Issue with differential, maybe PDAS related?
01-31-2019, 03:32 PM
#1
Issue with differential, maybe PDAS related?
Hi,
A few months ago I had the gearbox out of my 1990 C4 for a bit of maintenance. At the same time I also took the break calipers off for painting.
Ever since then I sometimes get the PDAS light on after about 10km of driving, it happens perhaps twice a month on average. I know that's probably because I need to get the hydraulic system professionally bleeded and I'm not too concerned about that, I'll get that done next time I'm near an OPC.
What I've noticed is that since having the work on the gearbox done (it was actually a seal replacement, so nothing too invasive) the car's performance is about 15% slower than before, that is I'm not reaching the same speeds in each gear as I was before.
A few days ago I needed to move the car by just a few inches, so rather than crank it up I pushed it, and it was so heavy I could just about move it! Even for a C4 that can't be normal. No wonder it's been slower!
So last weekend I lifted the car and had a look at everything; calipers are not seized; adjusted the handbreak just to make sure; bearings seem to be ok. But when I crank it up and put it in gear with the wheels off the ground in second and third gear from about 2400 rpms I can hear a faint griding noise which seems to be coming from the drive train somewhere in the center/front area. It sounds like a breakpad rubbing against the disc, so I pulled all the pads out and I could still hear it, although a bit fainter.
What makes me suspect a differential problem is that with all four wheels in the air, turning them by hand, they don't turn as I believe they should, as the following experiment shows:
Rear right and front right do not turn together (although they did after activating/disactivating the switch on the console)
Rear left and front left do turn togther (wheras these didn't after activating/disactivating the switch on the console)
Rear right and rear rear left do not turn together
Front right and front left do turn together (although with the engine running and in gear the front right turns much faster than the left)
* by "turn" i mean rotate/spin.
Other than this the car has no other symptoms. The ABS functions as it should, and the car generally runs very well, smooth; tyer wear is consistent; doesn't pull sideways or anything like that,
The only thing of note, although it may not be of any significance, is that while replacing the gear linkage bushings I noticed some metal shavings under the gear stick in the torque tube.
So my suspects fall onto:
1. Air in the PDAS/hydraulic system
2. Wheel bearings
3. Torque tube bearings
4. Differential
I've done a search and can't find anything like this. But maybe somebody else has had this problem, so any thoughts and opinions would be greatly appreciated.
Thanks in advance
A few months ago I had the gearbox out of my 1990 C4 for a bit of maintenance. At the same time I also took the break calipers off for painting.
Ever since then I sometimes get the PDAS light on after about 10km of driving, it happens perhaps twice a month on average. I know that's probably because I need to get the hydraulic system professionally bleeded and I'm not too concerned about that, I'll get that done next time I'm near an OPC.
What I've noticed is that since having the work on the gearbox done (it was actually a seal replacement, so nothing too invasive) the car's performance is about 15% slower than before, that is I'm not reaching the same speeds in each gear as I was before.
A few days ago I needed to move the car by just a few inches, so rather than crank it up I pushed it, and it was so heavy I could just about move it! Even for a C4 that can't be normal. No wonder it's been slower!
So last weekend I lifted the car and had a look at everything; calipers are not seized; adjusted the handbreak just to make sure; bearings seem to be ok. But when I crank it up and put it in gear with the wheels off the ground in second and third gear from about 2400 rpms I can hear a faint griding noise which seems to be coming from the drive train somewhere in the center/front area. It sounds like a breakpad rubbing against the disc, so I pulled all the pads out and I could still hear it, although a bit fainter.
What makes me suspect a differential problem is that with all four wheels in the air, turning them by hand, they don't turn as I believe they should, as the following experiment shows:
Rear right and front right do not turn together (although they did after activating/disactivating the switch on the console)
Rear left and front left do turn togther (wheras these didn't after activating/disactivating the switch on the console)
Rear right and rear rear left do not turn together
Front right and front left do turn together (although with the engine running and in gear the front right turns much faster than the left)
* by "turn" i mean rotate/spin.
