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Synchro springs 3 rail 4 syncro


Darron
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Hi

new to the forum, looking for some advice on my gearbox rebuild ,I have a three rail four synchro gearbox that I have removed from my vitesse 6 ,I am rebuilding it due to the reverse idle gear constantly trying to engage the first and second gear synchro while in first gear, the problem I have is that after I stripped it all down the springs in the  synchro hubs 1st and 2nd and 3rd and 4th are the same ,! and the rebuild kit I have as two different types one  trio looks stronger than the other any advise or help would be much appreciated, I have read somewhere that they should be different but which goes where ?

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the spring length gives enough ball protrusion to work in its sleeve groove if you geta short sprint in a deep hole its too easy to pop together , conversly get a long spring in a shallow hole you can fight the flying balls .

simple idea to reassembly is pop the hub and sleeve into a poly bag,  work through the open end and with light pressure on the sleeve pop each ball down with a small screwdriver , when all 3 are just nudged in press the sleeve down,  easy to check the axial release load just press on some bathroom scales etc.  keep the units bagged and when ready to assemble tie them up with fine wire cut it odd when man handling has finished 

to stop the 2nd gear collet thrusts from continually jumping out assemble the box in a vertical position , make a dummy mainshaft support 

(lump of hard wood with a spigot bore in it ) in a vice and lower with 6 pairs of hands the mainshaft/lay cluster and case down over the support  so when you tap the rear bearing down the shaft and into the case and gravity stops the split collets jumping out with every mallet strike  

make sure the gear dog teeth and the sleeve have un chimbled  well defined tooth chamfers   /\  not /~\  as this is a integral part of what makes syncho work

Pete

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Hi all

thanks again for the post earlier in the week, going on from what Pete Lewis has 
Enlightened me with checking the release load of the synchros on a set of bathroom scales ,the 1st and 2nd is about 15 kg (33lbs) and 3rd and 4th is 14kg (31lbs) I will add there are no shims in either synchros, my question is this too high or except-able as the manual I have says 10 to 21lbs 

regards 

Darron 

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my manual says 19/21lbs for both. I know that if its too low you run the risk of gear changes where the engagement starts too soon before the synchro ring has fully matched the speeds so giving a crunch. Too high and obviously youll need more pressure on the lever although yours will probably easy up once immersed in oil....

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Thanks for the quick reply Johnny ,funny thing is that before I took the gearbox out when driving it I always thought it was very stiff to put into each gear it never crunched or anything but wasn’t as slick as I thought it ought to be !

regard

Darron

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HI Johny

i had a good look and also probed at them with a pick but could not make any thing move will have to try again tomorrow and get in with a lighted magnifing glass but would of thought that one or two would have come out while i was washing and cleaning the hubs and gears

Darron

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yes it could just be that the pattern part springs (which I wouldnt have thought are easy to replicate accurately due to the tempering of the steel wire etc) are stronger than they should be. Hopefully they'll soften up with use or you'll have to have more weetabix.....

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Ahh well Pete I would love to just use it and let you guys know but that’s a awful lot of work to put back in and then to take all out again ☹️ Bit of a stickler for things right ,that’s why I am on here with you gurus ,Going to strip them down again and really check for the allusive shims if I can’t find them then perhaps see if I can measure the old spring rates ,and use them  mix and match but with the right amount of coils , even face a bit off the old ones as Johnny as suggested some how try to get the release loads lighter fingers crossed 👍

Darron

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Hello Darron

                        I rebuilt my single rail gearbox last winter and there are different springs(fogot which way) but i think if you check the holes in the hubs one deeper than the other and if you put the long springs in there it will not go together but short ones would not give the 19/21 lbs needed

Roger

 

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i fought the loads on my 2000 box  could get anywhere near the spec  but it works ok  ie they were lighter than spec'd 

this is from a Rootes WSM ( they dont hide useful clues)   often written by a uncle)  its one of the best explanations of how syncro works 

ive been into truck gearboxes for life  i wouldnt worry too much if its a tad high or low,  even is the king the idea is to give a snap movement at the ring , not a soft squiggy 

the tooth chamfers on sleeve ring and dog teeth do all the work  the balls and springs make sure you really want to engage and not let selection load drop off halfway through a change  

Pete

 

 

 

syncho and howi.jpg

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Well gents decided to go with the loads that the new springs give after Pete’s previous comments ,as the loads are the same . will be putting the 1st and 2nd synchro back into the box though there is some damage to the reverse gearing On this but I have had trouble sourcing another with 29 teeth I will attach a photo to see what you guys think

Darron

7E9C5373-6CCC-451D-AAB5-F65A48E06164.jpeg

B4966372-06B8-42EF-A858-0080232F3F7D.jpeg

DDABDF11-8A91-4D10-B02B-F8BAB4453174.jpeg

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it can have a hard life if the driver tends to put the car into reverse while its still rolling forwards and also a high tickover can worsen the crunch.  However I think that gear is good for a few more miles yet just treat it gently (as you should do with the whole box).

Are you replacing the synchro rings themselves or are they still ok?

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