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Old 08-23-2020, 02:02 AM   #1
FreeEMSFred
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Default Strongest redblock auto? AW BW ZF

Contenders are:
  • AW71/72 (I drive 3 of these regularly and own 4, was 4/5, sold 1, no complaints, max power 153hp B234F though)
  • BW55 (or is it 35? I have one, tag is missing, seemed to drive fine)
  • ZF 4HP22 (a friend has one, claims it's a dog)

Are any of these considered to be unreliable?

Are any of these considered to be unreasonably weak?

Are any of these considered to have poor shift quality?

Are any of these considered to be overly power parasitic?

Any other comments, (common?) wisdom, or knowledge to share on the differences/details, especially of the last two, I know the first one pretty well :-)

Cheers :-)
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Old 08-23-2020, 03:58 AM   #2
iamrolling
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I've read some manuals and gathered some information from FAQs, so I'll chime in. I'll just start talking. Hopefully something in here will be useful.

The only one I've actually driven with is the AW71. Among the transmissions you listed, I hear the best things about the AW71's ability to take a beating. Up to about 300HP, if I'm remembering correctly. The AW70 is similar but not as durable. All I know about the AW72 is that it's commonly paired with the dual cam redblocks.
The BW55 is the direct predecessor of the AW70 series. There are a few small differences, but the main one is the BW55 doesn't have an overdrive built in. There was also an AW55 which was almost identical to the Borg unit. The BW35 is a little more different: it uses bands where all the other Borg and Aisin units only use clutch packs.
Everything I know about the 4HP22 is from the FAQs, but it sounds like a disaster. The clutches partially engage in park, so a single emissions test will cause severe internal damage. It has teflon and aluminum pieces with a short lifespan. The only good thing about it is that it can be directly replaced with an Aisin transmission.
None of these boxes are very efficient. The valve bodies are controlled by unyielding mechanical logic. The up side of that is not having to deal with computers and embrittled electrical connectors.
The only solenoid on the transmission is the overdrive control, where equipped, and it's on the outside of the casing. You can safely delete that one if you never tow with your car. There are both cast and milled blockoff plates available. They're probably both fine, but each style makes claims of being better than the other.
You can also get rid of the shiftlock solenoid in the shifter, and then the only wires you have to deal with are the neutral safety switch and the light bulb. I highly recommend not deleting those even if you're observant enough to never start your car in drive or reverse. Plus removing the overdrive lockout and shiftlock gets enough crap out of the way anyway.
I've only been as far in the AW71 itself as the valve body, but it was almost fun to work on. It would be more fun if there were spring and valve kits available for it. I really want to do a full rebuild, but I only have the one in my car which is my daily driver. Maybe someday I'll try to source a busted AW71 so I can take my time building one.
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Old 08-23-2020, 10:28 AM   #3
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AW71/2 > the rest.
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Old 08-24-2020, 08:16 AM   #4
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Thanks for that 'iamrolling' - The Borg Warner unit I have does have an overdrive and solenoid to go with it and the button. I directly swapped an AW72 and B234F into the car (RHD) with one small custom engine mount, otherwise all bone stock. I will post some pics of the BW unit I have, without a tag, see if anyone recognises it as 55 or 35 - can get more / better photos if someone wants. But without a tag, who knows.

The AW72L in my 90 740 GLE is at the point of soft clutch-slipped shifts after 5 years of my abuse, though if you lift to shift, it grabs and holds. Could do with a freshen up, but it hasn't let me down despite the burnouts and donuts I've made it do repeatedly and for long periods

The AW71 in my 91 240 GLE wagon makes a grinding noise in 1st and has for 5 years. When I did the ATF 5 years ago it came out brown/silver and I thought "this won't last long" but 30,000km later with synthetic ATF in it, it's still rolling just the same with the same noise. I bet it's dirty again now, though.

Most autos will take a bit of a beating provided that you shift kit them :-) I know Kenny ran a 9.X on an AW71 with shift mods - there's an interesting thread on here somewhere with all the details.

I actually really like the mechanical autos compared to electronic ones, for the most part, and when they're working 100% right. I like that I can drive it at 95% throttle and labour it and I like that I can lift-shift them and other consistency/shift-behaviour things. I find electronic autos always shift down when I don't want them to. They drive fine gentle/slow and hard/fast but any kind of heavy throttle short shifting strategy is nearly impossible.

