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No reverse

998 views 9 replies 6 participants last post by  Hayraker 
#1 ·
727 auto, pulls good, doesn't slip, shifts good into all forward gears.

Last time I wheeled it, it started shifting into reverse hard and with a delay. Now it won't shift to reverse unless I raise the rpms quite a bit, and when it goes in it goes in hard.

Once it shifts into reverse it pulls fine and doesn't slip.

Diagnosis? Simple fix? kind of strapped for cash at the moment so I'm looking for a patch. One guy recommended running some Lucas additive thru it, he said it was probably the O-ring on the reverse gizmo(whatever).

Discuss amongst yourselves:p
 
#2 ·
I've heard (so take this for what it is worth) that using the additives with an iffy tranny can send it to the final resting place. No problems with low? You might try adjusting the band and changing out the fluids.
 
#4 ·
Joe, no problems with low, and reverse is strong once it engages

Chief, the reverse servo is the gizmo I was referring to, couldn't remember what he called it. I'm not to familiar with the inner workings of an auto, as far as I'm concerned they work from PFM.......(pure fucking magic )
 
#7 ·
Hayraker said:
727 auto, pulls good, doesn't slip, shifts good into all forward gears.

Last time I wheeled it, it started shifting into reverse hard and with a delay. Now it won't shift to reverse unless I raise the rpms quite a bit, and when it goes in it goes in hard.

Once it shifts into reverse it pulls fine and doesn't slip.

Diagnosis? Simple fix? kind of strapped for cash at the moment so I'm looking for a patch. One guy recommended running some Lucas additive thru it, he said it was probably the O-ring on the reverse gizmo(whatever).

Discuss amongst yourselves:p
The reverse band servo seal is split or torn, or the servo bore is scored. The tranny uses the same clutches for low as for reverse. If you have low, but not reverse, it is because the reverse band is not engaging. When you give it high rpm's, fluid pressure in the tranny goes high enough it will push the servo, even with a torn seal, and the band will engage. Unfortunately, when it does this, you have a lot of engine mass spinning at high rpms, and when the band engages, it engages hard and fast, transferring all that energy to the ouput shaft of the tranny. Since you usually have your foot on the brake, that force goes out through the drivetrain and something is going to break. In my case, with precisely the same symptoms, I sheared the tranny output shaft. Interestingly enough, the tab on the band and the band strut were fine, despite the abuse. But, the output shaft sheared cleanly, and suddenly.
 
#8 ·
Additives will not help

Hayraker said:
727 auto, pulls good, doesn't slip, shifts good into all forward gears.

Last time I wheeled it, it started shifting into reverse hard and with a delay. Now it won't shift to reverse unless I raise the rpms quite a bit, and when it goes in it goes in hard.

Once it shifts into reverse it pulls fine and doesn't slip.

Diagnosis? Simple fix? kind of strapped for cash at the moment so I'm looking for a patch. One guy recommended running some Lucas additive thru it, he said it was probably the O-ring on the reverse gizmo(whatever).

Discuss amongst yourselves:p
Additives will not help much. They might thicken up the tranny fluid, so the servo engages a little better, but that torn seal, moving up and down in the servo bore, will just get worse and worse, quite quickly.

You can drop the valve body and replace that servo seal, without rebuilding the tranny...

Here is a pic of the servo bores
 
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