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4spd manual crunch 1st - 2nd

Started by oscar, 02 October 2008, 04:45 AM

oscar

I've done a bit to POVO with still a few things to be replaced but after getting new transmission bushes and a left upper control arm I was eager to take it for a hard spin.   When I drive it hard I'm getting a gear crunch between 1st and 2nd.  Any thoughts why or what I can do to remedy it?
1973 350SE, my first & fave

13B

Take off in 2nd?

Or double de-clutch between 1st and 2nd...

I.
450SEL 6.9 #5440 = V MB 690 , 450SE # 43094 = 02010 H , 190E/turbo # 31548 = AOH 68K

oscar

Quote from: 13B on 02 October 2008, 05:19 AM
Take off in 2nd?


No way Jose!  That means I got a 3spd manual. :-[  Sedate driving it's fine for 1st - 2nd or a 2nd start but I need 1st for racing.  You'll see when you get a turn at driving it.  I'd go take a vid and show the difference between a 1st gear take off and 2nd except I'm over the limit.  Maybe tomorrow. 

I'll try that double clutch thing too and see if it makes the shift .  My only prob with that I assume will be the time it takes. 
1973 350SE, my first & fave

13B

Its probably worth changing the oil in the trans if you haven't done so already.  You also may want to read up on what additives are around and what may help...

IMHO, if you need 1st gear regularly on a racetrack, somethings wrong.  Speaking for my rotary driving, I only ever use 1st to get the car off the mark, and 2,3,4 are where all the actual work is done, and even 5th gear is used only on the straights and only then if I've had a good chance to wind out 4th.  Even when i was rallying 1st was rarely used.

Whitey and Ol'silver both run the 3 speed auto (obviously) and 1st gear on those is roughly the same as 2nd gear on Povo, meaning that even if you slow down to 40km/h in 2nd you're still likely to waste time (and thus lose time) by dropping into first for a short burst to 50km/hr, then putting it into 2nd etc.

Also remember you'll be running sticky R-spec tyres and have a low centre of gravity so you'll be cornering much faster than a standard height 280S with road radials. 

I would make sure the gear-down from 3rd to 2nd is as crunch-free as possible, as thats a crucial gearchange, it sets you up for entering and accelerating out of corners.

Just my 2c worth.

I.
450SEL 6.9 #5440 = V MB 690 , 450SE # 43094 = 02010 H , 190E/turbo # 31548 = AOH 68K

koan

Is the clutch disengaging completely oscar?

I regularly drive my daughter's Toyota something or other and often crunched 1-2 changes if I was too quick. I put it down to synchro trouble. But after a new clutch I can do the 1-2 change without pause.

koan
Boogity, Boogity, Boogity, Amen!

craigb

I agree with all the other points, but number one I would be changing the oil and maybe the first one you try is not the answer. I went through this in my alfa and can't remember what I used but the advice from the club was 'use this or this but not that' sort of thing. I have seen Ian suggest a brew on here before also. Even straight trans fluid is a possibility.

I haven't looked inside one of these but I am assuming it is a cone type synchro. If you imagine it like a cone clutch, as you push forward (or back) on the lever it is engaging this cone first to spin the gear up to the right speed. If the clutch is worn and slips, it will not spin it up quick enough if you are in high revs. So what you are looking for is a fluid that will give the most grip for that clutch while still giving enough lubrication to your bearings. I would imagine something thinner is better but I am not sure.

I agree with the comment about the clutch and also are you getting right off the gas, ie the slower the engine is revving at the point of engagement, the less that gear needs to be spun up. Throttle springs, timing may affect this also but at the time of changing you get right off the go pedal straight away that will give you your best chance.

Depends what sort of event you are doing too. Our first sprint lap is timed, and while it can be fun to have a drag with the car next to you, it is never going to be a quick lap so I don't try too hard to kill the car there. Also I thought you interstaters did rolling starts and we were an oddity? Also for regularity, I think that goes too. I think it only matters in full race club cars etc. and then I think you need a bit more prep for that sort of thing and a gearbox rebuild could be included.

Happy to stand corrected, but I don't think double declutching works on the upshifts, just the down? My straight cut no synchro box in the Amilcar I am pretty sure it doesn't but it is too early for me to start thinking about it logically!

I highly recommend double declutching using heel/toe on your down changes though, even just to be easy on the gearbox and you won't lose anytime while you are busy slowing it down anyway. Just takes a bit of practise to get it all smooth, i would practice in quiet stretches on the way to work - but like riding a bicycle, once you have it, it is there.

Just for info sake in case anyone doesn't know what i am talking about - the heel toe part is just about being able to use all three pedals while braking into a corner and being able to 'blip' the throttle. There is not just one way to arrange this (watch the video of Ari Vatinen going up Pikes Peek and his feet look like the fingers on a pianist!)- it is what works best for you on any particular car. On my Alfa I use my 'toe' or ball of foot on the brake and roll my foot sideways to press the throttle. On the Benz I found the ball come arch of the foot on the brake and toes on the end of the throttle works best for me.

