Trans problem

[BDH]

My truck is a 93. Its putting out a decent more than stock power, and it has 170,000+ miles. Honestly I am suprised the trans hasnt let got sooner. About a year ago, I put in a DTT converter and a shift kit. I have had no proplems with it until just last week.

The truck has not been driven much over the past 5 months. I went on a 100 mile drive on the freeway at 75mph. About 50 miles into the trip, the trans felt like it poped into neutral (rpms shot up a little, truck slowed down) I let of the gas. After a few seconds it kicked back in. I shifted between drive and neutral a few times to make sure the shifter and linkage were good. I got on the gas again and continued on. The rest of the 50 miles, it did the same thing about 10 more times. Pop into neutral, then back into drive all on its own. It was always on flat ground at steady speed. Once I got home, I checked the fluid. It was about a quart or two low, but still on the dip stick. I then drove it and gave it hell. Floored it from a dead stop. It took of like a bat outta hell like always, shifted normal and firm through all the gears. Everything seamed fine. I beat on it hard for a good 30 min. Constant full throttle aplications, a few donuts!! I figured, if its broke, might as well see how broke it is, but nothing. Then back on the freeway. 2 miles into it, cruising at 55, it did it again!!!

I am lost. Is it a valve body issue?? It shifts fine. Holds up to my abuse. But cant take a gentle cruise.

 

[Bill Stockard]

It sounds like a Throttle Position Sensor (TPS) problem shifting in and out of Overdrive.



Bill

 

[cerberusiam]

When it goes to neutral it is in OD correct? When you were thrashing it and testing you never made it to OD for very long, correct?



My guess is you have a problem in the OD clutch pack. Cracked piston, broken snap ring, or a torn lip seal on the piston. The initial apply works then as you cruise it slowly bleeds the pressure off faster than the circuit can supply it at low rpms.

 

[BDH]

yes it has been in OD everytime. If it was the TPS wouldn't it just drop out of OD and go to drive (3rd)? it is going into neutral. Drive would over rev the engine at 75 mph and it would realy want to slow the truck down. Everytime it did it it just coasted in neutral. I could hit the gas and the engine would just rev. Then I could feel it reengage. The same as if you intentialy shift from N back to gear.

 

[BDH]

I did have one full throttle OD acceleration passing a semi up a 7%+ grade that I reached about 95mph and it held no problem.

 

[BDH]

When it goes to neutral it is in OD correct? When you were thrashing it and testing you never made it to OD for very long, correct?

My guess is you have a problem in the OD clutch pack. Cracked piston, broken snap ring, or a torn lip seal on the piston. The initial apply works then as you cruise it slowly bleeds the pressure off faster than the circuit can supply it at low rpms.

Are these parts in the valve body or the OD unit at the back of the trans? Would that have effected my up hill pass at high rpm? Or is only at low rpm like you said?

 

[cerberusiam]

The OD clutch is in the OD unit on the rear of the trans.



It is entirely possible the computer is dropping OD also, but you should feel the downshift to drive and have a 400-500 rpm jump. If its a minimal jump in rpm it did not come out of OD via computer control.



It could also be forward clutch pack releasing or even direct clutch pack releasing from a loss of pressure. At light throttle the TV pressure is dropping the applied line pressure so on of those clutch packs could be bleeding off and releasing.



Under heavy throttle it might not be noticeable because the rpm's and pressures are up. You could try and duplicate the problem by locking out OD and driving it. Gonna be slow because you want to keep the rpms in the same general range as it happens in OD for a comparitive test.

 

[BDH]

Definately not computer involved. it completely is coasting when it happens. The rpm raise is just because there is no longer a load on the engine. It only for a split second while I still have my foot on the pedal, then I let off.

If the OD unit failed, would it just default back to direct drive, or could it fail and not have any output? all OD is, is the trans in 3rd(direct drive) and the OD unit engaged?

After reading you posts, it sound like the probable cause is 3rd gear related parts in the valve body. I should probably start with a vavle body teardown/inspection. Maybee something failed when I put it back together when instaling the shift kit.

