Tranny rebuilt 4l60e 1995 still with harsh 1-2 shift, help with springs?

[95Noobie]

I'm way overdue for an update but the transmission rebuild turned into a several month mess. The first guy got injured halfway through the rebuild and had a friend come and 'finish' but ended up cracking the pump while reinstalling (apparently the torque converter was not in correct position when tranny was bolted back in). Then during disassembly and repair of the cracked pump plus putting the pump cover back on one of the bolt holes on the housing had a chunk of aluminum crack off right at the threads so the case became unusable. Gave up on that shop, flatbed to another shop, sourced a used late 1995 case online and had the new shop take everything out and start over.

Originally we always had a firm 1-2 shift but reason for rebuild was difficulty in getting reverse to apply. It would engage on level ground but trying to reverse with a slight load or go up a slight grade it would slip.

The new guy got new gasket kit and some new 'steels' and put it back together.. He ran into a few other minor issues, reinstalled and still had weak reverse. Took it all back out and found a C clip not positioned exactly in one of the small holes and corrected that and then reverse was good. He put in a corvette servo and also used a reman oem torque converter. We picked it up last night and noticed the 1-2 very firm shift is still there. Feels just like before.

I put in a sonnax pinless accumulator. When we got the truck there were 3 springs in the accumulator, one smaller very strong spring and 2 larger weaker ones. I replaced with the stock GM larger purple weaker spring and smaller stronger yellow spring.

Since the firm shift seems identical before and after the rebuild I'm thinking the corvette servo may not be to blame here although I've read it can give a chirping tires between one and two and some 'like that' feature. I'm looking for smooth shifting if possible.

I've also read that in this case since the piston is against the separator plate then comes springs and there is no piston and piston hole is sealed that a firmer spring would give a softer shift.

The first tranny guy before he was injured was mentioning that he often puts a stack of 3 standard hardware nuts (I forget the size maybe he said nuts for a 7/16" size bolt?) in the accumulator instead of a spring so that the piston can't move very far at all which would be like a very VERY firm spring and helps give a smooth shift.

I'm working on the idea that a completely rebuilt tranny and valve body with new solenoids and no worn steel or bands etc that still gives a rough shift would then go back to the line pressure the corvette servo or the accumulator springs.

I plan to drop the pan (again!) and replace the 2 oem springs with something and looking for advice!

Thanks in advance!

 

[NickTransmissions]

I'm way overdue for an update but the transmission rebuild turned into a several month mess. The first guy got injured halfway through the rebuild and had a friend come and 'finish' but ended up cracking the pump while reinstalling (apparently the torque converter was not in correct position when tranny was bolted back in). Then during disassembly and repair of the cracked pump plus putting the pump cover back on one of the bolt holes on the housing had a chunk of aluminum crack off right at the threads so the case became unusable. Gave up on that shop, flatbed to another shop, sourced a used late 1995 case online and had the new shop take everything out and start over.

Originally we always had a firm 1-2 shift but reason for rebuild was difficulty in getting reverse to apply. It would engage on level ground but trying to reverse with a slight load or go up a slight grade it would slip.

The new guy got new gasket kit and some new 'steels' and put it back together.. He ran into a few other minor issues, reinstalled and still had weak reverse. Took it all back out and found a C clip not positioned exactly in one of the small holes and corrected that and then reverse was good. He put in a corvette servo and also used a reman oem torque converter. We picked it up last night and noticed the 1-2 very firm shift is still there. Feels just like before.

I put in a sonnax pinless accumulator. When we got the truck there were 3 springs in the accumulator, one smaller very strong spring and 2 larger weaker ones. I replaced with the stock GM larger purple weaker spring and smaller stronger yellow spring.

Since the firm shift seems identical before and after the rebuild I'm thinking the corvette servo may not be to blame here although I've read it can give a chirping tires between one and two and some 'like that' feature. I'm looking for smooth shifting if possible.

I've also read that in this case since the piston is against the separator plate then comes springs and there is no piston and piston hole is sealed that a firmer spring would give a softer shift.

The first tranny guy before he was injured was mentioning that he often puts a stack of 3 standard hardware nuts (I forget the size maybe he said nuts for a 7/16" size bolt?) in the accumulator instead of a spring so that the piston can't move very far at all which would be like a very VERY firm spring and helps give a smooth shift.

I'm working on the idea that a completely rebuilt tranny and valve body with new solenoids and no worn steel or bands etc that still gives a rough shift would then go back to the line pressure the corvette servo or the accumulator springs.

I plan to drop the pan (again!) and replace the 2 oem springs with something and looking for advice!

Thanks in advance!

What a mess, sorry to hear.

Check servo travel, too much will cause a harsh 1-2 shift.

If you have a pinless accumulator with Stock springs in the 1-2, lesve it for now and see the next paragraph...

Drop the valve body, spacer plate and gaskets - check the 1-2 feed orifice and check ball seating location.

