Where slack in gears is coming from

[Nicks501]

I recently picked up another bronco. 1971 351W, c4 transmission, Dana 20 transfer case and factory 4.11 gears in the axles. 35x12.50x17 wheel setup on Duff 5.5 inch lift. When I place in park on the slightest incline, the entire bronco will roll almost 18-24" before "park" catches and holds the bronco in place. Just seems very excessive amount of play in the transmission and/or transfer case. I have just rebuilt the rear end (bad axle bearing and brakes) so pulled the third member and everything looked good in it. My 1975 bronco with 37's had a similar build did not have this much play in the transmission /transfer case. Any suggestions why it has so much slack in it?

 

[Broncobowsher]

Park on flat ground. rock forwards and back. How much play do you get. Watching the driveshaft, where is the play at?

6-8" I would think if pretty normal. I have never seen 2 feet of slack. Broken tooth on the park pawl? Even then that should only be where that bad tooth is and not everytime.

 

[SP73]

Park on flat ground. rock forwards and back. How much play do you get. Watching the driveshaft, where is the play at?

6-8" I would think if pretty normal. I have never seen 2 feet of slack. Broken tooth on the park pawl? Even then that should only be where that bad tooth is and not everytime.

Broken park pawl tooth is the only thing I could think of. That much movement is a new one for me.

 

[DirtDonk]

Do you have a Detroit Locker? They can make for lots of play in the differential at least. Then you have spline damage potential in the transfer case. Then you have transmission damage.

You just have to find it manually as mentioned. Pull the driveshaft and spin the yoke on the diff. Is the play in the thousandths of an inch, or is it a 1/4" or more?
What about the rear output yoke on the transfer case? Is it tight, or is there an excess of slop?

You already had the diff out and said it looks good. Does that mean it's also only got a few thousandths of an inch of rotation?

Paul

 

[Nicks501]

Park on flat ground. rock forwards and back. How much play do you get. Watching the driveshaft, where is the play at?

6-8" I would think if pretty normal. I have never seen 2 feet of slack. Broken tooth on the park pawl? Even then that should only be where that bad tooth is and not everytime.

When I get home, I will try on the flat garage and roll the bronco, then pull the rear of the driveshaft off the axle and see how much how much slack is truly on the differential side or is the transmission/transfer case side.

Thanks for the input.

 

[Nicks501]

Do you have a Detroit Locker? They can make for lots of play in the differential at least. Then you have spline damage potential in the transfer case. Then you have transmission damage.

You just have to find it manually as mentioned. Pull the driveshaft and spin the yoke on the diff. Is the play in the thousandths of an inch, or is it a 1/4" or more?
What about the rear output yoke on the transfer case? Is it tight, or is there an excess of slop?

You already had the diff out and said it looks good. Does that mean it's also only got a few thousandths of an inch of rotation?

Paul

Thanks Paul, I will try those when I get home and see where the culprit really lies. Not a detroit locker, but it does have the factory limited slip differential in the rear.

 

[okie4570]

That's a new one, and that's a ton of movement. I have a Np435 with a Detroit in the rear and I get hardly any roll in any gear. I would think it has to be C4 related.

 

[sprdv1]

I recently picked up another bronco. 1971 351W, c4 transmission, Dana 20 transfer case and factory 4.11 gears in the axles. 35x12.50x17 wheel setup on Duff 5.5 inch lift. When I place in park on the slightest incline, the entire bronco will roll almost 18-24" before "park" catches and holds the bronco in place. Just seems very excessive amount of play in the transmission and/or transfer case. I have just rebuilt the rear end (bad axle bearing and brakes) so pulled the third member and everything looked good in it. My 1975 bronco with 37's had a similar build did not have this much play in the transmission /transfer case. Any suggestions why it has so much slack in it?

yikes.. definitely not good

 

[Nicks501]

Broken park pawl tooth is the only thing I could think of. That much movement is a new one for me.

I think it must be the park prawl or related. rolling in the garage on flat ground it will move 2-3 feet. But I can hear clicking which I assume is the park prawl trying to engage.

 

[Timmy390]

I think it must be the park prawl or related. rolling in the garage on flat ground it will move 2-3 feet. But I can hear clicking which I assume is the park prawl trying to engage.

Bingo.......

Tim

 

[DirtDonk]

Is it possible for the linkage to by slightly out, not letting the pawl engage fully? Or is it either on or off, and can only fail to grab if broken?
If not certain, you might at least try the shift linkage. Disconnect it and manually put the lever on the side of the trans into park. See if it was going all the way before.
If it seems like it went a little further, try the rolling test again.

Paul

 

[Nicks501]

Is it possible for the linkage to by slightly out, not letting the pawl engage fully? Or is it either on or off, and can only fail to grab if broken?
If not certain, you might at least try the shift linkage. Disconnect it and manually put the lever on the side of the trans into park. See if it was going all the way before.
If it seems like it went a little further, try the rolling test again.

Paul

Great idea, it could be. This bronco does have a ididit steering column in, installed by PO. So fingers crossed maybe that's it. I will try again this evening!

 

[ugly74]

I think dirtdonk nailed it.

I've seen C4 and C6 transmissions that would hesitate to really grab "park", or would even pretend for a bit, then drop themselves into reverse because the linkage was out of whack.

 

[bigmuddy]

If its a bad parking pall, do not let it idle in park. It has the ability to put itself in reverse and back up.

I had this happen to me and total a very clean 75 years ago. I hear and audible clunk as the rig was idling and then it backed up in to a 100 year old live oak tree before I could get it shut down (I was standing in the front with the hood up)

Not good at all.