montvaleplace

I have a 71 toronado that shifts from first to second almost imediately unless manually shifted. I have 20" of vacuum at modulator and a new modulator. I removed the governer to check the gear and springs and everything looks normal. The valve is free to move inside the governer and the drive gear is intact. any ideas would be appreciated..

Fun71

Have you tried adjusting the modulator? There's a screw inside the vacuum nipple.

montvaleplace

I've tried going 2 turns in or out with no change.

lemoldsnut

Turn it more. Sometimes up to 5 or 6 turns

montvaleplace

Am I going in or out to delay the shift. When I hold it manually it shifts nice and firm.

montvaleplace

I finally got a chance to spend some time on this trans. I checked to see if the modulator valve was stuck in the bore and it isn't. I turned the modulator valve adjusting screw 6 turns in with no change. Next I got a factory service manual and ran the mainline pressure tests, all pressures are normal so according to the book I'm dropping the valve body to see if during the rebuild (prior owner) a checkball was left out or installed in the wrong spot, 1-2 accumulator problem in valvebody or rear accumulator problem. Also a problem with the intermediate clutchpack . So basically it's coming out, i'll post an update when I get it out and see whats up.

BangScreech4-4-2

Are you sure you actually have a problem? Most TurboHydros that I've driven shift pretty short at light throttle settings. What RPM is it shifting at when you feather it? What RPM is it shifting at under full throttle?

droldsmorland

Change out the modulator. Use a TM-50 from Standard. If the modulator doesn't fix it go at the governor. Id do both of theses before going through the complex trouble of yanking out a FWD trans. Inspect the vacuum line to modulator. Is it running off full intake vac or through a TCS or worse ported vacuum. The hydraulic pressures read good so Id say its a control problem verses a failed hard part.

montvaleplace

69442Ragtop, It shifts into second as soon as I move the car regardless of rpm,idling or wot.

droldsmorland, That is a standard modulator but it exhibits the same symptoms as the original fat gm style one did. It has 20" of vacuum at the modulator running off manifold vacuum through the original steel tube. What would you suggest doing at the governor? The first time I was looking into it I took the governor out and inspected the valve for burrs and smooth operation as well as the teeth not being beat-up.

BangScreech4-4-2

Wow. Okay, you've got a problem. And it sounds as though you've already done everything that would occur to me plus a few things that wouldn't. I've never experienced the problem you're describing, at least not to that extent. Hopefully somebody who has experienced it will chime in soon.


Best of luck.

Koda

Pull the modulator vacuum line and see what it does. It SHOULD stay in first. If it doesn't and shifts on its own, maybe something is amiss in the valve body.

droldsmorland

Lets start off with... what have you recently modified or changed? Did this trans ever shift as desired for you? What were your pressure readings? How did you preform the pressure reading test?
Koda Good advice.. without the vac sig to the mod the trans will not up shift. The modulator controls part throttle shifts by sensing engine vacuum. The gov controls full throttle shifts by sensing road speed. Are you sure you have the TM-50 with the orange stripe? Is the diaphragm adjustment turned in at least 50-60%? Does the mod hold vacuum(likely or youd have delayed upshifts)? Pull it and check it. Careful to not go too far in on the adjustment screw or the screw will unscrew from the diaphragm and render the mod useless, though with patience I have managed to re-thread a couple I over adjusted. I have had some success using a ported vacuum signal to the adjustable mod. I use this as a troubleshooting method too. The ported signal will delay the shift. This along with playing around with the mod adjustment could get you the 1-2 your looking for but may induce other drive-ability problems. The ported check is a quick n dirty to see what the mod and or trans is doing in my mind. Generally a sticking governor will effect down shifts. It will not down shift or will have delayed down shifts. Weights n springs affect the up shifts.

Again what have you done to this trans? Whats changed? Did you recently modify anything? Using the same torque converter? Did it ever up-shift satisfactorily? Significant change in tire size? Etc...

