48 replies to this topic

[lemonaro]

A question for the gearbox specialists out there.

As the heading says when I move the lever into reverse the gearbox crunches, it's fine selecting any other gear.

The vehicle is a 253 VB Commodore, Aussie 4 speed.

I have only recently acquired the vehicle so don't know to much about the history of the car but can say the gear box oil is new (Penrite 80w-90), I have tried adjusting the cable clutch so am certain its not adjustment. Brand new clutch cable.

Is it worth trying another grade of oil?

I'm thinking clutch replacement but thought I would get a second opinion before I go spending a couple of hundred on a new clutch, machining flywheel and wrestling with a gearbox lying underneath the car on my back.

Any feedback would be much appreciated.

Thanks

[yel327]

Very old memory and don’t act quickly on this until others with more recent experience give you some tips.
I remember that I have had similar on an old WB, and I think the problem was a 6cyl clutch pedal operating V8 clutch so it wasn’t getting full clutch release. You’d get similar I guess with a poorly setup clutch which could be the fork pivot adjusted badly, the wrong throw out bearing or a worn clutch.
What you are describing tells me the input shaft is still spinning which makes the cluster gear spin. It won’t affect forward gears as much as they are already meshed with the cluster and selected via synchro rings and teeth. The reverse idler will be spinning with the cluster, and selecting reverse is done by meshing reverse gear with the idler, one of which is stationary and one moving. This a crunch.

The only other thing I can think of is possibly the circlip on 1st gear has done the normal trick and fallen apart damaging the main shaft so that 1st gear doesn’t spin freely on the shaft. It can cause 1st gear to begin to bind to the main shaft (rather than spin freely) causing the main shaft to have minor rotational force on it opposite to what reverse wants to when it meshes thus the crunch. It may not be this but I can’t think of many other ways.

[RallyRed]

Hi..just my uneducated experience..

If you can, with the car jacked up, or better still, up on a hoist -
Remove the moon shaped clutch cover.
Then do a few checks.
For Clutch connected to flywheel-
Can you put your fingers up in there and freely spin the thrust race...if so, you know the clutch is not being influenced by a tight cable, dodgey clutch fork setup when the pedal is not operated.
For Clutch operated( disconnected from flywheel)-
Careful now, with the engine running, and someone pressing the clutch pedal in, can you see the flywheel spinning?, but the gearbox input shaft not spinning?.
If not, you may find the clutch is not fully releasing?. Also may be the input shaft / crank end/ spiggot bushing is a bit tight?
And thus, even with the clutch fully released, there is a little bit of torque transmitted to the box, making the shafts spin?
Had this recently in the fwd gears,and found a warped clutch plate (1) was dragging on the flywheel and causing the crunch...but then also found a trashed syncro (2)..not sure if 1 caused 2.
Think so
I have also found that oil can be the issue..so ensure that the oil is as per GMH specs.
The other old trick is to always briefly stick it in 2nd, partialy let the clutch out,before selecting Reverse ( assume it stops the shafts spinning? and thus stops crunching.
Like I said, just my shed experience.

[S pack]

A question for the gearbox specialists out there.

As the heading says when I move the lever into reverse the gearbox crunches, it's fine selecting any other gear.

Reckon it will be the clutch is not fully disengaging.

[Bigfella237]

Almost certainly either a clutch or spigot bush problem. I'd definitely rule-out those before delving deeper anyway. Don't see much point buying a new clutch kit as your problem isn't clamping, in fact just the opposite, it sounds like the clutch is dragging.

 

So, I have to ask, is this a factory V8 4 speed car or has someone been 'playing'?

 

How far off the floor does the pedal get before the clutch starts to take-up (IE before the car starts to move)?

[lemonaro]

Almost certainly either a clutch or spigot bush problem. I'd definitely rule-out those before delving deeper anyway. Don't see much point buying a new clutch kit as your problem isn't clamping, in fact just the opposite, it sounds like the clutch is dragging.

 

So, I have to ask, is this a factory V8 4 speed car or has someone been 'playing'?

 

How far off the floor does the pedal get before the clutch starts to take-up (IE before the car starts to move)?

