Hello, I have a 1987 Iroc 5.7 and I have read where people have installed in their 700R4 "Corvette Servos" what are the Corvette Servos and what do they do for the transmission are they worth it in a stock 5.7?
Thank you

 

read and understand:

http://www.trutechtrans.com/High-Per...rvo-Guide.html

watch and understand:


for a stock 3rd gen the stock servos are just fine... when you make 360-460 HP the corvette servos are necessary.

 

That link is a good explanation.
I differ though on the stock servo being just fine. For trans durability...you could argue that. For shift quality to anybody but Granny......definitely not. The article says the same.
Every 700R4/4L60/4L60E will benefit from the Vette servo. The only exception would be if valve body mods were made specifically with the stock servo in mind.

 

I stand by my original statement.

 

I stand with Bird on this 1. The 4l60e also needs the same mod even with stock power.

 

I have read and watched the vid but still not sure what they do. Firmer shifts???

 

Yes, poor mans shift kit

 

It improves both the 1-2 and 2-3 shifts.
Even if you plan to install a complete shift kit such as a Transgo, I'd still recommend the 093 (Vette) servo. I've set up the valvebodies to work with the stock F-body servo and can get a decent 1-2 shift, but the 2-3 is never as good as it is with using the Vette servo.

 

I think I need one of these. When I gun it on the highway, the engine roars but the car doesn't move for like 1-3 seconds. I narrowed it down to stock 700r4 transmission lag.

 

Engine roar/car doesn't move isn't necessarily due to the servo piston.

What the servo does, is generate the pressure that applies the band, which is what is applied to create 2nd & 4th gears. The Corvette version fits in the same space but is a larger piston, therefore for any given level of fluid pressure, applies the band harder (better for long life since it slips less) and faster (better for "feel"). Doesn't affect shift timing; that is, the TV vs governor point at which the trans logic decides to shift, stays the same. Might make the clutch respond sooner, but the command from the valve body comes at the same time.

Doesn't really affect how long the trans takes to shift down, because it doesn't affect the logic that drives it; you need a shift kit for that.

 

It could also be the TV cable. When I'm doing 65, then hit WOT, I get a long downshift to 3rd gear and connection of power that takes 1-3 seconds. It's feel as if the transmission doesn't know what to do with the sudden power, which is 75% more horsepower over stock onto the factory f-body 700r4. So a corvette servo wouldn't help on this? Could it even be the 2.77 rear end ratio affecting drivetrain response?

 

[QUOTE=IrocRoadRacer;5713038]When I'm doing 65, then hit WOT, I get a long downshift to 3rd gear and connection of power that takes 1-3 seconds. It's feel as if the transmission doesn't know what to do with the sudden power, QUOTE]

Classic symptom.

Stock 700s will not cruise in OD at high speed past 1/2 throttle the trans will always downshift to DRIVE and stay there until you let off the throttle.
You can correct that by replacing the stock throttle valve.

http://www.tciauto.com/tc/700-r4-4l6...er-sleevehtml/

read the instructions...

This will allow high speed cruising in OD... up to 85% throttle when you mash the pedal it will still downshift to 3rd but it will not be as sensitive.


Provided the trans has been recently refreshed and is not simply a worn out unit with a bajillion miles on it, a valve body kit will help improve the shift firmness.

http://www.tciauto.com/tc/700r4-tran...-up-82-uphtml/

If you are not comfortable modifying your valve body you can now buy a new "constant" pressure one. This eliminates issues with Improper TV cable settings and comes with a new heavy duty ("corvette") servo.

http://www.tciauto.com/tc/1987-92-gm...ve-bodytmhtml/

you will still need to modify the throttle valve if you want high speed cruising in OD.

Good luck.

 

Stock 700s will not cruise in OD at high speed past 1/2 throttle


Really? So I was cruising at 130 with my stock tranny in 3rd?

 

That wouldn't be odd at all with mild rearend gearing.
Or, if "cruising" means less than ~1/2 throttle, you may have been in 4th ?? 1/2 throttle on a healthy motor can push a 3rd Gen along at 130 in 4th.

 

B&M TH-700R4 Throttle Valve Sleeve:


TH-700 transmissions will downshift from fourth to third gear anytime there is more than half throttle (except Corvette and some Camaros and Firebirds). So it’s impossible to cruise at high speeds in overdrive (fourth).

This new part prevents a forced part throttle kick-down from fourth to third gear, and allows cruising at higher speeds in over-drive. The transmission will only kick down from Fourth to third at 3/4 throttle.

"SOME" 3rd gens referring to the higher-end TPI cars... (IROC Z, GTA, Formula 350)

My Formula with the 305 TBI in stock form did the same thing as described until I replaced the throttle valve.


This is not new information I did this mod over 15 years ago, most of you were still in diapers LOL !


SO IF you were legitimately going 130 you have the 140 MPH speedo which means you have an original GTA, Formula 350 or an IROC..... OR the trans was modified by a previous owner.

 

1/2 throttle on a healthy motor can push a 3rd Gen along at 130 in 4th.[/quote

Really? So I can expect somewhere in the 200 mph range at full throttle with the trusty little 305?

 

John Wright

10-28-2005, 09:44:00 AM

The police cars, corvettes a maybe a few other that I don't know about came factory with the anti-part throttle kick down valve(for the lack of the proper term) in the 700R4s. This was very handy in my S-10 with a 355ci and the 700R4 and 4.10 gears on the street as it allowed high speed cruising in 4th gear without it dropping back to third gear. WOT still produced a downshift if required, but as rpms rose it would upshift into fourth gear and allow the continued building of speed. Where as the vehicles without this valve you could not run top end without a down shift to third where it would not shift back into fourth until you released the throttle and then with any pressure on the throttle it would fall right back into third gear again. You can buy this valve from B&M for the standard 700's but it was factory installed on the police and corvettes. I'd build what you have since you have it already.

