TH400 - no 3rd gear in boost
Thread Starter
Joined: Nov 2009
Posts: 1,621
Likes: 31
From: THORNTON, PA (NEAR PHILLY)
TH400 - no 3rd gear in boost Even with only 11psi I can't get into 3rd gear. Normal driving it ok, and the trans shifts fine otherwise. I installed the Transgo bleeder valve deal and installed an additional check valve to bleed any residual pressure - no changes. What else can I do? The mechanical modulator/700 cable deal will approach $200.00 and I don't think I want to spend that kinda money for something like that unless necessary.
Thanks!
Thanks!
Thread Starter
Joined: Nov 2009
Posts: 1,621
Likes: 31
From: THORNTON, PA (NEAR PHILLY)
Actually, I did do a 3rd gear boost run, but when the boost started to come in strong, the trans forced itself into 2nd and it didnt feel very nice the way it did it - like it was being forced to do it. I dont havethe kick-down hooked-up either.
FormerVendor
Joined: Apr 2014
Posts: 263
Likes: 2
From: Justin, TX
Ok, I would put a pressure gauge on the transmission.
Thread Starter
Joined: Nov 2009
Posts: 1,621
Likes: 31
From: THORNTON, PA (NEAR PHILLY)
Thanks Jake but I don't want to bother you at work. I just want to make sure I did all the testing I can do before dropping the trans. I tried running straight manifold pressure, same thing - no shift to 3rd. Trans Specialties is basically down the street, I was going to have them look at it.
Vince and I have been discussing via PM for awhile.
I use a vacuum check valve that was OEM on turbo Biuck GN cars. Goes inline with the vac modulator so it can/t see boost. I tested it with a bike pump to 30psi.
On the modulator side of the valve, I drilled a .020" hole so the vacuum has a vent otherwise it would just hold vacuum in the modulator line.
It works well.
I had issues with the 1-2 shift after turning up the boost but it turned out that the boost comes on so hard, the rpm climbs faster than I could move the shift lever. There is a slight delay in my 1-2 shift, and in that slight delay, I was on the limiter.
Ended up just letting the trans do the 1-2 shift, and it does so at 6200. I've no idea why that rpm. The big block would shift at 5000, but it had nowhere near the power or rate of change in rpm. So that might be it?
I gave you a call today Jake. No doubt you are busy. I would like to discuss taming down the harshness of the 1-2 shift. It is pretty brutal. I have the 3 plate intermediate kit that you set up for me.
Ron
I use a vacuum check valve that was OEM on turbo Biuck GN cars. Goes inline with the vac modulator so it can/t see boost. I tested it with a bike pump to 30psi.
On the modulator side of the valve, I drilled a .020" hole so the vacuum has a vent otherwise it would just hold vacuum in the modulator line.
It works well.
I had issues with the 1-2 shift after turning up the boost but it turned out that the boost comes on so hard, the rpm climbs faster than I could move the shift lever. There is a slight delay in my 1-2 shift, and in that slight delay, I was on the limiter.
Ended up just letting the trans do the 1-2 shift, and it does so at 6200. I've no idea why that rpm. The big block would shift at 5000, but it had nowhere near the power or rate of change in rpm. So that might be it?
I gave you a call today Jake. No doubt you are busy. I would like to discuss taming down the harshness of the 1-2 shift. It is pretty brutal. I have the 3 plate intermediate kit that you set up for me.
Ron
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Topdon ONE vs. Artidiag 800 BT2: Which is the Diagnostic Tablet For You?
Pouria Savadkouei
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo There are some tricks to running boost with an auto shift TH400 that I have developed through the years. If it's burning up high gear clutches there's a couple of things to pay attention too. Nothing I want to discuss online but you can call the shop.
Thread Starter
Joined: Nov 2009
Posts: 1,621
Likes: 31
From: THORNTON, PA (NEAR PHILLY)
You know what Jake, this thing never had 3rd gear since I installed it.
Trans was given to me by a neighbor who had a "performance rebuild" done to it. I dropped it off at Trans Specialties in PA and they called me later that day stating the high gear clutches were gone, and that there was no shift-kit installed at all, and it was just a stock rebuild and it look like somebody installed somekind of "ball" or whatever to increase performance or pressure of the trans. Builder feels there wasn't enough line pressure for the kind of power the car is making. They talked me into the sprag/drum upgrade, clutches and a shift-kit. They really wanted a manual valve body in there but I resisted.
They only want 430.00 for a 10" converter for my turbo car - sounds too cheap???
Trans was given to me by a neighbor who had a "performance rebuild" done to it. I dropped it off at Trans Specialties in PA and they called me later that day stating the high gear clutches were gone, and that there was no shift-kit installed at all, and it was just a stock rebuild and it look like somebody installed somekind of "ball" or whatever to increase performance or pressure of the trans. Builder feels there wasn't enough line pressure for the kind of power the car is making. They talked me into the sprag/drum upgrade, clutches and a shift-kit. They really wanted a manual valve body in there but I resisted.
They only want 430.00 for a 10" converter for my turbo car - sounds too cheap???
Trans Specialties is good. They make some of the parts we use for converter builds and they've been around for a long time. Sounds pretty cheap but depending on power level it may be fine. That's likely a furnace brazed, non billet setup.
Yeah if the trans wan't built properly, it won't last, especially if it was stock.
A shift kit may help but I learned some lessons along the way making auto shift valve bodies work with big power and boosted combos.
Yeah if the trans wan't built properly, it won't last, especially if it was stock.
A shift kit may help but I learned some lessons along the way making auto shift valve bodies work with big power and boosted combos.
Thread Starter
Joined: Nov 2009
Posts: 1,621
Likes: 31
From: THORNTON, PA (NEAR PHILLY)
Thanks Jake.
It is a furnace job but I was honest about the use of the car and they feel the cheaper converter is more than adequate for street use and don't want to oversell me.
It is a furnace job but I was honest about the use of the car and they feel the cheaper converter is more than adequate for street use and don't want to oversell me.
