ZF 6 speed Transmission Question

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gapfilms
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ZF 6 speed Transmission Question

Post by gapfilms »

I was talking to a fellow bus owner the other day and he told me that ZF 6 speed transmissions have a problem with water (coolant) getting into them. He said he has know several buses that have had water loss issues and the water has turned up in the transmission but only in the 6 speeds.

My bus an RN Hino slowly looses water and I don't know where it is going. It also has a 6 speed ZF transmission in it as well. Is there anyone out there that has heard of this or experienced this problem before?
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Andrew
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Re: ZF 6 speed Transmission Question

Post by Andrew »

Have you checked the gearbox fluid? If water was in it , I assume like engine oil it would turn the gearbox fluid into a creamy colour/consistency...
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ZF 6 speed Transmission Question

Post by mrobsessed »

Also, if the coolant level in the header tank is too high, it could be coming out of the overflow.
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Re: ZF 6 speed Transmission Question

Post by Maladjusted »

The coolers do leak trans fluid into the coolant not usually the other way. However anything is possible, if water or coolant gets into the box then it will unglue the clutch linings off the plates quicker than you can say "Bugger". If water is getting in then perhaps it could be through the dipstick/filler.

With the Hino losing water does it only get down to a certain level and then stops or just keeps going and empties the tank? It could be lots of places leaking the water, even down or up to the a/conditioning or floor heaters, water pump, the list goes on.
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gapfilms
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Re: ZF 6 speed Transmission Question

Post by gapfilms »

Thanks all for your replies.
I haven't yet check the transmission fluid as I was told that it doesn't make the fluid go milky it evaporates or something like that as it is only a small amount going in at a time??? I did think that was strange but not sure, hence why I have made this post.

The coolant level drops slowly over about a month or two. When I pull out of my yard the bus rolls on the air bags and the low coolant warning buzzer will trip for a brief second. I top the coolant back up again and it will last for about a month or so before doing it again. I have checked for leaks and nothing, well a slight weep on one joint but that has been fixed but the coolant still slowly drops.

Hino know about this problem with some of there buses but don't have the answer why. The bus is only a year and a half old and has been doing it since new. Fortunately it is still under warranty for a little while longer....however Hino have most certainly not impressed me with there after sales service...but lest not go there :(

I am going to get back to the person that told me of this problem and see if I can track down the owners of these buses to get there input. Also thought of dropping some tranny fluid and getting it tested.

I am grateful for anyone that has any further input to this.
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Daz
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Re: ZF 6 speed Transmission Question

Post by Daz »

All the Hino's I've driven drink a bit of water, but I think thats because they run very hot as standard and evaporate a bit.

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gapfilms
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Re: ZF 6 speed Transmission Question

Post by gapfilms »

Hey all, I have looked further into this problem.
After speaking to ZF they said the buses that had experienced this problem had transmission breather issues. It was believed water ingestion was through the breather on a type of Volvo body. Breather extensions were fitted to fix this.

Now I paid real good attention to my buses transmission gear changes and could not notice 6 specific changes but only 5, with the exception of a small gear change (200 rpm) in the first gear...maybe a converter lock up. I slipped under the bus and had a look at the compliance plate on the transmission. It turns out that I have the 5 speed 5HP502C transmission so I should be pretty save here.

Now here is the interesting thing, I went back to the specs. sheet supplied by the bus seller and it clearly says....
"Automatic, six forward and one reverse speed with integrated retarder"

Makes you wonder how much you can trust your suppliers glossy brochures.

Thanks all for your inputs.
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Re: ZF 6 speed Transmission Question

Post by Maladjusted »

Thanks Gapfilms for giving an update, Looks like the salesman is the one who can't be believed maybe? The ZF breather is the dipstick/filler tube as well.
Perhaps with the radiator/coolant loss put a bottle on the end of the overflow off the pressure relief cap and see how much coolant is collected out of that. You may be surprised how much water is lost. It would be good if it was just water too with it more than likely being glycol, over a period of time it could end up being expensive topups!
The fleet of buses I used to look after i would put coolant in them and try to maintain them that way. However the owner used to top up with the same amount of plain water every day to the top of the neck, the bus would then dump that water when it got hot back down to its normal level and over a short period of time all the coolant was diluted to become ineffectual.
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Re: ZF 6 speed Transmission Question

Post by Daz »

Ineffectual.

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gapfilms
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Re: ZF 6 speed Transmission Question

Post by gapfilms »

Thanks Daz.
Yeah I don't top up to the top of the neck, I go to the Max line on the header tank.
I will try the bottle idea to see if it is purging water out the expansion hose, that way I can see if that is the problem. It doesn't use to much but if the level gets to low the coolant level alarm will sound when I turn a sharp corner, about every few months. It maybe like you said as these engines run hot they may evaporate a little bit off and the header tank is not very big either. Although the bus does take forever to warm up in the mornings and the engine de-rates until it's at operational temperature. A pain in the ass when I pull out onto a 110km HWY on an uphill pull, all those inpatient cars sitting up my ass :)...... arrr the joys of heavy vehicles.

I will try that second collection bottle idea and let you know.

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Bill2
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Re: ZF 6 speed Transmission Question

Post by Bill2 »

If there are no water leaks, the the lossof water will be via evaporation through a slow leak of the radiator cap seal. I suggest you have the cap tested.
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Re: ZF 6 speed Transmission Question

Post by User7526 »

If you people are topping up cooling systems with plain water then I will say as a mechanic that you ought to be shot, you will quite simply dilute the actual inhibitor/antifreeze level and then the whole system will slowly perish. If the coolant is getting into the inside of a 6 speed auto then you will be having a problem with the transmission oil cooler and this needs to be sorted ASAP, if it is a 6 speed manual ZF it will not be using an oil cooler on the transmission so no coolant is expected to be inside that casing at all.

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Re: ZF 6 speed Transmission Question

Post by Guy_Arab »

If it is a five speed box I will check my Manual to see what it says
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Re: ZF 6 speed Transmission Question

Post by Guy_Arab »

Guy_Arab wrote:If it is a five speed box I will check my Manual to see what it says
Guy Arab
If you where told it was six speed According to Manual it could be a five speed with a emergency switch
I can not find any quote on your problem in manual
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Re: ZF 6 speed Transmission Question

Post by azz419 »

We have 17 various Hinos in our fleet (BD, FD1J, FD8J, RK, RG, RN) and almost all of them use some coolant. The RG and RN models with the large high pressurized header tank all lose alot from the overflow, to the point where the buzzer sounds when cornering, only solution we have found is to top up every so often, but no so much that it's wasted on the ground. I agree with you also that the RN's are pathetically gutless. My daily driver is an 01 RG with Express body and considering the tiny engine it goes like a rocket, even loaded. A 12 month old RN with 6 speed ZF auto and Express bodywork is down to 50km/h on a 6% gradient unloaded, the RG will do 80 up the same hill full of kids... To add insult to injury the RN uses alot more fuel.
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Re: ZF 6 speed Transmission Question

Post by drpeps »

azz419 wrote:We have 17 various Hinos in our fleet (BD, FD1J, FD8J, RK, RG, RN) and almost all of them use some coolant. The RG and RN models with the large high pressurized header tank all lose alot from the overflow, to the point where the buzzer sounds when cornering, only solution we have found is to top up every so often, but no so much that it's wasted on the ground.
Why doesn't the overflow go into a receiver tank instead of to ground? When the coolant cools it is sucked back into the radiator. This way the header tank is always full.
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