Hi guys, I'm looking for some information regarding the th350 in my 72 supreme. It doesn't seem to upshift at WOT unless I let off on the throttle a bit. The kickdown cable is adjusted correctly, trans fluid is the right level and clean as well. When WOT in 2nd gear, I hit about 5000 rpm before I chicken out and let off a bit for the upshift. I don't even know if it will upshift on its own, or if it does, its past the motor's redline and powerband.

Any help is appreciated. At 19 years old, I've never messed with transmissions much and never a GM transmission yet.

 

Check the vac line from the intake to the modulator for leaks and obstructions (vacuum source should be off intake not on the carb). If its still not to your liking get a TM50 adjustable modulator and ditch the OEM.
Two easiest ways to control/adjust the upshifts are the modulator and governor. Passing gear detent cable controls the full or part throttle downshift. Are you getting part throttle downshifts or only WOT downshifts?
How did you adjust the kick down?

 

I do not get part throttle downshifts, only full throttle. I adjusted it as per the CSM, pull the cable stop all the way in and let the gas pedal self adjust it. Will the modulator change the WOT shift? I like where the part throttle shifting is now. I'll check the modulator.

 

As stated, you need vacuum through the modulator for smooth shifts. I’m running quite a bit of cam.....I had to put a modulator on my th350 that was made especially for engines that don’t make a lot of vacuum. (Black/red stripe modulator). Another time about 50 years ago my 66 Cutlass wasn’t shifting......took it to the trans shop....all that was wrong was the modulator hose was disconnected.

 

The modulator has zero effect on WOT shift points. You can adjust the modulator to dial in part throttle shift points, but only about 2-4 mph up or down.

What is the 1-2 shift point? If you want to lower the shift point, you need to get a different govonor, or recalibrate the one you have. Get a recalibration kit from B&M, TCI etc. it
includes weights and springs.

I would suggest getting a different govenor to modify. Head to your nearest trans shop, see if they either have another govenor,’or can order one. Install it, see where the shift points are, then you can start charging things to get it to shift where you want.

 

I have nice smooth shifts right now yet so I doubt anything is wrong with the modulator anyways. When did your th350 force an upshift at wot when it was stock?

 

The TH350s in both my 1970 Supreme and the '71 convertible shift 1-2 at 4800 RPM. I'm not 100% on the 2-3 shift, but I think it's at the same RPM. I usually have my eyes on the road and not on the tach when going that fast. I'd go for a spin and let you know where it shifted, but it's currently 108ºF outside. I can get back to you in October when it cools off.

 

Mines about the same as kens but I think the 2-3 shift might be a couple 100 rpms lower than the 1-2 shift like 4500ish

 

That sounds right. I was thinking the 2-3 was a bit lower than 1-2, but I wasn't certain.

 

I need:
1. warm pressure readings in PRND21,
2. verification the vac source to the modulator is in spec and the mod doesn't leak vac or fluid, Yes both.
3. verification the kick down detent is properly adjusted(check it again).
4. a governor visual inspection Pull governor, look at the springs weights, freedom of movement and inspect for any burrs or varnish on its shaft its bore.

I can't help you any further without this info.

If everything above checks THEN drop the pan.

These are the proper troubleshooting procedures to avoid tail chasing.
Stock engine, stock trans...then a stock governor, no need for modification.

Ask yourself something...whats the simplest easiest non-oily mess way to verify the health of your hydraulic pump behind your engine?
Pressure checks. Its step one period, well, step two, fluid level is first...

If you suspect low oil pressure in your engine would you drop the oil pan first or hook a gauge to it to verify data?

 

The govenor controls WOT shifts. You may need to change the weights.

