727 Torqueflite issue

Hoping to get some direction from some members with more experience with this than I. I recently acquired a '78 D150 with a mild 360 that I have been sorting out. When I got it, it had a Summit 650 with a totally mis-adjusted TV linkage. I don't believe it was run long this way, but it now has a TQ with properly set-up linkage. Fluid checks fine. It runs well and the trans shifts very well and at the right points, however.... Primarily when warm, I am getting a "bang" or "klunk" coming off idle such as when pulling away from a light. This does not occur all of the time, but enough to be concerned. The truck will start to move, and then the noise. It almost feels like it is slipping before engaging. I have been thru the driveline and all u-joints and rear are play free. It almost seems pressure related. I haven't touched the bands because it seems to shift and work so well otherwise. Any ideas where to look?

Does it also do this in manual low? If so I don't believe it's in the trans. When working at the Chevy dealer thiis was a common issue with pick-ups. The driveshaft slip yoke would stick on the trans output splines. It could be cured by cleaning the splines if dirty/rusty and lubing them.
Doug

Thanks. I really don't believe it's there. I have experienced that in 4x's and have cleaned/ lubed them. This is a 2x and splines are clean free and no rust. Has a different feel too. They snap as you move. This moves then snaps or klunks. I'm not a trans expert, but I am wondering if a servo piston is losing pressure at idle or if there is something in the trans that could cause this. Doesn't feel/ sound like loose converter bolts either. I will have to try manual low and see if the symptoms change. I think the band applications are different in that case.

One piece driveshaft or two?

If two, check the center bearing for the same spline issue.

Only thing “on” in drive, standing still, shifter in D is then rear clutch and ORC.

The rear clutch may be partially on, then as you open the throttle the rise in line psi further applies the rear clutch.

That may be apparent with the ever popular but really used pressure test.

The ORC - possible something going on there but that could be eliminated by testing in manual low.

Thanks. Single piece driveshaft. There really is no spline, u joint or rear issue that I can find and I have looked. It really feels like something inside the trans engages as I apply throttle. The harder I apply throttle, the more pronounced the issue, but again it does not occur all of the time. More often when warmed up. Truck will start to roll, but doesn't feel positive until the dreaded klunk. I've become accustomed to feathering it off throttle, but have not tried manual low. I'll do that and will do whatever kind of test is needed to troubleshoot, just don't know where to begin Again, the trans works very well otherwise. So, starting in low will eliminate the ORC as an issue? I have read these can be damaged by abuse? I don't think the PO was kind to this rig in the short time he had it as evidenced by the rubber inside the wheel well...

Manual low application will lock the rear drum, just as the ORC does. So if that fixes it, that’s a possibility.

Other quick test that may help, lock the the throttle pressure lever all the way back. That will raise line. If that helps, then sounds like a leak in rear clutch apply.

ok. Thanks. Will try those. It did take me a bit to get the TV adjusted right. In fact right now the lever is just off the fwd stop to get full rearward motion at wot. I did have some flare on 2-3 at very light throttle and early shift points with that lever just a bit further fwd.

You don’t have to “adjust” it, just use something to hold it back all the way, like a rubber band or some thing. Just a test.

Yes, I understand that. Was just saying how sensitive that adjustment seemed to be, but its been a while since I had to play with one. Don't recall how normal that was.

Ok, Had a chance to do those couple tests. The results were not what I expected. I can report:

1.) This condition does not happen until the truck is fully warmed up, like 10 min.
2.) Starting in Low or first had no effect. Still had the "slippage" and klunk
3.) Reverse does not show this problem
4.) Rigging TV lever fully back had no effect other than raising my idle speed a bit.
5.) It is more pronounced when starting up an incline. It seems to always do it then.

Any further ideas? Maybe at this point gotta drop the pan. Maybe I'll see something then. Again, aside from this, it operates as it should. The fluid looks and smells fine although it was maybe a full quart and a half low in addition to the misadjusted TV when I got it. The PO really didn't do it any favors. Thanks for your help.

If it’s in the trans my best guess is hard parts related to the rear clutch. Could still be an ORC issue but can’t say I have ever seen this before the way you describe it.

So, you are thinking hard parts as opposed to a seal? Trying to think of how I could further troubleshoot this. Maybe I'll pull the shaft and look at the rear backlash independently, but I just don't see it. It definitely comes with heat (time). No rear noise or trans pump whine either. Is it true you can check the sprag by turning the rear yolk in both directions and it should be tougher to turn in one direction? Would a clogged filter act this way at all? Maybe I'm grasping here, but pulling the trans is not something in my immediate plans unless absolutely necessary. Thanks.

If you had a gauge on it the line pressure should have risen when you brought the TV lever back. That “should” have helped things if the rear clutch seal was at fault but you never know. If a seal was bad I would expect some slip or chatter even when warmed up. Dropping the valve body and doing an air pressure test may reveal something.

I was waiting for your results before posting this but I had a bad converter do this.

If it was in the converter, wouldn't it do it in reverse as well? And your converter did this only when warm?

Just seeing this you don't have the TV adjusted correctly if it is like this , but this misadjustment isn't the cause of your problem.

This too ...
What do you mean by the rear being "play free " , that's impossible , there is backlash between the ring and pinion , if you truly have no backlash then something is not right with your rear axle. I had an 86 ramcharger and an 89 d150 and both had clunky rears but it mostly happened when first putting them in gear , it was the rear backlash opening up .

