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post #1 of 14 (permalink) Old 08-15-2003, 01:45 PM Thread Starter
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OD and reverse on jmod

im sorry, but i have done many a search this past week and cannot find what the benefits to doing the OD and reverse would be in the jmod.
i also read a couple posts by people who left the lower 1-2 spring out, which i am planning to do. but they said it felt like a wave of stress was being sent through the driveline on the shift. will leaving the 1-2 bottom spring out hurt/stress anything? i want the hard shift, but not at the expense of catastrophe.
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post #2 of 14 (permalink) Old 08-15-2003, 02:00 PM
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you don't need to mess with the od servo or the reverse servo.

Without the spring its pretty hard, and somewhat harsh. I had mine without the spring and thought it was fine but many passangers asked what was wrong with my transmission.

If I do it again I would leave all the springs in and the servos and just drill the plate.

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post #3 of 14 (permalink) Old 08-15-2003, 02:01 PM
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I've been driving around my J-mod mild modification now for about a week. I love the firm shifts in the 4000-5000 range much better than the un-modified tranny. Unfortunately, unless you accelerate real, real gently until the 1-2 shift occurs, the shift is still very, very firm. It won't chirp the tires at the lower RPM, but it is a definately obvious shift. There is no way you would ever NOT be able to notice it. It's THAT firm. It is uncomfortable to me. I'm actually thinking of putting my purple bottom spring back in and see what happens then. The only problem is that I really WANT the shift to be REAL FIRM at the higher RPM's. I don't know if the bottom spring listed in the J-mod part list would do what I want. I don't know what the difference is.

Anyway, I guess the answer to your question is.....There will definately be more stress to your driveline components after the tranny. It would be my opinion that if you shifted at WOT all the time, you will eventually (sooner more than later) fail some driveline component(s). I'm not speaking from experience, only from the impression of driving my J-modded tranny for 1 week.

Oh...and I didn't do the reverse servo...didn't see the need. The OD servo will not cause you any problems with driveline stress. In fact, I don't believe 2-3 shifts would cause any problems either.....just that 1-2 shift. I am speaking only of the mild setting....

Glen "RustyUL" Weldon

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post #4 of 14 (permalink) Old 08-15-2003, 02:08 PM
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the best thing to do with a 94-95 transmission is just to drill the plate and keep the fluid clean and cool until the transmission dies.

The 94-95 4r70w is the weakest of the bunch, and is really not worth modifying or even rebuilding in my opinion.

When it dies either build a 98+ 4r70w to JW's thesis, or have dennis reinhardt build you one, or just pick up a stock 98+ trans.

JH
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post #5 of 14 (permalink) Old 08-15-2003, 02:13 PM
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1-2 is pretty firm, especially if you are chipped.

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post #6 of 14 (permalink) Old 08-15-2003, 02:43 PM
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Justin,

My 1995 4R70W has 166+ original miles and counting. I bought the car from the original owner with 75,000 miles on it. I drive really hard, but I also drive alot of highway miles. I love to shift at WOT and do it quite often. I've heard the horror stories of the 94-95 trannys, and I'm sure alot of it is true.

When mine goes...and it is true it's a matter of when, not...IF....I won't hesitate in rebuilding it. Of course, I will be doing it myself, not paying labor and making the mods specified in Jerry's thesis. Also, it will get the TLC that it deserves, instead of getting the production line treatment.

JustinH, When did your 95 tranny fail, and under what conditions?

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post #7 of 14 (permalink) Old 08-15-2003, 02:49 PM
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burned up the direct clutch at 70k.

I am not the original owner of the car, and I don't believe it had regular transmission fluid changes before I bought it.

I put in a 98 mark transmission to replace it.

JH
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post #8 of 14 (permalink) Old 08-15-2003, 03:17 PM Thread Starter
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my transmission was rebuilt 15k miles ago. at least aamco "said" they rebuilt it. i cant be positive after some of the horror stories i have read of late.
so yeah it's a 94 tranny. but it should be good for the life of the rest of the car (im assuming after jmod and tranny cooler).

*edit: can anyone tell me the benefits of doing OD and Reverse?

*edit again: i thought i remember reading in jerry's thesis that doing reverse will pick up some slack??? what does this mean?
if i dont do OD and reverse, can i still manually shift 1-2, 2-1?

Last edited by chilipepprflea; 08-15-2003 at 03:34 PM.
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post #9 of 14 (permalink) Old 08-15-2003, 09:03 PM
 
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Quote:
The 94-95 4r70w is the weakest of the bunch, and is really not worth modifying or even rebuilding in my opinion.
This is my opinion, of course, but...

Actually, the majority of the internal components are the same in all of them.

Major changes include different (better) frictions and steels on the direct clutches and better frictions on the intermediate clutches (easily upgraded), a slightly deeper direct clutch hub (not serious) and the mechanical diode one-way on the '98 and up (upgradable). The tapered and hardened stub shaft from the 5.4L truck tranny is cheap and easily installed. The stator shaft is modified in some later models to decrease sealing ring wear, but it is upgradable as well. But the stator shaft sealing ring grooves wear in BOTH styles, if your end clearance is not tightened up to .006" to .015" or so - or your fluid is contaminated. Stock, most of them seem to be around .030"-.040" - way too much. The pan and filter are different - the '96 and later have that stupid dimple in the bottom. IMHO, a deeper pan with baffles would be much better. But this decreases ground clearance, so... there you are...

The major change is the valve body recalibrations in the later model VB. This can be changed on the 'pre '98s to the later style, but it is pricey. For a street car, there is nothing wrong with the piece - with the proper modifications.

Apparently WOT manual shifting on the older VB is frowned upon. What is the point, however? Properly calibrated, the transmission will make more consistant shifts on it's own that you ever will.