And the process is brake (and continue braking as hard as you can and in the minimum distance), foot on the clutch, put the gear lever in neutral, foot off the clutch, blip the throttle to spin that gear up, foot back on the clutch, back one gear, foot off the clutch.... etc. It will be long winded and cluncky at first but take your time, get the process and order right and then start speeding it up. It will just become second nature and done in the blink of an eye and the point is it is all happening while you are full on braking and trying to wash your speed off anyway.

So good luck. Synchros are one of those jobs that don't affect the strength of the box so if you can work around it you will save yourself a lot of work.
1980 280s

oscar

#6
Thanks guys,

You're right 13B.  Fair enough, 1st wouldn't be used during racing.  I was thinking more of starts and hillclimbs.  Particularly for 2nd gear starts I thought it might be too much for the clutch and as for the hillclimbs, I wont know till I try the track at Canberra but it's a steepish climb after a tight bend and I imagined a roll on 1st to start the climb would benefit.  It'll only take one lock up and bunny hop to change my mind though ::)

Amongst all this is technique.  I'm lacking it.  The heel toe thing is interesting.  Seeing "feet cam" on youtube clips and on the TV of the heel toe technique it'll take a bucket load of practice.

koan, I reckon the clutch is disengaging fine but I want to replace the fluid as well.  I know you mentioned this earlier too Craig in your brake thread I think but I didn't know much about the clutch so didn't comment but whilst replacing the bushes I found the bleeder on the transmission.  Who knows when this was last changed.  The transmission fluid was replaced with Castrol Multitraxx which is a 80w-90 equivalent.  Thoughts??

3rd-2nd is good but again, as I start to get the hang of it, I might find the need to double declutch.  Each time I go out I push a little bit harder and it's part of the reason I haven't noticed the 1st - 2nd crunch before.   To give you some idea I've put a rev limiting rotor in and still haven't got it to cut in.  I know the rev limiter doesn't signify max power but you'd think I'd hit it occasionally before a 1st gear change.


1973 350SE, my first & fave

13B

I think you'll find Camster does the hillclimbs in 1st, which is the equiv. of 2nd on Povo.  I suppose just try it and see.

You need to get that tacho installed bro... who knows what revs you're doing...

Also re. tranny fluid, i reckon its changed a bit over the years.  In the mid 90s we were using Penrite 80/90 and it was always a fairly heavy fluid but worked well in manual boxes.  We had a bit of crunching and/or reluctance of the car wanting to come out of gear while cold but when it warmed up it was good.  Back 3 years ago when we were putting a new box in the RX4 we went and bought the same stuff, Penrite 80/90 and found it a) much thinner, b) more clearer / less brown looking, c) more smelly... we double checked and advised it was an updated formula and geez it worked well, in all temps.  So I think its not just engine oils where technology has improved over the years. 

Looking at Castol website for maunal trans oils, I would be more inclined to try VMX 80 which they reckon its the shit for shift problems. 

Ian.

450SEL 6.9 #5440 = V MB 690 , 450SE # 43094 = 02010 H , 190E/turbo # 31548 = AOH 68K

craigb

And without the torque of the 8, you definitely want a 1st gear start, but having said that if only crunches once for a run, you are probably not doing too much damage.

If that VMX80 is thinner, then I would say try that and if you want to go all the way for an experiment you could try some trans fluid in there and see what it does. Sort of the other end of the scale and if it doesn't work you know nothing else will and if it does you can work back, maybe even use a shandy.

As for the tach, someone must have a spare they would donate for the cause! Really easy to install.

And like I said, with the heel/toe, take it really slow at first and do all, kinda like learning a dance step or martial art. Once your brain adopts it you will do it quickly and easily. Touch typing is another example, once your brain learns where the keys are, you don't need to look anymore.

The clutch fluid probably doesn't matter too much, like brakefluid, because it is under a whole lot less pressure and doesn't get hot like the brakes, but it can't hurt.

Also even if you don't need to double declutch from 3 to 2, it will still be a lot easier on the synchro if you do, and like I said, once you have it mastered it is no harder than riding a bike.
1980 280s

oscar

Re the tacho, I have got one but it's a bit unreliable.  I had two actually but popped a cap in the first one because I wired it back to front.  This second one is erratic at idle and it follows the revs and seems ok on a 0-100+ run, but when I'm cruising in 4th doing 60km/hr it's showing 3-4000 rpm.  If I take my foot off the accelerator it jumps to a higher rev range.  The signal's coming straight off the coil and the power is piggy backed off the clock.

I'll try out some more oils like that VMX 80 plus I saw too the 75w-85 oils like Syntrans which also sound attractive via the company blurb.

