Strange slipping issue..

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FURY440

FURY440

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Ok,.1966 Valiant, Slant 6, 904 trans, 7 1/4 Sure grip. Had the car for only 2 weeks. Something strange is happening. When I drive the car normally, it shifts fine and well, is fine. When at a stop light and on heavy acceleration something feels like it's slipping and sounds like banging. When this happens and I let up and continue with normal acceleration,.it's fine. I'm wondering if it's the clutches in the rear? Trans is shifting fine with no slip at all. This only happens when stopped on heavy acceleration. If I'm at 35/40 or more and if I hit it,.it's fine. Not sure what this is. Motor mounts are fine and trans mount is fine. It has me stumped so far. Any ideas of what this could be? If it's the clutches in the rear,.how is this checked?
 
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I've never seen a rear end do that, even ones that were well worn but if it is indeed the clutches in the rear slipping you'll see it on the speedometer as it will go up and read a lot faster than your going when it happens

BTW: what's "bagging"?

BTW2: is the throttle pressure (kickdown) linkage hooked up?
 
fishy68 said:
I've never seen a rear end do that, even ones that were well worn but if it is indeed the clutches in the rear slipping you'll see it on the speedometer as it will go up and read a lot faster than your going when it happens

BTW: what's "bagging"?

BTW2: is the throttle pressure (kickdown) linkage hooked up?
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Thanks and yes,.it has me stomped. If it's not the rear,.then the only thing I can think of is maybe a few clutch discs in the trans are stuck together from sitting. The car sat for 36 years and was barley driven. I changed the trans fluid/filter and it seems a little better, but not right. I'm going to drive the car for a weeks back and forth to the shop and see what happens.

LMAO,.I meant banging, not bagging.

The kick down is working fine, but I will check to see if it's adjusted correctly.
66 Valiant Signet 3.jpeg
 
FURY440 said:
Thanks and yes,.it has me stomped. If it's not the rear,.then the only thing I can think of is maybe a few clutch discs in the trans are stuck together from sitting. The car sat for 36 years and was barley driven. I changed the trans fluid/filter and it seems a little better, but not right. I'm going to drive the car for a weeks back and forth to the shop and see what happens.

LMAO,.I meant banging, not bagging.

The kick down is working fine, but I will check to see if it's adjusted correctly.
View attachment 1714989151
Click to expand...
 
It's also possible that after sitting for 36 years and seldom driven the internal lip seals are in need of replacement and/or as you say some of the clutch discs are stuck together.
 
How does it act on a cold start when you drive it?
Does it seem sluggish when cold?
Ever had to rev it a little to get it to move in the mornings?
 
That's the thing,.it doesn't show any signs of slipping even when cold. I can start it cold and shift right in to drive and go with no slipping and no delay going into gear. My 66 Fury had that issue. I had to start it and put it into neutral for 30 seconds to get the pump going then it would shift solid.

I'm agreeing with transman that the seals could be hard also. I need to get it on the road and drive it to see if this will pass. I'm hoping it will get better after driving it a week or so.
 
Still having the same issue. I can power brake it and it makes this noise like something is slipping and it makes a metallic noise. I'm going to get my son to look under it and use a camera to record this. I want to see what is going on with the driveshaft. It's coming from the rear for sure. I'm wondering if the PO had someone change the gear oil and they didn't put in the right fluid.

If it ends up being the rear clutches, does anyone know where I can gets parts for it?
 
No shroud on the car and fan isn't hitting the rad. This only happens on medium to hard acceleration from a standing stop. If I take off normally no noise and no vibration. Trans shifts fine and has passing gear.
 
Flex plate bolts contacting the dustshield is my guess. Pull the shield and check for rub marks and rotate the engine and check bolt heads for impact or for looseness. They can contact the block if they back out
 
It was in drive. I will also check the flex plate. The u-joints are good. Has me stumped because the trans shifts fine and doesn't slip. Like I said, I can take off normal with light throttle and I get no noise,.as soon as I take off medium to hard,.the shake happens and the noise.
 
Ok. redid the test and it's happening in Low 1 also. I'm guessing it's a bad sprag.
 
Did you end up checking the flex plate bolts where they thread into the converter like Threewood suggested? It is difficult to tell in the video but does sound like something rubbing or scraping when flex is induced under heavy load. That needs to be ruled out first. Also, I did have two completely different 727 transmissions in a 74 Newport that, at the time, I thought were not slipping. Under harder acceleration it would start to shake or vibrate and then sounded like a hollow grinding noise from the middle of the car. That noise is something I have never again heard duplicated in any other car I owned, regardless of what went wrong. After some brake torque testing while stopped in drive, similar to the video shown for your problem, it was determined that the transmission WAS in fact slipping. The rpm was going higher than it should according to the specs in the service manual (car was completely stock so specs were valid). At no time did my car ever slip badly enough to be obvious to me until right before it completely gave up and had no forward motion at all and would just rev up like it was neutral. Teardown and rebuild showed absolutely no damaged hard parts but I did find the forward clutch pack (rear position with the input shaft attached to it) was completely burned out, like no clutch material left on the discs at all. The steel plates and even the clutch drum was discolored from heat caused by all the slippage. After rebuild, the rpm was normal during brake torque testing and the noise was completely gone. Definitely need to rule out anything that could be rubbing first, and also check the actual rpm it gets up to when holding it against the brakes.
Good luck. Bob.
 
Thank you. I'm going to pull the inspection plate and look at those flex plate bolts.
 
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