D7R parkbrake not releasing

[Alan Tute]

D7R Dozer park brakes not fully releasing due to having only 340-370psi hydraulic pressure at test ports both left & right brakes have identical same low pressure. When the dozer is up to operating temp the pressure at test ports does not alter.

 

[Nige]

First thing as usual - Serial Number..?
How did the problem start. Suddenly, got worse over time, etc, etc..?
Any recent repairs or service work..? The recent repairs don't necessarily have to be brake-related.

 

[Alan Tute]

Have only just purchased dozer at auction and put it to work so history is an unknown apart from cat history saying there have been no major faults recorded and service history shows been well looked after. Will supply serial number as soon as i can.

 

[Andre van Greunen]

What was the cause of parkbrakes not releasing?
I have a similar problem. The oil for the brakes is coming from the transmission valve block priority valve to the parkbrake valve

 

[R.D.G013]

I have been on a D 7 R2 LGP recently that that has a habit of grabbing its brakes momentarily when shifting from fwd to rev or vice versa and sometimes when upshifting from 1 st to 2nd, won't do it all the time only intermittently, any ideas Nige ?. Our fitters are at a loss as to what it is, cant get the S/N at the moment coz Im not on it but will be in a couple of weeks,Cheers.

 

[Nige]

Don't need a Serial Number at this stage. To me that's an indication of a pump that is struggling to keep up with flow requirements. When the oil gets dumped from the transmission clutches during a shift and the pump is being required to supply oil to keep the brakes released plus at the same time to fill the clutches up again for whatever gear is selected, it momentarily cr@ps out on flow until the transmission clutches engage. Result - the brakes grab momentarily. I bet it doesn't do it when the tractor is cold, right..? Edit: Yeah I know it never gets cold in Brizvegas but you know what I mean.......

For me - full powertrain pressure test (converter, transmission, brakes) and report back with numbers. Do some transnmission shifts and see both how far the pressures dip and how long it takes them to recover. If your gauges are glycerine-damped it may be difficult to spot.

 

[Mark250]

No serial number, but has the transmission accumulator been checked. low charge pressure or an accumulator with oil on the wrong side can cause similar problems
Mark

 

[Andre van Greunen]

Hi Nige
I tend to agree with you. Check the pressure with a Psi gauge. If its lower than spec its best is to remove the pump, strip and check for worn housings.

 

[R.D.G013]

Yep Nige is right it doesn't do it when its cold, only when its at operating temp. Will have to get on to the fitters when I get back on it, on a 9 R at the moment. Thanks for all of your in put.CHEERS.

 

[Andre van Greunen]

The D7R is it electronic transmission?
The D7R I have the same problem is non electronic 2012 model. Lever gear selection.
Do you have hyd schematic for non electronic transmission? S/N DSH00189

 

[Nige]

Yep Nige is right it doesn't do it when its cold, only when its at operating temp. Will have to get on to the fitters when I get back on it, on a 9 R at the moment. Thanks for all of your input. CHEERS.

Here's another thought. Brake piston seal leakage..? Might be worthwhile pumping up each brake individually to check to see if the piston seals are holding OK.

 

[Andre van Greunen]

Check dead end pressure on the pipe leading to the footbrake valve.
Seems the piping on the electronic and non electronic teansmission is different.
Non electronic from transmission to parkbrake.
Electronic transmission pipe from transmission goes to the footbrake valve.

 

[R.D.G013]

Don't need a Serial Number at this stage. To me that's an indication of a pump that is struggling to keep up with flow requirements. When the oil gets dumped from the transmission clutches during a shift and the pump is being required to supply oil to keep the brakes released plus at the same time to fill the clutches up again for whatever gear is selected, it momentarily cr@ps out on flow until the transmission clutches engage. Result - the brakes grab momentarily. I bet it doesn't do it when the tractor is cold, right..? Edit: Yeah I know it never gets cold in Brizvegas but you know what I mean.......

For me - full powertrain pressure test (converter, transmission, brakes) and report back with numbers. Do some transnmission shifts and see both how far the pressures dip and how long it takes them to recover. If your gauges are glycerine-damped it may be difficult to spot.

Well finally some action, fitter came and pressure test the accumulator, put a 500 psi gauge on and it bent the needle when it hit the 500 mark so who knows what was in it, bleed it offf to 250 and it shifts like a dream, only taken 4 yrs LOL.

 

[R.D.G013]

No serial number, but has the transmission accumulator been checked. low charge pressure or an accumulator with oil on the wrong side can cause similar problems
Mark

Well finally some action, fitter came and put a 500 psi gauge on the accumulator and it bent the needle when it hit 500 so who knows what was in it. Bled it off to 250 psi and it shifts like a dream, only taken 4 yrs of moaning to get this to happen, LOL.

 

[Nige]

Jeez, that must be a record, even for HEF.........

 

[Andre van Greunen]

400psi measure it on the priority valve tap on the transmission housing, thats what the brakes need to release once the parkbrake is off.
Sounds familiar hey Nige?

 

[Nige]

A bit like the Indian guy who lives just up the road from me - Bindair Dundat......

 

[Andre van Greunen]

Yes been down that road.
What keeps you busy, no time to retire?

 

[Danny63]

I’m having an issue with a D7R type 2. Issue I am having is the machine will not move in forward and reverse. Only time it moves is in forward on second gear. Machine does not go in reverse in any gears or forward in 1st or 3rd gear. Machine has no active codes. I have flashed the ECM and have also recalibrated the transmission solenoids. Transmission oil is new and at the right level and oil temperature stays in normal operating temperature. CAT ET shows that the parking brake disengages aswell

 

[Andre van Greunen]

Remove the screen, check for debri, metal and clutch material. Remove filter cut open check for metal and clutch material. If you find any debri, remove, transmission, torque converter, pump, oilcooler and pipes...... Strip and rebuild.