As for the governor you can lighten up the outer weights (keep OEM springs) as they affect 1-2 up shifts. The inners are for 2-3. You could also shim out the 1-2 valves shift spring in the VB. That will raise the 1-2 shift point. I use this as a troubleshooting method. If it works I know I need a different spring.

To modify the governor, take weight off the outer weights by grinding or drilling. I prefer the drilling method. If I take out too much I can plug weld the hole and start over. Concentrate on the portion of the weights farthest from the pivot point and maintain the shape if grinding. Take out small amounts at a time. You need to disassemble the governor to preform this mod by grinding the "arrow" end of the pins, then replace these pins with #6 finishing nails, then peen or stake. Or eliminate all this and get one of the many Gov mod kits offered by all the trans vendors. Sounds like you need to drop the valve body as well. Might as well look into a Trans Go shift kit and governor mod kit.

Be aware a shift kit is not a fix for a worn out trans. Your pressures will tell you if its OK or not.

The real fix is the VB reprogramer (shift kit) and governor mods, if needed. You will also need an inch pound torque wrench. Over/Under torque on the valve body will induce all sorts of unwanted problems...warpage...leakage etc...

Call Trans Go before ordering and speak with a tech. They will guide you to the right kits.

montvaleplace

I bought this car this past summer and it never has shifted properly unless I shift it manually and then it is nice and firm. I have the readings written down at the shop so I will get them tomorrow The guy I bought the car from said it was rebuilt using"all heavy duty truck parts". I took the readings from the 1971 service manual section 7 page 7. I might have gone in too far on the modulator screw because it was feeling funny the deeper I went in. I'll check that out also. I am assuming the converter was changed at the time of rebuild, I can see that it is orange through a hole in the casting but it is stock and I'd likely change it for something with a little more stall.

droldsmorland

If a higher stall converter was installed that will screw with the gov and modulator. Try some of the things I mentioned before you start yanking the trans. Could save you that hassle. Sounds like a gov tweak and a properly working modulator could solve the prob, and a shift reprogramming kit.

oldcutlass

There is no stop on the modulator screw, so if you turn it too far it simply drops the diaphragm into the housing and it is almost impossible to get it back in threaded area rendering it useless. The adjustment is about 5-7 mph difference in shift points you'll gain a bigger change with a governor mod.

montvaleplace

The pressure readings are as follows
D, brakes applied @1000 rpm 80 psi
Low, brakes applied @1000 rpm 180 psi
R, brakes applied @1000 rpm 115 psi
N, brakes applied @1000 rpm 75 psi
D, @ idle 80 psi
D, @30 mph coast closed throttle 75 psi

I was wrong on the modulator, it is a pro king MD48

droldsmorland

Your a little low all the way around IMO...But it could be the converter stall is higher then OEM spec? I dont have my book in front of me but knowing HP TH400s the TH425 could be about the same...not sure till I verify with my GM Turbo Hydromatic Chilton Manual. Id imagine these would be ball park at least the mins. for a stock application with a healthy trans: (readings below are in PSI)
D should be 135-165.
2 should be 135-165.
3 should be 135-165.
N should be 55-70 min...150-175 max.
R should be 95-150 min...235-260 max.
P should be 55-70 min...150-175 max.

Several assemblies have a direct affect on the line pressures. The converter, the pump, the pumps line regulator(spring & valve), and yes the governor AND the modulator. And of course worn, damaged or leaking components.

Aprox what RPMs does the converter flash? Stock stall should be around 12-1400rpms. If you see it stalling at anything above this say 2-2200 it has a higher then OEM spec converter installed. This can be part of the problem. Take your line PSI readings at 1500+ and see what they are.

