First tow on rebuilt transmission - ISSUES

[mrasmussen]

So, I just had the trans rebuilt for 2k, reputable trans mechanic. Here is what I noticed towing my boat (weighs 5k lbs):

1. I had to FLOOR the throttle quite a few times to MAINTAIN speed on very minimal uphill areas, these are just slight uphill sections
2. Sort of the same deal as number 1, I had to hit 4-5k revolutions MANY times on the motor during towing, to accelerate from a stop etc
3. shifts seem tighter, especially 2nd and 3rd, satisfying shift

The trans place said to come back in two weeks, they like to look at it and they want to make sure the pressures (pressure per gear I think) are correct.

So, is this just a break in thing? Is it the torque converter? Is the trans still crap?

BTW, before the trans blew up, I was able to tow the boat much easier.

NOTE: I did make an adjustment on my trailer, I moved the BOW STOP back (putting less weight on the trailer tongue) by 3 inches. Folks on the boat site I visit recommend moving it further back as this aids in towing because they feel the boat isn't balanced on the trailer as bet it could be. If I new the trans would go before I could test it I wouldn't have made the bow stop move, but now I have to variables. I really don't think its the trailer weight, it was a SLIGHT MOVE that others with my exact same boat have done.

 

[drewactual]

there is a mechanical correlation between speed, and RPM's that is mathematically validated by knowing the overall gear ratio in each gear.

I'm going somewhere with this....

if you know the speed and the gear ratio, you can easily and accurately extrapolate the RPM... any two of those three can provide you with the third.

caveat: something is slipping somewhere, most likely in the transmission.

knowing that.........

what are your RPM's during this event (flooring it to maintain speed on grade)? ... the question is if your transmission is slipping.... and if it is, it needs to be fixed pronto.


the other question (and i don't know to what extent these rigs use it) is torque management the PCM directs to the transmission/engine. So, there is a 'learning curve'... many folks will put the transmission through it's paces to get a good baseline to work with... it goes like this:

0-60 Wide open throttle. stop.
0-60 Moderate throttle WOT to 80. stop.
0-80 Moderate throttle. stop.
0-80 WOT. stop.....

..... this supposedly sets your baseline and gives you a good Torque Management point to start from. But realize the transmission/TM is ALWAYS learning, so...... it will adjust to your use/style of driving.

I'm more interested if you're slipping or not... take it up to 50mph or so, and stand on it- watch the tach... there is this thing called 'flash' or 'flare' stall, which is described as the jump in RPM prior to the torque converter engaging. it's usually about 100RPM- you'll see the needle jump and settle back... this is unavoidable in an automatic transmission and is a function of the torque converter... if it flare's higher than 200~250rpm before settling back in and biting, there is something going on that needs addressing. if it's between 100~150RPM, this is likely your torque management messing with you.

 

[mrasmussen]

and now I am more confused. I drove the trailer back today and it seemed fine. I was under 3k RPM, maintained 70 without an issue.

I'm going to take a look and see if I can determine this RPM flair and see as you said if the RPM flair stays under 200.

I am going to talk to my trans people tomorrow and I'll update the thread.

 

[TXWarthog]

I'm curious. What was the finding?

 

[mrasmussen]

I haven't towed since I had the trans rebuilt. As of now the trans feels solid. The shifts are snappier and i've been getting on it more after the rebuild. Feels great.

I am writing it off as Don't know until the 50 mile "learning" phase is completed.