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700R4 2nd to 3rd shift; how can I speed up this shift?

15K views 21 replies 5 participants last post by  Rick Johnson 
#1 · (Edited)
Looking for some advanced technical information on 2-3 shift timing:

I data log RPM during my 1/8 mile runs at Irwindale(appro 7.26 ET). I had to slow my car slightly so all shifts now occur in D3. My 1-2 shift is very sharp, but my 2-3 shift is slightly lazy - but does not flair at all. I realize that 1-2 is just a band engagement while 2-3 is a combination of band release and clutch engagement, so maybe I can not have as sharp an RPM drop during the 2-3 shift. I am hoping the trans experts help me out so I can be sure I am doing everything right. I am no threat to the great rebuilders who help with this site, just an enthusiast that rebuilds and tunes engines, trans, diffs, suspension, etc.

My Det (WOT) line pressure in D3 is 225PSI (I just fine tuned this due to a minor flair at 170PSI). My 1-2 band feed orifice is .110 and I have the Corvette servo with the Trans-Go modifications. My feed to D4/D3 which goes through the manual valve, then to the 2-3 shift spool, and then on to the 3rd clutch is .116.

Is this .116 orifice 3rd clutch orifice large enough? Can it be larger?
Could I be loosing flow through or around the white rings on the input shaft?
Is there some other restriction in the path of the 3rd clutch oil, or a restriction to the release circuit of the 2nd servo?
I see posts discussing double feeding the 3rd clutch, but I think they are for another trans?
What changes would best ensure fast oil flow to the 3rd clutch?

Thanks, any ideas would be appreciated!
 
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#4 ·
Maybe it is shifting well enough. Since it was 'flairing' at 170ish PSI, but completely OK at 225PSI, I am just trying to ensure I have enough clutch life safety margin and understand if there are any basics I do not understand.

What is the servo travel/band clearance.

Unfortunately I do not know the clearance at this point. I also do not know how I establidhed the clearance 5 years ago when I built it.

I remember that the 9 clutch Alto 3rd gear had very little clearance and I remember being shocked that the literature said to allow a very tight number (probably about .015 or less). Unless the clutches really wore out, I doubt the excess shift time fill time is spent at the 3rd clutch. Maybe your question is suggesting the shift time is lengthened by time spent filling the servo chamber as the 2nd band is being retracted. This would make sense to me.

When the valve body was out recently I remember removing the band anchor and noting that the band was very loose, but did not try to put a number on it.

Could excess 2nd servo clearance from a short pin cause this?

How do you set the band clearance without the special tool? How much clearance should there be?

Can I somehow direct a higher volume of oil to the 3rd circuit to compensate for excess clearance, or do I have to reduce clearance?

Thanks for all your help!
 
#3 ·
I don't think you'll ever get a 700 to go 2-3 as hard as it goes 1-2. I've had several that were pretty extensivley beefed and none of them did, and the tranny man at my old dealership said he's never gotten one to do it.
 
#6 ·
Thanks for the help.
On band adjustments to other transmissions, we are told to tighten a screw to a specific torque and then back of the adjustment a specific number of turns. Since I do not believe this is possible in the 700R4, what range of clearance am I looking for with this band?
 
#8 ·
Thanks, you have been extremely helpfull. I will rest (and sleep) better with this knowledge.
Please answer me one final question. A local rebuilder told me that the 9 disk alto clutch pack I used does not dissipate heat well enough because the metal plates are too thin. Another said they will warp in a performance application and then drag causing more heat. At some point I will rebuild this trans again and want to use the best parts.

What is the best 3rd gear clutch pack arrangement these days and how much clearance should the clutch pack have?
 
#16 ·
Jay, for some reason I did not see your e-mail yet but I contacted Sonnax and they e-mailed me some good info.

I believe I understand how it works so I thought I would share my understanding to confirm and you guys can correct as required.