 

[cerberusiam]

Costing is normal on a downshift though due to how OD is designed. When the computer demands OD the solenoid routes fluid to both the OD directs and the OD clutch pack. The OD directs are backed up by an 800 psi spring and naturally take more lfuid to release, but, they need to release first. The transition is handled by a sprag clutch in the OD direct unit that will keep things locked until the OD clutches apply and the power gets routed thru the OD pinion to speed the output shaft beyond what it is at when in 1:1. If the OD clutches release because of a leak and the OD directs are still released you get free wheel becuase the truck is going faster than the out put shaft speed. OD is normally free wheel when you lift off the throttle anyway until the OD directs engage.



Generally if the trans shifts into gear fine its not the VB, runaway upshifts, cutaways, no shift, could be the VB but if it hits the gears good then goes out its normally a servo or clutch pack problem.



You could be just on the verge of a VSS issue and as soon as you lift and set the throttle again it cures the issue. Before I would tear into the trans I would put a switch on the Sense side of the OD circuit and manually lock it into OD then see what happens. The OD sense wire is th esmaller of the 2 on the trans connector, not the neutral safety switch. Scotch lock a wire to the sens ewire under the truck, run it to a SPST switch in the cab and the other end to a good ground. When you flip the switch to on, it will ground the OD circuit and engage the solenoid. The computer neither knows nor cares and you can verify if its computer related, TPS or VSS, or a mechanical problem.



You might try leaving your foot on the acclerator when it goes away and see if it will eventually downshift and pickup drive. If you are lifting at the slightest feel of neutral you may just be missing the downshift.

 

[BDH]

I know one time it did it, it was for about 10 seconds, i actually started to pull onto the shoulder thinking that it was finally done. during the 10 seconds i hit the gas multiple times, flooring it, the engine only revved, i held it at 2500 rpm for a second with nothing. if it was still in any gear, it should have done something, right? once it slowed to about 50, i felt it kick in again. that was the worst time it did it, every other time it only took a few seconds, and it always kicked back into OD.



I will try the switch trick as well as driving with OD locked out at the same rpm. It wont be until next week till i get back to it.

 

[BDH]

I sent you a PM cerberusiam.

 

[cerberusiam]

Yeah, sounds like it is complete free wheel for some reason. I will have to let that percolate in my brain for a bit. Something is trying to retrieve a memory, but alas, to much junk in the way yet.



Maybe if I consult with Patrone it will come to me.

 

[HHhuntitall]

Yeah, sounds like it is complete free wheel for some reason. I will have to let that percolate in my brain for a bit. Something is trying to retrieve a memory, but alas, to much junk in the way yet.



Maybe if I consult with Patrone it will come to me.

Heyyyyy, I like the way you think..... To me, and my experience is limited with overdrive units, as I'm just beginning to explore that option this last month, it sounds like the overdrive solenoid is working intermittently. Just a suggestion, as I have seen it before when the transmission is hunting between gears (although it usually just downshifts)..... check your plug-in on the side of the transmission to make sure it's seated good. I don't think that's the problem, as it should just do some hunting in and out of gear, downshifting... ... then there's the inline temp sensor; it'll do the same thing if it doesn't have signal from it... ... also, have you changed the filter and fluid recently? Or since you installed the new VB and TC? If there were some trash in there and it's blocking the pickup... . although I would think it would have given up by now with no coolant flow..... Cerebrusiam, if the little arm bent on the front band servo, couldn't that cause it to not lock in and cause it to slip in OD? But it slips in Reverse, when it does that, doesn't it? If I remember correctly, that was a common failing on the 727 when you upped pump pressure or over-adjusted the front band... ... I think the BD Shift kits for the diesels came with a larger, heavier link arm.....

 

[cerberusiam]

Cerebrusiam, if the little arm bent on the front band servo, couldn't that cause it to not lock in and cause it to slip in OD? But it slips in Reverse, when it does that, doesn't it?

That is one of the weak points with a shift kit, the 2ng gear apply lever. However, its not applied in OD.



Forward clutches, direct clutches, and OD clutches are all that is applied in OD.



In reverse, yes, both front and rear bands, direct clutches, and OD direct clutches are applied.



Since it all seems to shift fine until he goes to OD and light throttle it makes me think that the OD clutch pack is releasing for some reason.

 

[Bill Stockard]

yes it has been in OD everytime. If it was the TPS wouldn't it just drop out of OD and go to drive (3rd)? it is going into neutral.

Yes, it would go from OD back the 3rd gear. Some drivers mistakenly think the transmission is shifting to neutral. It's clearly evident you know the difference and my suggestion doesn't apply.



Bill