My gearbox was rebuilt last year, and I have really only just started driving the car a lot. Apart from the whine I get when in 5th, it's impossible to change down to second without it crunching. Yes, I've tried most things, clutch pedal to the floor, different revs etc. Any ideas? It's standard 5 speed manual box.
-
The Z Club relies on the support of it's paid members - join the club or renew your membership here.
Crunch in second
- Thread starter Andrew
- Start date
Farmer42
Club Member
Is your clutch aligned properly & was it replaced with the gearbox rebuild? A poorly aligned clutch will put pressure on the input shaft and could cause the bearing to whine which sounds more apparent in a higher gear. It would also give you problems selecting gears.
My 5-speed box is stiff getting into 2nd but doesn't crunch. I also get a mild hum in 5th gear but it soon goes when the engine note drowns it out. Stick yer clog down and you won't hear it!
MikeB
Well-Known Forum User
Surely as soon a you release the clutch plate for the first time with the engine running, any minuscule misalignment is taken out as the plate self-centres, otherwise you would get a judder every time you try to change gear ?
Thanks for the replies.
Not sure what oil I'm running to be honest. I can find out and report back.
The clutch was also done at the same time. It's stiff going up the gears, but always crunches going down. Bit disappointed to be honest. The place that rebuilt it was commissioned by another garage so whatever happens I guess it's me whose going to pay for more work. We shall see.
Not sure what oil I'm running to be honest. I can find out and report back.
The clutch was also done at the same time. It's stiff going up the gears, but always crunches going down. Bit disappointed to be honest. The place that rebuilt it was commissioned by another garage so whatever happens I guess it's me whose going to pay for more work. We shall see.
I don't understand that Farmer. Are you thinking of the friction plate during rebuild? If so that would be ok after the first use of the clutch surely.
tel240z
Club Member
My thoughts exactly
Albrecht
Well-Known Forum User
Which one?
The FS5C71-A had a reputation when new of having slightly 'baulky' synchros (the Porsche/Servo type synchros seem to respond better to quite firm shifting) which take time to bed in properly, then become nice to use before gradually becoming more baulky again. Many of these 'boxes had a notable gear whine in 5th even when new (which I rather like, but you might not feel the same way). The FS5C71-A tends to be very oil-type sensitive too.
The (later) FS5C71-B tends to be a little less characterful, but all of these transmissions are quite complicated pieces of mechanical equipment and you get 'good' ones and 'less good' ones. It all depends on how the tolerances stack up.
Some of your disappointment might possibly be down to somewhat unrealistic expectations for 45+ year old pieces of equipment. What you are describing is quite likely not all that different to how they were when new...!
Not sure which box it is. I will attempt to find out. It is always possible that I do have unrealistic expectations, and hence my reason for asking the question on the forum.
It was seem however that the crunching going down into second is not perhaps meant to be. The whine in fifth I can live with. To be fair I was told to expect the whine.
It was seem however that the crunching going down into second is not perhaps meant to be. The whine in fifth I can live with. To be fair I was told to expect the whine.
racer
Club Member
Andrew have you checked your clutch master cylinder and slave?
Make sure you're pushing enough fluid and there's no air in the system.
When they "rebuilt the gearbox" did they replace any of the syncrose? Especially 2nd.
They are very difficult to by new now.
Make sure you're pushing enough fluid and there's no air in the system.
When they "rebuilt the gearbox" did they replace any of the syncrose? Especially 2nd.
They are very difficult to by new now.
Last edited by a moderator:
SeanDezart
Well-Known Forum User
Err non !
Follow the money - you paid someone who took the profit - they are reponsable !
However, I've known a fully rebuilt OEM gearbox start 'crunching' in less than a year and Alan has a point - these are old boxes conceived a LONG time ago and for different power plants.....don't expect miracles....but there are well-tried and tested options.
MikeB
Well-Known Forum User
Re the oil, if it is a modern synthetic oil, these sometimes don't work with old syncros, a change to older thicker stuff might help. The change on a 240 isn't like a modern car, the change down is a tad slower and more deliberate, but it still shouldn't crunch if the syncro ring is in good nick.
If it isn't crunching when putting it into 1st, there's probably nothing wrong with your clutch
If it isn't crunching when putting it into 1st, there's probably nothing wrong with your clutch
I would learn the skill of 'double declutching' especially for downchanges into 2nd gear. I've been out in my standard 240Z today (lovely weather) and I quite often 'double declutch' with a blip of the throttle into 2nd even though the gearbox is fine. These gearboxes ratios have a big gap between 3rd and 2nd.
Rob, I double de clutch loads. I have a Ford 7Y without synchromesh. I do it on the 240z all the time to no avail. I did 60 miles in her today. Every time down to second, crunch. I'm not saying I'm a ace driver, but I have a few old classics, and I don't believe this is me.
Well if the clutch is operating ok, you are double declutching and it still crunches the synchro is worn out. However if you are matching the revs well you could do it - many old cars didn't have synchro on 1st.
The whine in 5th is quite usual unfortunately - these cars are direct drive when in 4th not 5th. However a rebuilt gearbox should be better than this.
The problem is that the parts are hard/impossible to source.
The whine in 5th is quite usual unfortunately - these cars are direct drive when in 4th not 5th. However a rebuilt gearbox should be better than this.
The problem is that the parts are hard/impossible to source.
Oil wont have anything to do with the 'crunching' when downshifting to 2nd.
What model gearbox is it?
If it's a late 240Z or 260Z 71B unit, it'll be a Steel 'Bulk Ring' type syncromesh.
2nd & 3rd in these gearbox's cop the most abuse, and I'd say when the box has been rebuilt, they did not inspect the surface of the bulk ring for wear.
New Bulk Rings are still available from Nissan IIRC - but make sure you are sitting down when you are told the price.
I suggest you take it back to the shop that did the work...
FWIW I convert the 71B to brass Warner type syncros - they are a much design, are cheaper to buy new from Nissan & give a much nicer shift.
Just requires the older GL4 spec oil.
What model gearbox is it?
If it's a late 240Z or 260Z 71B unit, it'll be a Steel 'Bulk Ring' type syncromesh.
2nd & 3rd in these gearbox's cop the most abuse, and I'd say when the box has been rebuilt, they did not inspect the surface of the bulk ring for wear.
New Bulk Rings are still available from Nissan IIRC - but make sure you are sitting down when you are told the price.
I suggest you take it back to the shop that did the work...
FWIW I convert the 71B to brass Warner type syncros - they are a much design, are cheaper to buy new from Nissan & give a much nicer shift.
Just requires the older GL4 spec oil.