The last major difference is the torque converter. The early TC's suck. The later designs were modified with 7/8" larger internal clutch diameters. This should always be upgraded.

As for the JMod, for street use and long life, I replace the springs: 1-2 with the purple bottom spring, the blue top spring - and leave the 3-4 spring in place.
I also open up some of the restrictions a little differently than in the Thesis, so that the 1-2 shift occurs later, rather than at 3500rpm. Still firm and quick, just not SO quick that I have to reprogram the chip to alter the shift points back up into the power band.

IMHO, that chirpy 1-2 shift, while pleasing to your ego, is stressing compenents in the driveline that are already troublesome. And breaking the tires loose in the rain is not a desirable trait for a street car.

FWIW
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post #10 of 14 (permalink) Old 08-15-2003, 11:05 PM
 
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Quote:
Originally posted by chilipepprflea
my transmission was rebuilt 15k miles ago. at least aamco "said" they rebuilt it. i cant be positive after some of the horror stories i have read of late.
so yeah it's a 94 tranny. but it should be good for the life of the rest of the car (im assuming after jmod and tranny cooler).
As for AAMCO, well... you know what P.T. Barnam said...
And the '94 tranny is not going to just fall out - but...

If they didn't upgrade certain frictions, they wear out with extended mileage and highway driving. The stock paper material just doesn't cut it. The improved material lasts MUCH longer, and will fit your transmission. If they used a plain stock rebuild kit, you probably got the old material - that's what comes in the kits. I have been throwing it away and paying more for the better stuff. Want a stack of it?

Accumulators should be upgraded, they probably didn't - but you don't know unless you look. The mechanical diode is a good idea, but the 14 roller element works on the street - unless you are a cop, a taxi, or drive really hard. BUT, I have seen rebuilders replace it with the old AOD 7 roller design - NOT a good idea. Either way, an improved spiral snap ring retainer is advisable on this. Peen over the shield after installing so that it doesn't fly out at high RPM like the stock piece does.

The cooler is always good news for transmission life - any car, any age.

Quote:

*edit: can anyone tell me the benefits of doing OD and Reverse?
The increased diameter OD servo piston give greater holding power. This is essential for pulling a trailer or extended highway driving. I always do it. The minor amount of slippage with the smaller piston is not noticable while driving, but heat buildup and OD band friction wear IS.

Quote:

*edit again: i thought i remember reading in jerry's thesis that doing reverse will pick up some slack??? what does this mean?
There are several (3) reverse servos available. The ONLY difference is the shaft length. This either increases or decreases the preload on the reverse band, depending on the piston you use - and what you started with. Increased clearances will reduce drag - important for 1/4 miles times, but not so critical for street use. Generally, you should compress the piston and have about 1/4" between the piston and the snap ring. If not, either change the servo to a shorter style, or grind and reform the shaft length to fit.

Quote:

if i dont do OD and reverse, can i still manually shift 1-2, 2-1?
Not recommened unless you change the valve body to a '98 ('99?) or later design.
Sure, you can do a few, but don't make a habit of it. This is mostly of concern to drag racers - besides, why shift manually? The transmission can shift more consistantly than you can - every time. For general street use, I would live with it.

FWIW
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post #11 of 14 (permalink) Old 08-17-2003, 11:00 PM Thread Starter
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wow greg. i am impressed and i thank you so much for the help. that's more than i ever could have hoped to learn.
one more question though...

Quote:
The increased diameter OD servo piston give greater holding power
Quote:
Increased clearances will reduce drag - important for 1/4 miles times
are you saying that the reverse servo affects forward driving?
also, are you saying that the slippage in OD is losing some of the power the engine is making?
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post #12 of 14 (permalink) Old 08-18-2003, 12:45 AM
 
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Quote:
Originally posted by chilipepprflea
...are you saying that the reverse servo affects forward driving?
also, are you saying that the slippage in OD is losing some of the power the engine is making?
Selecting a servo that holds the reverse band farther away from the drum decreases that bands drag on said drum. So yes, there is a very minor influence that the reverse band would have on forward performance. This difference is quite small. For the street, I would leave it stock - you WANT reverse to work normally on the street. On the strip, expecially when high RPMs might make the drum swell, increased clearances would reduce drag in a minor amount.

Slippage of any type is not good. It causes heat buildup and wear of the band and drum. Extended slippage only results in more slippage, as things wear, until it just stops working. Optimally, the only time anything should slip, is between 'gear' changes - once the shift is completed, everything should hold firm. It could take years for the wear to become apparent, or haul a trailer once, and it could fail - it all depends on the amount of power it is called upon to transmit. The larger OD piston is just hedge that things will have a greater chance of not slipping unduly.

One thing I feel is often overlooked by folks, IMHO, is that many of the more radical recommendations in the JMod are aimed towards people with built engines running at the track - some exclusively. Too aggressive a shift is not good on the street, and the shock loads only wear components in the drivetrain unneccessarily.
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post #13 of 14 (permalink) Old 08-18-2003, 01:29 PM Thread Starter
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ok thank you very much. all of this is noted and i will probably now tackle OD when i do the jmod. i'll consider leaving in the bottom 1-2 spring bc of what you said about drivetrain wear and tear. it's knowledgeable people like yourself that make things possible for the not so mechanically inclined. much appreciated.
rob
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post #14 of 14 (permalink) Old 08-18-2003, 01:37 PM
 
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Good luck with it all.
In case you are interested, the overhaul I finished yesterday, with all accumulator springs in place, will still spin the tires on a full throttle 1-2 shift. It's just a little more sedate when operating at part throttle.

I'll have to say that when it did this, I got a big grin on my face...
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