68SS98Z28

98 Z28 with only mods SLP lid and bottom bottom breather.
Intermittently the 1-2 shift feels like i got rear-ended. Sorta like if you were stationary and reved the car up in N and dropped it into gear, that same surge you feel and kuh-lunk of the drivetrain sucking up the torque. It isn't noticable in WOT conditions or if i really get on it, but is more likely if i just ease off the brakes and am taking it easy. And it doesn't happen all of the time. Car has about 65K miles, i just got it last year so don't know the history. The ATF is at correct level and appears to be nice and clear and correct color. No DTCs are thrown for the tranny. Anyone have any idea what the problem is, how to fix it? Thanks in advance!!

melchoir

iTrader: (4)

My 98 TA does something similar, and is bone stock. It *always* slams into 2nd gear, one mechanic said the car drove like it has a shiftkit. No noise from the changing, just a very quick and hard shift.

flyin red TA

1-2 is late and hard, then it probably feels pretty soft going into 3rd? Worn out clutch packs. The shift hits hard because it's late then finally catches, as opposed to the normal quick and smooth. I see a rebuild in your future.

LastGenZ28

I think you should get someone to pull the valve body down. There is a spring in the 1-2 accumulator and when they brake they cause a hard shift. You can only feel the hard shift when you are in a light throttle condition.
Good luck

68SS98Z28

Thanks for your thoughts--if rebuild is necessary, can/should i get a performance rebuild? If so, can Mr. Goodwrench do it or do i have to go elsewhere? Anyone know a shop they can recommend in Hawaii?
Thanks again!

melchoir

iTrader: (4)

Does the rebuild apply to me also? Or could my car just have had a Hypertech hooked up to it and had things adjusted? My fans also kick on at startup, every start so a friend thinks my car may have been "messed with."

BLUE99T/A

iTrader: (2)

There's one way to find out. Have GM reflash it.

XxXTransAmXxX

iTrader: (12)

As LastGenZ28 said, a harsh 1-2 shift is almost always traced to the accumulator springs...it could be broken, now we learned in the AT ASE Tech class, that even if you just want to firm up the shifts you can remove the accmulator springs, or flip the piston and spring around to firm it up...What the spring does is the pressurized fluid is carrying such great force that when it hits the piston it HITS it, so the spring is there to initially cushion the engagement....Essientially most fullblown shift kits have you remove, or flip them around exchanging places between the piston, and the spring... Just a lil $.02, if you were around IL, IN and could get it out of the car I would be more than happy to take a look at it for ya, and rebuild it if necessary for less that the OUTRAGEOUS prices shops have...Most dealer's wont replace anything with a perf. deal.....However they will replace the Reaction Sun Shell in the transmission though with an aftermarter unit referred to as "The Beast" because ont he back of it where the splines are for one of the planetary sunshell's was brittle, and hardly had material there, so someone beefed one up, and added material to make it stroner, and the other main weak area is the sprag units....If you've ever seen one, you would know why...

flyin red TA

If it's just a slightly harder shift, I probably wouldn't worry too much about it. It wouldn't surprise me at all if your line pressure is raised up from a program, and that would make sense about the fans as well.

Start worrying when the shifts are coming late and hitting really hard...or when you can just barely feel them at all.

68SS98Z28

Well, i started programming with HPTuners and the first step is putting the car in SD mode by dissabling the MAF. The 1-2 shift eems worse now and occasionally kicks going into drive from park. I read in another post that earlier cars the shift pressure is higher during MAF fail? Anyone know about this? It was happening before the program change so i think it's real, but i flashed the stock program back and it was much less noticeable. I got a few quotes for rebuilds and the guy who seemed most knowledgable predicted that it was throwing 1870 and said it was just the valve body and he could replace it.

Should i consider beefing anything up while i'm at it?

Thanks again all commenters. Saving me a lot of dough.