A friend of mine in the US did a full rebuild on his Tacoma trans (same as AW71) and in the end, it didn't work. No idea what he did wrong, but he put a lot of hours in and got no good results So be careful, if you do have a crack!

And yes, that ZF sounds terrible, he reckons it sucks 50hp and makes the car slow

BW-something:







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Old 08-24-2020, 09:16 AM   #5
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Wow. Yeah, there's the solenoid. For some reason I didn't remember reading about an overdrive on the 55 transmissions in the green books.
My AW71 has the lift to shift "feature" and has for about 25k miles. It shifts late if unless I release the throttle a very small amount. That's why I had the valve body out. Replacing the checkballs helped it a little, and it hasn't got any worse since then. I don't fully understand this problem. Does this mean that the transmission has serious damage and I need to start looking for a new one? It does immediately grab when I relax my foot a tiny amount, at least.
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Old 08-24-2020, 06:26 PM   #6
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I thought the BW55 was a three speed
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Old 08-24-2020, 06:46 PM   #7
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Re number of speeds, I guess that's possible? I may never find out unless I swap this into one of my cars so I can rebuild/upgrade the AW that's in there.

Re lift to shift, the shifting is based on the throttle linkage position and RPM from a governor so it could simply be a subtle adjustment to that cable that's required.

On my 16v 740 sedan the 1->2 shift is lazy/slow/delayed to the point of bouncing off the rev limiter, esp when the trans is cold (even if the engine is warm). Other shifts are fine. So I guess the passages for the 1 2 shift are clogged or something. It hasn't really gotten better with fresh oil and lots of kms though. And it's not consistent, either. Sometimes its fine, other times it hangs, more often the latter.
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Old 08-24-2020, 09:35 PM   #8
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Quote:
Originally Posted by FreeEMSFred View Post
On my 16v 740 sedan the 1->2 shift is lazy/slow/delayed to the point of bouncing off the rev limiter, esp when the trans is cold (even if the engine is warm). Other shifts are fine. So I guess the passages for the 1 2 shift are clogged or something. It hasn't really gotten better with fresh oil and lots of kms though. And it's not consistent, either. Sometimes its fine, other times it hangs, more often the latter.
You could try changing out checkballs if you ever feel like going in. And maybe try cleaning the valves and bores. I didn't mess with valves because I was afraid of pulling out a broken spring and not knowing how to cram the pieces back in.
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Old 08-24-2020, 11:03 PM   #9
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How's this a discussion? AW71/2.
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Old 08-25-2020, 07:24 AM   #10
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I looked it up, and the BW55 is a three speed. Yet there's the overdrive solenoid in the picture, and the casting around it looks like the one from the AW70 series. But it has a Borg Warner logo on it. What is that thing?
I did a bit more looking, and found this thread on Brickboard.

Quote:
Around 1979, Borg-Warner (US engineering) added an overdrive to the front of the AW/BW-55 transmission by request of Toyota for use in its luxury Corona model. It was produced by Aisin as the Toyota A42 and first installed in the 1981 Corona.

> In 1982, Volvo started using that OD equipped gearbox in 4 cylinder 240s and named it AW-70. Case marked "03-70"
It's probably most like an AW70. But that doesn't explain the Borg Warner logo. The one installed in the Corona would have been made by Aisin. Where did you find that thing?

Last edited by iamrolling; 08-25-2020 at 07:31 AM..
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Old 08-25-2020, 09:56 AM   #11
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doucheNozzle, perhaps the question is not to find only the strongest, but also to understand the weaknesses of the others I already knew the non AW had a bad name, was looking for more detail since I discovered:

1. I owned the BW
2. I discovered ZF existed
3. A friend claimed the ZF sucked hard

I wanted to know if my BW spare was any good, or not, and what was wrong with the ZF exactly.

iamrolling: Straight out of my 1988 240 GL B230K carby sedan

What you found in BB is quite interesting. Maybe the early ones had a BW casting/mould? Or maybe there's more to the blend of stuff out there than the internet has has time to document for us? I strongly doubt this trans is NOT original to the car (ie, I think it is).
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