904 front clutch issues!

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1968notch

1968notch

Too many projects, not enough time/$$$
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Hi all,

I did a 904 swap on my 1968 Notchback. Swapped due to no reverse and no 3rd issue. The only part in common with 3rd and reverse is the front clutch. After the swap, i noticed the rev between 2nd and third just like the previous 904 prior to ultimate failure of 3rd altogether and eventually reverse. Here's the thing though, in both situations, when it did hook up in reverse, I could smoke the tires with either tranny.

The first issue is that the replacement failed much quicker than the the original from the point of "extra rev between 2nd and 3rd" (running in drive natural shifts) to ultimate total failure , The second issue is WTF over?

This isn't a clutch friction material problem, it's a front clutch "apply" problem. Meaning that the fluid required to press the clutch pak together (the steels and friction material) isn't there. Like I said, when it does hook up in reverse, it fry's the tires. That is NOT a friction material problem, it's an apply problem.

My question is, the fluid that is sold today and what I used (dex-merc) which states dex3 compatible is causing this issue or is it just bad luck on the apply O-ring?

I will provide tranny #'s later for which one to rebuild based on 1st gear ratios. Running a 7.25 @ 2.73 rear so the lower the better. Rear end swap and a modded TQ (excellent carb rebuild by me, as in scary fast through first and second) 4bbl teener to 340 swap in progress.

Thanks,
Paul.
 
Did you run the kick down linkage and have it adjusted correctly?
 
I want to say........oh brother!
The KD link is vital. It control the apply pressure,relative to throttle position. The 2bbl to 4 bbl conversion is not complete, until the 4bbl throttle bracket goes on and the KD linkrod is either swapped out for the 4bbl link, or modified to correctly work.As you are finding out.
Dont forget the air pressure test,to prove the apply-piston is moving.
And burn-outs in reverse? Really? That is so wrong.

I think its time to make a sticky on this, cuz its expensive to learn this the hard way.Especially if it takes 2 or 3 tries to figure it out.Or is there one already?
 
AJ/FormS said:
I want to say........oh brother!
The KD link is vital. It control the apply pressure,relative to throttle position. The 2bbl to 4 bbl conversion is not complete, until the 4bbl throttle bracket goes on and the KD linkrod is either swapped out for the 4bbl link, or modified to correctly work.As you are finding out.
Dont forget the air pressure test,to prove the apply-piston is moving.
And burn outs in reverse? Really? That is so wrong.

I think its time to make a sticky on this, cuz its expensive to learn this the hard way.Especially if it takes 2 or 3 tries to figure it out.Or is there one already?
Click to expand...


I totally agree on this point, as the geometry is AFU using 2 barrel linkages with a 4 barrel.
The Lokar kit is a really good way of solving this, but be warned that if you end up using the lokar kit you need to lube the cables well before it goes in or they bind up.
I don't know why, but they ship them dry and a lot of people had problems with them until they were lubed. (graphite powder works great for this)
 
Stator shaft sealing rings, drum bushing, input shaft seals & hook rings must be in good condition also.
 
mguner said:
Stator shaft sealing rings, drum bushing, input shaft seals & hook rings must be in good condition also.
Click to expand...

What if someone took out the hook rings and used Teflon? :D

Forgot that didn't ya? :D
 
View attachment bracket.jpgitem #: HF0060

The geometry still isn't exactly perfect but I'll keep looking for parts to fix it. But it kicks down just fine. Drops to low @ 30 mph when floored and doesn't upshift till 45 at least so that oughtta be plenty of pressure on kickdown lever. Attached a jpeg for the part. Hope the jpeg works.

The 2nd to 3rd rev was there the day I first drove it on the very first shift. Trans was a 150 dollar JY unit. I know all about the kickdown rod controlling apply pressure. And I only did the reverse tire smoke test AFTER the trans had no 3rd and would seldom hook in reverse. the trans was already toast. Also, the fact that it hooks in reverse that good tells me the friction material is just fine and that the "lack of apply pressure from a mis-adjusted kickdown lever burning up the clutch pack" is not the issue. This is a seal problem.

My question dealt specifically with the fluid blowing by the 0-ring seal due to seal failure thereby failing to apply the clutch pack and whether or not that particular fluid I mentioned could cause early seal failure. I was installing a JY unit and wasn't interested in dropping the valve body to do an air test. It's just not necessary. Don't like messing around with valve bodies unless and until it's absolutely necessary. Just a thing with me. This was to be a very temporary install while I rebuild the one in my trunk. It may not have been a total waste of money though if it has the low gear set. Will research that later. Maybe some wasted time and a grunt or 3...

I guess another question is, I thought I remember reading about a bushing failure in that area of a 904 that can cause this issue as well or leave a wobble that can cause an early seal failure. Is that correct and if so, is there a new design or better parts that can be used in that area when I do the eventual rebuild that will fix this problem for good?

Thanks for the feedback, although I think some of it was based on a particular situation that didn't actually exist. I wasn't exactly accurate in my second post (and I attribute that to everclear and tequila) which may have caused some confusion. The linkage was adjusted tight enough to prevent the problems that can be attributed to it. I flipped and modded the rod (bent it the opposite direction) and added a shaved sided bolt to the slot to get the necessary pressure on the rod.


Paul.
 
There is such a thing as "worn out" that can cause flared shifts due to overly worn clutches taking too long to apply.
I'm not going to even venture a guess on a JY trans, because there are so many possibilities.
 
I've seen numerous torqueflite's toasted because the throttle pressure linkage wasn't hooked up or wasn't adjusted correctly. That also causes the 2-3 flare up. And it has nothing to do with the spring in the front clutch. If that spring is weak it'll overlap which of the exact opposite of flare up.
 
TrailBeast said:
There is such a thing as "worn out" that can cause flared shifts due to overly worn clutches taking too long to apply.
I'm not going to even venture a guess on a JY trans, because there are so many possibilities.
Click to expand...

This too. You have to figure any 904 you get from the JY is nearly 25 yrs old now. How many automatics found in the JY that are 25 yrs. old work properly. Not many I bet. An since torqueflite's depend so heavily on the throttle pressure linkage being adjusted correctly for long life they are on the high side of percentage of likely being worn out
 
fishy68 said:
This too. You have to figure any 904 you get from the JY is nearly 25 yrs old now. How many automatics found in the JY that are 25 yrs. old work properly. Not many I bet. An since torqueflite's depend so heavily on the throttle pressure linkage being adjusted correctly for long life they are on the high side of percentage of likely being worn out
Click to expand...

Agreed.
 
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