Manitou MLT 633 steering problems

[Corné de Jong]

Hello,

I am New here and maybe somebody can help me.
Since the last time our manitou have kind of steering problems but it seems to i will be more worse.

Hydrauliek works fine, but when machine is Cold steering wheels somethines stuck and steering go's very heavy, this is then for probberly 5 or 10 minutes after that steering works ok and no problems. First i thougt that it has something to do with the cold whether but also now we have troubles and it becames more/longer.

I think there is maybe something wrong with the priority steering valve at the main control valve but is here maybe someone Who can advise how to handle or what to do?

Regards,

Corné

 

[David Bliss]

I know nothing of how the system works on a Manitou, If it does have a diverter valve to use the oil flow from the main pump? Yes it could be that, however by what you said it gets better as warms up, but now getting worse, is it just a blocked filter, when was that last changed.

 

[TripleSix]

Probably the priority valve.

If you work the joystick does the steering get better?

 

[ACEngineering]

Hello,

I am New here and maybe somebody can help me.
Since the last time our manitou have kind of steering problems but it seems to i will be more worse.

Hydrauliek works fine, but when machine is Cold steering wheels somethines stuck and steering go's very heavy, this is then for probberly 5 or 10 minutes after that steering works ok and no problems. First i thougt that it has something to do with the cold whether but also now we have troubles and it becames more/longer.

I think there is maybe something wrong with the priority steering valve at the main control valve but is here maybe someone Who can advise how to handle or what to do?

Regards,

Corné

When posting you are missing a key bit of information, EXACT model number and spec.

alot of mlt 633 are 120 LS which are a totally different hyd system. I'm guessing you have a lower spec MLT 633 Turbo possibly will say Mono ultra in small print on the serial plate and will have a casappa gear pump, these are common to get heavy steering caused by the steering prority valve on the back of the main hydraulic pump, normally while holding a hyd service under full pressure then the steering will work better and is the classic sign of priority valve sticking.

With this problem it is better to replace the whole pump and valve as an assembly, clean the hyd tank out, change the return filter and new oil. Just replacing the valve on it own may only fix it for a short time and the valve was at one point more money than the whole pump assembly!

 

[Corné de Jong]

When posting you are missing a key bit of information, EXACT model number and spec.

alot of mlt 633 are 120 LS which are a totally different hyd system. I'm guessing you have a lower spec MLT 633 Turbo possibly will say Mono ultra in small print on the serial plate and will have a casappa gear pump, these are common to get heavy steering caused by the steering prority valve on the back of the main hydraulic pump, normally while holding a hyd service under full pressure then the steering will work better and is the classic sign of priority valve sticking.

With this problem it is better to replace the whole pump and valve as an assembly, clean the hyd tank out, change the return filter and new oil. Just replacing the valve on it own may only fix it for a short time and the valve was at one point more money than the whole pump assembly!

Hello,
Sorry you are richt! Our manitou is an manitou 633 120LS With serial number 178599 from 2002.
This type has an plunger pump, and for so far i can see it is the priority valve located the back of the main control valve

Pressure of main pump is ok, low idle around 190 bar en above 1500 rev 280 bar so this looks good, and hydrauliek feels also good .
Only problem for now is steering stucks when cold, en somethines when you lift heavy or relief an function you can feel this in your joystick it looks life if somethines high pressure enter the pilot pressure .

Is there something i can check or can Do? Because replacement of the back from control valve is very epensive and a lot of work because control valve needs to take out completely

 

[ACEngineering]

Hello,
Sorry you are richt! Our manitou is an manitou 633 120LS With serial number 178599 from 2002.
This type has an plunger pump, and for so far i can see it is the priority valve located the back of the main control valve

Pressure of main pump is ok, low idle around 190 bar en above 1500 rev 280 bar so this looks good, and hydrauliek feels also good .
Only problem for now is steering stucks when cold, en somethines when you lift heavy or relief an function you can feel this in your joystick it looks life if somethines high pressure enter the pilot pressure .

Is there something i can check or can Do? Because replacement of the back from control valve is very epensive and a lot of work because control valve needs to take out completely

okay these work very differently.

first thing you measure on pump is the standby pressure which is 19bar +/- 1bar you can do this on the main test port BUT you will get pressure spikes from using steering/brakes or anything else so try not to touch anything. Ideally you need a digital gauge to test this accurately with out damaging a normal low pressure gauge. This standby pressure is critical and has to be correct for anything to work correctly.

Main pump pressure is 270bar and you should be getting this at all rpm including idle speed, use aux or main lift to test this pressure. You definalty should not be getting 190bar at engine idle speed.

Steering pressure i think you can see that too on the main test port which i think roughly is 160bar

Yes the steering priority valve is located in the main inlet section of the spool block/valve bank, under a big hex plug that sticks out. you can remove that and use some fine wet and dry paper to polish it BUT if you will probably end up having to replace the inlet section which will be expensive and means taking the whole spool block off the machine.

