HWY rpms too high & Line Pressure Readings

Morkai

Morkai the Red
Joined
Nov 24, 2002
I have just over 3000 miles on my rebuilt BRF now (in stock 87GN), I've noticed the highway rpms seem to be too high. It runs about 2800rpm at 70-75mph (3 bars over from 2000 on stock digital tach) Could this be the lockup clutch slipping, the converter is about a 2800 stall.

I took some pressure readings, They aren't what I would like, but are they 'ok'?

1st col: idle tv attached
2nd col: idle tv disconnected
3rd col: 1500rpm tv max

P 115 110 210
R 110 100 175
N 125 120 190
4 100 95 190
3 95 90 185
2 95 90 180
1 85 80 170

+/- 5 psi from fluctuations
 
Well

Pressures are just a little low but ok. As for the tach I would bet money if you got a real tach you would see a difference. The digital ones on the dash can be way off. Borrow a tach or scan tool and go for a ride. See what it actually is. I bet if we took a poll on who's factory digital tach is correct, it would be a land slide that MOST are not even close.

Bruce
WE4
 
Bruce is right on regarding the tach.

Have you tried gently depressing the brake while keeping your other foot on the accelerator at cruise speed? If the lock-up is functioning, you should see the rpms rise slightly as the brake pedal causes the TCC solenoid to shut off.

As for your pressures, did you install a higher rate pressure regulator spring and/or a larger diameter TV boost valve during the rebuild? If not, these items can be easily installed by just removing the transmission pan.
 
pressure

He has the PTS tv boost kit and a TransGo shift kit. I gave him the convertor. The lock up works but when in my car it would shudder when locked and under 8-10 pounds of boost. Hell I had my scan tool on it before and didn't think to check that.
Hear that Eric!:D
 
Yeah, what he said... ;)

It's a 690 7-vane with the .500 pts regulator kit in it. (not the .570) I expected to have slightly better pressures than that. It 'feels' like the converter is working ok, and when disengaging with the pedal it usually lights up another light on the tach. So that leads me to believe the tranny might be slipping, unless the tach is way off, that would make me feel good.

I forgot to mention I also recently starting getting a 2nd gear start when it's cold, usually stopping less than a mile or two from the house in the morning. I also think I might be getting a 2-3 flare under WOT. I don't see why the directs would be slipping, I put alto red clutches in and tightened it up to .040" clearance.

If the direct is slipping wouldn't that affect 4th as well, don't they hold in 4th? I could believe 4th clutches slipping easier than the directs because it's only 2 regular BW clutches, but 4th still slams pretty hard.

I'm gonna pull the pan and change the fluid/filter this weekend, and see what inspection I can do w/o removing the VB.

Today, it seemed I was turning about 2500 rpm at 45mph in 3rd and 2500rpm at 65 in 4th. Stock rearend and tires.
 
Update...

Well, we hooked up the scan tool and it seems the factory tach is about 300rpm high. I think it was reading 2300 or so at 70mph. So I guess that's fine, but I definatelly have developed a 2-3 flair at WOT, low throttle it's fine.
 
Readings

Morkai,

When locked up and going 60mph my rpms are 2000. Ratioing this, you should be ~2500rpm at 75mph. Perhaps within accuracy differences in our tachs. I have a 3800 stall converter.

Here's my tranny test results with line pressure
taken at 2000rpm (mfr data):
min max
Park 100 260
L1 230 230
L2 230 230
Drive 100 270
O/D 100 270

-Brad 87TR
 
those pressures are wrong in r,1 and 2.look again.there is no slip because you are driving in od.bt something is not right with them.the tcc probably is not locking but look at the psi again its off.especially with the bigge boost valves you installed/later holloween party in manhattan hope there is not going to be any surprises good night all.out the door
 
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