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2nd Grinding


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Hi all/fountain of knowledge

I've come to the well one more time ;)

 

I recently (April-ish) had my Gearbox and overdrive out and work done on same. The overdrive was done and I took the opportunity to check the gearbox, and replace the old Transit clutch with a good B&B one. Once all back together, she worked and drove like a dream. However, see has now started to develop a problem. The gear change has been fine, great even. Now though it has developed a slight "grind", but only when dropping from 3rd into 2nd. In other words, there are no problems moving through the gears bar 2nd, and only when dropping from 3rd :unsure: I thought at first I was just shifting too fast (to match the way I like to drive her ;) ) but it does this 7 out of ten times no matter how fast, slow or deliberate the change is.

 

Anyone here had a similar problem before ? Or have any thoughts on same ??

It's strange as the whole lot has only just been done.

 

As always, many thanks in advance

 

Kevin

 

P.S.

Here she is below with her new "winter" hard top on, Which I picked up when over at Stafford and the IWE

 

 

IMG_0968_zps7eb7be6b.jpg

Edited by keving
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Exactly how much work did you do on the gbox?

 

Its awfully hard to replace everything thats likely to be worn. Its easy to replace a few major items like the big bearings on the input and output shafts and syncro cones.

 

Anything to do with layshaft bearings is hard. There is fiddly stuff with end-float that will mess up the syncro-mesh.

 

Al.

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May seem a stupid question, and believe me, I ask my fair share ;)

But why only grind from 3rd-2nd and not 1st to 2nd ??

Guess it'll be box out again this winter. Don't mind the thoughts of it, to be honest, seeing as I'm experienced and all ;)

 

Kevin

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OK you asked for it. Here it comes. Hope you follow OK.

 

First the basics. The engine drives the layshaft via a gear on the input shaft. The "gears" that set the ratio are always engaged with the layshaft. When you change, the new selected gear is locked to the output shaft by a sliding part.

 

The sliding part has to go into a new gear that wont be going at the same speed. This is what causes the grinding.

 

To stop the grinding a brass-ring, the syncro-cone, is placed between the new gear and the sliding part. This only makes friction contact with the new gear.

 

It relies on this friction-contact to bring the whole of the layshaft, input shaft and clutch driven plate to rotate at the correct speed. This is a big ask.

 

When you change from 1 to 2 the friction only has slow this lot down. They are slowing already because of oil-drag. You have de-clutched so they are getting no drive. This isn't such a big ask.

 

When you change from 3 to 2 the friction has to speed everything up. Now the syncro has a big job on.

 

Before we had syncromesh boxes you would go into neutral, engage the clutch, blip the throttle and de-clutch again. This was called double de-clutching and my Dad taught me in 1965, it being standard practice at the time.

 

Double-declutch has the effect that the syncro has a much easy job matching the speed of the layshaft because you have accelerated it beyond the speed required and the syncro only has to slow it, as when changing up.

 

You can now see why I asked how much work you had done on you box. If you fitted new cones they will have worked OK for a while, But once they bedded in you lost some friction and the grinding started.

 

These boxes have really heavy parts. They were designed right in the early days of syncromesh. There is a biggish ratio gap between 3 and 2.

 

If you have an OD you may be using quite thick oil. On my test-rig, which you can just see in the thumbnail, a 300W electric motor struggles to spin the gear-box up when the oil is cold. So there is a lot of drag in these boxes. And you are expecting friction between well oiled brass and steel to drive it.

 

If you strip this all down again I dont think you will find much thats obviously wrong, as in broken. Just lots of little tolerances that mean you are short of the required friction.

 

To do it properly means new layshaft bearings, new cones, new "exactly sized" thrust washers, new centre-bearing. Even then you didnt take out wear on the spigot. Even then you will probably always be short of syncro-power. The cones are all the same.The 2nd gear synchro has much more to do.

 

Learn to double-declutch when changing down.

 

See http://www.vtr.org/maintain-index.shtml for pictures of all this.

 

Al.

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Yes I agree, double declutching ( and heel and toeing ) will ensure the synchromesh is never a problem. And the clutch plate lasts forever too since there is little speed differential for it to accommodate. I learned the year after Al - no syncro on first in Morris Minor 'box.

 

IIRC there are posts commenting that repro synchro cones are rubbish.

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I got new syncro cones from Moss about 4 years back.

 

They looked identical to the old ones apart from the wear points. I almost put the old ones back. But this is an area where a few thou matters.

 

At last I have posted something on here and somebody has agreed with me! Mainly they argue.

 

Al.

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I learnt on a Ford 100E, only 3 gears on these. Mine had no syncro left on second. There never was any on first. So every downchange needed double-declutch.

 

I always wondered why its called heel and toe. As you can see from the film he uses the left and right side of the ball of his foot. You only need to do this if braking and downchanging at the same time of course.

 

The young girl at the insurance company asked me "have you got 4 years or 6 years no-claims bonus". Oh no, I said " thats 46 years". She did not know what to say next!!