 

I'm finishing up the driver side roof rail weatherstripping and then I will get under the car and take a look. Will there be any fluid where the governor bolts up? I'd really rather not get all messy. I don't have a pressure gauge for the trans, even if I ordered one, it wouldn't get here for a week at least so that is out of the question currently. As far as the kickdown detent, is there a detent/adjustment at the trans itself? All I did was set the cable stop at the gas pedal itself. This may become apparent when I am under the car, but if I ask the question now, maybe I'll have an adjustment to set it to by the time I'm under there

I sincerely doubt there are any trans problems except for the late shift. PO has a new output seal, pan gasket, and who knows what else. At the very least the externals have been regasketed, which is more than most 40-50 year old cars have anyways

 

Thankfully, on the TH350, the govenor pops out the side. It's the big round cover. Don't need to drop the pan. A little fluid will come out, but not much.
Kickdown adjustment is only at the throttle.

 

Well my kickdown is set up right for sure, I checked it again. Still the same as when I set it the first time. Looking underneath, the modulator looks good and has a new vacuum line to it. I only got a quick chance under there today. I'll put it up on jacks hopefully tomorrow night. That governor sure is a tight fit in there it looks like...

Today I took it for a drive. Shifting great, it's just that 2-3 shift that happens at about 4900 that I'm not liking. I can hear the motor getting wound up. It does shift nice and firm though. On a stock 350 quadrajet I can chirp into 2nd.

 

I would not be concerned about a 4900 RPM shift point for 2-3. I wonder why this seems too high?

 

Mostly because it sounds like the valves are floating at around that rpm and because the engine is past it's powerband. If other transmissions are shifting at 4500 or so that would be better for my stock setup. Maybe nothing is wrong and the modulator needs an adjustment is all.

 

Snap a pic of the modulator. It may be an adjustable unit. Will it up shift to 1-2, 2-3 at light throttle?

 

Yes shifting is completely normal except for the WOT upshift. photo46.jpg

 

If your engine is having problems with shifting at 4900, then its an engine issue. The transmission is shifting right. Disconnect your distributor vacuum advance and see if that corrects the engine miss at high rpms.

 

It could be the timing was too far advanced. Now that I think about it, the HEI distributor I bought had 20 degrees of advance in it. I set the timing for the 1974 HEI specs which was 20 btdc. As I'm typing this, I set the timing back down to 16 degrees, giving me a total advance of 36 degrees, not 40.

 

That appears to be a TM 50 which is adjustable. Pull the nipple off and look in the inlet for a slotted screw. That's the adjustment. Try backing it out CCW a quarter turn at a time.road test repeat.
Are you getting normal part throttle upshifts and just delayed WOT upshifts. 5K is a bit high for a stock Olds

 

I'll give that a shot then. Yes, just a delayed upshift.

 

Next is to open up the governor pull it out and have a look. Is it stock or not? I have had instances where the only thing I had was WOT upshifts. That problem was attributed to a plugged steel modulator line. Another instance was the lack of downshifting when coming to a stop. That was a governor hanging up in its bore.

 

Once again, the modulator has nothing to do with WOT shift points. The VACUUM modulator uses engine VACUUM (duh!) to reference shift points to engine load. High vacuum, low engine load=low speed shifts. High engine loads (like WOT) results in low vacuum (or no vacuum) and high shift points.

Engine speed of 5K is no big deal, assuming the engine is sound and in good tune. Get the timing sorted out, the see what happens. The engine may have its tongue hanging out st 5K because the timing curve is screwed up. Btw, vacuum advance is zero at WOT, because once again, vacuum advance uses ENGINE VACUUM to reference ignition timing to engine load.

 

I understand that, and to me it doesn't make sense that the modulator would control that, but when when I've searched, lots of people have said that the modulator DOES change the WOT shift pattern a tiny amount. A tiny amount may be all I need.

Now that the timing is set back to 16*, the car is slower and more gutless with a little change up top. I'll be backing it up to 18*, a good average and see what's what.

Yesterday I also tried to get the governor out but ran out of time. The clip that holds the governor side cover on is a PITA to get off with the dual exhaust and crossmember being in the way.

I'll try to get back at it tomorrow

 

I understand vac can at wot drops off, but once you release all that timing comes back when he lets off the throttle a bit to get it to shift. Just wanted to make sure there was nothing else contributing.

