VR 6 auto - uphill winding road mystery

[Dunlop]

A lot of the discussions on this forum are unfortunately about various problems, but this is a breakthrough for me...

Where I live in north east Vic, there are at least two winding uphill road sections - one that's about 2km long if that - and that's on a main road out of town. For some time the car has struggled a bit with only me in it getting up this bit of road, and the engine temp easily goes up to nearly 2/3rds in summer. I've tried pressing the Power button on the gearbox which increases the rpm by about 500, but it still doesn't feel like it's running in the best power band.

Recently I thought of putting the selector lever into 3rd - which the gearbox normally shifts into as I enter the first bend (average decent speed around these bends is about 60kmh) - and the engine seemed to have more power and be more responsive.

I just came back from a similar winding uphill section on the other side of town, and shifting the lever into 3rd did the same thing - the car seemed to run much better even though it normally drops back to third as the bends get tighter.

Can someone suggest as to why the engine seems to have more power on these uphill sections even when the gearbox normally automatically shits into third anyway? By the way, I assume that when the shift lever is put into third, it will still shift down by itself - ie it won't just stay in 3rd?

Thanks.

 

[Immortality]

I'm just guessing here but when you leave it in drive and it downshifts to 3rd it's in kickdown mode with probably a decent amount of throttle been used and it will upshift once you come off the throttle, manually shifting to 3rd you are staying in 3rd and I wonder if you are getting converter lock engaging which might feel a bit different as power is been applied directly to the wheels rather than the converter slipping and turning that power into heat in the transmission fluid.

There is also a possibility the transmission is tired and under reasonably high load is slipping in the high gears when kicking down a gear but again, when you manually shift into 3rd under lower throttle settings it's allowing the clutch pack to lock up properly.

Have you checked the transmission fluid level? When was it last changed? Are you using DEX III fluid?

We used to have an old VS, was a great car but the transmission always used to slip in 3rd going up a really steep incline but never acted up in general day to day driving.

 

[Dunlop]

Thanks for that - could very well be the reason. Wish I'd known sooner.

I found out recently that there's a type of O ring or seal made of plastic in these that can split over time and reduce the car's ability to drive up a steep hill with a heavy load. If this part is replaced by a brass fitting, it usually solves the problem. I suspect mine is probably split.

The trans fluid was replaced about five or so years ago - because I don't do many kms, when it was checked recently it was found to be quite ok.

Auto trans function is something that I've been interested in for some time now - I need to do a fair bit of research on how they work...

 

[Immortality]

Auto transmissions are a bit of magic, even I don't fully understand them but auto's rely on hydraulic pressure and everything inside a auto can wear out, there are multiple valves etc that all wear with age.

Something I recently discovered is that GM made a change when going from the older T700R4 to the 4L60e, this means the forward sprag isn't engaged and reduces the torque load capacity under certain conditions.

Sonnax 77754-41 Transmission Shift Valve, 2-3 (Heavy Duty) 4L60E 4L65E 4L70E | eBay

For greatly improved input sprag and Forward clutch durability, Sonnax heavy duty 2-3 shift valve 77754-41 for 4L60-E, 4L65-E and 4L70-E units will apply the overrun clutch in D3 1st, 2nd and 3rd Gears.

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I'm not saying this is your issue but one example of how GM modified a transmission to make it better in one respect (coasting) that has made it worse in others.

There are lots of plastic bits in these transmissions that can fail or wear out.

Something I've done and is normally done as part of a shift kit instal is to fit a larger reverse boost valve, this basically increases the line pressure (hydraulic fluid pressure) in the trans and helps to reduce some of the issues from wear and tear leakage inside the transmission.

https://www.ebay.com/itm/3225309378.../m0/5eImCAHKZ9NVgdioej/w==|tkp:Bk9SR6rq242cYw

Definitely a worthwhile mod and can be done at home with basic tools (internal circlip and long nose pliers) once you drop the trans sump.

 

[Dunlop]

Where did my text go?

Thanks for all the info and sorry for the delay as I couldn't log in earlier. Was talking to someone yesterday and he suggested refilling the trans with synthetic instead of mineral based atf, so I'll try and have that done as soon as I can.

He also suggested using an additive which is not a bad idea. Am still absorbing your suggestion to see if I can have that mod done - cost is an issue.

It's just amazing that one of the earliest auto transmissions was used in a GM (?) car in 1940 and it was a four speed...

Some of Scotty Kilmer's videos are pretty useful too:

 

[Immortality]

No, don't fill with synthetic oil, it'll make it worse. Been there, done that, went back to regular DEX III on the advice of a transmission expert (on another forum).

edit:

I'm going to disagree with that video. Transmission fluid is the life blood of a transmission, when it gets old it effects how a transmission shifts to the point you will loose gears. It's like it thins out which means you don't seem to build enough pressure in the various circuits to effect a gear change. New fluid can fix that (assuming there is no major wear and tear in the clutches themselves). Although the transmission fluids primary purpose is to provide hydraulic pressure and act as the medium in the fluid coupling (the converter) as well as a lubricant, it's secondary function is help transfer heat out of the transmission, heat is what kills transmission fluid.

Transmission fluid should be pink, if you pull the dipstick and it's gone red, especially a deeper shade of red it's time to change it.

 

[Dunlop]

No, don't fill with synthetic oil, it'll make it worse. Been there, done that, went back to regular DEX III on the advice of a transmission expert (on another forum).

edit:

I'm going to disagree with that video. Transmission fluid is the life blood of a transmission, when it gets old it effects how a transmission shifts to the point you will loose gears. It's like it thins out which means you don't seem to build enough pressure in the various circuits to effect a gear change. New fluid can fix that (assuming there is no major wear and tear in the clutches themselves). Although the transmission fluids primary purpose is to provide hydraulic pressure and act as the medium in the fluid coupling (the converter) as well as a lubricant, it's secondary function is help transfer heat out of the transmission, heat is what kills transmission fluid.

Transmission fluid should be pink, if you pull the dipstick and it's gone red, especially a deeper shade of red it's time to change it.

Oh no... the person I spoke to suggested synthetic works better as its molecular structure can cope with heat and has better viscosity standards. The Nulon pack states that it's compatible with a number of commonly used mineral atf's.

I had a look at some of the posts on this site and a couple of other VR/VS owners stated they found that synthetic was fine. I assumed that the actual viscosity/lubrication specs would be the same as mineral atf and that they found smoother shifting using it.

I might have made a bit of an error with that video - I watched several last night.

Grateful again for the advice - I called a transmission specialist yesterday but he was busy and I forgot to call back - willl try again now to see what he says... Must watch Scotty's video again.

 

[Immortality]

A lot of modern oils and lubricants state they are backwards compatible but I have my doubts.

Yes modern synthetics can withstand heat better but your old transmission was designed to run DEX III, the modern synthetic DEX VI has a slightly lighter viscosity at operating temp, that means it's thinner, that means on a old worn transmission it will leak faster internally.

There is also the question of who is trying to sell what, when someone recommends the more expensive stuff is it because they get a better profit margin on it or because it's actually better for your application.

I tend to use Penrite products and they have a handy selection guide by vehicle which is generally fairly accurate.

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