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ideas?
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Section : Gearbox
Clutch, gearbox, overdrive, propeller shaft.
Posted By : Colin Lindsay, 10-Apr-2004,
08:36pm
Remember a few years back I banjaxed the engine on my GT6 Mk1 by fitting a new overdrive gearbox? The car has a Mk1 2000 engine block and on converting to
an overdrive gearbox it ran for 30 seconds then seized solid resulting in damage to the thrust washers. I found that the original non-overdrive gearbox
input shaft had been crudely modified as shown in the picture by having about 3/4 inch removed from the tip; once I fitted a proper gearbox with the
unmodified end it pushed the crankshaft forwards and wrecked the thrust washers. I was unable to find out why, the pilot bush etc seemed standard but in
order to get the new box to fit I had to have the new shaft machined to the shorter length. The gearbox has now developed a rattle on idle which I had
assumed was the release bearing until this month's Practical Classics tells another owner it's the first gear rattling when idling and on it's way out...
start the car, no rattle; depress and release the clutch: rattle. It's very loud outside the car and very noticable. I hadn't intended to work on the
mechanics until the bodywork is paid for and the bank balance recovers, so the engine has been largely left alone and I assume at the worst it's a standard
2000 saloon block with the saloon crank, flywheel etc. plus an unleaded GT6 head which I added.
So: a barrage of questions for the gearbox experts among us:
1. Is it the release bearing rattling, or first gear?
2. Why on earth do I need 3/4 inch off the input shaft? Is the crankshaft in the 2000 saloon different from the GT6; similarly, is the input shaft in the
saloon shorter than the GT6?
3. Does the end of the input shaft fit into an aperture on the crank, or just into the pilot bush and no farther?
I'm trying to weigh up my options here - new gearbox, new bearing, modify the new shaft, drill a hole in the end of the crank, buy a new crank etc. etc.
Your opinions and advice would be appreciated!!
Colin
Gearbox rattling - any ideas?
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Posted By : Michael Rantell, 12-Apr-2004,
10:59am
Colin,
If you remember I e-mailed you directly regarding my release bearing rattle. Mine is definitely release bearing and here's why :
It rattles (not grumbles which would be gearbox bearing as mentioned in practical classics).
It rattles when the clutch peddle is fully released and goes quiet on the slightest peddle pressure. i.e. not enough pressure to actually operate the
clutch but enough to move the bearing against the fingers of the clutch.
It also occurs in any gear or neutral.
If yours is the same symptoms then I guess you have the same as me.
For information my rattle sounds similar to engine pinking - more of a tinckling than a rattle (if there's such a word).
The need for a shorter input shaft is a strange one, but I do remember reading somewhere that there is something different about the 2000 gearbox but I
can't remember any specifics, sorry.
good luck.
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Posted By : Colin Lindsay,
13-Apr-2004, 08:31pm
thanks Mike - yes I remember your e-mail and decided at the time that it was the release bearing on both our cars, however PC have sowed the seed
of doubt with regards to mine... start the engine, no rattle - depress and release the clutch, horrendous rattling!! People outside the car turn
round to see what it is!! I don't know if it's the same in gear, I usually can't hear it over the engine (!)
In any case the engine and box will have to come out later this year, new paintjob or not, to sort out the input shaft once and for all...
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Posted By : Rick Fairhurst,
14-Apr-2004, 12:00pm
I had a similar thing, although when you started the car the rattling started and when the clutch was depressed it stopped although sometimes
you couldn't change gear.
It turned out to be the springs on the clutch plate, all of which were broken. The reason I couldn't change gear is that one had dropped out
and was jamming the clutch. Soon got the hang of driving without using the clutch!
It also turned out that the wrong clutch had been fitted in the first place.
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Posted By : Colin Lindsay,
21-Oct-2004, 09:11pm
Have removed engine and gearbox - again - and replaced the release bearing however on inspection I reckon it's the input/main shaft bearing
as the entire thing wiggles around... however - there's some oddities afoot as I've compared the bits with an old MK2 engine I have
recently acquired and firstly the flywheel is HUGE - about an inch thicker than the GT6 one and secondly the rear of the crank protrudes
out of the back plate about an inch further than the GT6 one. This would explain why it keeps eating the tip off the input shafts! I
presume since all gearboxes are outwardly the same (correct me if the 2000 one is different) and assuming the extra thickness of flywheel
makes no difference then the 2000 gearbox must sit about an inch further back from the engine - is the bellhousing diffferent? - or the end
of the crankshaft is able to take more of the tip of the gearbox shaft, so by fitting the GT6 gearbox and bellhousing to the MK1 2000
engine I'm having to remove half an inch from the input shaft to get them to mate. It always was a shortterm solution... new gearbox and
crank here we come!!