If the orifice has been hogged out, that's the source of the harsh shift. If the check ball seating location is excessively worn, that will make it worse and ball will eventually get stuck in the plate.

If any of the above is observed, replace the spacer plate with Transgo's 46-95 PLT spacer plate, drill the 2-3, band release and 3-4 feeds to .093. Leave the 1-2 feed alone.

That will give you a civilized 1-2 upshift and crisp 2-3 and 3-4 shift which is what you want.

Pinless accumulator - keep in place for now, road test. If 1-2 shift is still too harsh, replace with stock aluminum 1-2 acc piston and factory springs.

 

[95Noobie]

Thanks for the reply and yes it was a mess for a long time.
Unfortunately I don't have tools or know how to drill out band release or feeds and to get it to a certain precise bore size. I don't know if the 'hogged out' orifice will be obvious but I could probably tell if the ball is stuck I would think.

I can ask the 2nd tranny guy if he would have addressed or checked for an enlarged orifice in the 1-2 feed area. I would assume if the valve body was replaced or 'rebuilt' that would have been back to stock settings? Can I see this feed orifice easily with the pan down or valve body has to come completely out first? You probably have a video on your youtube channel I could watch?

So when the truck came to us it had the factory aluminum 1-2 piston type accumulator but it had 3 springs inside each other and still shifted hard. With this transmission is stronger springs in the 1-2 accumulator equal to more firm or softer shift rather than weaker or a single spring?

I note no issues shifting 2-3, 3-4 or reverse or backwards through the gears.

It seems like the hard shift is related to a delayed or difficult pressure buildup as if you are going easy on the gas or going down a slight grade it shifts quickly and smoothly but if you are going up a slight grade or steady on the accelerator it will hang and then go in hard.

 

[NickTransmissions]

Thanks for the reply and yes it was a mess for a long time.
Unfortunately I don't have tools or know how to drill out band release or feeds and to get it to a certain precise bore size. I don't know if the 'hogged out' orifice will be obvious but I could probably tell if the ball is stuck I would think.

Ok, you will need to bring the vehicle to a competent transmission shop that knows these units so they can correct the problems. The 1-2 acc feed works by having regulated accumulator oil push against the piston until it comes to a full stop inside the housing...Once this occurs, the 2nd gear apply servo fully applies the band and your 1-2 upshift is completed. The stiffer the spring and/or thicker the piston (a la the Pinless) the shorter the piston's travel time, hence the faster (and firmer) shift.

If you have the ability to swap the 1-2 accumulator piston and spring back to the factory spring and piston yourself, do that and see if it makes a difference (assuming you haven't done so already)
If not, take to a trans shop, explain the problem and let them give you a quote to fix it.

I'd not bring it back to whomever worked on it last since they obviously don't know how to resolve it.

It seems like the hard shift is related to a delayed or difficult pressure buildup as if you are going easy on the gas or going down a slight grade it shifts quickly and smoothly but if you are going up a slight grade or steady on the accelerator it will hang and then go in hard.

There is no delay in pressure build up (proper term: line rise) unless you have a leak in the 1-2 apply circuit (which you may have - the previous builder should have vacuum tested your TCC regulator valve in the valve body and converted the PWM apply strategy mechanically to "on-off" TCC apply. That would help solve for a late/harsh 1-2 shift, all other things equal).

Another reason not to take it back to whomever worked on it previously as they likely didn't do any of what I'm describing. Otherwise, you wouldn't have a harsh 1-2 shift after a complete (and proper) overhaul.

 

[95Noobie]

so in regard to the spring question in the accumulator, you are saying a weaker spring or a oem pin style would give a longer travel time of the piston and a smoother shift. So if the only change I made on my own was to put in more or firmer springs in the pinless setup I have now or even a stack of nuts that would create a condition of very little possible travel of the piston then I would be making the shift SOONER and more FIRM (would make it worse) Right now the pinless accumulator only has one purple spring in it which is less firm then what we had before and the shift seems still hard.

I'd like to change one variable at a time, and can tackle changing the accumulator and springs easily on my own. I was thinking of going to a very firm spring as a way to check that variable but it sounds like you would advise going the opposite way, go back to the oem pin style accumulator and stock spring. Sounds like I want more travel on the piston and more time for pressure to take hold before the 'apply'.

If changing the variables inside the accumulator do nothing then it seems the issue would have to be the hogged out feed orifice or the 1-2 apply circuit leak. I can ask but I think it is likely that instead of vacuum testing the TCC valve it was PROBABLY assumed that the new valve body would be sufficient to solve for problems like overworn holes and leaks, but thank you for giving me the questions to ask.

You are correct that the 2nd tranny guy would not be the one to convert to a non-PWM apply and does not have computers to reprogram trannies. The other challenge is the obd1 setup of the truck makes communication with the transmission's electronics a different type of project.

 

[95Noobie]

Sorry another thought. So the 'upgrade' to the corvette servo wouldn't be involved in this situation and it wouldn't make any difference to go back to a stock servo?

