New gearbox needed or synchro replaced?

[tomdnNissan]

Hello,

 

I'm new to the forums and the site, but hoping you might be able to advise me re my 2008 350z (done circa 30,000 miles).

 

The car broke down recently at the side of the motorway - it wouldn't go into gear and I've had a new clutch fitted at a South London Nissan dealership (cost me £1k all in) which has fixed the problem. But they said when I picked up the car it was still notchy in third - and the gearbox can be notchy so I didn't think anything of it, but it turns out it graunches loadly whenever it goes into third - it's driveable but not on a long -term basis so needs looking at. The dealership said it may be the synchros but that by the time the gearbox has been stripped, synchros and bearings replaced as needed, that I may as well get a new gearbox. This seems excessive to me? They are quoting just under £3k for a new gearbox and £1k labour. I'm considering taking it to a gearbox specialist instead and seeing if they can strip it and fix it rather than just replace the whole thing.

 

Any advice gratefully received! Thanks Tom

[GIXXERUK]

In your shoes I would price up a repair at a gearbox specialist ( also need to consider will the damaged synchro have caused extra damage as pieces of swarf and metal will be swimming in the oil) and also consider a 2nd hand unit, quite a few zeds breaking on here and 2nd hand boxes are readily available from the forum traders

[tomdnNissan]

Thanks GIXXERUK, I'll get a repair quote from a specialist to compare against fitting a second hand box.. guess they aren't going to be able to tell me exactly though until they've stripped it back and seen where the problem is..

[rabbitstew]

The dealership said it may be the synchros but that by the time the gearbox has been stripped, synchros and bearings replaced as needed, that I may as well get a new gearbox. This seems excessive to me?

 

Depending on the cost they may well be right. I had a similar problem on my Yamaha R1. I blew the gearbox up through too many 2nd gear wheelies. I didnt even bother going to the dealer for a quote, but a garage I trusted quoted me £1200 to fix the gearbox - basically remove it, strip it down, replace broken bits, put it back together etc.

 

Instead I just bought a complete 2nd hand engine/gearbox off ebay for £450 and swapped them over. Bit easier on a motorbike than in a car, so it only took me about 3 hours work. As a plus side I sold the old broken engine/gearbox back on ebay for £250 to a racer who wanted spares, and my new engine only had done 5000 miles compared to the 45000 miles my old one had done.

 

Risk you take tho, if its a 2nd hand unit like mine you may not know the history of it and if its any good. Plus if you supply the unit and a garage fixes it, then it goes bang, the garage will blame the unit and the seller of the unit may blame the garage.

Edited March 25, 2014 by rabbitstew

[GIXXERUK]

Thanks GIXXERUK, I'll get a repair quote from a specialist to compare against fitting a second hand box.. guess they aren't going to be able to tell me exactly though until they've stripped it back and seen where the problem is..

 

They will have to give you a ballpark figure mate, which I'm sure will be enough to make a decision on

Zmanalex will have a gearbox, shoot him a pm to get a price and you will know what you're dealing with

 

Hth

 

Paul

 

People may be able to advise better if you post you're location

[tomdnNissan]

Thanks rabbitstew, I'm just a bit surprised the gearbox has gone after 30,000 miles.. Maybe it can be stripped and repaired, unfortunately I won't be able to do it myself. But I've been recommended Hardy Engineering in Leaterhead for gearbox work, so will see what the quote compared to Nissan Ancaster Penge's £4k...

[GIXXERUK]

It's not too common but not unheard of

 

http://www.350z-uk.com/topic/81066-the-gearbox-issue/

[KyleR]

I was quoted £500 by Nissan for the gearbox refurb plus the labour involved in removing and refitting it as they would be sending it to someone else to fix it.

 

£3k for a new box sounds about right, but the £1k labour is a joke, it's only a couple of hour long job, if that.

[tomdnNissan]

Thanks Kyle, so £500 all in from a Nissan dealer for refurb? That sounds more like it.. I'm going to get a few quotes, can anyone recommend a London gearbox specialist please?

[KyleR]

Not quite, they would remove the box for me and refit it and whatever labour costs, then it would be £500 for have it refurbed by whomever they use. But it really can't be that much more than £500, £650 maybe…

[Husky]

The reason it's gone is that Nissan designed the gearbox badly, specifically relating to the synchros. This is why they developed the automatic rev matching in the later cars, they played it off well as a "feature" but in reality it was to save premature wear on the synchromesh's.

