View Full Version : Questions how to fix 700r4 hard 1-2 shift


RockinZ
02-07-2010, 10:41:28 PM
Hi Guys,

My 700r4 shifts damn hard 1-2.

Here are the mods I made to my '89 700r4:

.500 boost valve. too much pressure?

L type accumulator valve assy with pink firm shifting spring. maybe that's it? This one was chosen because it was recommended for a heavy car, but maybe my gear ratio affects this?

5600 rpm Corvette governor, Corvette servo & piston assy (does not shift that high).

2600-2800 stall

I have a 3.73 gear
Thanks

wiseryder
02-08-2010, 02:58:22 PM
Yup, Hopefully Jake will jump in But ,Mine shifts damn hard too..
You can rock yer Molars loose sometimes ,lol
Wife hates it ..

green 1977
02-08-2010, 03:04:09 PM
My 700 shifts hard too..... Lol .... But my th350 shifted harder so wifey thinks this is an improvement:D

Twisted_Metal
02-08-2010, 03:22:19 PM
When you say it "shifts hard"......

Do you mean under light throttle, heavy throttle or all the time?

I can't help you myself but this info will probably help Jake diagnose the problem(s) when he sees your thread.

jakeshoe
02-08-2010, 03:32:25 PM
The 1-2 shift on a 700 can get really brutal, really quick when you do all the improvements to make it live.

Better band, bigger servo, increased pressure all contribute to the harsh 1-2.

The problem is that most guys drill the 1-2 feed hole too big.
Some block the 1-2 accumulator.

I wouldn't mess with the TV boost valve or any of the pressure regulating parts. Let it have the pressure, it keeps it alive for the 3rd and 4th gears.

You can check the accumulator, but chances are you will need to pull the valve body down and replace the plate or make the hole smaller for the 1-2 feed.

You could check the servo and be sure the cushion spring isn't omitted, or even put a smaller servo in, however I like to work with the larger servo and use my feed orificing to control the apply feel.

RockinZ
02-08-2010, 07:24:14 PM
lighter the throttle harder the bang. Best is when it's got enough throttle to chirp the tires, then it feels great!

I can get a softer shift by adjusting the TV cable, but then I loose my kickdown.

Jake, if I go with the mid range 1-2 spring will that make any difference?

Thanks!

ZS10
02-08-2010, 08:59:47 PM
I used to adjust the TV cable 2-3 clicks for street and track. Just enough to soften the shift a little.

jakeshoe
02-08-2010, 09:10:38 PM
I would first look at the servo, because you can do this without even dropping the pan. They sometimes have you omit the cushion spring and install shims to tighten up servo clearance and kill the cushion. I do NOT like this method, even though it is what TransGo does.
I would look at the 1-2 accumulator next, make sure it's not blocked.

Then you can go from there. If the servo doesn't cushion it enough, go to the accumulator. If it isn't blocked or has a super stiff spring, plan on installing a new seperator plate.

I do not like to to adjust the TV cable for shift feel. I like to adjust the TV cable for proper shift timing and pressures. Once the pressures are right and it's shifting at the proper time, if the feel is too hard, you need to adjust this through the accumulators and orificing.

The biggest thing is the orificing. Most shift kits recommend a hole that is too big.

2-3 shift feel is somewhat controlled by band clearance (servo clearance). Less is better to a point.

There isn't really an accumulator for the 2-3 feel, it is the servo release.

RockinZ
02-08-2010, 09:28:25 PM
I would first look at the servo, because you can do this without even dropping the pan. They sometimes have you omit the cushion spring and install shims to tighten up servo clearance and kill the cushion. I do NOT like this method, even though it is what TransGo does.
I would look at the 1-2 accumulator next, make sure it's not blocked.

Then you can go from there. If the servo doesn't cushion it enough, go to the accumulator. If it isn't blocked or has a super stiff spring, plan on installing a new seperator plate.

I do not like to to adjust the TV cable for shift feel. I like to adjust the TV cable for proper shift timing and pressures. Once the pressures are right and it's shifting at the proper time, if the feel is too hard, you need to adjust this through the accumulators and orificing.

The biggest thing is the orificing. Most shift kits recommend a hole that is too big.

2-3 shift feel is somewhat controlled by band clearance (servo clearance). Less is better to a point.

There isn't really an accumulator for the 2-3 feel, it is the servo release.

There were no mods to the valve body in my trans, just the boost valve, accumulator, servo and governor from PATC. Everything else is stock. oh yeah, and a BTO kit.

bigdav160
02-08-2010, 09:29:38 PM
There's something wrong in you're accumulator circuit.

Just the Corvette servo and 1/2inch boost valve wouldn't cause an overly harsh shift.

jakeshoe
02-08-2010, 10:24:13 PM
The plate has probably been drilled, maybe not on this rebuild but some time in the past.

You start getting a feed hole too big and the accumulator can be stock and still have a harsh shift on the 1-2.
A stock spring can actually be harsher on light throttle than a firmer spring.

Knuckle Dragger
02-08-2010, 11:11:15 PM
The plate has probably been drilled, maybe not on this rebuild but some time in the past.

You start getting a feed hole too big and the accumulator can be stock and still have a harsh shift on the 1-2.
A stock spring can actually be harsher on light throttle than a firmer spring.

The "stock" plate in my 700R4 I just did some work in was modified at the feed hole Jake describes. Fortunately for me it was the size I was looking for, but it had been changed.