 

[NickTransmissions]

Sorry another thought. So the 'upgrade' to the corvette servo wouldn't be involved in this situation and it wouldn't make any difference to go back to a stock servo?

Please quote my post or mention me - I don't get alerts if someone responds plus it lets me know you're specifically requesting a response from me vs in general.

The vette servo will produce a firmer shift all other things equal due to its larger apply surface area relative to the 553 servo. So you can go back to the stock servo as well, to further tame the shift. But I'd check band clearance/servo travel. For a factory borg-warner high energy band, you shouldn't have more than .125 total inboard travel, if you do band clearance is considered excessive. Take the servo assembly out of the case, remove the two o-rings and scarf cut sealing ring at the front of the servo..Then reinstall it with the snap ring. Once installed, push in on the cover as far as it will go (You can do this with a pry bar - put the back of the pry bar against the cover and pry against the transmission tunnel) and measure the travel...

My guess is it's excessive, as most of these and 700R4s that come in have way too much. I set it as tight as I can get away with before the band starts making unwanted contact with the rev input drum's surface.

 

[95Noobie]

Please quote my post or mention me - I don't get alerts if someone responds plus it lets me know you're specifically requesting a response from me vs in general.

The vette servo will produce a firmer shift all other things equal due to its larger apply surface area relative to the 553 servo. So you can go back to the stock servo as well, to further tame the shift. But I'd check band clearance/servo travel. For a factory borg-warner high energy band, you shouldn't have more than .125 total inboard travel, if you do band clearance is considered excessive. Take the servo assembly out of the case, remove the two o-rings and scarf cut sealing ring at the front of the servo..Then reinstall it with the snap ring. Once installed, push in on the cover as far as it will go (You can do this with a pry bar - put the back of the pry bar against the cover and pry against the transmission tunnel) and measure the travel...

My guess is it's excessive, as most of these and 700R4s that come in have way too much. I set it as tight as I can get away with before the band starts making unwanted contact with the rev input drum's surface.

Thanks for the reply and clear answer (i'll quote your reply in hopes you get a notification)

Back to clearing up my confusion on what would change if we do a weaker/more travel setup in spring and piston vs less travel, I'll repost my question below:

so in regard to the spring question in the accumulator, you are saying a weaker spring or a oem pin style would give a longer travel time of the piston and a smoother shift. So if the only change I made on my own was to put in more or firmer springs in the pinless setup I have now or even a stack of nuts that would create a condition of very little possible travel of the piston then I would be making the shift SOONER and more FIRM (would make it worse) Right now the pinless accumulator only has one purple spring in it which is less firm then what we had before and the shift seems still hard.

I'd like to change one variable at a time, and can tackle changing the accumulator and springs easily on my own. I was thinking of going to a very firm spring as a way to check that variable but it sounds like you would advise going the opposite way, go back to the oem pin style accumulator and stock spring. Sounds like I want more travel on the piston and more time for pressure to take hold before the 'apply'.

 

[NickTransmissions]

I'd like to change one variable at a time, and can tackle changing the accumulator and springs easily on my own. I was thinking of going to a very firm spring as a way to check that variable but it sounds like you would advise going the opposite way, go back to the oem pin style accumulator and stock spring.

That's a good approach...First, change the Servo piston - remove the vette servo and install the original 553 servo (you'll need to locate a scarf-cut sealing ring for the smaller diameter grove on the piston as it's larger than the same groove on the corvette servo that's currently installed.

See what effect that has on your shift...If you can feel an improvement, but it is still a bit harsh go ahead and replace the pinless accumulator piston with the factory alum piston in the 1-2 acc housing - reinstall the factory spring. Then road test...

If neither of the above changes result in any perceivable difference, more extensive work will need to be done and valve body vacuum tested at the TCC regulator bore to see if it's worn...At that point, you may want to take it to a competent trans shop...

Sounds like I want more travel on the piston and more time for pressure to take hold before the 'apply'.

Yep, you got it...now you're beginning to understand how accumulator circuits work in an automatic transmission.

 

[95Noobie]

That's a good approach...First, change the Servo piston - remove the vette servo and install the original 553 servo (you'll need to locate a scarf-cut sealing ring for the smaller diameter grove on the piston as it's larger than the same groove on the corvette servo that's currently installed.

See what effect that has on your shift...If you can feel an improvement, but it is still a bit harsh go ahead and replace the pinless accumulator piston with the factory alum piston in the 1-2 acc housing - reinstall the factory spring. Then road test...

If neither of the above changes result in any perceivable difference, more extensive work will need to be done and valve body vacuum tested at the TCC regulator bore to see if it's worn...At that point, you may want to take it to a competent trans shop...


Yep, you got it...now you're beginning to understand how accumulator circuits work in an automatic transmission.

the factory alum accumulator, it came with one spring, or two in the 1995 4l60e? Do you know part number or color of the oem springs? I have some here but since the truck came to us with 3 springs (non factory setup I presume) I'd like to have the correct spring or springs on hand