Transman is on to something when he says it sounds like HARD PARTS , I see a trans removal in your future .

That is the best can adjust the TV. Having the lever just off the fwd stop (probably no morethan .25) is the only way I could get full travel rearward at WOT. And that last adjustment to obtain full travel made a big difference in shift points and kd. All factory parts, but not sure if the levers are matched, or if there were different ratios.
And yes, there is a small amount of lash at the rear, but nothing that would account for this condition.

What I recall was after "it" happened the truck was still driveable but the converter felt tighter but not efficient. It did it the first time pulling out from a stop on hill. And as I recall it was bad at all conditions hot cold ,front/backwards. It wasn't like that long. I replaced it that week after getting home. The initial clunk wasn't a slight clunk either. My main reason for putting this post out here was when I read your situation the first thing I though off was that converter failure I had. But these guys responding know more than me. That's why I waited until their diagnosis was complete.

Just add, if it isn't tranny, converter, then it would have to be driveline or chassis.

Then you don't have the right TV parts, .25 is a 1/4 " that's actually off a lot and the fact that when you put it to wide open and it raised you idle tells me it's not adjusted properly .

Can you post a picture of the linkage at the carb at idle ?

I can't post a pic here for some reason, but I've done dozens of these adjustments over the years. Typically with the TV lever pulled forward you can get full rearward travel at wot. This one lacked that full rearward travel by and I'm guessing, maybe 1/4 " max. I biased it by pulling the lever just off the fwd stop by about that amount. So I have full rearward travel at wot. The throttle linkage pin is touching the rear of the slot in the TV linkage and of course it moves immediately with throttle opening. This is the best I can do. The linkage is the full rod type as opposed to the bellcrank type. I was surprised when I rigged the tv open to test and the idle was affected as well. My understanding is the slot in the linkage was supposed to absorb that but I never tested that. My guess is that there are some mis matched componets contributing to this. All this aside the trans works well except this issue. It is more than slop in the driveline. If it was, it would be like half a turn of the pinion.

edit: As a further test, I pulled the shaft. Again, rear seems not to be an issue. Shaft could turn easily in one direction and more difficult, but not impossible in the other. I compared that to two 727's I have out and seemed to match one. The other which has a known issue could turn easily in one direction, but was about impossible to turn the other. I'm discounting that one, but these are things I never really looked at before so I don't really know. Was able to attach pic also.

I saw in one of your posts that the trans fluid level could be a quart to a quart and a half low. Did you top off the fluid level?
Any Mopar trans I've ever had that was a quart low functioned poorly after the trans warmed up.

The 1st step in troubleshooting an auto trans was to be sure the fluid level was correct, not low, and not over full. With the fluid warm, vehicle on a level surface, trans in neutral (newer stuff is in park, but park doesn't work on the old transmissions), the fluid level should be at the full mark. If it isn't add, if its more the the distance between the "add and the full" above the full line, drain some out.

Until the fluid level is correct, almost every test will give incorrect info..

Fluid level is correct.

There are at laest 2 different length KD levers at the trans itself. You may have the shorter of the two. Thus your range of adjustment is off.
Doug

Yeah, that’s what I am seeing. Wondering what the rhyme or reason for that was. I have a few kicking around. I’ll have to measure them up. And I believe I have the longer installed and need the shorter, but yeah. Thanks.

What you are getting with spinning the shaft one way verse the other is correct for a properly functioning overrunning clutch/sprag.

If that picture is of your setup I see a problem , the flat bar from the carb to the top link is not supped to be angled like that , it has to be pretty much horizontal , it is screwing up the movement of the throttle linkage being like that and more than likely why the idle is changing.

What is that carb from, the connection point is way to low, if you can't raise it up put a spacer under the carb to raise it assuming you have hood clearance.

"Shaft could turn easily in one direction and more difficult, but not impossible in the other." Since the problem only comes on with heat, I'm assuming it is leakage to the rear clutch apply at this point rather than a sprag issue, which I would think, should be evident all of the time.

The carb is a TQ from a '74 400, but the throttle pivot location is in the same as every production TQ I have or have seen. I am using a thick base gasket and am not going to use an additional spacer. The kd linkage is unknown. I'm assuming it is 4bbl since it lines up with the 4bbl carb, which is more outboard than 2bbl, but can't say for sure. I didn't love that bar lean either, but in all of my research I have seen it on others and assumed it was ok. Did they have lower KD linkages for 4bbls? The only difference I noticed was for single piece vs the bellcrank type. Both were used on trucks of this era seemingly with no rhyme or reason (at least to me). EDIT: Below is a 3,400 mile '78 LRT and another un-modified 360 4bbl same era. Note the bar positions

this has nothing to do with heat or rear clutch apply leakage , that is how the sprag operates , it's NORMAL. If you had rear clutch apply leakage you be having slipping issues in ALL forward gears.



ok scratching my head on that one as it does not look right to me. The width of the carb linkage attachment points side to side are the same 2bbl and 4 , what is different in the location front to back 2bbl vs 4bbl, 4 is more forward.

"this has nothing to do with heat or rear clutch apply leakage , that is how the sprag operates , it's NORMAL."- Yes, we both agree. That is what I was trying to say, sprag seems not to be an issue

If you had rear clutch apply leakage you be having slipping issues in ALL forward gears.-ok. Hmmm. There is no slipping at all that I can discern other than what I noted.