=)

Dustin 98TA

A common problem with the 4L60 is the overdrive valve bore wearing out causing loss of line pressure. The PCM will then raise the line pressure because it thinks the trans is slipping. There is usually a 1870 code thrown with it. This causes the trans to shift VERY hard. Try to reset the PCM and see if it works right for a while, usually it will act right for a few miles before going back.
There is an easy fix for it, unfortunately you will have to remove the valve body. A good trans guy can drill out the bore and replace the valve with a larger one and change the spring, not only does this fix the problem, but it gets rid of the PWM also. This means when it goes into OD it will immediately go into lock-up, instead of slipping in.
This may not be your problem, but its worth looking into, ive seen it happen many times in the past.
Good luck.

SgtB

iTrader: (3)

first things first...have you checked your trans fluid????

is it low??? does it look/smell burnt???

68SS98Z28

Thanks for the additional thoughts. It is throwing code 1870 now, i think since i'm running SD mode while i tune the VE table and this is causing harder shifts and it's less intermittent.

I called a few tranny shops. First guys says it needs rebuild but last guy i talked to said valve body and he can do it for $200 in a few hours, with new filter and ATF (remember i'm in Hawaii before telling me this is a rip-off). He seemed much more knowledgable and predicted it would throw DTC 1870 so i'm going to talk to him right now. Thanks again for all of the input everyone on this thread.

Paul

SgtB

iTrader: (3)

good luck

btw..you sig pic is huge and will be deleted as soon as amod sees it.

sig limits are 500x150 pixels

68SS98Z28

Sorry to all if i bogged machines down...
=)

BlackHawk T/A

iTrader: (3)

I thought I read that it commands full line pressure all the time when you put it into SD mode (no MAF)?

SgtB

iTrader: (3)

no problem.just helping out

Dustin 98TA

If it is throwing a 1870 code, and shifting hard, it is probably in the limp home mode. When the PCM does that it wont shift into OD, and wont allow fluid to go to the trans cooler. Dont drive it far or hard it will get hot.

Cody Brooks

iTrader: (2)

if you have an 1870 your problem is most likely a seal problem not a valve body problem. I've talked to my asep instructor about that code and he said he has found that the input bushing being worn or a cut seal to have been the cause more than anything else. the valve body fix is at best a 50/50 shot. I would recommend doing a reseal and replace all the bushings if you find brass in the pan. you can check the valve body but i doubt you'll find any real wear or a sticky valve. this so called wonderful valve body fix is a band-aid fix sometimes it might work and sometimes it'll help but most of the time it'll do no good at all or the problem will come back quickly.

68SS98Z28

Well, i took my car to a local tranny shop called Kiyo's run by Wayne if any happen to be interested here in Hawaii. Wayne was very nice, was more knowledgable than other shop owners i had talked to, and replaced the valve body for $175 plus tax.

Since i've been programming the car and it was in SD mode while i have been logging my fuel trims to adjust the VE table, i re-enabled my MAF before taking it to him. I did experience the "surge" on the 1-2 once on the way home but have put about 2 hours of driving on the car since then and it hasn't shifted rough once since. I called him and told him about the 1 time and he said if i bring it in he'll take another look at it, but it hasn't happened again.

A friend of mine here suggested maybe just a bubble or something from having the fluid and filter changed and if it doesn't happen again i'm good to go? What are other's thoughts, does that make sense?

Regarding line pressure during SD mode, i have no idea but it definetely shifts stiffer and with this rough 1/2 shift in normal mode in SD it was a killer, felt like i was getting rear-ended. Maybe i should start another thread and see if anyone knows what is exactly happening with shifting in SD mode with the A4. I haven't put it back in SD mode but was planning to do so after i've driven some more with the MAF just to make sure the tranny problem is licked.

Thanks again for all who contributed to the thread--it was really helpful in picking the right shop--even if the car isn't fixed yet i think Wayne is the guy to help me get it right.