Why syncros wear out (a.k.a. How not to shift)

[gamiller]

I haven't seen this posted before, but made for a good read regarding what happens when you shift. From the FAQ over at FordContour.org

Originally Posted by Terry Haines

Why do syncros wear out?

The syncro is a mini-cone clutch. as you change up the gears it starts to engage with the next gear you are going into before the 'cogs' mate....for example say you are in 2nd gear and second gear is spinning at 4000 rpm and you want to shift without a 'crunch'...the syncro on 3rd gear has to spin up 3rd gear to 4000rpm also to 'syncronise' the gear speeds...it does this with the cone clutch 'blocker rings' all in the space of time it takes to move the stick out of 2nd and towards 3rd....it works damn hard

why does it wear?

if you go over the normal revs for a gear and the engine speed is higher the syncro has to work harder to speed up the next gear. in the same time it wears more in this situation.

OK but what about downshift?

Same rule applies, if you are in 5th at 3000rpm and want to shift to a lower gear the syncro has to do the same job in reverse on 4th gear....unless you can 'double de-clutch' on down shifts,in which case YOU are setting the speed of the next lower gear to syncronise the 'cogs' without a crunch...saves a lot of sycro wear if you can double de-clutch'.

Why do the diffs fail?

The V6 is a bit over on power for the MTX75 trans. for example diff components are the same for an MTX in a Zetec as they are in a V6!..as its an 'open' diff the planet and side gears take a lot of 'shock' loads in say wheelspin and 'wheel hop' situations and can break very easy or worse send the gears or parts of the diff thru the gear casing...best cure is to have a Quaife or Torsen diff fitted.

Why did my gears jam or get stuck in one gear?

On the cable shift boxes prior to 2000 the 'tower' on top of the trans was/is prone to 'jumping the gate' and not pulling one gear out of engagement before trying to select another,this causes the 'jammed in gear' problem.

Total loss of all gears is usually a pinch bolt that holds the main vertical selector shaft to the selector arm. it breaks off and all gears are lost...worse case is it breaks off and the bolt head drops into the trans, gets wedged between a gear and the ally case and is punched thru the case!...

So whats the fix?...Fit either a better designed post 2000 Contour or Focus tower assy......

'How much will the parts be to repair my bad syncro?????

Depends how many 'parts' of the sycro are shot and which gear.Blocker rings (the 'brass') is the first parts that wear out,as can the syncro hub itself.Some
gears have a combined 'blocker' assy,that is two blockers for each gear Vs one on some of the other gears.Between the double blocker gears is a steel cone...just a tapered ring of steel...it wears aswell but not as much as 'the brass'...cost of just the 'cone'...over $45....that is just one piece of many that makes up the syncro assy's.....Just a thought when you 'power shifting'....better wrap the gear stick with $100 bills!...

[whiteboy477]

def should be a sticy for us

[DanG]

Also wanted to add with regards to the "V6 is a bit over on power for the MTX75" comment.

Shock loading the trans and fighting the stick are the ways to kill this trans. The MTX-75 in my old (Now Topik's) turbo was a BONE STOCK 1999 MTX-75 with only a Torsen LSD unit installed. Stock shift tower, stock synchros, stock (and original!) blockers. 400fwhp and not a hiccup or a grind after 2 years attached to an F/I motor!

It comes down to this- Abuse and mistreat the trans and/or clutch, you're going to need a rebuild sooner rather than later (if at all). If you're shifting with more than 1 or 2 fingers, YOU'RE SHIFTING TOO HARD.

No double-clutching (up or down). Only very sparse "race-style" hard shifts where only your toe hits and lets off the clutch. Drive it right, it'll last. Drive it wrong, and it doesn't matter if you have an I4 or a 3L turbo- You'll break it!

With regards to the fluid- Synchromax or "honey" is best- However, that also being said (and I appreciate and respect Terry's weigh-in here), I ran Mobil 1 ATF in the above MTX- and after 115k miles when I pulled it for the turbo build, the insides were "immaculate", to use the words of the trans builder.