Having some problems with my 67 spth400. Its been rebuilt with the valve body changed from a 69 trans to change the 2-3 shift points as per the advice of Mark DeConti over on the Buick forum. It used to shift from 2-3 in about 3 feet before! A bit better now.

So here's my problems.

1st; it shifts to soft even with a shift kit.
2nd; it shifts too soon or to quick between gears.
3rd; its feels like its slipping between 1-2 shift at wot, but not driving normally.

I spoke to my trans guy and he says that it could be a modulator or could be the govenour. My worry is that theres to much pump clearance not giving the trans enough pressure. Iv read that the 1-2 shift needs twice the fluid pressure of the 2-3 because of the torque multiplication in 1st gear.

Does the modulator also control the fluid pressure that much, that if I turn it in a couple of turns to try and get the shift points spread out more, it would also help the soft 1-2 shift?
Any other thoughts?

 

Did you just get it done? the reason I ask is when my shift kit was first done it was really soft shifting but got better after some use. the quick shifting might ne the TV cable. Can't say about the slipping.

 

No TV cable on a th400. Only the th350, 200r4 and I think the 700r4 as well.
It was done about 1200 miles ago.
Going to change the modulator tomorrow and play with the adjustment. I also bought a govenor weights and springs kit. If that doesnt change anything then its got to be internal??? IDK???

 

Actually the TH350 has a kick down cable (valve open and closed) where the 200 4R and the 700R4 use a TV cable (variable valve). They look similar, but perform slightly different things for the trans.

 

Tony, If worse comes to worst, I have an excellent T400 available and I am not that far from you.

Bruce

 

Thanks Bruce.
I really like the sp converter thats why I didnt just use a regular th400. I just need the shifting problems cured. My trans guy never worked on one of these till he did the 2 I brought him. And he's scratching his head now because he builds a regular 400 to handle 1200hp race motors without any problems.

 

Oh that's why the new Olds powered truck doesn't have one. Good to know thought it was something I might have to look into.

 

Sounds like you are close to me as well.

 

Hmmm, you just put a 69 valve body in the SP400. By doing this is the converter still switching pitch? Just wondering if the SP function uses the valve body in any way to change pitch? If so, is the 69 valve body causing the converter to be stuck in lo or hi angle and not changing. If stuck in hi angle, I would think this may cause some slipping. Would check this out first, then perhaps to a pressure check to see if pump pressure is ok. If so, then the modulator may need adjusting to bring TV pressure up for the crisper shifts.

 

I don't know if that works or not, but I suspect it is an issue.
Here is some info on the SP trans that I found.

http://www.buickperformance.com/switchpitch.htm

My car also used a 2 prong plug on the trans, but it's not a SP trans. The second plug is for the TCS solenoid. It has to do with retarding the amount of vacuum advance the car has.
So be weary. Not all TH 400s with 2 prongs are SP transmissions.

 

http://www.buickperformance.com/SPTrans.htm

Its definatly a switch pitch trans. I have 2 of them, one in the car, the other at my trans builders. The one in the car had a stock converter that worked very well with the Bruce Roe control box. I have an article for that somewhere that I'll post later telling how it works. I took the stock converter out and put a PAE3000, thats a 3000 on high stall, and 1100 on low stall converter. You definatly know when its in high stall and when its in low. When the converter is in high it will launch at 3000rpm and burn the tires up for a block. When its in low, it barely brakes them loose.

As for why I canged the valve body. Read the article above. That guy knows way more than I do, I never would have known those things were the reason the trans wouldnt downshift, and upshifted from 2-3 in about 10 feet.

UPDATE: I changed the vacuume modulator today. The trans will not short shift like it was anymore and there's tunablility with the b&m modulator that wasnt there with the stock one. So that cured one of the 2 problems. I stll have a slip from 1-2 but not 2-3 at wot. And its still not a firm shift like it should be with a shift kit.

 

Forgot to mention. The valve body has NO bearing on a sp converter. The fluid pressure is sent to the converter thru the solinoid from the pump.

 

Tony

The stuff I have is SP, from my '66 98. The trans was rebuilt by Cottman and the converter is new. They have about 3000 miles on them. I took them out when I installed the 200R4. Where did you take your work, to that shop on Route 37?

Bruce

 

Hmmm, is that a long or short tail 400 trans? Also does it have the speedo on the front wheel or on the back, drivers side of the trans? What was the rpm stall's on the high and low ranges of the new converter? What was done to the trans? Basic rebuild or performance with shift kit ect?

Who did your 200r4? Do you using the lock up or non lock up converter in that 200 trans? I have one out of an 87 442 that I was thinking of having done to use in the wagon. Its still an option if I can get it done to handle the weight and power.

 

400's have no 2 band, so they use a clutch for second, and if it is anything like a th350 there is a 2nd gear accumulator. If so this may be applying the clutch slowly. Sounds like the valve body has some issues regarding the 2nd gear apply or the accumulator is malfunctioning.

Try a test, put the trans in L2, S, 2, whatever the range is between DR and L. Then see if the 1-2 shift is any better. This range uses different paths in the transmission. Let us know what you find out.

 

Did this. The 1-2 shift was a little more positive, not as good as the 2-3, but the trans was making a strange whining noise in both 1st &2nd gears that went away when I shifted into 3rd.

 

Sounds like that valve body has some issues. Do you have the old valve body, if so re-install and try.

Take it to the builder and get pressure checks done! This may clue you guys in on the problems