C6 - problem engaging reverse

C6 - problem engaging reverse

Joined: May 8th, 2011, 6:48 pm

May 8th, 2011, 7:14 pm #1

I've recently installed a used C6 (which had first been checked by a trans mechanic & given the OK) into my 83 F250 with a new modulator, fluid & filters, adjusted the intermediate band etc.

It drives well & shifts well, no slipping, but engages hard going into reverse after a delay. The forward gears all engage normally.
Once in reverse, there's no other problem either.

When it's cold I can avoid the thump by selecting low gear manually, then shifting straight into reverse - but this doesn't help once it's warmed up.

There are no issues with engine mounts, driveshaft, idle speed etc. - this problem has only been since the original AOD was replaced with this C6.

I added a bottle of LubeGard in case of a valve problem (the governor had been sticky for the first day) but after 2-300 miles there is no change.

Is anyone able to point me to the likely cause of this? Thanks
Last edited by bken123 on May 8th, 2011, 10:16 pm, edited 1 time in total.
Quote
Like
Share

Joined: November 18th, 2004, 4:20 am

May 9th, 2011, 3:28 am #2

You may have a sticking pressure regulator valve or the clutch packs could be a tad worn.
Quote
Like
Share

Joined: May 8th, 2011, 6:48 pm

May 9th, 2011, 9:35 am #3

Thanks

If it's the sticking valve, is it likely to free up with the LubeGard & some time & use?

Or if it's clutch wear, is a strip-down the only option?

Also it has begun occasionally for the first couple of take-offs in the morning, to shift 1-2 fine, 2-3 fine, then in quick succession shift 3-2-3-2 etc, unless you either press or release the accelerator.
As soon as it has warmed slightly this stops.
Is this anything serious?
Last edited by bken123 on May 10th, 2011, 6:36 pm, edited 1 time in total.
Quote
Like
Share

Joined: November 18th, 2004, 4:20 am

May 11th, 2011, 5:29 pm #4

Have a look at the modulator pin length.


Someone may have installed a shift kit and replaced the pin with a shorter one to lower the shift points.
Quote
Like
Share

Joined: May 8th, 2011, 6:48 pm

May 16th, 2011, 6:03 pm #5

I haven't had a chance to measure the pin yet - I'll try to today.

If a shift kit has been installed, could it cause the hard shift into reverse?
Last edited by bken123 on May 27th, 2011, 8:47 pm, edited 1 time in total.
Quote
Like
Share

Joined: May 8th, 2011, 6:48 pm

November 11th, 2011, 6:17 pm #6

If it helps anyone in the future, two things were contributing to this problem.

I found the vacuum to the modulator was coming from a restricted port on the tree - remedying this helped, but didn't totally solve the problem.
The main issue probably was (I'm assuming), as Stuart suggested, a sticking pressure regulating valve.
Initially after adding the Lubegard there was no change and, after the improvement with increasing the vacuum, I hadn't chased the problem much more.

But the delay & hard reverse-engagement issue progressively improved, & is almost non-existent, without any deterioration driving or shifting in the other gears.
Also the bouncing between 2-3 when cold stopped not long after adding the Lubegard.

So in this case - yes, sometimes an additive can fix it.
Last edited by bken123 on November 11th, 2011, 6:31 pm, edited 1 time in total.
Quote
Like
Share