Other than this the car has no other symptoms. The ABS functions as it should, and the car generally runs very well, smooth; tyer wear is consistent; doesn't pull sideways or anything like that,
The only thing of note, although it may not be of any significance, is that while replacing the gear linkage bushings I noticed some metal shavings under the gear stick in the torque tube.
So my suspects fall onto:
1. Air in the PDAS/hydraulic system
2. Wheel bearings
3. Torque tube bearings
4. Differential
I've done a search and can't find anything like this. But maybe somebody else has had this problem, so any thoughts and opinions would be greatly appreciated.
Thanks in advance
02-01-2019, 06:11 AM
#2
I would test whether your longitudinal is locked up when it shouldn’t be. (Or if there are any grinding noises)
Jack both front wheels off the ground (leaving rear wheels on the ground)
Spin both front wheels forward at the same time. You may need to have someone help you on the other side. (Be very careful doing it yourself from under the car! It can be done yourself if your arms are long enough)
The fronts should turn freely in the same direction at the same time. Maybe slight resistance. (It’s an important part of the test that they are turned at the same time as the front diff is open left to right...)
Then turn on the the diff lock switch and you should no longer be able to turn them both forward at the same time.
Jack both front wheels off the ground (leaving rear wheels on the ground)
Spin both front wheels forward at the same time. You may need to have someone help you on the other side. (Be very careful doing it yourself from under the car! It can be done yourself if your arms are long enough)
The fronts should turn freely in the same direction at the same time. Maybe slight resistance. (It’s an important part of the test that they are turned at the same time as the front diff is open left to right...)
Then turn on the the diff lock switch and you should no longer be able to turn them both forward at the same time.
02-01-2019, 03:16 PM
#3
Hi Midnight,
First of all, thank you so much for your response.
Over the years the AWD system has never given me any problems at all, so it's an area of the 964 that I have very little knowledge of. But hopefully together we'll be able to get this diagnosed.
Now, I did what you recommended: front wheels off the ground, rear wheels on the ground, spun both front wheels forward at the same time, there was more than slight resistance but I was able to turn them (I did this both with engine off and on) However, if I turned just one the opposite would not turn in unison - I don't know if it's supposed to or not.
Then I activated the diff lock and I was not able to turn them.
No abnormal noises to report.
So I guess we can assume the longitudinal diff is functioning correctly, right?
Would you reccomend I now do the same experiment on the rear wheels?
First of all, thank you so much for your response.
Over the years the AWD system has never given me any problems at all, so it's an area of the 964 that I have very little knowledge of. But hopefully together we'll be able to get this diagnosed.
Now, I did what you recommended: front wheels off the ground, rear wheels on the ground, spun both front wheels forward at the same time, there was more than slight resistance but I was able to turn them (I did this both with engine off and on) However, if I turned just one the opposite would not turn in unison - I don't know if it's supposed to or not.
Then I activated the diff lock and I was not able to turn them.
No abnormal noises to report.
So I guess we can assume the longitudinal diff is functioning correctly, right?
Would you reccomend I now do the same experiment on the rear wheels?
02-02-2019, 06:51 AM
#4
I’m tend to think your driveline is ok. But you can check rear diff easily by jacking up one rear. (Front wheel will probably come up too...that’s ok) you should be able to spin the rear...and when you turn on the diff lock you will not be able to turn.
Yes, you need to find someone who can do a full system bleed including diff locks. I would double check gearbox and front diff oil levels as a matter of course...
Are you now able to push the car on level ground?
Does the car coast normally without resistance when out of gear or clutch in when driving?
Is there a chance you’re running on one coil since the gearbox and engine was re-installed, hence the power loss?
Yes, you need to find someone who can do a full system bleed including diff locks. I would double check gearbox and front diff oil levels as a matter of course...
Are you now able to push the car on level ground?
Does the car coast normally without resistance when out of gear or clutch in when driving?
Is there a chance you’re running on one coil since the gearbox and engine was re-installed, hence the power loss?
02-02-2019, 10:54 AM
#5
I had intentions of changing the oils anyway, I'm curious to see if there are any metallic debris in it.
Same as before. That is only just, but it's heavy. It's as if it weighs 10 times.
My other cars I can push with one hand. This one I need to put all my weight into it to just move it a few inches!
