mrvedit

You are correct that we don't know if the band clearance is the problem.
The only way to loosen a tight servo is to grind down the pin.
The way to tighten the servo is to install the Transgo shims, weld a stub to the end of the servo pin, install an extender on the pin (IMHO a bad idea), or purchase a longer pin and grind it down as needed.
I don't know how critical this clearance is, but GM makes a tool for checking it. I always tighten with the Transgo shims.

fishcrazy

Here is another thought that I had in pondering the build. When I removed the Orings on the pressure switch the first one I removed stuck to the round film over the pressure switch and came off with the Oring when I removed it. I did put it back on before replacing the Oring with the new one. I dont know what if anything this could cause but it was the one marked D4 in the ATSG manual. The other Orings came off leaving the film intact.

mrvedit

Hmmm, the pressure switch tells the PCM which gear the shifter is in; if the o-ring leaks, the PCM might be confused.

Your local shop should have a new pressure switch; trivial to put in after dropping the pan.

fishcrazy

I think I need to see what codes if any are being set. Cant I just take it to the local autozone and get them to read the codes? Or do I need to go to a tranny shop?

fishcrazy

Talked to Jeff at TruTech and he seemed to think the band was too tight also. Said I should check the servo pin travel and get it into spec if out first and i fthat did not fix it then get any codes that have been set and see where to go from there.

mrvedit

Glad to get agreement that this sounds like a band clearance issue; I'm not an expert.

The tranny shop can do much more that just reading the codes. They can force the trans through all the gears, thereby testing most components. They can read your gear selection, i.e. test your pressure switch. The wheels are best up in the air for these tests.

I know you want to finish the job yourself, but even I would now take it to my local trans shop. On a hoist it is so easy for them to get the servo out, check the clearance and grind down the pin if it is too tight. Getting the servo out in a tight space, especially without the special tool, is a real pain. The trans shop may have to remove the rear trans mount and drop it a bit; again pretty easy for them on a hoist.

fishcrazy

I thought I would at least look at it to see how tight it is to get to. It is tight to the catalytic converter on that side. It isnt much trouble to drop the tail support crossmember but the clearance may be an issue. I just hope this is the issue and it isnt something else mysterious.

fishcrazy

I took the truck to a tranny shop and he put it on some kind of scanner and said I had a code for the defective manifold pressure switch which he said was in the transmission and could cause my symptoms. Im thinking this is the pressure switch assembly that bolts to the valve body tells the computer what gear it is in. do know that when I was replacing the o'rings on the face of the switch I inadvertantly removed the plastic film with one of the o'rings and just put it back on with the new o'ring. Could this be my problem?

mrvedit

Yup, that's what I said in my post #163.
If the film came off with the o-ring, then it is ruined; you didn't mention before that you removed the film. New one is about $30.
Do you know any experienced trans mechanics that could install it for you.

fishcrazy

I did not think that the film was that important at the time but I should have known. I just let myself skate right by that. We live and learn. I certainly have learned a lot by doing this and am glad that I did it. I certainly owe you and carlsonauto a big thanks for the help. I cant tell you how much it helped getting advice all along the way from the two of you. I got lucky finding this site.

I did find the switch here locally and wish i had found the supplier sooner as they have almost anything you want. I guess we will soon see if this is indeed my problem.

fishcrazy

I plan to install the new pressure switch today. I have adjusted the length of the servo pin thinking that it was the cause of my problems and at this point I am wondering i fi may have gone a bit far in my adjustment since I have seemingly created a shift issue that did not seem to be there prior to my pin length adjustment. I seem to be getting a short period of slip between gears in the shift and a somewhat hard engagement into the higher gear. I plan to put the switch in and then see what it acts like before doing anything else with the servo to see what the new switch does to the shift. then if I still am showing this symptom making a decision on what to do. I had the thought that I may have taken too much off the pin when I noticed this behavior but it did not appear to be from the pin specifically because I have had shift issues going on from something obviously. And I think that the pin travel is at the higher limit of the spec now but not out of spec. I guess my thoughts should also include the question that I have about this pin extender tip I bought in case I did decide to make the pin longer. I have read in one post that a builder has seen more than one of those pins fall off. So I question whether I should use one of these if I should think I needed to lengthen the pin or just order a new pin.