 

If this is your daily driver and you are going to be driving it until it's fixed then you need to change your driving style to cope with the lack of a working synchro in 3rd. Synchros are designed to bring the input shaft of the gearbox (layshaft) to the mathcing speed of the chosen gearset when engaging a gear. This is how it goes for a 2nd to 3rd gear shift:

1. Car is in 2nd gear
   
2. You decide to change gear to 3rd and push in the clutch
   
3. The clutch disconnects the engine from the layshaft
   
4. you shift into neutral disconnecting the layshaft from the 2nd gear gearset
   
5. the layshaft begins decelarating as it is not being driven
   
6. you begin to engage 3rd gear (the 3rd gear synchro engages, taking speed from the 3nd gear gearset and spinning up the layshaft)
   
7. once the 3rd gear gearset and the layshaft are at a matched speed, the teeth mesh and the gear goes in.
   
8. you release the clutch connecting the engine to the layshaft (the clutch allows the mismatched engine speed and layshaft speeds to come together by allowing an amount of slip).
   

As you can see, there is a time that needs to be given for the synchro to spin up the layshaft (step 6). If you are too quick on this and force the change you are going to damage the synchro as it has to do it's job a lot faster/harder, increasing heat and resulting in premature wear. The 350z synchros are quite weak and so this happens easily.

 

With this in mind you can understand how to drive with a broken synchro. You need to do the job of the synchro yourself, this means that you want the layshaft and specific gearset to be doing a matched speed when you push the lever into position. Just don't force the gear in or it'll make it worse, you should feel the point when it wants to drop in, keep it in that point and change gear. Here's the same change with no synchro:

1. Car is in 2nd gear
   
2. You decide to change gear to 3rd and push in the clutch
   
3. The clutch disconnects the engine from the layshaft
   
4. you shift into neutral disconnecting the layshaft from the 2nd gear gearset
   
5. the layshaft begins decelarating as it is not being driven
   
6. the engine decelerates to the appropriate rpm for 3rd gear
   
7. While in neutral, you re-engage the clutch to slow the layshaft from 2nd gear speed to 3rd gear speed.
   
8. With the layshaft now at the correct speed for 3rd gear you disengage clutch disconnecting the layshaft from the engine.
   
9. You change to 3rd and with the layshaft and gearset at a matched speed, the teeth mesh and the gear goes in.
   
10. you release the clutch connecting the engine to the layshaft.
    

Sounds complicated but it's pretty simple. It can be simplified to:

 

"Changing up: Release throttle as you depress the clutch as normal, with the throttle still at idle shift to neutral let the clutch up briefly with the throttle still at idle, this uses the engine to slow down the layshaft, then clutch down shift into new gear and clutch up and depress throttle as usual."

 

Changing down is simplified to:

 

"Changing down: A bit harder: Shift to neutral, let the clutch up and blip the throttle - how much is a bit of a knack but it feels good when you get it right, this gets the gears spinning at the higher speed needed for the low gear. Clutch down and shift to new gear as usual."

 

 

 

 

 

Sorry I rambled on

[tomdnNissan]

Thanks Husky, that will help until I can get it fixed at the garage!

[Stutopia]

The reason it's gone is that Nissan designed the gearbox badly, specifically relating to the synchros. This is why they developed the automatic rev matching in the later cars, they played it off well as a "feature" but in reality it was to save premature wear on the synchromesh's.

 

If this is your daily driver and you are going to be driving it until it's fixed then you need to change your driving style to cope with the lack of a working synchro in 3rd. Synchros are designed to bring the input shaft of the gearbox (layshaft) to the mathcing speed of the chosen gearset when engaging a gear. This is how it goes for a 2nd to 3rd gear shift:

1. Car is in 2nd gear
   
2. You decide to change gear to 3rd and push in the clutch
   
3. The clutch disconnects the engine from the layshaft
   
4. you shift into neutral disconnecting the layshaft from the 2nd gear gearset
   
5. the layshaft begins decelarating as it is not being driven
   
6. you begin to engage 3rd gear (the 3rd gear synchro engages, taking speed from the 3nd gear gearset and spinning up the layshaft)
   
7. once the 3rd gear gearset and the layshaft are at a matched speed, the teeth mesh and the gear goes in.
   
8. you release the clutch connecting the engine to the layshaft (the clutch allows the mismatched engine speed and layshaft speeds to come together by allowing an amount of slip).
   

As you can see, there is a time that needs to be given for the synchro to spin up the layshaft (step 6). If you are too quick on this and force the change you are going to damage the synchro as it has to do it's job a lot faster/harder, increasing heat and resulting in premature wear. The 350z synchros are quite weak and so this happens easily.