Thanks to all that have replied.

I have tried the trick of depressing the clutch pedal and selecting 2nd, then with the clutch pedal still depressed selecting reverse and the gear still crunching.

This I assume is a sign that the clutch is dragging/input shaft still spinning?

Car is original v8 4 speed and doesn't look like it's been played with.

Clutch used to take up just before the pedal was fully released but since I adjusted it as per factory specs it's about half way, still crunches as before adjustment.

Bigfella you mention (don't see much point buying a new clutch kit as your problem isn't clamping infact just the opposite, it sounds like the clutch is dragging) 

What could cause possible dragging? Spigot bush? Clutch pressure plate faulty?

This issue prevented me from getting the car registered. I had to get the car inspected as was purchased interstate. Failed the inspection because it crunches when selecting reverse gear, didn't think crunching into reverse would effect road worthiness especially in a 40 yr old car!

Edited by lemonaro, 02 February 2023 - 11:08 PM.

[76lxhatch]

To add some more possibilities to check, it is also possible to over-travel the clutch release and have it make contact that causes some movement, or if the clutch is coming apart it may not be releasing completely. I would start with the spigot bushing though as others have mentioned, may just need fresh lubrication or perhaps replacing.

 

If it were me I'd remove the inspection cover and try moving things around manually (engine not running) to see where the drag is, while a helper releases the clutch to varying degrees. It should be possible to turn the clutch by hand easily enough with the box in neutral, watch your fingers.

 

If the crunching is bad then you will also experience some difficulty getting into forward gears, presumably the inspection failed as they see as an indicator of clutch failure. However if its only really minor it could be simply technique, even with everything perfect you can cause this by rushing it into reverse while gears are still spinning.

[Bruiser]

How much free play in the pedal do you have at the top of the pedal travel?

[Bigfella237]

~. It should be possible to turn the clutch by hand easily enough with the box in neutral, watch your fingers. ~

Or with the rear wheels raised, have your helper disengage the clutch (engine NOT running), engage a gear, then turn the tailshaft by hand to see if the clutch plate is spinning freely between the flywheel and pressure plate.

 

I wouldn't have thought that crunching into reverse was grounds for a rego inspection knock-back, the guy must've had a bad day, or he was trying to drum-up some work?

[UCSLE]

how did you adjust the clutch , was it just the cable or the pivot point on bell housing  ?

 

set the pivot point if you haven't 

[lemonaro]

How much free play in the pedal do you have at the top of the pedal travel?

About 40mm

[lemonaro]

how did you adjust the clutch , was it just the cable or the pivot point on bell housing  ?

 

set the pivot point if you haven't 

roughly checked pivot point on bell housing and looks to be in specs, my manual says 48mm and my rough measurements are around that.

Cable adjusted as per manual also 168mm pedal to floor, I've played with the cable adjustment trying longer and shorted with out any better results.

[lemonaro]

I've taken the inspection cover off as some have suggested and with my helper engaging the clutch and selecting the gears the clutch plate seems free to spin by hand, even by turning the tail shaft whilst in gear and foot on the clutch the clutch plate turns freely.

With motor running clutch depressed the plate spins but as you select the gear the plate stops.

thanks for all the reply's, much appreciated

[Bruiser]

May have been better to say how much freeplay at the end of the clutch lever ( where the cable joins)
In your adjusting back and forth, did you get to the point where the play disappears completely?
As in the thrust bearing contacting the pressure plate springs?
Too tight and the clutch thinks you’re riding it, and might be just engaged enough to slip under power and wear everything out quicker.
Too loose you might not be able to disengage the clutch enough, and crunchcrunch
I’ve always set mine just back from there so there is only minimal play so the fork will move with the cable as much as possible
disengaging the clutch as much as possible

[Potta]

I had a cable setup on my old four door and I had this issue if I wasn't able to get enough clutch disengagement.

 

Was fine in forward gears, but reverse needs just a bit more.....

 

I made a spacer out of a bottle top which fixed the issue by taking the flop out of the cable and I think it was still on there when I sold the car.

 

I kept popping the end off the cable though, which was annoying...

