shepss217

iTrader: (5)

Ok heres the deal. I just got my transmission rebuilt and upgraded to kolene steels alto reds and sonnax beast smart shell etc. it only has about 100 miles on it since the rebuild. Today i left a 4 way stop moderately hard and it shifted fine from 1-2 and 2-3 but when it went to Shift to 4th it banged real hard and acted like it fell out of gear. I pulled over and shifted it to park then back to OD and it wouldnt move. I put it in drive and it was fine. So i drove it all the way home in drive. Got home let it cool down for a while and went out put it in OD again and drove it around with no issues until if started heating up again then started slipping in between 3-4 then the same baging and shuttering started again. Any ideas of what it might be?

performabuilt

iTrader: (25)

Best guess is the input sprag is failing to hold when hot ,this or crack in the forward apply piston circuit placing the car in the D3 position would apply the overun clutch bypassing both of these and allowing movement.

shepss217

iTrader: (5)

Hmm interesting! The kit did come with a brand new sprag, do you think it failed already?

performabuilt

iTrader: (25)

That is a best guess though other possibilities do exist with the input drum forward clutch etc

shepss217

iTrader: (5)

Damn, so tired of this car

mrvedit

Since 4th gear is mostly a combination of 2nd and 3rd gear, when 2nd and 3rd work, 4th usually does too.
There have been other posts where loss of 4th gear were due to either a cracked 4th servo piston, a worn band (shouldn't be after a rebuild) or a stuck valve in the valve body. I don't recall all the symptoms of those.
I don't think it is the sprag because it is not used in 4th gear; it is used in all other gears.
In [D3] the overrun clutch is applied only in 3rd gear in a stock trans; however if the Sonnax HD 2-3 shift valve is installed, the overrun clutch is applied for all gears in [D3].

Will the rebuilder not warranty his work?
If not, I would do the following:
1. Measure the servo end play - with a ruler next to it, press on the servo cover with a crowbar and estimate how much it moves. With a new rebuild it should be less than 1/8".
2. While non-trivial, I would remove the servo cover and carefully examine the 4th servo piston and seals.
3. Since step 2. typically requires removing the driveshaft and unbolting the rear trans mounting, if the servo looks OK, you might as well remove the trans.

If the servo is OK, a clearance or other problem between the overrun clutch and forward clutch is, as mentioned, a high probability.

performabuilt

iTrader: (25)

I was thinking sprag because it he stated it would not move in the 4th gear position from a stop was what I understood but would move in the d3 position normally ,
The Overun clutch in in the d3 position is on in first and 3rd but off in second unless of course the HD 2-3 valve has been installed in which case it is on in the 1-2-3 in D3 ,
The sprag must hold to take off in the D4 OD POSITION but you are correct it is not used in the D4 4TH GEAR,
This is why I made and still make a best guess of a sprag issue or of course some issue could exist with the forward clutch,
The servo would only have affect on 2nd or 4th gears functionality,
In any case I would say his issue is in the input drum the only odd thing his he said it stopped pulling in 4th gear driving sorta odd since the 3-4 clutch and the band make that happen and the forward clutch. sprag, Overun is not in the picture.
I will still have to go with sprag or forward clutch since it did not move in the OD position from a stop but did move in the D3 position .

mrvedit

I seem to be interpreting the OP's description a bit differently - I read that only 4th gear is acting up.
Obviously you and perhaps I could diagnose it better if we drove the car, but we only have the OP's description.

OP: please give us a better description - is there any problem starting in [OD]?

Also, while a problem in the input drum is most likely, if there is a possible fix which has even a 5% chance of working and doesn't require removing the trans, I like to point that out.

On a minor point, according to the Sonnax info on the HD 2-3 shift valve, the Overrun clutch is off in 1st and 2nd gears in [D3]:
http://www.sonnax.com/parts/2464-hea...-3-shift-valve
If true, then with a broken sprag the car will not move even in [D3], but will start in [D2] or [D1] where the overrun clutch is always applied.
Its a shame that the ATSG manual for the 4L60E made a mistake in their doco.

performabuilt

iTrader: (25)

Yes I see you are correct on the 1st gear you know I did not know that it was always my understanding it was on, I stand corrected lol.
But back to the OP
"Today i left a 4 way stop moderately hard and it shifted fine from 1-2 and 2-3 but when it went to Shift to 4th it banged real hard and acted like it fell out of gear. I pulled over and shifted it to park then back to OD and it wouldnt move. I put it in drive and it was fine. So i drove it all the way home in drive."

This part is where i got it would not move in OD position then as it says he moved it to DRIVE D3 and it went fine and he drove it home that way,
Though that makes his problem a bit more perplexing since the overun clutch does not come on in D3 1ST, Unless of course he did install the TG HD 2-3 VALVE during his rebuild ,
But I think we need more info.