If it isnt the problem then you will need to be looking at the steering orbital unit under the dash.

 

[ACEngineering]

standby pressure adjuster is the top adjuster on the pump. Main pressure adjuster is on the inlet section of the spool block.

Do not adjust the bottom adjuster on the pump, this is set higher than main relief valve at 290bar and not used.

 

[Corné de Jong]

thank you for this information! this is helpful.

I think the measure point for checking standby pressure/main pressure is located also at the priority valve on the main control valve?
do I have measure the standby pressure with low or high RPm or should this be in all range the same?

strange about the main pressures, when we buy this manitou the sales guy noticed that this was normal that here is an shifting in the hyd. power around 1500 rpm because otherwise the engine has to less engine power when pump gives max pressure/litres at low idle, you can also mark up when you relief an function with low idle and you give more throttle to 1500 rpm that hydrauliek load is more, it looks like if the pump then makes a sihifting step in a bigger angle or something. but this is not normal then?

I Will remeasure the standby-pressures and high pressure and will discuss that then later.
for brake/steering use they the same outlet port for the priority valve? because also sometimes when oil is hot and you operate everything like boom raise, steering and braking the brake pedal sometimes would push back to neutral, further braking operation is Ok.

First I will measure al pressures, and maybe I can take out the priority spool and make it proper, but even then I think disassembling of control valve is needed to remove the big hexagon? because that hexagon is located at the underside of the control valve?

 

[ACEngineering]

thank you for this information! this is helpful.

I think the measure point for checking standby pressure/main pressure is located also at the priority valve on the main control valve?
do I have measure the standby pressure with low or high RPm or should this be in all range the same?

strange about the main pressures, when we buy this manitou the sales guy noticed that this was normal that here is an shifting in the hyd. power around 1500 rpm because otherwise the engine has to less engine power when pump gives max pressure/litres at low idle, you can also mark up when you relief an function with low idle and you give more throttle to 1500 rpm that hydrauliek load is more, it looks like if the pump then makes a sihifting step in a bigger angle or something. but this is not normal then?

I Will remeasure the standby-pressures and high pressure and will discuss that then later.
for brake/steering use they the same outlet port for the priority valve? because also sometimes when oil is hot and you operate everything like boom raise, steering and braking the brake pedal sometimes would push back to neutral, further braking operation is Ok.

First I will measure al pressures, and maybe I can take out the priority spool and make it proper, but even then I think disassembling of control valve is needed to remove the big hexagon? because that hexagon is located at the underside of the control valve?

standby you measure at engine idle.

the system you are discribing is the later machine MLT 634 onwards with the electric solenoid on the pump to control flow. A MLT 633 LS (you dont actually have a 120hp model which is very odd given it is an LS model) wont have that system so the pump has no idea what the engine rpm is, it only works off the hydraulic load sense line to the pump which tells the swash plate in the pump what to do once you start to demand oil from the pump.

 

[ACEngineering]

thank you for this information! this is helpful.

I think the measure point for checking standby pressure/main pressure is located also at the priority valve on the main control valve?
do I have measure the standby pressure with low or high RPm or should this be in all range the same?

strange about the main pressures, when we buy this manitou the sales guy noticed that this was normal that here is an shifting in the hyd. power around 1500 rpm because otherwise the engine has to less engine power when pump gives max pressure/litres at low idle, you can also mark up when you relief an function with low idle and you give more throttle to 1500 rpm that hydrauliek load is more, it looks like if the pump then makes a sihifting step in a bigger angle or something. but this is not normal then?

I Will remeasure the standby-pressures and high pressure and will discuss that then later.
for brake/steering use they the same outlet port for the priority valve? because also sometimes when oil is hot and you operate everything like boom raise, steering and braking the brake pedal sometimes would push back to neutral, further braking operation is Ok.

First I will measure al pressures, and maybe I can take out the priority spool and make it proper, but even then I think disassembling of control valve is needed to remove the big hexagon? because that hexagon is located at the underside of the control valve?

yes i forgot valve is on the underside of the block so not as easy to get too as i remember.

 

[Corné de Jong]

Hi,

sorry for late replay it was a little busy the last few weeks.

yesterday i've checked all pressures etc.
LS pressure was around 17 bar at Low idle, adjusted it to 19 bar.
main pressure was around 260 adjusted to 275 bar at high idle.
pilot pressure is 40 bar (brake circuit is also 40 bar)
during stall steering is around 140-150 bar.
so this looks not very weird I think, also operations are smooth and fast.

steering now also give not problems, but the problems where there not always but only sometimes when oil is cold.

so for now we will look if the steering stays ok.

but a latest question, if I indeed have problems with an sticking priority valve can this damage the main pump because priority valve is before main relief valve? or can the oil go to somewhere else? because when the only complaint is that steering sometimes stuck after cold start is that for us not an very big complain because when you left your steering wheel for approx 30 sec. after that everything works fine the rest of the day.

thank you for so far.