4L80E TC Lockup and (also) Exhaust Brake

[rustyk]

I have the AMG/Peninsular 6.5L TD in my 16K lb. motorhome. Everything's mechanical except the throttle position sensor sending instructions to the tranny.

I have two questions:

1. If I make the TC lockup mod, would this disengage if the transmission absolutely decided it needed to up-/down-shift, or does it have to be disengaged manually (electrically)?

2. While my RV has very, very, good brakes (the same as longer versons of the same model at 20-22K), I'd prefer some way of retarding its progress down long grades (having had a belt throw, losing the Hydroboost, and having a master cylinder take a hike another time holds my interest in this issue). I've seen no market for a Jake Brake or Pac-Brake for this engine-tranny combo. Any suggestions?

[DA BIG ONE]

Exhaust brakes are a restriction (cross shaft and disk) in exhaust system if not properly sized. I had read one article about a 3" brake was so restrictive on a 3" system it actually reduced the exhaust efficiency back to smaller stock sized exhaust.

A 6.5td should be ok with a 4" brake and exhaust. I've seen a 4" one listed with one of the big suppliers but forget which one.

[Jim Faire]

I have the AMG/Peninsular 6.5L TD in my 16K lb. motorhome. Everything's mechanical except the throttle position sensor sending instructions to the tranny.

I have two questions:

1. If I make the TC lockup mod, would this disengage if the transmission absolutely decided it needed to up-/down-shift, or does it have to be disengaged manually (electrically)?


I have one answer. Yes, when the TCC lockup is switched in, the sucker stays locked all the time. You have to unlock it (turn it back over to PCM control) in order for it to get out of lock.

It WILL, however, shift up and down in TCC locked mode... ie: from 2(locked) to 3(locked) to 4(locked) without ever going into 3(unlocked). It's like if you just cut that wire... it will still shift, but it will never lock.

[tanker]

I had the "BD" exhaust brake and the "BD" Torq-Loc on my 95 6.5 suburban and it worked great. I was electronic not mechanical injected. It held back on hills while towing my travel trailers, one weighed 8700 lbs, the other 11,500 lbs. I put over 165,000 miles of mixed driving from Canada to Florida and west to Washington State, crossed the Rockies several times without a problem. The torque converter would unlock below 30mph. The Torq-Loc helped keep transmission temps low, and saved brakes. I would not just put in a manual lock up, as it needs to unlock at lower speeds. Check with "BD" and see what have to offer.

[rustyk]

tanker, thanks for the info - I'd not been able to find any source for a 6.5L TD exhaust brake (nor something to keep the TC locked).

Jim Faire: Thanks for the info, but I'm a bit confused...your post says the tranny will go from 2 to 3 to 4 (locked), but then you say it will "still shift, but never lock". Did you mean "never 'unlock'?"

[Kick Ass Matt]

While we're no the TC subject. You know your TC is locked when your RPM drops correct?

[Jim Faire]

tanker, thanks for the info - I'd not been able to find any source for a 6.5L TD exhaust brake (nor something to keep the TC locked).

Jim Faire: Thanks for the info, but I'm a bit confused...your post says the tranny will go from 2 to 3 to 4 (locked), but then you say it will "still shift, but never lock". Did you mean "never 'unlock'?"


Need to read closely, Rusty. I said if you cut the wire, it would never lock.

TCC Lock is controlled by one wire that goes from the PCM to the Tranny. When the PCM grounds that wire, the TCC locks up. When the wire is un-grounded (open circuit), it unlicks.

If you put a 3-way switch into that wire, you can:
- manually ground it (forced TCC lock)
- Manually open the circuit (forced TCC unlock) - same as cutting the wire
or
- let the PCM control the tranny.

NOW - that operation (TCC locking) is independent of the 4L80-e tranny... it will still shift through the gears with the switch in any position... but the TCC will either stay locked, unlocked, or the PCM will control it, in which case under easy acceleration, it will feel like you have 6 gears... 1, 2, 3L, 3H, 4L, 4H.

Is that better?

That being said, if you can find a 4" BD TorqueLoc Exhaust Brake, get it... for your application, it would be sweet.

Me, I use the toggle switch and let the PCM control the thing ar lower speeds.

[rustyk]

While we're no the TC subject. You know your TC is locked when your RPM drops correct?

Yep, but at cruise, mine's always just borderline.

Jim: I don't have a PCM - mine's all mechanical, with only the TPS feeding the tranny.

But I intend to call about the exhaust brake/TC lockup combo.

[Jim Faire]

Jim: I don't have a PCM - mine's all mechanical, with only the TPS feeding the tranny.

But I intend to call about the exhaust brake/TC lockup combo.

Yeah, you still have the PCM - but maybe I'm getting the terminology wrong...

An ECM (Engine Control Module) will control an electronically-injected truck with a non-electronic tranny.

A PCM (Powertrain control module) can control the 4L80e tranny... it still shifts electronically, and still uses the same computer-controlled TCC solenoid system. The TPS should feed that, not the tranny (directly).

But yeah, keep looking into the BD brake. It'll work better than the switch I'm talking about, for your application.

Jim

[rustyk]

Yeah, you still have the PCM - but maybe I'm getting the terminology wrong...

An ECM (Engine Control Module) will control an electronically-injected truck with a non-electronic tranny.

A PCM (Powertrain control module) can control the 4L80e tranny... it still shifts electronically, and still uses the same computer-controlled TCC solenoid system. The TPS should feed that, not the tranny (directly).

But yeah, keep looking into the BD brake. It'll work better than the switch I'm talking about, for your application.

Jim

Thanks for the amplification - I replaced the engine in December, '06, but the prior owner replaced the tranny with an after-market HD part, so I've not delved into that yet. I DO want an exhaust brake (having had a master cylinder failure on one occasion, and a serpentine belt break on another...footnote: It's hard to stop 8T of motorhome with 1. 30% brakes, or 2. No power boost...)