Gearbox Chugging At Idle

[Andrew_L26]

So when I did my manual conversion I noticed my gearbox has a significant chugging/whiring in neutral. It goes away when the clutch is depressed so it's not the throw out bearing. I've taken apart the trans expecting to find one of the bearings to be munted but they all seem fine. It would appear that it is these two gears fouling on each other.

 

 

 

I was thinking I could possibly grind down the side of the gear to stop them from touching but that seems extremely hack!

 

The synchros felt fine when driving the car but I was wondering if there is any easy way to check their condition (tolerances etc.)

 

Also, is there any way to tell the ratios from counting teeth etc. As it would be nice to know what this box is!

 

 

 

Edit*

To confirm its the upper step's side that is fouling on the other gear

 

 

Edited July 2, 2017 by Andrew_L26

[Simestime]

Mate i think you over thinking this.if the noise goes away when you put your foot on the clutch then its probably cluctch related.nothing in the gearbox changes when you depress the clutch only.is the thrust bearing collar the correct length? Was the flywheel machined?was the cluch kit new?correct weight oil in box?

Just my thoughts...

[Andrew_L26]

Mate i think you over thinking this.if the noise goes away when you put your foot on the clutch then its probably cluctch related.nothing in the gearbox changes when you depress the clutch only.is the thrust bearing collar the correct length? Was the flywheel machined?was the cluch kit new?correct weight oil in box?

Just my thoughts...

 

It was a brand new clutch and the flywheel was machined, the thrust bearing carrier is the correct length. The oil in it was whatever weight recommended by the factory service manual (can't remember what it is)

Why I think it's the gearbox is because when the clutch is depressed the gearbox stops spinning with the motor and the noise is only heard when the gearbox is spinning. When it is in gear and driving it doesn't make any noise. Also, with the trans removed the noise can be heard by turning the input shaft. 

 

Andrew

[CBR Jeff]

Andrew you are correct. If the gearbox is in nutral and the clutch is not depressed the gearbox still has rotating parts. When you depress the clutch you disingauge drive to the box and what was rotating stops.

 

Jeff

Edited July 2, 2017 by CBR Jeff

[Simestime]

Ok fair enough.thanks for saying that the noise can be heard when gearbox is out because my next thing i was gunna say was check the cluch is facing the right way.oh well ill stand down i cant help.

[Linton]

clutch out whirring, front gearbox bearing,  clutch in whirring thrust bearing.

but yeah they are pretty close. more investigation is required

Edited July 2, 2017 by Linton

[Agno]

I changed the spigot bearing in the crank and the throwout bearing last year chasing this noise to no avail. I spoke to an old hand about what it might be and he said it's probably just a bit of play on the input shaft bearing and it's no big deal.

[KatoKid]

Gearbox roll over noise is pretty common. You can replace bearings chasing this and still be the same.

[Andrew_L26]

Hmm, I have no idea, the bearings really seem to be pretty good so I might take it to a gearbox specialist and see if they have any idea.

[C.A.R.]

All your assumptions are incorrect Andrew.
You need to replace the input bearings, but while it's apart you might as well rebuild it with a full set of new bearings.

And FWIW, it's a (wide ratio 3.3 1st) 280ZX gearbox.

[Cozza]

And FWIW, it's a (wide ratio 3.3 1st) 280ZX gearbox.

The gearbox whisperer speaks.

How can you tell?

[Howdy]

G'Day Andrew, if the countershaft is pushed all the way back, 5th shouldn't be hitting reverse but this sometimes happens after pulling the housings off and the countershaft slides forward. I can't see any countershaft thread out the back of the nut but is hard to see from the side view, normally there is a little shaft showing or it is flush with the nut. If the nut is overhanging the countershaft, maybe there is something not quite right.

 

You can check alignment by bolting only the front bell-housing up and front cover with the countershaft shim (or no shim) installed (leave the extension housing off) tap forward both shafts and check there is clearance between 5th and reverse. If not you may have incorrectly installed spacers somewhere. There shouldn't be any grinding when you turn the main shaft. I reckon it will look right when you bolt the front up. Make sure you get measurement "A" right by using the correct countershaft shim and allow for any gasket you use on the front cover.

 

As the others said, if it is a quiet whiring sound, probably OK but if it is a whine and there are no chips, rust etc on the teeth, probably input shaft bearing. It is always important to put new, good quality bearings in while it is apart, especially if you have reasonable power because these boxes are not very strong. Worn bearings allow too much gear spread under load, especially 3rd gear, and is the reason for a lot of failures in my experience.

