help diagnosing drive plate and/or flex plate issue

WaltNYC

Well-known member
Mar 3, 2010
427
3
NYC
Unlike many other transmissions, the Discovery has a two plate system to connect power from the engine to the transmission.

Starting from the block and working towards the rear of the car...
1. The drive plate with reluctor tabs for the crank sensor and the starting ring gear on the outer edge. This is attached to the main output shaft of engine (#1 in the diagram)
2. a spacer
3. a flex plate which bolts to the torque converter (#7 in the diagram)






These items are bolted together and form the 'drive plate assembly' The second disc, aka the flex plate (#7), allows for longitudinal movement (front to back) of the torque converter.

Over thanksgiving my truck ruined the starter...





I have also heard, intermittently, what sounds like a very light bottom end knock. I thought I might be looking at replacing journals but now I'm putting 2 and 2 together and am suspicious that my drive plate is cracked or faulty in some way.

Talk to me fellas. What am I looking at? How deep is the water? Anybody with a lift want to help drop a transmission?

So, I'm looking for your educated thoughts, experiences, and information.
 

fishEH

Well-known member
Jan 26, 2009
6,355
9
Lake Villa, IL
Dropping the transmission isn't all that hard. I've dropped both a manual and auto Rover trans in my driveway. The transfercase was by far the heaviest, most awkward, and most difficult part.
 

WaltNYC

Well-known member
Mar 3, 2010
427
3
NYC
Did you leave the xfer case attached when you dropped the trans? I'm guessing you separated them.

The difference for me is that I have no business in the transmission "south" of the bell housing and it won't be down very long. Just long enough to pull the drive assembly (4 bolts and two spacers), remove the flex plate , and re-assemble the drive assembly onto the spigot (which is on the crank).

Maybe I'll do the rear main seal if it looks like it needs it.
 

p m

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Apr 19, 2004
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Did you leave the xfer case attached when you dropped the trans?
You don't have to separate them, but you'll definitely need a good transmission jack.
I farmed out the flexplate replacement to a shop - but I was told that for a shadetree mechanic it would be faster to remove the engine. Keep in mind that you're going to drop both driveshafts and pretty much the entire exhaust to get to it.

I'd pull the engine oil pan and take a look from the front. There are additional "while you're there" benefits with that.
 

proper4wd

Well-known member
Jun 11, 2015
62
11
boston
you dont have to pull the engine oil pan on a D1, just the bellhousing cover. i guess even that is too much to ask though.
 

WaltNYC

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Mar 3, 2010
427
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NYC
First thing on the list is to pull the bell housing cover and the bottom inspection plate and see what I can see w/ a boroscope. I don't expect to see much, but for $25 it might just pay off. It might not.

If I go forward I am thinking doing what p m suggested and pulling the engine and doing a head gasket job while it is on a stand. My HG is original and shows no signs of failure, but eventually everything fails, right?

From my perspective this is an opportunity to take it off the road for 3-4 weeks and go through it more fully and properly and get another 160k out of it. The rest of the truck is super nice. Very little rust. I don't use it much and use it less in winter than any other time of year.

This will be a crappy job one way or another. I suppose I want to get maximum benefit for marginally more effort to the extent that is practical.
 

proper4wd

Well-known member
Jun 11, 2015
62
11
boston
you won't need a borescope. its four 8mm bolts to get the cover off. you will see a lot. stop wasting time and positing on the internet.
 

WaltNYC

Well-known member
Mar 3, 2010
427
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NYC
peoper4wd, could you please describe what you?d expect to see and/or hear if it were cracked.

It looks ok to me. I got a boroscope between the plates and saw nothing unusual.

https://youtu.be/3G6cWH58hKI
 
Last edited:

degride

Well-known member
Sep 22, 2008
62
0
Somewhere on Earth
To the OP, I went through this exact thing last year on my DII (230k). As to what the other post indicated, the flex plate fails from the center, outward. I think it will be difficult to tell with the housing off, even on a DI as it does not take much for the flex plate to begin making noises once it goes. And those cracks can seem like hairline cracks until you take it apart and they open up.



Mine sounded like rocks in a dryer, not consistent, like the video posted; but only at very low RPM ( < 750). Once the plate was out there were cracks around three of the four bolts and one small piece was completely separated from the plate itself but still "intact" because of the bolt it was connected to.


I would suggest attaching a go-pro or something to the underside, start it while it's cold (mine was more susceptible to the noises when cold versus not - something to do with the metallurgical nature of the material I'm assuming), and post back the results.
 

WaltNYC

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Mar 3, 2010
427
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NYC
JohnnoK, that video is helpful and thankfully I have no such sound.

degride, I suspect the cold weather makes the fluid in the torque converter a bit more viscous and that stresses the flex plate more than if it were warm.

I drove it 300 miles (almost entirely highway) yesterday without incident.

I'll revive this thread if something more develops. Thanks to all for the help/guidance/advise/ball busting! :)
 

JohnnoK

Well-known member
Mar 19, 2017
93
1
Cape Town, South Africa
For what it's worth, my P38 has lost drive and while I haven't dropped the box yet, a mate who knows them well tells me that he is sure the flex plate has failed and that causes the remaining bits to deform from the load which pulls the torque converter forward and disengages the pump drive in the tranny.

My symptoms were a grumble type sound when I selected D to pull into my drive after opening the gate. That was when the pump drive disengaged according to my mate.
I have managed to source a CAD file for the flex plate and I will have a multi layer one cut when the guy sends it to me.
 

Payson

Active member
Aug 14, 2017
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0
SOUTHERN CALIFORNIA
JohnnoK, that video is helpful and thankfully I have no such sound.

degride, I suspect the cold weather makes the fluid in the torque converter a bit more viscous and that stresses the flex plate more than if it were warm.

I drove it 300 miles (almost entirely highway) yesterday without incident.

I'll revive this thread if something more develops. Thanks to all for the help/guidance/advise/ball busting! :)

Is your issue solved? I recently replaced my 4.6L Bosch with a top hatted block and have a low knock at the bellhousing. I pulled the inspection plate and all looks good. I am going to retorque the 4 bolts and see if that fixes it.....
 

WaltNYC

Well-known member
Mar 3, 2010
427
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NYC
Not so much solved as it never was. I still have some noise on cold starts but I am now thinking it is a very mild catalytic converter rattle. As far as the starter, I can only surmise that a bolt worked its way loose.

Something like this, but not as bad....
 

Extinct

New member
Mar 26, 2013
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United States
I thought I had same issue, a pronounced tick from the bottom, louder at the bellhousing on an 03. Pulled the engine oil pan and saw zero evidence of cracked plate - rotated several revolutions and could not see a single crack. Wondering if I could only be cracked at the center mounting plate?
 

WaltNYC

Well-known member
Mar 3, 2010
427
3
NYC
Extinct, it certainly could be cracked near the center. I bought an inexpensive endoscope on Amazon. It creates its own wifi network and you can see the images (and record them) on an iphone. I was able to get the scope in between the drive plate and the flex plate. For $25 it was as close as I could get to being certain. The trouble with a potential flex plate issue is that, unless you pull the transmission, you can never really be 100% sure. I've run the truck about 2,000 miles since without issue.