 

Cut the clip off, mangle it, whatever it takes to get it off. Don’t bother reinstalling it when your done. GM eliminated the clip on the later 350, and never used them on the 700. Btw, the 700 and 350 governor covers will interchange if you bend it trying to remove it. Depending on how long since it was last off, “environmental loctite” can be a hassle.

 

Disconnect the modulator plug off the vacuum source and take er for a ride and get back to us.
And again I will give up on this thread until I get pressure readings per the specs. I cant troubleshoot an automatic w/o pressure readings cus I know nothing about them...for the last 40 years.

 

I apologize for no updates guys. I'm in the middle of moving at the moment. Hopefully in a few weeks I'll be able to give an update!

 

Thread revival almost a year later! Finally have some time to check the PSI on this ole car!

I went and bought some gauges, still need to get some permanent gauges in the car, but I can at the least test the trans function at idle. Right now I am testing oil pressure, and possibly tomorrow trans pressure. I will update you guys soon. Hopefully not in a year

 

Hello!

Sorry for posting this old thread, but i have EXACT the same issue with my stock 71 350 since years. I was never able to find out whats really the cause of this problem.

71 350, all stock, swapped from 2bbl to correct 71 QJet + headers, MSD ready to run (18° mechanical stop bushing, 35-36° all in close before 3000rpm, vac advance hooked to ported on qjet)
TH350 with Transgo shift kit, Hughes GM20 converter, 3.23 rear.

Everything works fine, no issues in part throttle shifts, detent cable adjusted due to 71 CSM (full travel at WOT) but when going WOT, the trans shifts down, but when i leave my foot on the Pedal, RPMs climb up to 5000, a terrible noise appears (floating valves?) engine stumbles until i let off the throttle a bit.

Im really clueless, if thats a transmission or an engine issue, or both. Because when i let the trottle off a bit before 5000 rpm, the trans shifts up as it should and on the other way, as stated here some times, a healthy, even stock engine should be able to get wound up to 5000 without a problem. I have a governor recalibration kit from B&M here, but it seems that calibrating WOT shift points down is just fighting the symptomes, not the reason for this issue.

again, sorry for posting this old thread, but i found it while searching around for some possible reasons for this issue and this is the only thread i found, which describles exactly the same problem.

Edit:

Or am i maybe missing something here? Maybe running out of fuel in high RPMs at WOT? I rebuilt the QJet years ago an set the fuel float level like shown in the CSM.

 

Back in the 1980s my engine would not go past 5000 RPM due to weak valve springs. It would pull strongly all the way up to 5000 RPM then feel like it was bogging down.

In D the transmission would shift at 4800 RPM and all was well, but if I manually held the gear the engine would stall at 5000 RPM. After replacing the valve springs the engine would rev to 5800 RPM with no issues.

 

Yeah, already tried this. Swapped the springs to Melling VS720 (what rockauto lists as stock replacement). Does not helped much. I searched for other springs to give it another try, but i couldnt find a proper spring which is the same spec as the stock springs.

i guess, my issue is that i dont really know if i really have floating valves, or WOT fuel starvation, or something else. The fact is just, when flooring it, at around 5000rpm, the engine falls on its face, Sometimes sooner, sometimes later, sputtering and bogging, until i let the pedal off. Then it catches up like nothing happend.

I cant believe that not more people with stock, non rebuilt engines have similar issues at WOT. This thread is the only obe i found, where someone is describing exactly this problem.

 

Your description reminded me of an issue that I experienced long ago. If the rear tires spun a lot from a stop, the engine would bog at the top end of 1st gear, and it would recover if I let off the throttle slightly. If there wasn’t a lot of wheel spin off the line, the engine ran fine with no bogging. I eventually determined it was due to fuel starvation. I resolved the issue by changing the carburetor float level slightly so the bowl didn’t run dry. It didn’t take much of an adjustment to resolve the issue.

 

Thanks for the help! I was thinking to try exact the same and re-check/re-adjust the float level. What i also will do if i have the air horn off is check/replace the plastic cam which lifts the secondary rod hanger. I havent replaced it when i rebuilt the QJet.