 

Al.

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I learnt on a Ford 100E, only 3 gears on these. Mine had no syncro left on second. There never was any on first. So every downchange needed double-declutch.

 

I always wondered why its called heel and toe. As you can see from the film he uses the left and right side of the ball of his foot. You only need to do this if braking and downchanging at the same time of course.

 

The young girl at the insurance company asked me "have you got 4 years or 6 years no-claims bonus". Oh no, I said " thats 46 years". She did not know what to say next!!

 

Al.

 

Al

Yes, no idea why its misnamed - its 'ball of foot and side of foot'. Gives a very satisfying rhythm approaching say roundabout going down through the gears braking hard and using engine braking. And the clutch plate never wears - no friction involved in speeding up engine to match faster box input speed in the lower gear.

Peter

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Heel and toe has nothing to do with the clutch. It allows the engine to stay on cam, the clutch is then slipped to keep the revs up

 

Neil, The clutch does not slip - thats the whole point of it. The clutch is very briefly disengaged while the throttle is blipped and the lower gear engaged. Done correctly the faster engine rpm from the blip then matches the faster rpm of the gearbox input shaft when the clutch is re-enaged. The speeds match and there is no possibility of clutch slip. As for keeping on the cam??? - heel and toe is a braking manouvre, the engine is strangled....

cheers

Peter

Edited by Peter Cobbold
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If you do get the box to bits again check the state of the 2nd gear top hat bush.

Rock on the shaft, rock in the gear. These all add to poor synchronising as well as worn synchro cone/rings.

 

A good solution is the 2 piece steel 2nd. speed bush and washer from the early Stag, instead of the brass thing fitted as standard. Usually sold as an uprated item.

 

Cheers

Peter W

Edited by BlueTR3A-5EKT
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Now thats a really great tip. The only way you can get that kind of info is somewhere like this.

 

I very carefully ground all the end-float shim washers down from a bigger size to get the fit I wanted. This is the kind of thing you cannot get done if a professional does your rebuild. They have to make a living.

 

Al.

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Great thread...loved that Senna clip!

 

I too come from the mid 1960's having learned to drive in a Van with a crash gearbox, double de-clutch was essential as it was with the other van in my dads business that was Diesel which in those days had huge throttle lag, if you just changed down without double declutching or if you just did too quickly without a long slow rev it would just lock it's rear wheels! :wacko:

 

Part of the buzz I 'still get' from driving my old TR is the sound of the beast when doubledeclutching and (okay... 'Ball & sideoffooting') :ph34r:

 

P.S: They only gearbox issue I've experience in my 40 years of ownership was noisey layshaft/bearings. I was told the original shafts wern't hardened enough?

Edited by Denis
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The layshaft runs in tiny little needle-rollers. There are a few variants I think. The rollers aren't captive. You have to push the layshaft right through the box with the gear-cluster in place so its v.heavy and enter it into the rollers without dislodging any. You cant see a thing while doing this.

 

To get this right first time I made up some special sliding taper plugs from nylon. These guided the layshaft in while lining up the rollers in front of it.

 

Al.

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  • 2 weeks later...

Sorry for the late reply all, and many thanks for your thoughts on the above.

 

I will do a bit of rooting around during the winter and see what comes up.

 

In the mean time I'll "Learn to double-declutch when changing down" :P

 

Have a great weekend

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Hi all/fountain of knowledge

I've come to the well one more time ;)

 

I recently (April-ish) had my Gearbox and overdrive out and work done on same. The overdrive was done and I took the opportunity to check the gearbox, and replace the old Transit clutch with a good B&B one. Once all back together, she worked and drove like a dream. However, see has now started to develop a problem. The gear change has been fine, great even. Now though it has developed a slight "grind", but only when dropping from 3rd into 2nd. In other words, there are no problems moving through the gears bar 2nd, and only when dropping from 3rd :unsure: I thought at first I was just shifting too fast (to match the way I like to drive her ;) ) but it does this 7 out of ten times no matter how fast, slow or deliberate the change is.

 

Anyone here had a similar problem before ? Or have any thoughts on same ??

It's strange as the whole lot has only just been done.

 

As always, many thanks in advance

 

Kevin

 

P.S.

Here she is below with her new "winter" hard top on, Which I picked up when over at Stafford and the IWE

 

 

IMG_0968_zps7eb7be6b.jpg

 

could be brass 3 rd gear top hat has cracked as already mentioned.but if it was ok before gearbox out and presume new oil change, i doubt it.

is it worse when cold.if so.

try some modern thinner 75/90 semi or fully synthethic gearbox oil in it.

richard

Edited by rpurchon
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Are these thinner oils OK with OD?

Because if they are this is a great idea.

 

There is a lot of oil drag in these boxes with the "recommended" oil because everything is so big.

 

Al.

 

ive used it for 6+ years no problem ,A type.

 

richard

richard

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