 

No, not unless that motor makes over 500 HP


You need to understand that top speed depends on 4 key elements. throttle position is not one of them.

Coefficient of drag
Frontal area
Vehicle weight
Engine HP

To sustain 200 MPH in a 3rd gen that weighs at least 3800# (loaded with fuel & driver) takes 507.90 HP just to overcome air drag.

Rolling resistance takes another 26.35 HP

For a total of 534.25 HP to run 200 MPH

and this is just an approximation since the gear ratio, tire height, & engine RPM also have to be calculated & optimized to reach & sustain that speed.

If you want to get into real performance and not just imitate what you hear in the parking lot or see in the movies there is a lot more to it than you think. The guys that race (1/4 mile, Bonneville, etc) are not just winging it.. there is a lot of thought, planning, and money that goes into it.

There are plenty of excellent books you can read if you want to learn..

 

http://www.carcraft.com/techarticles...ar_craft_math/

http://www.ima.org.uk/_db/_documents...a_One_Iss2.pdf

 

Really? So I can expect somewhere in the 200 mph range at full throttle with the trusty little 305?[/quote]

 

That was a joke you didn't get. Fact was, I was at WOT when the little motor was going 130

 

Indeed with 2.73 rear gears a high top speed is possible provided you have the HP.

with this gear OD is pretty useless if you don have enough HP because the car will slow down.

My car when still completely OEM (180 HP 305) clicked off to 110 MPH on the highway revving at about 4000-4500 RPM and in 3rd gear if I remember.

I got the speeding ticket as my reward..way way back in 1994... LO

 

This is true and I would like to add something.
I conciderer myself hands on when it comes to fixing/replacing/upgrading my car but I pass on installing a shift kit. I have major macanic issues so taking in my perfectly working transmission to one is out of the question.
I installed a corvette servo and it made such a difference in the shifts that for me a shift kit is not nessary.

It took full advantage of the 3.42 ratio and Eaton posi. I had installed earlier that year. I get nice firm shifts. Hit WOT from the line and it spins them for a second then hooks and barks the tires nice and loud from 1st to second and chirps them from 2nd to third pushing me back into the seat locking the shoulder strap.

I can be cruising in second and hit WOT and it will drop down into 1st pushing hard then shift nice and firm with a loud bark from the tires into 2nd chirp them from 2nd to 3rd no problem.

This is with a 5.0. and a "working well" stock 700r4 with the servo. (the gears obviously play a roll) I can just take it easy and cruse nice and still be able to"feel" and "hear" the Trans shift either up or down.

You can do it your self and here's how its done.
It will cost you around $ 25.00. =
http://sethirdgen.org/servo.htm

 

My local Tranny shop tells me it should take about 3-4 hours to replace the servo. In the linlk it seems pretty easy and the shop charges $85.00 per hour. Are they correct in a 3/4 hour job? I do have a 4 post lift in my garage so getting under the car is not a issue.

 

Anybody got a part number for the seals the link talks about?

 

Just buy the kit off ebay, all inclusive. For $40 you can buy the kit and the shortest Delco rod.

 

I guess you could make it a 3 to 4 hour job if you take lots of breaks as you're consuming a half case of beer while doing it!
Seriously, it's more like a 1-hour job. From car on the ground to back on the ground. Quicker for any shop that's done it before.
Maybe 2 hrs for a first-timer on your back without a lift, loosening the trans mount to get clearance between the trans case and floorpan.

 

One more question...When not in WOT will the shifts still be very hard or do the servos just change the shifts under WOT? This car is a daily driver and I don't want to be slammed every time it shifts. I do own a 1992 Corvette with the LT1 and auto so I'm trying to get the shifts the same on my IROC.

 

If you like the shifts on your 92 Vette, then installing the servo in your IROC is EXACTLY what you want to do. No, part throttle shifts will not be hard at all; you'll just get rid of that sloppy slow shift that your IROC currently has.
There's a progressive line pressure increase with throttle position in both of your transmissions; the servo doesn't change that. There won't be any "bang" shifts at any throttle position.

 

Thanks everyone I have ordered these items and will let you know how it goes.

http://www.ebay.com/itm/230657514873...S:3160&vxp=mtr

http://www.ebay.com/itm/251177030981...S:3160&vxp=mtr

 

Whoa!.....why the Superior part? That would be necessary only for a high hp application shifting into 4th at WOT. I have it in my Impala, but that's 660 hp on the spray shifting 4th gear.

 

[B/C that's what the seller told me would get the most out of the servos. I guess you can call me "sucker".

 

[QUOTE=cmk-2;5715109][B/C that's what the seller told me would get the most out of the servos. I guess you can call me "sucker". My 5.7 is only 256RWH and 365 RWT so it looks like way overkill.

 

Yes, no use whatsoever. At your power level, it's just unnecessary stress on the internal band apply parts. Just install the Corvette Servo kit.

 

10-4 and thanks, I'll send it back and get my $60.00 back.

 

Well I just got back from the Transmission shop (not the one that said it would take 4/5 hours). When I took it in,the owner said, "I thought all 5.7 Irocs had the "Corvette servo) in them but let's take a looK". Well he took it out and guess what it DID have the 093 Corvette servo from the factory. He showed it to me and we put it back in the tranny. SOOO, if you have an 1987 5.7 Iroc you most likely have the servo. I can't speak for the rest of the years but 1987 yep don't spend the money. Oh, the TV cable was misadjusted a small bit and he took care of that and it does shift better now.

 

It's usually a good idea to install a Red Eagle wide band with the "fast" servo due to clamping force and friction. Routinely replacing input clutch housings is not a a fun thing to do.