Install a Standard Automotive Inc. Modulator TM-50. Then reread the line pressures AFTER you have the mod adjusted. Start with the out-of-the box adjustment then turn in the adjusting screw one full turn )CW) at a time. Paying attention to not bottoming it out and loosing the diaphragm. You want some resolution on it, its not effective with near zero movement (bottomed out).

Report back. I have a suspicion if you cant get the line pressures up with gov or modulator tweaks something isnt right internally or needs to be modified to deal with the non-stock converter. Tried to attach the links below PDF style but this turd site cant handle anything over 1 KB. One site explains Stall/Flash, the other is a section out of the Chilton manual explaining some of the hydraulic basics. Dont be afraid to take this car into a competent ATRA certified trans shop for some hands-on and a second opinion before you start going crazy and wasting $$$

http://www.converter.com/faqs.htm

http://www.ckperformance.com/Files/1...HAPTER%206.pdf

montvaleplace

Well I took the engine out of the car for some work and decided to take the transmission out after looking at how little there was remaining. Anyway I pulled the pan off and noticed some sludge and soot but no more than usual. I noticed there is a pipe plug screwed into the valvebody where there should be a pressure sensor wired with the detent solenoid.There is a photo of it on page 7E-16 pic 7E37 of the factory service manual. I took the valvebody off to check on the location and number os checkballs, and they are all there and correctly located. Next I cleaned the soot off the valvebody and laid it out on the bench to take the valves out. The only thing that doesn't match the factory service manual is the 1-2 modulator valve, spring, and bushing. On page 7E-40 is a photo of what should be there and on page 7-57 there is a th400 photo with the arrangement I have. (not the OW). The flow chart Iv'e been following on page 7-9 also wanted to check the rear accumulator for sticking or leaking or blocked passage. Well the passages to it are clear, and the piston moves freely in it's bore but I don't know about possible leaking. The last thing it asks is to check the int. clutch for operation and correct plate arrangement. I haven't gotten to that part yet. Well that's where I am right now..

montvaleplace

Well I have a little update on where I am on this unit. Under the governor tubes there are two little filters, one was partially blocked with sludge and the other was clear. There was also a gouge in the case where the 2-3 accumulator piston enters it's bore. There were some high performance modifications done also, one being the center seal was removed in the direct clutch piston, and the piston was replaced with one that allows for 6 frictions instead of 5. The intermediate clutch one way roller was replaced with a heavy duty 34 element sprague. So not alot found inside to point to my issues. Iv'e gone through each clutch pack and replaced all frictions with red Alto clutches and Kolene steel plates. I also replaced the bands with heavy duty Alto ones. I installed a Transgo 425-1 shift kit , and I'm speaking with Manny's transmissions in San Jose ca. about replacing my 3.07:1 with a planetary version 3.21:1 coupled with a change in chain and sprocket to give a final drive of 3.67:1. B+M sells a governor reprogramming kit with weights and springs that I got last week but haven't touched that yet. I spoke to a guy named Wally Anderson in kentucky that rebuilds 425 governors for Applied GMC in california and he directed me to this B+M kit. As soon as I get the final drive squared away I'm taking it to a place in Bristol RI. to have it run on a dyno and we'll see how I did. I will report at that point. Thanks so far for the help..

TripDeuces

Buddy's place in Bristol RI?
He was the #1 guy for GM transmissions back in the day. GM's top guy. He'll figure it out no problem. He can be rough around the edges but he knows his stuff and is a wealth of knowledge once you get to know him.

http://www.maximumperformance.biz/staff.htm

montvaleplace

Yes it is, It's called Maximum Performance. As soon as I finish the last few things it will be test run. It's nice to know that he is a tranny guy in case there are "issues".

bw1339

How did it go?

Juan Simon

Hello All

I have a problem with my th425,when I put drive and then put retro the car make a hit and again put drive and another hit.
The hit appear when I change from drive to retro and the same retro to drive.
I rebuild all the transmission and taxle,the hit its the same,can be the modulator or line? or valve body ??
Thanks,
Juan