The pin extender is like this one. http://www.transmissionpartsusa.com/...-00077605g.htm

mrvedit

Personally I would be hesitant to use a pin extender.
My local builder told me he just welds a blob on the end of a too-short pin and then grinds that down as needed.
I would suggest a new pin; mostly likely that won't need any grinding.
Both standard and extra length pins are available.

fishcrazy

Thanks for the input. I am going to see how this pressure switch works out and then decide where to go from there. I did not upgrade to the corvette servo and may think about that as well. I will let you know how the pressure switch turns out.

carlsonauto

Do not use a pin extender!!!! BAD NEWS... dont ask how I know that..

If you need a different servo pin I have lots of them. You can have a used one or two if you pay for shipping. Let me know

fishcrazy

Well thats all I needed to hear! Thanks for the warning Carlsonauto. I appreciate the offer also. I will let you know how my pin grinding has me shifting and may take you up on your offer if I need another pin.

I dont have the experience to know first hand just how critical the pin travel is. I have heard some say that the travel up to 1/4 inch is fine but maybe a bit sloppy. I am at 1/8 inch now or maybe just a tad over. Im going to try to top off the fluid today and drive it some to see how the new switch has changed the shifting. If it is better I may leave it as is unless someone would advise otherwise.

fishcrazy

I finally got tyhe fluid warmewd up and toped up and drove the truck around a bit yesterday. It seemed fine and did not go back to the no downshift to 1st mode again. So i think the pressure switch must have fixed that. I still have the CEL lit on the dash though. Will that correct itself or do I need to have it reset? The only thing that I had happen was a 2-3 flare one time. It only occured once and is not repeating. That seems strange to me but it is what it is I guess.

I will say that the last time i drove it to get the codes read at the tranny shop it did not go into the stuck in second gear mode then. I dont know if the adaptave learning feature of this transmission has anything to do with that compensating with pressure to make the shift happen better and override signals from the pressure switch or not keeping the stuck in second mode from happening. Or if no wthat the problem is fixed is it now trying to relearn the current behavior and caused it to flare once in the corrective learning process. Or am i just asking for trouble. I will test it again today and see if it flares again.

fishcrazy

Drove it again today and the stuck in 2nd problem seems to be fixed. I do have a minor sporadic flare in the 2-3 shift. It doesnt happen often. It happened once just now but only one time. Do you think i need to tighten up the servo pin travel?

mrvedit

Glad to hear you are making progress.
Sorry not to reply earlier - I'm on vacation in Tampa, FL.

A 2-3 flare indicates the band is releasing before the 3-4 clutch if fully engaged. I can see how a too-short servo pin might release a band a bit early, but Carlsonauto or other builder would need to confirm that.

fishcrazy

Well I hope that the sky is clear and the sun is warm because my inlaws report COLD weather in Michigan!!

I am going to replace the pin though and see what the results are then. The shift is not a major problem but I do want to at least undo what I did prior to replacing the pressure switch. I guess the other thing that could affect this is the clearance of the 3-4 clutch pack. I did measure that to be within the spec given in the ATSG manual but I have read elsewhere that some think that spec is to large. I am not however that smart about trannys to know if that is right or wrong though. I am just glad that the thing works! I do think that replacing the pin will help and I will let you know how that works out.

Thanks and ENJOY the vacation!

carlsonauto

If its flaring on the 2-3 ted is correct the band is releasing before the 3-4 clutch applies. The servo pin being too short could certainly do that. I think I remember you saying somewhere earlier that you didnt put the corvette sero in either, the corvette servo will also help "tighten" up the 2-3 shift as well.