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Posted By : Jonathan
Binnington, 21-Oct-2004, 10:32pm
bloody hell Colin, what a set of questions posed, answers hopefully in some kind of logical order.
Big thick flywheels = 2.5 especially saloon about 35lbs
thinner ones = gt6 about 22lbs from memory
crankshafts very early 2.5 litre (tr5) had a long tail crankshaft, mating gearboxes had the tip of the input shaft ending about 1"
inside the plane of the bellhousing front face (rare in my experience)
later 2.5 and all 2 litre engines except the very early gt6 mk1 with the small size ineternal components like tappets (?) have a short
tail
but, the 2.5 engines carry the bronze pilot bushing in the centre of the flywheel. the gearboxes for these engines have the tip of the
gbox input shaft ending at the plane of the front face of the bell housing, ie no input shaft protrusion beyond the bell housing
the GT6 engine takes a gearbox which has a longer input shaft tip, it protrudes by about 1" beyond the front face of the bellhousing.
To accomodate this the pilot bushing is carried in the tail of the crankshaft not in the flywheel, ie about 1" further forward.
In my experience the GT6/vit box isn't up to the job (I have killed about 6 of them) I have a TR6/big saloon box in my car, shorter
input shaft. I built a 2.5 engine with a gt6 flywheel which had been machined to take the TR6 pilot bushing. ie a 2.5 litre GT6 engine.
you will also need to use the engine backplate which goes with the engine as the bell housing bolt holes aren't in the right
places.
hope this is clear
binman
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Posted By : Colin
Lindsay, 24-Oct-2004, 09:39am
Very clear and thanks for the comprehensive reply - I've found out the hard way (2 gearboxes so far) so now I'm going to replace
crank and bearings in the 2000 engine for the GT6 version and refit a recon GT6 box; big expense so bang goes wine women and song
for a while... hopefully the GT6 crank (not the early version) will be a straight fit to the 2000 (MB code) engine?
This would never have come to light if I had not had a second scrap engine for comparison so I'd advise all to buy a second engine
and then keep it for a rainy day..!!
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Posted By : Jonathan
Binnington, 24-Oct-2004, 09:59am
as far as i'm aware the gt6 mk2 engine and the 2000 saloon engine of the mk2 variety (ie the cyl head not having the tubes for
the pushrods and 7/16unf head studs all the same lenght) are basically the same engine with different camshaft profiles
flywheel and front pulley weights and also the 2000 sal engine was mated up to the bigger gearbox and had the pilot bush in the
flywheel instead of the crankshaft.
I would caution against using a vitese box as i've broken so many, the non-o/d saloon box is an easy fit although the propshaft
will need to be shortened, the o/d saloon/tr box isn't much harder to fit if youhave got everything else out already
jonath
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Posted By : William Davies, 26-Oct-2004, 00:20am
Does the saloon box not sit higher in the chassis, putting an angle in the driveline? No personal experience, just what
I've been told from a number of sources. Did you need to modify the chassis in any way to get the back of the box lower, or
is the driveline kink not an issue in fact?
Cheers,
Bill.
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Posted By : Jonathan Binnington, 26-Oct-2004, 08:25am
Does the saloon box not sit higher in the chassis, putting an angle in the driveline? Did you need to modify the
chassis to get the back of the box lower, or is the driveline kink not an issue in fact?
Cheers,
Bill.
yes to all of that!
there are a number of ways of tackling this, the od big box does indeed foul the chassis rails( the non-o/d box
doesn't), some modify the chassis to restore the drive line, I wasn't brave enough to cut the chassis so I made a
bracket to raise the gt6 o/d box rubber mount by the minimum amount required to clear the chassis (sloenoid and speedo
angle drive).
the drive line has a kink in it through the UJ. I was warned that vibrations would result but hasn't proved to be the
case, probably helped by the shorter propshaft.
anyone who is ultra picky (and with deep pockets) could indulge with a CV jointed propshaft.
In the end i think it boils down to development, push a 2.5 engined car hard enough for long enough something will
break, uprate that and then you will discover another weakness somewhere else.
So far i had no ''excess power'' breakages, but with 175 tyres there is only so much extra that can be transmitted.
for worry-monkeys i have also taken a deal of weight out of the car (GRP bonnet and boot, shell doors no screen no
interior no trim) and haven't needed to do anything radical to the brakes other than braided s steel lines, twin
circuit/m cyl/servo with balance bar.
now discovered that the suspension is too soft and need stiffer springs and damper all the way round - ah
development
ought to weigh bridge and rolling road it I suppose!
bin