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Synchro springs 3 rail 4 syncro


Darron

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Im no expert of Spitfire models but if the replacement rings have the same inner diameter as the old ones then you had a bargain and youre good to go. You can check the rings by carefully inspecting the profile of the concentric serrations (should be nice and sharp and not flattened off) and also how far they can be pushed onto the 'cone' of the gear. They should grip the cone well before the front of the ring meets the gear face. Put the best ones on second and third as these have the hardest life.... 

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So after a week got back into workshop today to make a start on putting back together the gearbox ,made a dummy rear bearing and a fixture to fit to the front of the gearbox which will double up as a aid for driving on the rear bearing with a nylon bush so as to not damage the shaft tip , this was done as I was taking the main shaft in and out on a regular basis to set the reverse idling gear up ,by adjusting the selector so it doesn’t fowl the 1st and 2nd synchro hub. which worked very well , also machined up another sleeve  to just under 1”as the original was short and a extra small spacer behind it ! 
my question to you guys is when I put the lid back on temporary and select first it still fowls the hub with it set just in front of 1st ,so took the main shaft out and there seems to be a lot of movement on the hub to shaft back and forth to where it comes up against the split thrust washers allowing it to move back a fare bit and touching the idler there is nowhere near this movement on the 3/4 hub is this normal

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Thanks for the quick response Pete that puts my mind at rest for hub float but leaves me pondering on the fact that the reverse idler still fowls because of the float bringing the hub so far back ! These things are sent to test us .

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Interest Pete as I closed my browser on my phone opened it and it took a few seconds but down loaded ok so don’t know what going on there , the video is only 40 something mb it was taken on my iPhone strange . It shows the idling gear clear of the first gear but only just which is fine but when the syncro hub is engaged the idling gear catches the the hub teeth so much so that when I put the top on and select 1 st it almost locks up by hand 

Darron 

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Does the idling gear turn when not selected to be in reverse ,ie because the proximity of it to the hub and first gear it  spins or should it be stationary, sorry for being a pain with this guys but I want to get it right and never doing a triumph box before

regards

Darron

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marcus did a post about the reverse pivot  lever getting bent , it does need to clear the sleeve teeth when 1st is engaged as in your photo  its a tad tooooo  close 

thats my view  without a box in front of me  doesnt the reverse spacer tube control the out of gear idler position  or am i getting too old for this 

Pete

 

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Hi Pete yes the tube stops the idler from hitting the first gear which I have machined a new one ,so a few thou short of touching the gear, it’s the bloody hub the problem when I took the gearbox apart the idler had some teeth partially missing and the selector was to far forward, so the gear must of been in mesh when first was selected this is why when pulling away in first it used to knock because of the partial missing teeth and the spacer tube was the right length 23.71mm but had another smaller spacer of about 2 to 3mm behind it pushing the idler even further foreword !

I have bent the selector back into its right position as per Marcus thread but that bloody hub gear just catching the idler. I’m in two minds to grind a little off the back edge of the idler, put the original size tube back in so it clears the hub , it’s just the question why that bugs me !!

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you havnt got some single rail parts in a 3 rail ???

subtle differences   not checked all the offending in the parts lists but i had a vit box as a slave it was a mess of mix and not matched 

especially the 1st 2nds hub and sleeve make a rattling good fit on the mainshaft splines also do a count of the 1st 2nd sleeve reverse teeth 

they are different by 1 tooth i seem to remember 

pete

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well Pete 

the answer to that is i really dont know, the 1st and 2nd hub has 29 teeth the idler as 17 as this is another one replacing the old one which had 17 teeth , the main shaft has a small ball bearing that locates a thrust washer between 1st gear and the syncro hub, that i dont seem to find i any exploded veiw of three rail main shafts ,it has a j type OD fitted to it ,and i know from the gearbox number its a mk 4 spitfire box the end of the main shaft as the smaller roll bearing too.

The problem is i dont know whats the difference between the the two and where to look to find out, not knowing the history of who rebuilt either other than it was done not that many miles ago but before i aquired the vehicle there is a possibility that i could get intouch with the previous owner and find out, but thats not going to really help

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well to my search the 4 sync   3 rail   Mk4 spit box has 33 teeth  same as vit and GT6 

the 29 may be why idler teeth had sheared 

dolly single and 3 rail all 33 theeth 

where as the single rail  spit  1500  has 29 teeth ,  so think theres a mis match going on 

idler is the same on both by p number .

pete

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Thanks for the reply Pete ,hmmm so where do I go from here! I take it the hub is dimensionally the same just a different amount of teeth in which case the idler shouldn’t interfere with it any way or is it different if I source a 33 tooth hub will it mesh with the 17 tooth idler

Darron

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the idler is pretty std across   both 3 rail and 1 rail

tooth count and gear centres  all contribute to the mesh ,  as i said i ended up with a box someone had spent good money fitting all the wrong parts 

 sorry  i dont think i have a 33 tooth going spare , 

all i can say is the evidence says 33 tooth is what you should have , i cant confirm the hub , but i know a 1 rail hub is a awfull fit on a 3 rail shaft

Pete

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Thank you for that Pete I will go to his site and check it out my only concern is the 17 tooth idler as there are three listed for the box 17 ,19 and 21 as long as the 17 meshes with that pitch! sorry to go on but just want it right if I’m going to lay out about  another £150 as I have paid best part of £200 with the new idler gasket and bearings , snap rings , circlips  synchros and seals at least doing it myself it will be done thoroughly and learned a lot at the same time

Darron

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  well a 17 /29  is not as std.    a lot depends where you look but 144580 is listed for a spit IV 4 sync box  its used on  others  and shows here as 19t

https://rimmerbros.com/Item--i-144580

https://www.canleyclassics.com/demoapp/?ptno=144580

if the 29/17 works  well ok.... there must be a small backlash when engaged 

but does this affect your out of gear pinion position ....  no idea

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Dont want to complicate things further but my w/manual for Vitesse 2L says 34 teeth on hub, 21 on idler and 15 on layshaft. Unfortunately I cant find a Spitfire manual online but this should give an answer for exactly how many teeth you should have....

Also I would imagine your car has had its diff changed from standard to compensate for the different ratios in the Spit box

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Hi Johny

thanks first of all for your replies ,first that’s my worry with purchasing a 33 tooth and secondly is the lay shaft gear which to be honest haven’t checked how many teeth yet , and going back to Pete’s last thread the over all length size of the the hub is surely the same so it’s not going to make any difference with the out of gear pinion problem I have with it just touching .

when the gear box was in it drove ok all gears selected with out grinding apart from reverse obviously, as for the diff I haven’t checked but drove and pulled beautifully.

Darron

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