[Andrew_L26]

All your assumptions are incorrect Andrew.

You need to replace the input bearings, but while it's apart you might as well rebuild it with a full set of new bearings.

 

And FWIW, it's a (wide ratio 3.3 1st) 280ZX gearbox.

Thanks, where would I source a new set of bearings. Just match the part numbers on the bearings and order some quality replacements? I'm not wanting to spend stacks on this box as let's be realistic I purchased it for $150 and I might upgrade to a SR box as I'm hoping to be pushing 220KW at the wheels (Turbo L28)

 

How are you able to identify the box?

 

G'Day Andrew, if the countershaft is pushed all the way back, 5th shouldn't be hitting reverse but this sometimes happens after pulling the housings off and the countershaft slides forward. I can't see any countershaft thread out the back of the nut but is hard to see from the side view, normally there is a little shaft showing or it is flush with the nut. If the nut is overhanging the countershaft, maybe there is something not quite right.

 

You can check alignment by bolting only the front bell-housing up and front cover with the countershaft shim (or no shim) installed (leave the extension housing off) tap forward both shafts and check there is clearance between 5th and reverse. If not you may have incorrectly installed spacers somewhere. There shouldn't be any grinding when you turn the main shaft. I reckon it will look right when you bolt the front up. Make sure you get measurement "A" right by using the correct countershaft shim and allow for any gasket you use on the front cover.

 

As the others said, if it is a quiet whiring sound, probably OK but if it is a whine and there are no chips, rust etc on the teeth, probably input shaft bearing. It is always important to put new, good quality bearings in while it is apart, especially if you have reasonable power because these boxes are not very strong. Worn bearings allow too much gear spread under load, especially 3rd gear, and is the reason for a lot of failures in my experience.

 

I'll defiantly check all that and seriously look at some new bearings. There is a little rust on a few of the gears as well as one of the selector forks. There is a fair amount of pitting on the first gear (closest to bellhousing) on the countershaft, would this be the cause of the noise and is it an issue? I would imagine that it will wear the opposing gear quicker and possibly cause the tolerances to go out of whack over time leading to failure. There doesn't appear to be any chips in any of the gears however the oil that I put in it about a year ago (has probably done maybe 30Km on it, was really black and had plenty of metal shavings in it. the gearbox did have some sort of grease additive caked on the inside of the housing which had plenty of metal shavings in it. I will investigate further when I get home!

 

Thanks stacks for your replies!

Andrew

[Howdy]

Hey Andrew, black deposit is normal in a long service box and some small fine metal flakes like small hairs on the magnetic drain plug but not lots of metal shavings on the inside of the bell-housing. Work out if the shavings are alloy, brass, or magnetic - will give you and idea where they came from. Best to pull it apart and check the needle roller bearings and inner races which each gear rides on. The box may have been sitting for some time and surfaces have rusted.

 

That box will break the countershaft drive gear, 3rd gear or 5th with a turbo L28 @ 220 RWKW if you use the power a bit. An SR box in very good condition might last for a while but may eventually break 3rd or 5th gears after a bit of abuse. You can beef them up a bit by adding a heavy duty 11 ball bearing on the input shaft (std is 9 from memory) and a HD needle roller bearing (the contained type so it holds thrust) on the rear of the counter shaft and limit oil flow through the sandwich plate - late model SR boxes have a 1 way trap door to block flow towards the rear under acceleration which causes starvation of oil to 3rd. The bearings are available at most bearing suppliers.

[dat2kman]

Have you tried a different oil?

Plenty have filled with Redline Lightweight Shockroof 90, ( smurf blood) with very good results.

Gearbox rebuilders hate the stuff as it sticks everywhere inside the box, and is a bit hard to clean, on teardown.

 

This oil quite often solves a noise issue.

However, looking at bottom pic in your post, with red circle, IIRC there should be a spacer fitted before fifth countershaft gear, that lower gear usually does not sit that far forward..

Edited July 4, 2017 by dat2kman

[Andrew_L26]

 

Hey Andrew, black deposit is normal in a long service box and some small fine metal flakes like small hairs on the magnetic drain plug but not lots of metal shavings on the inside of the bell-housing. Work out if the shavings are alloy, brass, or magnetic - will give you and idea where they came from. Best to pull it apart and check the needle roller bearings and inner races which each gear rides on. The box may have been sitting for some time and surfaces have rusted.