As for starting off in 2nd, it doesn't work IMO.  Now that I've tried it the engine just labours too much and spends too much time below 50km/h or just getting off the mark.   Plus I'd be worried about burning the clutch.  You tend to ride it for too long.  You can't dorp it or let it go too quickly becuase it'll stall or labour no matter the revs.   I had a few different goes but thought it was not worth practising.  The difference between a 1st gear and 2nd gear takeoff for a 0-100km/h is around 2 seconds.  The best in 1st was around 9-10sec and from 2nd gear my best was around 12.

FWIW, after my few runs out of town, on the way in I thought I'd have a go at the heel toe thing.  :D Man I'm crap at it.  On one occasion coming into a sharp left I've readied the right foot over the brake and accelerator, toes down, brake on, clutch in, touch accelerator, shift 3rd to 2nd, brakes still on (or so I thought) clutch out, LOCK UP!.  ;D  I wasn't going that fast either but doing 2nd to 1st in the same circumstances guarantee a more severe lock up and time wasted.  Need to practice.

Anyway, here's today's vid with a sample of some 1st and 2nd gear takeoffs plus audible gear crunch between 1st - 2nd.


http://www.youtube.com/v/IwDt--fRSis&hl=en&fs=1
1973 350SE, my first & fave

craigb

Will have a listen when I get home. Perhaps a suggestion with the double declutch thing is forget the heel toe for now and just practise the double declutch thing. For the sake of practising you can go up or down but just getting in that rythm of the pause inbetween from stopping at the neutral position, foot off the clutch and give it a rev then back on the clutch and into gear. I remember thinking the same thing that I would never get it smooth but back when I was in the CFS I had to learn to get my truck license. It seems hard at first but you will be surprised how quickly you can teach yourself if you keep at it. Once you get the dd bit, then fumble about with your feet for the heel toe bit........ just thinking out loud here!
1980 280s

WGB

I learnt to drive in cars with crash gearboxes and some of them allowed faster changes than baulky early synchro boxes.

On the 1 - 2 change and up and beyond it was rare to need to blip the throttle , just a short pause in neutral with the clutch let in and out before the change up. The blip on the throttle was needed on the way down again of course to match the ear speeds.

I still practice on my Massey Fergusson tractor while mowing the grass.

On a more sombre note I hope you get lucky with the oil type or the possible dragging clutch but it sounds like a check through the bearings and a new synchro ring is a reasonable possibility.

Bill

oscar

Quote from: WGB on 03 October 2008, 08:57 AM
On a more sombre note I hope you get lucky with the oil type or the possible dragging clutch but it sounds like a check through the bearings and a new synchro ring is a reasonable possibility.

I think in all honesty it's the only proper way to address the situation.  :-\  But I can't see me doing it myself nor can I afford someone else to do it any time soon.  I'll do the oil again and just go easy on that change. 

Quote from: craigb on 03 October 2008, 02:02 AM
Perhaps a suggestion with the double declutch thing is forget the heel toe for now and just practise the double declutch thing.

I've got that bit sorted, drove a few crash box light trucks on farms during my late teens and never really forgot how to do it.  I'm at the stage of doing the heel-toe but it's hard.    Here's a thing though.  When I got my medium rigid license I did it in a truck with a synchro box (not that I knew at the time).  The instructor was irate the first time we went out and I changed down whilst approaching lights.   He said double declutching synchro boxes will *&#k em.   What's the thoughts there?  As a result of testing in that particular truck I'm only legally allowed to drive synchro boxes :(

Another thing.  No one's mentioned it but considering the three levers were removed to replace the bushes and I did my best to put them back on the splines on the same indents they came off, it's possible one of the levers didn't exactly go on the way it came off. 
Would adjusting the lengths of the rods (effectively changing the levers' position on the spline) make any difference?
1973 350SE, my first & fave

John Hubertz

If these are anything like USA boxes:

1.  finely made shims sometimes are necessary - internal clearances matter re gear spacing/sychro "throw" (I'm digging WAY back for this memory)

2.  The quick diag for clutch release is to run it up on a hoist, shift from 1st to second but leave the clutch depressed and see if the wheels stop rotating!

3.  Sychro replacements are no fun even on a bench, if I recall - cone shaped dealies methinks
John Hubertz
"When the going gets weird, the weird turn pro."
(Hunter S. Thompson) 

1977 450SEL (Max Headroom)
[img width=68 height=73][url="http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg"]http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg[/url][/img]

oscar

Quote from: John Hubertz on 04 October 2008, 04:43 AM
2.  The quick diag for clutch release is to run it up on a hoist, shift from 1st to second but leave the clutch depressed and see if the wheels stop rotating!

I should be able to try this on stands, thanks for that John. ;) 

1973 350SE, my first & fave