Jump to content

Flexplate


Dando
 Share

Recommended Posts

On my 90 4.0, my flexplate it cracked and seperated from the center section completely. I have read conflicting reports about some replacement parts not being made properly. I don't want to install a bad part. Anyone have experience with any manufacturer? Can anyone tell me one they have bought that worked for sure? Don't want to do this job and afterwards find out it still it's right. Thanks. Locally I have options from autozone, advance, orielys, etc. 

Link to comment
Share on other sites

Yeah, you'll definitely need the Renix plate, so be sure to order a plate for a '90. There was however a thread on here five or so years ago maybe suggesting that some of the aftermarket Renix plates, possibly even multiple brand names, had been made so the timing windows were timed one or two windows off when compared to the original plate, which was screwing up timing and preventing the truck from starting. Hopefully that manufacturing problem will have been fixed by now but you never know.

So as with anything else before you install the new part, make sure it's the same as the old one. It might be more difficult with the centre section broken out of it, but line up the crank bolt holes as best you can and then make sure the windows in the new flex plate line up with the old ones. 

Link to comment
Share on other sites

I'd rather run the risk of getting one I can verify won't work before installing and then have to return instead of taking on the risk of using one that may be fatigued to the point of being about to crack and having to do the whole job all over again. But I suppose a used one would be a good comparison to a new one you're uncertain about if you can't properly compare to your old one. 

Link to comment
Share on other sites

9 minutes ago, cruiser54 said:

I'm from the other camp. Good used is better than crappy new repro stuff, 

 

Probably true, but the problem is how to know if the used one is actually good.

 

Out of curiosity ... has anyone ever tried TIG welding a cracked flexplate (successfully)?

Link to comment
Share on other sites

The one I got was just as solid as the original was. The purpose is to make up for slight misalignments between engine and trans, and the more misaligned they are the more it'll be flexing, and the more fatigued it will get with time. Its hard to see fatigue or micro-fractures with the naked eye.

If you get one out of a low-mile Jeep it'll probably be okay but you never know. I will say that it was kinda tough to find a write-up to replace them so it's maybe not as common as all that, but there are enough references to it happening that I wouldn't say it's rare. One even popped up on r/justrolledintotheshop not too long ago. They all seem to fail in the same way as well, ring crack around the edge of the washer deal around the crank bolts. It's also not unknown among other manufacturers as well. But it does generally only seem to happen to higher-mileage vehicles, the plate just wears out. 

 

As far as welding one back together, I'm sure you could do it, but when you're dealing with fatigued metal, I imagine it'll likely just break again outside the weld pretty quickly.

Link to comment
Share on other sites

48 minutes ago, gogmorgo said:

As far as welding one back together, I'm sure you could do it, but when you're dealing with fatigued metal, I imagine it'll likely just break again outside the weld pretty quickly.

 

It might, but my guess is that it wouldn't. The metal of the flex plate is so thin that there's a reinforcing ring for the bolt circle. When they crack, they always crack around the perimeter of the reinforcing ring. I think if the crack is welded up by a good welder, it would probably be as good as new, or maybe better.

Link to comment
Share on other sites

Could be I suppose. When mine broke it wasn't at all a clean break, which in a way was a good thing because it meant I could still drive the truck because of the way it was wedged in there. But that also told me it wasn't just the metal fatigued in one spot, it was a jagged crack, zig-zagging around sometimes inside, sometimes outside the perimeter of the reinforcing ring, so the whole area around it is likely affected.  

Link to comment
Share on other sites

The damage that messes them up is usually being bent (during motor install or off-roading). The center reinforcement ring missing can cause it too. A dropped AW4 torque converter with the nub knocked off center or even totally off causes issues.
A broken starter nose can jam it too. People prying on the converter through the hole to turn the motor can start a crack.


Sent from my iPhone using Tapatalk

Link to comment
Share on other sites

As I've been thinking this work over for abit and really being picky about the part I get, I ended up with an ATP part number Z-205 and as far as I can tell it's identical to my broken stock unit.

 

But I think my issue stems from a catastrophic failure 4-5yrs ago now when I had first got the truck on the road. I broke a u joint and lost the rear shaft (when it was 2wd) doing around 60 on the highway. The resulting impact broke the bell housing, and god knows what else. Instead of repairing it I just started my 4wd swap instead and scrapped the 2wd trans. In that whole process I never really went over the flexplate, just changed what I needed to and got it on the road quick. After that it has had intermittent issues ever since, looking at the flexplate I just pulled out it's got all kinds of cracks and the center section is completely seperated. If I had been more focused I probably would have seen small cracks in the flexplate years ago, but honestly I was in a rush to swap an engine and transmission in two day and too distracted to take my time like I should have. 

Link to comment
Share on other sites

Ok help needed, I finished the flexplate install just about 30mins ago. The truck starts and runs now, just not well at all. Idles terrible unless I throttle it. When I throttle it it stumbles until 2k rpm then it runs smoothly but sticks at a high idle. Don't have my multimeter till after 5 bc I left it in the fiances car. Sounds like maybe a TPS issue to anyone? There seemed to be only one way the flexplate could be installed so I don't think it could be out of timing. 

Link to comment
Share on other sites

I think you need to check the position of the flexplate in TDC to figure where it’s incorrectly pointing when it’s supposed to fire. 30 degree intervals say you got it mixed up but you should be able to reset with just the distributor so timing is correct. The fuel just sprays in accordance with the position of the flexplate but the spark will affect the running. There is a witness mark to help with the alignment (the extra hole in the crank)
For the 2.5L Guy, you need FRA-418 but with tone ring.


Sent from my iPhone using Tapatalk

Link to comment
Share on other sites

As an update the truck starts up and idles fine now, still the stumble if throttle is applied. Wish I had a multimeter on me. 

 

When I installed the new flexplate there was only one orientation that would allow all bolt holes to line up. Going to look into the different methods on how to verify my timing against the flexplate.

 

how would I fix it with the distributor if I do find it's out of time? 

Link to comment
Share on other sites

Did you compare the new and old flex plates to make sure the timing windows around the edge were the same?

I wouldn't think an empty trans would make a huge difference in the way an engine runs. You'd just end up with a big box of neutrals if you don't have fluid splashing around the torque converter.

You didn't pinch any wires or hoses when you were putting the trans back in? Bump the CPS against the ring gear?

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...