 

That box will break the countershaft drive gear, 3rd gear or 5th with a turbo L28 @ 220 RWKW if you use the power a bit. An SR box in very good condition might last for a while but may eventually break 3rd or 5th gears after a bit of abuse. You can beef them up a bit by adding a heavy duty 11 ball bearing on the input shaft (std is 9 from memory) and a HD needle roller bearing (the contained type so it holds thrust) on the rear of the counter shaft and limit oil flow through the sandwich plate - late model SR boxes have a 1 way trap door to block flow towards the rear under acceleration which causes starvation of oil to 3rd. The bearings are available at most bearing suppliers.

 

Hmm ok, what about RB boxes such as the RB30 and RB20 (MF5) are they actually the same 71C or are they able to handle more power? What about the VL Turbo MX7 Boxes (I believe these are completely different but not sure)

 

 

 

Have you tried a different oil?

Plenty have filled with Redline Lightweight Shockroof 90, ( smurf blood) with very good results.

Gearbox rebuilders hate the stuff as it sticks everywhere inside the box, and is a bit hard to clean, on teardown.

 

This oil quite often solves a noise issue.

However, looking at bottom pic in your post, with red circle, IIRC there should be a spacer fitted before fifth countershaft gear, that lower gear usually does not sit that far forward..

 

 

That's what I was thinking. I'll check if the shim is missing but from memory I believe it is. I'll also check out some diff oil!

 

Thanks Guys!

Edited July 5, 2017 by Andrew_L26

[Andrew_L26]

"ACCIDENTAL POST*

Edited July 5, 2017 by Andrew_L26

[Howdy]

RB30 NA, RB20, RB20DET, SR20, SR20DET - pretty well all the same strength (gear widths wider so stronger than 280zx, 260 etc boxes) but differences in ratios and syncro arrangements). RB30ET, VG30DET & RB25DET = truck boxes - big and heavy, virtually unbreakable gears, bigger input & output shafts, crap 1st gear ratio except for pulling stumps, about the best box for the price for big HP. Can't put a L series belhousing on these boxes due to the physical size.

[aircobra]

i got EXACLTY the same problem , as soon as I press the clutch - all the noise goes 

so must be the front bearing, as per lurch's diagnostics. no other problems with box, no leaks, had new throw bearing fitted

couple of questions:

1. does anyone in melb do the rebuilds? prefer not to use warren, heard a few bad vibes

2. is this kit i need to get and does someone sell it locally? https://zcardepot.com/driveline/transmission/manual/5-speed-transmission-rebuild-kit-280z-280zx.html

[PB260Z]

, as per lurch's diagnostics.

1. does anyone in melb do the rebuilds? prefer not to use warren, heard a few bad vibes

 

Yes, Lurch (aka the gearbox wisperer) does.

[gav240z]

Lurch rebuilt my 260z close ratio box with 71C extension housing and put it in my 72 240z. He said gearbox feels great and car is going good now with Triples fitted. I'm still yet to have a go in it... ?

[dat2kman]

Lurch rebuilt my 260z close ratio box with 71C extension housing and put it in my 72 240z. He said gearbox feels great and car is going good now with Triples fitted. I'm still yet to have a go in it...

Sounds more like he used your bellhousing, and shoved into it, a Kameari equipped 71C cluster/ext housing.

[C.A.R.]

Sounds more like he used your bellhousing, and shoved into it, a Kameari equipped 71C cluster/ext housing.

 

 

[dat2kman]

Lurch,,,,

Master of Complication, Ba Hons, LLB, Letters, Dip Ed.

[C.A.R.]

Lurch,,,,

Master of Complication, Ba Hons, LLB, Letters, Dip Ed.

 

What do you want me to say, Jason?

Gav disclosed in the post above what I built for him, then YOU made an assumption - which is incorrect.

Hence my reaction.

 

How about YOU put yourself on the line & write an article / FAQ / Tutorial for this forum, instead of creating more white noise?

As you are so passionate about this subject, why don't you write an article about how to convert a 260Z CR box to brass syncro's.

I know you've performed this conversion before, so why don't you share your knowledge with the rest of us? Or are you going to come up with a excuse why you 'can't possibly do that'...?

 

As an aside, I DID fit a 260Z CR (2.9 1st) gear-set into a 71C long box for Gav.

It is possible & furthermore it's NOT the first time I've done it!!!

 

I've helped quite a few members of this forum with their gearbox issues, be it advice or actual work.

And i'm more than happy to help members in the future - all they have to do is ask.

Edited August 17, 2017 by Lurch ™