Hi Guys,
I don't currently own any LS powered vehicles, but I read this forum because it has great content, especially from the experts here in the transmission sub-forum.

I've rebuilt a '93 4L60e using a kit from Dana. It works GREAT and has totally transformed the way the car drives compared to the old hopped up 700r4, but it has one problem...

When in manual 1st, it has no engine braking. Engine braking works in M2 and M3 as it should. I can wind it out to 6k rpm in M1, get off the gas and it drops to idle while the trans freewheels.

The first question from knowledgeable people will be about reverse, it works as it should.
It's clear the overrun clutches are applied in M2 and M3, so they do work.... Why are they not applied in M1?

I've tried to study the nice colorful hyraulic drawings in the GM manual, and have compared the application of the overrun circuit in M1 and M2 to try to find a difference that may highlight where the issue is in M1, but I just can see anything.....

Can anyone offer any suggestions?

 

I'm going to throw this out there until the big boys comment but.... low roller clutch/sprag

 

Thanks for your reply.
I'm no expert (obviously), but I though the lo/rev clutch prevented the low roller clutch/sprag from freewheeling... but there's every chance I'm way off

I've searched and searched for any forum with a post with similar issues and only just found one now..
The suggested possible problem was with this plate under the A/B solenoids being loose/missing causing a leak.
I need to study the VB schematics to understand how it may affect engine braking in M1 only, but is this a reasonable suggestion?

 

i think you're hoping it's a hydrualic problem but it sounds mechanical to me. my money is on the lo roller clutch as well.

 

Oh I'm very much hoping it can be fixed in the VB

 

It sounds as if the low/reverse clutch is not applying in M1. Yes, checking that plate would be a good place to start.

 

Again, I'm no expert, but I understand it wouldn't move forward if this was the case. The overrun clutch not applying is more probable??? But why?

 

having studied the overrun circuit ALOT a few weeks ago, I can tell you the overrun circuit, even in manual low is fed by D2 oil in stock form. this oil comes from the manual valve and is active in manual 1st or 2nd. If you have the Sonnax HD 2-3 valve then it is supplied by D3 oil. This means oil is supplied to the overrun clutch all the time regardless of gear until the manual lever is put into 4th. the only valve that it goes through that is related to a gear is the 3-4 squencer valve that only comes into play when in 4th gear.

 

Yes that was the same conclusion I came to after looking at the drawings, hence my confusion as to why it's applied in M2, but not M1...
I noted that the D2 oil passes through an orifice along the way and it referred to as 'orificed D2'.. I wonder if I have a problem with this orifice that is preventing overrun apply in 1st?

 

if there was a problem with the overun circuit i think you would see it in all manual ranges, not just 1st.

 

Well...
Who knows what happens if the Low-Roller Clutch is Inoperable, or even installed Up-Side-Down...?
(Yes the Newer Parts for the last 10+ Years will fit Up-Side-Down... unlike the Original Parts).

Also, someone please Post the PR-Circuit (Man. Valve to Low-Rev Piston and to Low-Overrun Valve-Train... to both chambers of the Piston).
And the Manual 1st Position Circuit (lets compare as only One Piston Chamber is used).

Lesson time!
Bbond please help.

 

A lot of you guys get hung-up on the Hydraulics...
I admit it tends to be more fun!

But you also have to look at the "Power-Flow" (Mechanical aspects of the Planetaries and Shafts) to understand why the Unit does what it does.

Simple question...
What happens when the Overrun Clutch is Applied, the Forward Clutch is applied (in M1/ 1st) and the Low-Rev Clutch fails to apply?

 

I was hoping you would come along

 

hmmm.. I think you'd burn the overrun clutch pretty quickly because it's not designed to hold much load, but I'm going to do some more study to see if I can answer this properly....

 

With the shifter in D the forward clutches and low roller clutch are applied. With the shifter in M1 the forward clutches, low roller clutch and low/reverse clutches are applied. In M1 the low/reverse clutches are what gives you engine braking.

To answer vortecirocquestion. With the shifter in M1 with the forward clutches, low roller clutch and overrun clutches applied I would think that you have 1st gear with no engine braking and no it would not burn the overrun clutches because the low roller clutch is taking up most if not all of the load.

 

I was Hoping that someone would be interested in the "Power-Flow" of this Unit, so that I could ask the Follow-Up Questions...

 

THANK YOU.
I see this now, I was thinking that the overrun clutches were responsible for engine braking when manually shifting.
I'm now looking more closely at the low/rev clutch.
I'm now thinking I must have a leak/pressure loss on the low/rev clutch circuit.
Reverse works, but this has made me revisit why the line pressure in reverse was a bit lower than I expected.
I have had a LP gauge on this trans since the moment I fired it up. Idle in P/D/N shows 80psi. In reverse it jumps to 110psi. this is within the spec (64-324psi) but I did expect a bit more. I disregarded it at the time because it was in spec and reverse works okay.

In M1 at 0%TPS (when I expect engine braking to occur) the line pressure will be back down to ~80psi. I'm wondering if some of this is being lost via a leak and the lo/rev clutch is being applied with much less pressure and therefore ineffective. Maybe the 110psi in reverse is enough to hold the clutch for the low load placed upon it in reverse (I've never had to reverse up a hill or apply much throttle in reverse), but a leaky/less than 80psi may not be enough to hold it in an engine braking scenario?

I might do a brief experiment and command the LP to go higher when at 0%TPS in M1 to test if engine braking works with more pressure on the lo/rev clutch.
This might confirm a pressure loss problem so I'll know what to look for when it comes apart again.

I'm also pleased to know the overrun clutch won't be damaged while the transmission has this issue. I could probably just ignore this problem, but I like to do a proper job and everything to be correct.

Appreciate all the help and replies!

 

I'm interested in learning as much as possible.
I'm following up on the power flow learning now, so please ask away as I know your questions will prompt me to look in the right places

 

Did I not answer your Power-Flow question, if not I don't understand the question?

 

This was answered.