A mate reco'd my all syncro g/box new bearings shafts etc but used good original syncro rings it changes up the gears good but back down 4-3 3-2 at speed it crunches but at slow speeds it is fine( 20kph ish) it is fine is it the synro's as it goes into 1st & reverse no problem or have we overlooked something

What's your clutch travel like? Does it engage close to the floor?

If it's fine then it sounds like baulk rings with insufficient clearance to the gear face were used

cheers

Jacob

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'72 Clubman Van - 1022cc, 295 head, 731 cam - Daily Driver
'69 Morris 1100 S - Dinged by a bus, in shed under repair
'64 Morris 1100 - Early 1100, long term project

Hey after much stuffing around with clutch set up , just check it's not a bent ball end on clutch lever arm. Take it out and compare it to a new one. This affected my recently rebuilt g box until I worked it out. Easy place to start , rather than pulling out motor and splitting! Worth a look! Sorry did get to catch up at Wakefield, I ended up being pretty busy! Cheers.

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Now with 2 extra ports!

down-shifting is where the synchros do the most work, up-shifting they don't do much....

how 'good' were the ones that were put in?

Old synchros are OK to reuse if not worn bad, but I give them .020" extra back clearance for added life.
It could be the 3 springs in the synchro hubs. These get softer with age, then do not provide enough initial axial force to let cone friction spin the baulk ring to the baulk position, = crunch on downshifts.
These springs are only $5 ea, I change all 6 on unknown box rebuilds.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Another little problem can be the bushes/lubrication of the crankshaft gear on the crank.
Now as Simon said in his post easier going up than down and I have found sometimes that if the gear bushes are dry when re-fitted the brass can pick-up on the crank ,so even with the clutch plate fully dis-engaged the gear will not spin freely on the crank and so it's still driving the drop gears.
This is one thing that gets over looked during over hauls , but I always remove the gear and clean up the bush and coat the crank with copper grease so it has good lubrication until the oil works it's way into the bushes.

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Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com

Was heaps of clearance on back of the syncro's and they didn't look worn it goes in first and reverse good and pedal to floor clearance is good on take off will start with the simple things 1st

I had this problem, started catching, but then it got worse, the primary gear actually seized on the crankshaft! had been machined to spec'd tolerances, were advised that it should have slightly more clearance than spec'd in the workshop manual. Live and learn!

I guess to test this you could jack the front of the car up and start it up with it in 1st, clutch disengaged, and see if the wheels spin at all?

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tim
68 Deluxe 1293, HIF44, megajolt/EDIS4, daihatsu alternator..

'a mini is for life, not just for christmas!'

I'm using a new Minispares floating front bush in my 1412, had no problems since it was fitted 3400km ago.
I did lube it good (with KMX 20W/50) when fitted..

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Could also be caused by fitting a crap primary gear cover gasket. I had a similar problem when the gasket was too thin (grey gasket instead of the orange thick gasket). This causes the primary gear and idler gear to bind and therefore not allowing them to spin freely as you change gears.

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

All good suggestions and comments, but don't forget that the cones on the gears themselves have a sintered steel face that the synchro rings 'run' on and these too wear and chip.

What oil are you using?

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Kmart oil was going to look at it today but my hand is sore looks like off to the doctors