 

With this in mind you can understand how to drive with a broken synchro. You need to do the job of the synchro yourself, this means that you want the layshaft and specific gearset to be doing a matched speed when you push the lever into position. Just don't force the gear in or it'll make it worse, you should feel the point when it wants to drop in, keep it in that point and change gear. Here's the same change with no synchro:

1. Car is in 2nd gear
   
2. You decide to change gear to 3rd and push in the clutch
   
3. The clutch disconnects the engine from the layshaft
   
4. you shift into neutral disconnecting the layshaft from the 2nd gear gearset
   
5. the layshaft begins decelarating as it is not being driven
   
6. the engine decelerates to the appropriate rpm for 3rd gear
   
7. While in neutral, you re-engage the clutch to slow the layshaft from 2nd gear speed to 3rd gear speed.
   
8. With the layshaft now at the correct speed for 3rd gear you disengage clutch disconnecting the layshaft from the engine.
   
9. You change to 3rd and with the layshaft and gearset at a matched speed, the teeth mesh and the gear goes in.
   
10. you release the clutch connecting the engine to the layshaft.
    

Sounds complicated but it's pretty simple. It can be simplified to:

 

"Changing up: Release throttle as you depress the clutch as normal, with the throttle still at idle shift to neutral let the clutch up briefly with the throttle still at idle, this uses the engine to slow down the layshaft, then clutch down shift into new gear and clutch up and depress throttle as usual."

 

Changing down is simplified to:

 

"Changing down: A bit harder: Shift to neutral, let the clutch up and blip the throttle - how much is a bit of a knack but it feels good when you get it right, this gets the gears spinning at the higher speed needed for the low gear. Clutch down and shift to new gear as usual."

 

 

 

 

 

Sorry I rambled on

 

Best workaround I've read, and I work in IT, so I see workarounds all day long.

[Husky]

Thanks Husky, that will help until I can get it fixed at the garage!

 

I had the same problem with my gearbox just with 5th/6th gears. I ended up getting a used box fitted. The swarf that came out my box was pretty horrific I'm told, it got scrapped as it wasn't even worth refurbing.

[Husky]

Best workaround I've read, and I work in IT, so I see workarounds all day long.

 

Haha, I work in automotive control systems, so I deal with cars and lots of coding.

 

[ianboom]

£1k to fit a clutch which involves dropping the box plus parts and £1k to swap the box for a new one? Doesn't add up.

 

Was the box worse after the clutch was replaced?

 

Would be interesting to see how much a rebuild costs and what was wrong with the box :-)

[pmorg4]

Agreed on the labour price con... remove/refit a gearbox is a pretty straightforward job on most RWD cars, and they've already had the gearbox off to do the clutch.

[tomdnNissan]

Gearbox has been stripped now, synchros replaced and all working fine - this cost circa £1k, as opposed to the £4k that a Nissan dealer quoted to put in a new gearbox

[coldel]

Can we somehow make Husky's post a sticky!?

[ianboom]

Was that the drive in/out price?

 

The two things I don't like about my zed is the crxxpy box and the leather seats!

[tomdnNissan]

Yes, parts and labour was circa £1k.. I'd already previously paid another £1k though to have clutch replaced in Nissan dealership

[pmorg4]

Was that the drive in/out price?

 

The two things I don't like about my zed is the crxxpy box and the leather seats!

 

Interesting, I think the box is one of the best features of this car. It has a solid feel with no free play and a short throw.

 

I've had no issues with mine at all, I guess you just have to be smooth and steady with it, resisting the urge to change too quickly.

[ianboom]

Was that the drive in/out price?

 

The two things I don't like about my zed is the crxxpy box and the leather seats!

 

Interesting, I think the box is one of the best features of this car. It has a solid feel with no free play and a short throw.

 

I've had no issues with mine at all, I guess you just have to be smooth and steady with it, resisting the urge to change too quickly.

,

 

Fair comment, when my box changes smoothly from 1st to 2nd, it's great and I agree the short throw and feel of the box is really nice, it's just that frequent clunk as it goes in.

I've only owned my car from few months, it'll be interesting to see if it gets better in the warmer weather!

[Roscoe]

Mine is an 08 aswell and has always crunched slightly from first to second on cold mornings but learning to let it go through neutral with a slight pause on its way to second gear on cold mornings sorts it out. I personally think the gearbox has a nice feel to it, it's by no means a fast box though so a bit of mechanical sympathy between changes is always good

 

 

Sent from my iPhone using Tapatalk

[coldel]

Something I was never quite happy about on my zed was the gearbox, felt a little clunky and I had play in it - in the end just put up with it. It certainly wasn't as tight as a few other cars I have owned.