GM 8-speed

[Wageslave]

The root problem is computer science majors who have no idea the limitation of mechanical systems designing control systems that control mechanical systems. I'm not saying they are bad engineers, just that there is too much to learn to understand a coding language/controls philosophy AND understand manufacturing tolerances and quality control AND understand mechanical design math stuff. It's tough to find someone that knows one of of those things let alone two or all three.

In theory you can command a 0.0001 second shift time. In theory you can command line pressure to rise from 120 to 250 PSI in 0.0001 seconds.

But, inertia, losses, compliance and tolerances are a Be-yotch.

It's easy for the controls engineering group to say 'not my problem, it's the mechanical group's problem' and the mechanical group to say 'it's clearly a controls problem' and nothing gets solved. In my experience the mechanical design group ends up diagnosing and either fixing it with a mechanical part OR tells the controls group what they need to do. Problem is the mechanical group is trying to figure out the gears, clutches, housings, and sensor placement so they are stretched thin.

The fact that the problem is on 8l45 and 8l90's says it's a controls problem since they copied and pasted the solution (and problem) from one to another.

Having design flaws isn't just a GM problem, but it is a GM problem that they won't fix it. Because short term profits because shareholders yo!

I have also seen where they will try to overcome physics by using the thinnest, wateriest transmission fluid formulation they could come up with to get valves and clutches to move faster.

I had a Volvo where it would shift into all gears, but couldn't hold a gear for nothing. When it went to the dealer, they said that the valve body was shot because the spool valves inside the transmission had wore into the valve body itself. Apparently it is a well known condition, and the fix is to replace the valve body and switch to a Toyota spec fluid that has better lubricating properties.

This transmission is used across several brands, but the Volvos had a lot of issues with it simply because they specced a transmission fluid that was so thin that it couldn't even lubricate the moving parts that were bathed in it. All for a little faster shifting.

 

[gnvair]

I have also seen where they will try to overcome physics by using the thinnest, wateriest transmission fluid formulation they could come up with to get valves and clutches to move faster.

I had a Volvo where it would shift into all gears, but couldn't hold a gear for nothing. When it went to the dealer, they said that the valve body was shot because the spool valves inside the transmission had wore into the valve body itself. Apparently it is a well known condition, and the fix is to replace the valve body and switch to a Toyota spec fluid that has better lubricating properties.

This transmission is used across several brands, but the Volvos had a lot of issues with it simply because they specced a transmission fluid that was so thin that it couldn't even lubricate the moving parts that were bathed in it. All for a little faster shifting.

Aisin 55-50SN / 55-51SN.
They used that transmission on Volvo's, 04-09 Chevrolet Equinox/Pontiac Torrent and the 04-06 Nissan Maximas and a lot of Saabs.
The line pressure accumulator bore would wear out in the valve bodies and cause all kinds of operational issues. Typically replacing the valve body would rectify it if the person didn't drive too long with it screwed up.

 

[UNGN]

One thing I will say about ALL of the ZF based transmissions is that you never see hard parts failures like you used to see with the GM, Ford and Chrysler design/built transmissions.

Almost All. The ZF 5 speed have a lot of stupidity built into them that make them bad. Jag's don't even have a dip stick. You fill them through a plug in the side of the trans that is 1" from a 500 degree exhaust pipe, while the car is running.

Jag's hoods are so long (and open from the back) that you can see 6" of the top of the bellhousing when you open the hood, so a lack of a fill tube is just a way to charge $600 for a fluid change, and not a space issue. When people don't want to pay $600 for a filter change on a $4,000 car, everyone knows what happens next.

Later ZF's are good because the early ZF's are not.

 

[gnvair]

Almost All. The ZF 5 speed have a lot of stupidity built into them that make them bad. Jag's don't even have a dip stick. You fill them through a plug in the side of the trans that is 1" from a 500 degree exhaust pipe, while the car is running.

Jag's hoods are so long (and open from the back) that you can see 6" of the top of the bellhousing when you open the hood, so a lack of a fill tube is just a way to charge $600 for a fluid change, and not a space issue. When people don't want to pay $600 for a filter change on a $4,000 car, everyone knows what happens next.

Later ZF's are good because the early ZF's are not.

They all fill like that except the Ford's that have a stub on the right front of the case with a small dipstick that unscrews. But majority of modern transmissions lack dipsticks including the GM 8 speed.

 

[Wageslave]

Aisin 55-50SN / 55-51SN.
They used that transmission on Volvo's, 04-09 Chevrolet Equinox/Pontiac Torrent and the 04-06 Nissan Maximas and a lot of Saabs.
The line pressure accumulator bore would wear out in the valve bodies and cause all kinds of operational issues. Typically replacing the valve body would rectify it if the person didn't drive too long with it screwed up.

Close. Mine had the V8 and AWD, so it had the Aisin Warner TF-80 SC. The same issues though. And the best part is it is one of those sealed "lifetime fluid" transmissions. Too bad Volvo thought the design life of one of those is about 80,000 miles.

 

[airboatgreg]

Been a GM guy all my life. Drive a Tacoma now. No more GM's for me

 

[Clone TIE Pilot]

I love our beloved G body GM's, but I would NEVER purchase a new GM, FORD or CHRYSLER product, the quality control isn't there, along with the poor designs that are rushed out the door, the industry is moving at a pace that manufactures just cant cost effectively keep up, or perfect design issues for that matter, and ultimately the consumer is left holding the bag, or a handful of repair receipts that are not covered under the manufactures frivolous warranties, just unbelievable. I hope people vote with their hard earned monies and buy Honda, Toyota, and some other HIGHER quality vehicles that actually WANT to see you coming back to the dealer for your next purchase! What GM, Ford and Chrysler are doing, is nothing more than criminal and nothing shy of inexcusable!

Ford Panthers are built like tanks and last 400K, even abused ones that were cops cars then used as taxis. May not be fast but they won't let you down.

My Dad's 1984 Toyota pickup was swiss cheese by the time it was 4 years old, I can't even remember it without massive rust holes. By the time it was 5 years old the trans failed after he replaced the wheel bearings. 70's and 80's Japanese cars are famous for rusting out quickly, even leaving rust stains on new dealership lots and its difficult to find one thatt isn't a rust bucket. Plus Toyota had that runaway DBW issue a few years ago.

Of course many modern Amercian cars are made with parts sourced from the Japs and vice versa. Some Japanese cars are just rebadged Amercian cars. There is so much overlap it doesn't matter anymore. The Detroit airport has signs in both English and Japanese everywhere like a real life Blade Runner. My Ford P71 Crown Vic has several Mistubishi sourced parts in it. Many of the manufacturers including Honda, Toyata, BWM, Ford, etc bought defective airbags from the same Japonese supplier. One of the big issues with failing quality is outsourcing which is rampant in manufacturing anymore. Its great for reducing costs but the downside is it makes quality control much more difficult and nearly always results in quality decline.

 

[DRIVEN]

Can't say I'm surprised at the direction this thread has headed. I'll just keep biting my tongue.

 

[ssn696]

So as I read through the posts, I wonder, so why are we keeping these G-bodies alive?....

 

[fleming442]

The 8 speed problems seem to be software related according to 86CUT . He replaced the TCM and added a tune; all is mostly good in the 19 ZR1.
Therefore, it should be an easy fix for GM as they can throw the tune out over OnStar, not requiring a dealer visit. Just ask 69hurstolds