While coasting the resistance isn't perceived, but as I said it's not reaching the same top speeds in each gear as it used to, so there has to be something binding somewhere.
Definitely not. I replaced both ignition coils last summer.Same as before. That is only just, but it's heavy. It's as if it weighs 10 times.
My other cars I can push with one hand. This one I need to put all my weight into it to just move it a few inches!
I'm certain this is a drivetrain issue, not an engine related issue.
So I'll get the gearbox and front diff oil changed during the few days and report back then.
02-03-2019, 02:18 PM
#6
I did as you said, but activating the diff lock had no effect, that is to say the wheel would rotate (with the "usual" abnormal resistance) in the same manner with or without the diff locked (note, front wheel inevitably came up too)
Also, when I activate the diff I can not manually deactivate it by turning the switch in the opposite direction. In all these years I've only ever locked the diff a couple of times so I don't know if that's normal or not.
Something else I'd like to mention is, that while my mechanic was doing the gearbox work on the car last year, he dropped one of the discs that are situated at the fore extremity of the gearbox (see PET image below)
At the time I didn't know, but I have since found out that the discs need to be inserted in a certain way (grooves counter clockwise if I'm not mistaken)
If these discs were incorrectly fitted would they cause the kind of symptoms my car has?
If that's the issue I sure do hope it can be rectified without having to drop the engine and/or gearbox
02-04-2019, 03:47 AM
#7
Maybe some others can chime in now if there are any other ideas...
I’m stumped why you can’t push the car if the wheels are rotating ok...unless there is something very sinister inside the transmission.
I think you’ve possibly got multiple issues.
Yes I think a disc reversed would cause some noises.
The rear diff lock is likely not locking beacuase you need to bleed the entire system. That’s where I would start.
I think you need to do some research of a specialist in your area who knows the 964 C4 driveline. I don’t think the car should have been handed back to you in this state....
I’m stumped why you can’t push the car if the wheels are rotating ok...unless there is something very sinister inside the transmission.
I think you’ve possibly got multiple issues.
Yes I think a disc reversed would cause some noises.
The rear diff lock is likely not locking beacuase you need to bleed the entire system. That’s where I would start.
I think you need to do some research of a specialist in your area who knows the 964 C4 driveline. I don’t think the car should have been handed back to you in this state....
Trending Topics
02-04-2019, 10:38 AM
#8
Midnight, thank you so much. Your assistance has been invaluable!
Just for the record, today I tried driving it with the diff locked. Not only could i perceive any difference in feel/steering, but it may also be of interest to note that the diff didn't deactivate itself above 50km/h or whatever it's supposed to. I kept going until 70km/h but nothing.
Time to hand it over to the professionals I think
Just for the record, today I tried driving it with the diff locked. Not only could i perceive any difference in feel/steering, but it may also be of interest to note that the diff didn't deactivate itself above 50km/h or whatever it's supposed to. I kept going until 70km/h but nothing.
Time to hand it over to the professionals I think
02-04-2019, 02:26 PM
#9
Instructor
Midnight, thank you so much. Your assistance has been invaluable!
Just for the record, today I tried driving it with the diff locked. Not only could i perceive any difference in feel/steering, but it may also be of interest to note that the diff didn't deactivate itself above 50km/h or whatever it's supposed to. I kept going until 70km/h but nothing.
Time to hand it over to the professionals I think
Just for the record, today I tried driving it with the diff locked. Not only could i perceive any difference in feel/steering, but it may also be of interest to note that the diff didn't deactivate itself above 50km/h or whatever it's supposed to. I kept going until 70km/h but nothing.
Time to hand it over to the professionals I think
I had a very similar sounding problem with my 91 C4. When taking a very slow corner if felt like the diff wasn't totally free. It's hard to explain, but it felt like
a really old school 4WD (think early 80's Subaru). You couldn't engage four wheel drive in those cars and turn on a hard surface.
To fix my problem I would cycle the diff lock on and off. The problem hasn't reoccurred in well over a year.
02-04-2019, 04:22 PM
#11
02-08-2019, 09:04 AM
#12
Update: I'm embarrassed to say this, but I wasn't operating the diff lock correctly!
