Auto trans won't back up?

Posted By: DodgeCharger

Auto trans won't back up? - 10/11/11 09:07 PM

I have a 727 foward manual valve body with low band apply. It was working fine for a few hundred miles.
I parked it and went to back up and the car wouldn't move. All forward gears work fine. I ran the car on jackstands. Forward gears fine. In reverse the tires won't move and it pulls the motor down when I give it slight throttle.
Any Idea what might be the problem? Is it the valve body or something bigger? I am thinking something left loose in the modified valve body causing it to work like a trans brake.
Any ideas would be appreciated.
Thanks,

Posted By: dodger mope

Re: Auto trans won't back up? - 10/11/11 09:15 PM

the rear clutch plates are welded together

Posted By: challenger1320

Re: Auto trans won't back up? - 10/11/11 09:18 PM

I would say it pushed the piston seal out and has the clutch pack locked up

Posted By: Guitar Jones

Re: Auto trans won't back up? - 10/11/11 10:13 PM

If it drives in neutral the rear clutches are locked up.

Posted By: DodgeCharger

Re: Auto trans won't back up? - 10/11/11 10:19 PM

How does that happen?

Posted By: challenger1320

Re: Auto trans won't back up? - 10/12/11 01:24 PM

What I said. Is how it happens

Posted By: Guitar Jones

Re: Auto trans won't back up? - 10/12/11 01:36 PM

Quote:

How does that happen?

I have also seen the rear clutches welded together from slipping. Using the transmission instead of the brake pedal when going from reverse to drive will eventually wear the rear clutch discs until they start slipping all the time and will then eventually weld themselves together.

Posted By: dOrk !

Re: Auto trans won't back up? - 10/12/11 04:56 PM

PROBABLY the "spring" has flipped-over and locked the clutches up. From what I Have seen .. if the clutches are welded-up due to slippage ... the ATF has been toasted.

Posted By: dragram440

Re: Auto trans won't back up? - 10/12/11 05:03 PM

I dont know much about automatic trans but on mine the lever that applies the band for reverse broke and I had all gears but no reverse. Mine was on a fresh trans so I dont know if something didnt get put together correctly. The first time I put it in reverse there was resistance with a little pop and then it was just like in neutral when in reverse.

Posted By: John_Kunkel

Re: Auto trans won't back up? - 10/12/11 06:50 PM

Quote:

How does that happen?

In cases where the piston overtravels and pops out of its bore it's usually any one or a combination of things:
Weak Belleville
High Line pressure
No accumulator spring

Posted By: MRMOPAR

Re: Auto trans won't back up? - 10/13/11 02:47 AM

Quote:

I dont know much about automatic trans but on mine the lever that applies the band for reverse broke

Low/Reverse band, strut, or servo failure.

Posted By: Guitar Jones

Re: Auto trans won't back up? - 10/13/11 11:20 AM

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Quote:

I dont know much about automatic trans but on mine the lever that applies the band for reverse broke

Low/Reverse band, strut, or servo failure.

If this was the case it shouldn't pull the engine down liked it's locked up. It would just act like high gear. He also never said if it drives in neutral.

Posted By: DodgeCharger

Re: Auto trans won't back up? - 10/14/11 02:35 AM

Quote:

Quote:

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I dont know much about automatic trans but on mine the lever that applies the band for reverse broke

Low/Reverse band, strut, or servo failure.

If this was the case it shouldn't pull the engine down liked it's locked up. It would just act like high gear. He also never said if it drives in neutral.

It doesn't drive in neutral.

Posted By: 440Jim

Re: Auto trans won't back up? - 10/14/11 03:01 AM

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Quote:

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I dont know much about automatic trans but on mine the lever that applies the band for reverse broke

Low/Reverse band, strut, or servo failure.

If this was the case it shouldn't pull the engine down liked it's locked up. It would just act like high gear. He also never said if it drives in neutral.

It doesn't drive in neutral.

If it doesn't creep in neutral, then I think the rear servo, band, or strut. You should be able to see it just by dropping the pan. You should have smooth action pulling on the rear servo by hand and watching the linkage engage the band.

Posted By: DodgeCharger

Re: Auto trans won't back up? - 10/14/11 11:09 AM

Quote:

Quote:

Quote:

Quote:

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I dont know much about automatic trans but on mine the lever that applies the band for reverse broke

Low/Reverse band, strut, or servo failure.

If this was the case it shouldn't pull the engine down liked it's locked up. It would just act like high gear. He also never said if it drives in neutral.

It doesn't drive in neutral.

If it doesn't creep in neutral, then I think the rear servo, band, or strut. You should be able to see it just by dropping the pan. You should have smooth action pulling on the rear servo by hand and watching the linkage engage the band.

I'm sorry I missunderstood you. It most likely creeps in neutral. On jackstands the tires spin in neutral without the brakes applied. I thought you meant drives the car in neutral. Even when the trans was working ok it would creep if you rev it up in neutral. I was told it was a tight clutch pack and nothing to worry about?