The 700r4 shift valve directs oil at the 3rd clutch and the 2nd band release/accumulator simultaneously. There are no obvious restrictions so theoretically they both receive the same pressure. I suppose the GM designers felt they could determine which piston moved first (2nd band release or the 3rd clutch engage) by tuning the accumulator spring and the clutch release spring forces. Something in the tuning goes wrong as the clutch pack and the band wear and one of the pistons has to travel farther than expected. May also be the result of leakage along the path to the 3rd clutch. The failure mode is when the band releases before the clutch engages and the trans flairs during 2-3. This sonnax check ball and orifice allows us in the field to ensure that apply pressure goes to the 3rd clutch first. Their orifice delays the flow to the 2nd band release resulting in overlap, but at least a means to control it and guarantee that 3rd hits first.

I believe the total time for the shift can only be changed by increasing line pressure, the feed orifice to this circuit, or decreasing the stroking length of the 2nd band and/or 3rd piston.

I solved my flair by increasing the pressure from 170 to 225 PSI so apparently the 3rd clutch grabs first given enough flow/pressure?

Let me know what you think.
 
#17 ·
I'd have to look at a flow chart to confirm or comment on that. I'll tell you how we ended up using that Sonnax valve. We built 700's for 4x4's with large tires, alot of times shift "feel" wasn't that great. To correct 2nd we used Corvette servo kits, the problem after that was the shift into 3rd felt weak after a firm 2nd. So, after reading a Sonnax catalog, we found the answer 77701-076. You simply drill the new valve and plate to match the shift you need. It's cheap, easy and works great.
 
#19 ·
If you mean Ricky Johnson, the famous motocross racer from the late 80's to early 90's, not really. I said hello to him at some Nascar race in Bakersfield once, but that was all.
I raced against him at Saddleback MX park back in 1983 before he was famous and it created quite a bit of confusion for the announcer for the first lap or two. then he pulled away and it did not matter:(.
 
#21 ·
" Sonnax part# 77701-076 to improve the 2-3 shift. "
When using the TransGo Performance Shift kit you do not need this as this is already addressed in the kit. DO NOT remove the capsule and block it for the 3rd accumulator as this will create other problems. You can open the feed on the 2-3 shift to .155" - .187". This is for the TransGo Performance Shift kit only as there are other modifications in this kit that will allow the larger hole size. This will allow a firmer WOT shift. The .110" 2nd gear feed hole is large and if the part throttle 1-2 shifts are to firm this is the reason. The 170 psi was way to low and the 225psi is exactly what you want. To prevent further 2-3 shift problems, leave the selector in "OD", as this will prevent the overrun clutches from coming on the 2-3 shift when left in the "D" position and robbing 3rd gear feed oil. This is not as critical here on the 700R4 but is very critical on the 4L60E (different circuitry). If you are going to go to the larger apply servo (really not needed under 750FWHP) go with the Sonnax as this will allow smoother shifts at part throttle and not break the band anchors as the billet has done occasionally in the past. You will have to bring down the 2nd gear feed hole size to a somewhat reasonable .086" - .093" when using this apply servo. The Borg Warner Hi-Energy 8 clutch 3-4 pack is a good one, as I have used hundreds of these in my builds, and so are the 9 & 10 clutch Borg Warner Hi-Energy setups, they work well in high HP situations.
 
#22 ·
Thanks for your reply. I agree that my 2nd feed orifice could be a bit smaller than .110. My 3000 RPM converter helps me get away with it. I do like the idea of a much larger 3rd feed orifice. Net time I am tinkering I will enlarge it as you suggest.
Hopefully at 225 PSI the 2-3 shift will continue to perform as it does now and I will not have to change the 3-4 clutch pack, but I will try the 8 pack you suggest when needed.
I am curious about your sugestion on auto shifting in D4 rather than D3. My understanding is that in D3 I feed the overrun clutch in 1, 2, and 3rd gear. My thought was that if the overrun clutch was already suplied oil/pressure in 2nd, that no additional oil flow would be required when shifting to 3rd - just maintain what pressure it already had. Can you explain your thinking?
Thanks again,
 
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