I had been turning the switch clockwise for about 12 seconds until the lights came on in the oil temp/pressure instrument. I have since learnt that this actually disactivates the traction control and, i suspect, locks the central diff but not the rear. However, once this is activated I'm not able to manually deactivate it, neither does the car deactivate it after a certain speed, it is only reset by turning the car off.
Whereas to lock the rear diff a quick (2 second) turn of the switch is sufficient. Turning it anticlockwise then disactivates it (although there's a clack-clack-clack noise coming from the frunk which doesn't sound too good) and driving to about 40km/h also deactivates it automatically.
Is that correct?
So I think the actuators seem to be working after all.
Now I'm going to go back and repeat the tests Midnight recommended.
I had been turning the switch clockwise for about 12 seconds until the lights came on in the oil temp/pressure instrument. I have since learnt that this actually disactivates the traction control and, i suspect, locks the central diff but not the rear. However, once this is activated I'm not able to manually deactivate it, neither does the car deactivate it after a certain speed, it is only reset by turning the car off.
Whereas to lock the rear diff a quick (2 second) turn of the switch is sufficient. Turning it anticlockwise then disactivates it (although there's a clack-clack-clack noise coming from the frunk which doesn't sound too good) and driving to about 40km/h also deactivates it automatically.
Is that correct?
So I think the actuators seem to be working after all.
Now I'm going to go back and repeat the tests Midnight recommended.
02-11-2019, 02:15 PM
#15
Rennlist Member
Join Date: May 2009
Location: Bucks, Herts, Beds Tri-Border, UK
Posts: 1,135
Received 84 Likes
on
68 Posts
This is a copy 'n paste from the Streather PDAS doc I have. You probably have this already but I guess it makes it clear as to manual activation of PDAS.
"Traction control program
The traction control program is activated in the control unit by turning the **** to the right for less than 10 seconds. Activation can be accomplished from 0 to 30 kph (0 – 19 mph). Once the system is activated both the centre and rear differential locks will be engaged and fully locked. They will remain engaged until a speed of approximately 40 kph is reached. At this speed the locks will be automatically deactivated and the traction control will return to automatic mode. The driver can deactivate the system before 40 kph by turning the control **** to the left. The purpose of this system is to help dig the C4 out of deep sand or snow.
Traction control activation indication:
The yellow led used for traction control activation indication will only come on when; PDAS is in the automatic mode (normal) and when the rear differential lock only is activated or when the traction control program is activated and it flash continuously until the traction control program is automatically de-activated or manually de-activated by the driver."
What I couldn't find anywhere in the C4 books I have is any mention of what activation state the PDAS is in if the **** turning is exceeded for more than 10 secs. Maybe indeed it either a) doesn't activate in the first place at all (**** not released) or b) activates then deactivates. Odd, from a safety pov, that you say your system will not deactivate when exceeding the 40kph trigger - sounds like immanent self-destruction at that point!
All interesting stuff though.
"Traction control program
The traction control program is activated in the control unit by turning the **** to the right for less than 10 seconds. Activation can be accomplished from 0 to 30 kph (0 – 19 mph). Once the system is activated both the centre and rear differential locks will be engaged and fully locked. They will remain engaged until a speed of approximately 40 kph is reached. At this speed the locks will be automatically deactivated and the traction control will return to automatic mode. The driver can deactivate the system before 40 kph by turning the control **** to the left. The purpose of this system is to help dig the C4 out of deep sand or snow.
Traction control activation indication:
The yellow led used for traction control activation indication will only come on when; PDAS is in the automatic mode (normal) and when the rear differential lock only is activated or when the traction control program is activated and it flash continuously until the traction control program is automatically de-activated or manually de-activated by the driver."
What I couldn't find anywhere in the C4 books I have is any mention of what activation state the PDAS is in if the **** turning is exceeded for more than 10 secs. Maybe indeed it either a) doesn't activate in the first place at all (**** not released) or b) activates then deactivates. Odd, from a safety pov, that you say your system will not deactivate when exceeding the 40kph trigger - sounds like immanent self-destruction at that point!
All interesting stuff though.