand how the clutch mechanism could be doing this.
Could the cause be somewhere in the transmission or suspension?
I have a J type OD, new rear springs and telescopic rear shock absorbers.
About 4k miles per year use and a nice dry garage.
I would be grateful for ideas.
Tim
Blue 1964 SP250 in Berkshire

Vortex O'Plinth
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Joined: Fri Feb 12, 2016 8:15 pm
Location: Gloucestershire

Re: SP 250 clutch judder when reversing.

Post by Vortex O'Plinth »

Hello Tim. As you surmise, since the clutch elements rotate in the same direction in both forward and reverse, the problem is unlikely to reside there. Possible things to check that spring to mind are engine and gearbox mounts, prop shaft bearings and rear spring mounts and bushes.
Nick

"Don't bother with the Air & Space Museum - there's nothing to see.......".

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JohnM
Posts: 206
Joined: Thu Feb 11, 2016 1:31 pm
Location: N W London

Re: SP 250 clutch judder when reversing.

Post by JohnM »

Tim,
is your overdrive working OK?
Clutch slip/judder in reverse can be an indication of a serious problem with the overdrive not disengaging properly. At it's extreme it can shatter the unidirectional clutch in the overdrive unit.
Don't mean to worry you, but it is a possibility.........
Hopefully as Nick says it's a spring bush or something similar.

All the best,
John
John M in Middlesex, NW London
1962 SP250 "B" Spec
DLOC Herts Region Sec

tjt77
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Posts: 525
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Re: SP 250 clutch judder when reversing.

Post by tjt77 »

If the clutch is recent and in good fettle, the most likely cause would be weakness in engine mounts .. Im not fully familiar with the engine and gearbox mount set on the SP250..I believe the front lines are round composite 'sandwich' type.. of so, check for delimitation..
'stay rods':- most cars have a rod with bushings to eliminate backyard/forward movement of engine and gearbox attached between gearbox and mount as part of its mounting assy.... In almost all BMC cars, when the bushings on this 'stay rod' are worn, it will allow the engine and box to move slightly back and forth in the chassis, which will promote clutch judder, most prominent in reverse.. symptoms far more pronounced with a mechanical clutch linkage.. V hydraulic set up.. the Riley pathfinder and early C series cars were very prone to this problem.. clutch centre plate design was changed by adding springs to the central splined part to 'cushion' judder in the early 1950s..but it never fully eliminated the problem.. most simply learn to live with it and adjust driving technique to suit..

Sydsmith
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Location: Aberystwyth Wales

Re: SP 250 clutch judder when reversing.

Post by Sydsmith »

I had that exact problem with my SP prior to it's rebuild.

When I lifted the body off you could see that all the mounts were in a sorry state and gearbox mount parted when we lifted the engine and gearbox out of the car.After the rebuild it was perfect. Syd

Vortex O'Plinth
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Location: Gloucestershire

Re: SP 250 clutch judder when reversing.

Post by Vortex O'Plinth »

Since Tim has a 'J' type overdrive fitted, presumably the original gearbox mountings have been replaced with a Triumph Spitfire overdrive mount....
Capture.JPG
This is less beefy than the original double mounts and, while adequate for the Spitfire engine, may struggle with the SP's torque. Worth checking to see if any breakdown of the rubber/steel bond has taken place.
Nick

"Don't bother with the Air & Space Museum - there's nothing to see.......".

Crossley Stephenson
Posts: 255
Joined: Wed Feb 10, 2016 9:15 pm
Location: Victoria, Australia

Re: SP 250 clutch judder when reversing.

Post by Crossley Stephenson »

I don't have clutch judder but I do have a squeal. Recently had the gearbox rebuilt and fitted new clutch plate, the clutch specialist said the thrust bearing was OK. But....each time I take the car out of the garage, mostly in reverse, I get this horrible squeal when I release the clutch. - only once and it doesn't happen again during a days driving. But next day it happens again. I've been told not to worry about it but it isn't normal so I do🤔

Any ideas or suggestions (other than remove the gearbox again - ugh - but probably inevitable).

Cheers
Michael

martinj
Posts: 10
Joined: Sat Feb 13, 2016 6:15 pm

Re: SP 250 clutch judder when reversing.

Post by martinj »

Just to confirm the terminology - clutch released = pedal pressed to the floor.

Mine started to squeal when the clutch was released for more than a few seconds and after changing a perfectly good release bearing I came to the conclusion that it must have been a dry bush in the end of the crankshaft where the gearbox input shaft spigot locates. Relative rotation only occurs when the clutch is released. A bit of grease and no squeals since. But it is a gearbox out job!

Martin

Crossley Stephenson
Posts: 255
Joined: Wed Feb 10, 2016 9:15 pm
Location: Victoria, Australia

Re: SP 250 clutch judder when reversing.

Post by Crossley Stephenson »

Good point Martin. What I meant by clutch released was - the pedal was down and as I release it (the pedal moving upwards) the squeal occurs, only momentarily - I can't make it repeat during a few stops and starts - only first time each day.

My mechanic friend says it is a lack of grease on the spline but don't worry about it🤔

I have a big trip planned for early next year (Flinders Ranges - 2500km round trip)and really can't summon the energy to again remove the gearbox - yuk job!
😝

I will probably have to bite the bullet eventually and remove the go but I want to avoid if possible.

Cheers
Michael

timmartin
Posts: 65
Joined: Wed Feb 17, 2016 1:37 pm
Location: Berkshire

Re: SP 250 clutch judder when reversing.

Post by timmartin »

Thank you for all for your cogent and encouraging replies and observations.

Encouraging because the engine/clutch/gearbox/overdrive is about to come out for a visit to Russ Carpenter. That will provide excellent opportunity to inspect and renew the engine mountings (which could just be original), Gearbox/OD mountings (newish, but your comments noted, Nick) and transmission shaft universal joint bearings (for good measure, I already have "sufficient" backlash in the diff.).

Fortunately, John, the gearbox and overdrive seem to be working very well indeed (more than 1,000 miles in the past four weeks) so I hope that you will forgive me if I hope that you are wrong in my case...

Tim, the effect is very similar to a broken engine "stay rod" (many years ago I experienced a broken stay rod in a 1964 Mini). I don't think that SP250s were ever fitted with them. If I am wrong, I need to get one.

I have only thought of three reasons why the effect should be so much more pronounced in reverse.
* There might be asymmetry in the degradation of the engine mounts (one side has to fail first)
* When in reverse, the swinging link supporting the tail end of each rear leaf spring will be in compression caused by torque from the axle. Mechanical links in compression are more prone to instability than those in tension.
* Torsional oscillation of the rear axle may be damped by the shock absorbers. The damping of shock absorbers is not the same when pulling as when pushing.

And, of course, it doesn't have to be just one cause.
Tim
Blue 1964 SP250 in Berkshire

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