So I’m hopefully wrapping up this rebuild but was hoping the gurus here could help me out! First off I’m getting a crazy squealing noise from the low roller clutch. Sounds to me like the springs rubbing. It doesn’t have many miles on it which is why I didn’t replace it and it looks totally fine to me. Is it bad?

second issue is while I’m checking rear end play I kept getting different readings depending on


how the tail shaft is clocked and it turns out it’s showing around .005” of runout. I lightly sanded and scotch brighted where the bearing sits on the case. Everything seems clean and flat. Where else could this be coming from? Thanks in advance

 

Here is a shirt clip

 

It's not unusual to hear a squealing noise from the low roller clutch when turning in the non-holding direction. As for your other question I'll let someone with more 4L80 experience answer.

 

The sqeek is normal. .005 runout change is not much and could be attributed to tolerance variations in any number of hard parts and washers and IMO probably nothing to be concerned with.

 

Awesome thanks! I went forward with it anyway. I have a new found respect for transmission builders.lol

 

Ok well apparently I suck. Here I am thinking I did a good job, triple checked everything, clearances are all good and bam, truck won't even hardly move. Someone save me.
Fluid level is perfect
Pump seems to be working fine

In Reverse it will barely move and there is an light whirring noise
D4- Basically wont budge, It feels like it engages when I move the shifter, rpm's rise but truck no go, also hear the whirring sound
D3- pretty loud clank going from d4-d3, no whirring sound and I can get the truck to move but I have to give it some rpm's
D2-1, same as above, but there seems to be zero engagement, change, movement, sound etc. going from D3-2-1

what the hell did I do wrong?

 

Sounds like it may not be filling the converter, Check for cooler flow .

 

I pulled the inlet line off the trans and ran it into a bucket and it seemed to be flowing strong

 

Hmm that is odd , maybe you didn't get end plug in PR valve bore? Reverse and fwd are hydraulically separated the only commonality is the pump and the manual valve? have you put a gauge on it yet

 

One other thing I ran into with an aftermarket input sprag it simple would not hold at all , But then it should still move in Manual low .

 

not yet, I have a gauge coming tomorrow. One thing I overlooked is that it’s showing full with only about 8.5 quarts of fluid. I thought that it should take close to 13?

 

Yea this got me thinking. I thought there might be an issue when I put the overrun clutch together because I remember being able the turn the planets in both directions but I guess I just assumed that was normal bc it was a new sprag so I put it in the back burner and I guess I got overwhelmed and forgot to address it again.

the reason I’m was rebuilding it in was bc the previous builder didn’t lace the overrun hub fully into the frictions and it was riding on top of the last friction so maybe the surface that the sprag rides on is bad. It looked and felt fine to me
I should also add that I replaced the valve body with a reman Sonnax with their overrun valve installed on it.
It moves in manual drive but it’s still not normal

 

Yes that sprag must hold. And I have run into a couple non-GM ones over the years brand new that well simply did not hold at all , This only with the late blue sprag with the small rollers. would not even pull on the dyno.

 

assembly of the over running clutch can be tricky. when assembled correctly before installation in the transmission the splines on the planet almost disappear completely into the clutches. and rotation should only be in one direction, locked in the other. if replacing the sprag make sure it is identical to the one you took out. also check both sprag surfaces for any divots that might have been caused by the sprag rollers. if this is the case on either surface that part has to be replaced. otherwise scotch.bright both surfaces, do not sand. always use transmission fluid when assembling and only turn the planet in its normal free rotation until completely seated. when installing the assembly in the unit, make sure you are working in a upright position.it is normal for the planet to drop a little when doing this. constantly turn and wiggle the assembly till you feel engagement of the planet. to check to see that it is properly engaged pull up ever so slightly on the input shaft and you should feel a few thousands of play up and down.

 

Ok so I finally got a few minutes to work on the truck again. I was able to get it move in reverse enough to back it down the driveway. Reverse sorta works sometimes and not at all other times. Doesn't move at all in D4 and D3-1 it drives but I have to really get it revving to get it to go anywhere. Line pressures at idle:
P-120
R-130-150
D-90
D3-90
D2-120
D1-120

Revving in reverse it would hit around 250ish and D4 about 210
I believe these pressures are too low, correct?
One question I have, when I replaced the the pressure regulator springs in the pump, the inner spring moves/rattles freely inside the outer spring. Is this normal?
thanks

 

if you send me your email i have a gm tech bulletin that talks about correct line pressure and the proper way of testing. it also includes info about all solenoids and pin outs. as for the rattling spring i don't think so. i have a pump at home i am going to check and get back to you. i believe when you install the boost valve the piston inside that valve contacts the inner spring while the outer housing contacts the outer spring keeping pressure against both.

 

awesome thanks, yea I thought is was strange so I quadruple checked the install and orientation of everything and I’m 99% sure it’s all correct. I’m gonna pull the pan and check it again before I pull the transmission back out.

 

Ok so I followed the procedure from the GM bulletin Michaelvp sent me(thanks again) and I seem to have good pressure according to that. So assuming the pump is good and pressure are good then a bad overrun sprag would explain the lack of D/R but what about in manual drive? It won’t start to get off its *** until about 2500rpm

 

Also one more wrinkle to add. There has been a screeching noise at startup(think nails on chalkboard but amplified). It about 1 second long as soon as the engine starts running. I thought it was coming from the engine bay but I know believe it’s coming from the back of the engine/front of trans

 

i checked the pump i have and there is no rattle from the pressure regulator springs. they are seated as i described. do you get the noise on every start up or only if it's been sitting a while? also when you were checking your input and output clearances, it is normal as mentioned earlier to hear a squeak type noise when turning the output shaft in one direction. that rotation usually needs assistance from a channel lock or vise grip unless your hands are made like that!! easy to turn in opposite direction. as for the input shaft there should be a good amount of resistance turning in either direction using your hands only. if either shaft did not react in this manner, there is something not seated correctly and/or incorrect clearances in the unit. i know you have a lot of time invested into this unit, but if you can't solve 100% of your issues with the trans installed, i would take a deep breath, pull it again and start from scratch, rechecking every aspect of the assembly. i have saved on my computer the ATSG manual for 4l80. i'll send that to you tomorrow. it's a pretty large pdf.