 

So to summarise, you might just need a bit more travel, ie need the pedal to start moving the clutch a little bit earlier in the travel.

[lemonaro]

Just an update for those curious or those that have this problem in the future, after spending ages adjusting the clutch and getting my assistant to push down on the clutch and try and work out why the input shaft was spinning whilst clutch was engaged I decided to pull the box out, look at the clutch and remove the spigot.

No obvious issues I can find with the clutch or spigot but I think the clutch has over 150k on it so thought I'd replace it for peace of mind. Ordered a gasket n seal kit for the box so will pull the side cover off and see if there are any obvious issues inside.

Work, holidays and life will consume my time for the next few months so probably won't get to play with the car for a while.

Will keep those interested updated as things progress.

[RallyRed]

Ta for the update
Thinkin' you mean "..while disengaged"?
Just for reference, here was mine that was dragging a little due to warp. Bit hard to see.
Also checed face of Flywheel ( basic).
Good luck with it.

Attached Files

•  Screenshot_20230203-093959_Gallery.jpg   134.31K   2 downloads
•  Screenshot_20230203-094059_Gallery.jpg   68.65K   1 downloads

[yel327]

Just an update for those curious or those that have this problem in the future, after spending ages adjusting the clutch and getting my assistant to push down on the clutch and try and work out why the input shaft was spinning whilst clutch was engaged I decided to pull the box out, look at the clutch and remove the spigot.

No obvious issues I can find with the clutch or spigot but I think the clutch has over 150k on it so thought I'd replace it for peace of mind. Ordered a gasket n seal kit for the box so will pull the side cover off and see if there are any obvious issues inside.

Work, holidays and life will consume my time for the next few months so probably won't get to play with the car for a while.

Will keep those interested updated as things progress.

 

 

You may be able to see some obvious issues with the side cover off like 1st gear dog teeth. But you won't find the issues that kill these most. Case hardening wearing off the counter/cluster gear and also off the inside of the clutch gear (input shaft). Plus, the circlip on 1st gear Whilst it is out it is worth buying a small parts kit and pulling it apart for a look. 

[Bruiser]

Good on yer for the update, and thanks. I hate getting interested and never finding out the answer
Hope you find time to have a go sooner than expected and that it fixes up your problem for you.
Hope to hear the good news soon
Good luck

[lemonaro]

Ta for the update
Thinkin' you mean "..while disengaged"?
Just for reference, here was mine that was dragging a little due to warp. Bit hard to see.
Also checed face of Flywheel ( basic).
Good luck with it.

Have checked for any warpage but nothing really obvious apart from some ill regular wear patterns on the pressure plate

[lemonaro]

You may be able to see some obvious issues with the side cover off like 1st gear dog teeth. But you won't find the issues that kill these most. Case hardening wearing off the counter/cluster gear and also off the inside of the clutch gear (input shaft). Plus, the circlip on 1st gear Whilst it is out it is worth buying a small parts kit and pulling it apart for a look. 

Thanks for the advice about pulling it apart but I'm struggling for room, Most of the work im doing is on the ground, I have stuff all room to work in and my work bench isn't much of a bench. The wife won't let me bring the gearbox into the dinning room!

Im still thinking the problem is from the input shaft/clutch plate dragging so see how I go with that. If I notice anything with the side cover off then I'll reassess my  approach with the gearbox.

[lemonaro]

Attached Files

•  drive1.jpg   233.25K   0 downloads

Edited by lemonaro, 07 February 2023 - 10:20 PM.

[lemonaro]

 flywheel1.jpg   203.66K   0 downloads  flywheel1.jpg   203.66K   0 downloads

Edited by lemonaro, 07 February 2023 - 10:37 PM.

[lemonaro]

 pressure1.jpg   194.54K   0 downloads

pressure plate has ill regular wear around it but not sure that would cause my issue

Edited by lemonaro, 07 February 2023 - 10:48 PM.

[lemonaro]

 input1.jpg   142.7K   2 downloads

To much grease on input shaft?
 

 back.jpg   191.28K   0 downloads

wear on the spring fingers is ever so slightly uneven

Edited by lemonaro, 07 February 2023 - 10:52 PM.