Crunching gearbox

[jensenoodle]

Hello all,
I have a ZF S5 17 5 speed gearbox in a 1964 Maserati Sebring. I have carefully rebuilt the gearbox with new baulk rings from Zf and new bearings.
The problem I have is crunching in 3rd and 4th gears but even stranger it crunches as I move OUT of those gears as well as in. It improves when warmed up and I would put it down to the rings not bedded in, perhaps even not made exactly to the same taper as the cone on the gears, but the coming out crunch I can’t understand. When stationary all gears select great.
I am about to try thinner oil, maybe 20/50 instead if the 80/90 recommended.
Hoping for ideas,
Thanks in anticipation
Keith

[Sebring440]

Sorry, I've no ideas, but they always were awful until fully warmed up. May get better with use?

[Belle427]

Sometimes there will be a more modern lubricant suitable for it from someone like Redline,finding out what it is may be your only problem.

[E-bmw]

"Back in the day" pretty much all Italian exotica were renowned for having gearboxes that were at best a bit baulky and crunchy until warmed up.

If it were mine I would NOT be straying away from the recommended oil unless it were a more advanced version, definitely not a thinner version unless you are talking about just to test if it makes a difference.

[GreenV8S]

Graunching on the way out of gears would worry me. I've mever known that to happen on a healthy 'box.

Is it unusually tight or stiff? If it continues past a couple of hundred miles I'd do an oil analysis to see whether you have any mechanical problems building up.

[jensenoodle]

Thanks to all helpers.
I thought it might be a tricky one to diagnose.
The stick moves freely enough and the interlock to prevent selection of more than one gear is ok.

[Lotobear]

Tried to PM you but your account is not accepting emails.

I would give Motorsport Transmissions a call and speak to Wayne - he does nothing but build ZF trannies for competition use all over the world and is a renowned expert (to the extent that ZF in Germany sometimes call him for advice on their old boxes).

016977 41800

[richhead]

E-bmw said:

"Back in the day" pretty much all Italian exotica were renowned for having gearboxes that were at best a bit baulky and crunchy until warmed up.

If it were mine I would NOT be straying away from the recommended oil unless it were a more advanced version, definitely not a thinner version unless you are talking about just to test if it makes a difference.

Thing is, back in the day alot of those cars used treacle as gearbox oil, ive had good success using much thinner but better lubricating modern oils in old ferrari's and the like, but do a gentle test first. Some of the oils we use in hypercars is like water.
I would try something like dexron 2 for a test, but dont blame me if it goes bang.
The problem is that the thicker oils need to be hot to get to the places that its needed.
On the modern race lmp stuff we regualy run gearbox oil and engine oil well over 120 degc, modern oils can take huge abuse before breaking down.
Obviously if its a transaxle then you need to take into account the diff requirements aswell.

[stevieturbo]

richhead said:

Thing is, back in the day alot of those cars used treacle as gearbox oil, ive had good success using much thinner but better lubricating modern oils in old ferrari's and the like, but do a gentle test first. Some of the oils we use in hypercars is like water.
I would try something like dexron 2 for a test, but dont blame me if it goes bang.
The problem is that the thicker oils need to be hot to get to the places that its needed.
On the modern race lmp stuff we regualy run gearbox oil and engine oil well over 120 degc, modern oils can take huge abuse before breaking down.
Obviously if its a transaxle then you need to take into account the diff requirements aswell.

White metal in a lot of old stuff is not compatible with modern ATF's. I can't imagine any Dexron being a good idea without proper confirmation of what is inside the box, what materials etc.

The OP mentions engine oils....so is that what was in these to start with ?

Although can't say I've ever heard of a trans crunching coming out of gear, that makes little sense.

[richhead]

stevieturbo said:

White metal in a lot of old stuff is not compatible with modern ATF's. I can't imagine any Dexron being a good idea without proper confirmation of what is inside the box, what materials etc.

.

Fair comment, didnt think of that.

[GreenV8S]

jensenoodle said:

The stick moves freely enough

I was referring to resistance to rotation of the lay shaft, not resistance in the shift mechanism.

If there was a lot of internal drag, that might cause gears to lose synch much quicker than normal.

[jensenoodle]

Thanks to all once more.
I disconnected the prop shaft and tried turning the output flange by hand, it isn’t stiff but it doesn’t spin totally freely, ZF told me that the lay shaft end float should be zero.
The synchro rings are made of yellow metal.
Sorry for the late response but I am not receiving email notifications when I get a response, need to look into that.

[GreenV8S]

jensenoodle said:

I have carefully rebuilt the gearbox with new baulk rings from Zf and new bearings.

Do you have the knowledge and experience to do that reliably? I imagine there's more to it than simply throwing parts at it.

[jensenoodle]

Yes, I’ve rebuilt several successfully and have made special tools to help, this one is giving me problems but I will get there.