I just want to make sure, that this problem is not fuel-related, before i dig again into valve springs, but due to the lack of expierience, its hard for me to determine if its valve floating or fuel starvation.

 

I checked the float level of my QJet and figured out its correctly adjusted.

Finally, i was able to cure my valve floating problem.

Checked Valve Spring installed height with one of those micrometer-tools and found that all of my Intake Valves spring installed height was too wide. Some had 1.690 instead of 1.670 (factory installed height).

I bought a set of 1.480 OD Shims and shimmed the springs as close as possible to 1.670. Valve float @5000rpm is gone.

But, my TH350 is still shifting too late for this engine, WOT shifts are around 5000rpm. Kickdown cable clip is adjusted like the CSM says (pulled all the way at WOT).

my guess is, that the Trans detents to 1st at too high speed for a stock engine.
I have the Transgo 1-2 shift kit installed and did NOT installed the supplied "low control clip". Can this be the reason? I thought that this is only to prevent manual shifting to 1st at higher speeds.
Where does the transmission gets the signal from which says "too fast for detent to first"?
I have 3.23 gears in the rear.

I will try to play around with my governor to bring down the WOT shift points a bit when ill find some time.

What i still dont understand is that even with my stock, untouched governor, the shift points are more @5000 than @4800.

Damn, i would have swapped over to 4speed manual long ago, if there wouldnt be the infamous crank pilot bearing hole issue

 

I did the same thing to retain the "high speed downshift lockout" and did not have any problems. I talked to TransGo and they confirmed this is OK.

 

The low gear spacer (sometimes its a solid spring) in the low control valve once installed will allow the trans to downshift at any speed, or stay in a manual gear until you either move the gearshift lever, or drive over the crankshaft. It’s basically an invisible modification unless you have the shifter in 1st or 2nd gear.

Im wondering if you don’t have a fuel delivery issue or some other concern. A healthy 350 should easily run to 5000 rpm and still make power.

Just a thought, have you verified that the carb will go to WOT while flooring the throttle from the drivers seat? Make sure the floor mat or linkage flex isn’t keeping the carb from going WOT


If the kickdown cable is adjusted to the incorrect WOT, maybe that’s keeping the trans from upshifting because it’s not actually WOT? Maybe the engine is wheezing because the throttle isn’t actually opening all the way, while as far as the valve body is concerned the throttle is.

if the engine is healthy, and everything else is good, I bet your going to need to play around with the governor. Don’t try to tune WOT shift points with the modulator.

 

Here's an image of the TransGo installation instructions with my notes after talking to TransGo and Hughes Performance about the Low Control Valve.

 

Sorry for the late answer.

I shimmed my valve springs to the correct installed height (1.670), now the valve floating is gone.

My 350 was originally a 2bbl and i converted it to QJet. It still has its stock 2bbl cam. I dont know the stock 2bbl cam specs, but the engine is definitely on the end of its power-band at 4800-5000 rpm, so i would like to have the WOT shift points at 4800, not like now at around 5000 rpms.

at pedal WOT, the carb is also at WOT, and there, due to 71CSM, detent cable should be pulled for max travel.

I had the same thought, and i was running the QJet with the 2bbl throttle cable, so i bought the correct 4bbl throttle cable, but this wasnt the issue.

Just a thought.. are there different lenght detent cables too? One for 4bbl and one for 2bbl?

Trans is doing the detent just fine, but sometimes i have the feeling that it kicks down from 3rd to 1st at too high speeds (for my stock engine) and i was wondering if this also can be caused by the installation of the Transgo kit.

I have swapped from 2.56 open to 3.23. Where does the detent system knows how fast the car is going? Rpms of output shaft through governor? Maybe i really have to pull the governor and try it with the 2 yellow springs as the Transgo instructions say use the for passenger cars. Currently, i have the next higher step springs installed, if i remember correctly the blue and white.

Fun71, the Transgo Instructions you have show a LOT more details than the Instructions they supply nowadays!