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  #1  
Old November 29th, 2017, 17:22
BALTANAKT BALTANAKT is offline
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High Transmission Pressure & Crank Walk | Should I Replace Tranny?

Hi All,

I bought a really nice Cherokee last fall after searching for 2 years. Ran great, interior was amazing. 124K. Then my engine developed crank walk.

After investigating it, I am going to swap in a replacement 4.0, but before I do that, I want to figure out what caused the crank walk.

So, I took the XJ to the shop today to have the the transmission cooler line pressure checked.

The pressures were high. The tech adjusted them down as far as he could, but the FORWARD pressure is still more than the max spec.

Should I be worried about this tranny destroying another engine? Is there anything else I can do?

Note: I have already ordered a new torque converter in case that had been balooning and making things even worse.

Results below:

FORWARD PRESSURE
BEFORE: 270
SPEC: 161-196
Discrepancy: 74 Over Max
AFTER ADJUSTMENT: 210 (14 Over Max)

REVERSE PRESSURE
BEFORE: 320
SPEC: 223-273
Discrepancy: 47 Over Max
AFTER ADJUSTMENT: 270

Thanks in advance.
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  #2  
Old November 29th, 2017, 18:04
RCP Phx RCP Phx is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

There no correlation what-so-ever. The crank end play is set by the thrust bearing and the torque converter is on a slip spline.
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  #3  
Old November 29th, 2017, 19:33
BALTANAKT BALTANAKT is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

Makes sense.

Would this then not apply?

Quote:
...excess pump pressure can cause the converter to act like a hydraulic ram, continuously jamming the crank forward.
https://www.motor.com/magazine-summa...tion-analysis/
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  #4  
Old December 1st, 2017, 14:51
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Ecomike Ecomike is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

Interesting question. I had a Dodge V-8, 1978 that ate 6 TCs in 8 years, they got very frequent towards the end, then one day the engine made all kinds of racket. It had 1/4" of play in the crank "walk" as you called it. The thrust bearings were long gone. With 1/4" of thrust play it would not sie, LOL. About 450,000 miles on that beast.

After the engine was rebuilt, it killed another TC a year later. The only part they reused was the shirt block!!!! Everthing else was new, except the Crank was used and prepped from a rebuild shop....

I should have replaced the TC when I had the engine rebuilt, but never got to test that theory. To this day I am not sure which was causing the problem, the thrust bearing being bad and tearing up the TCs or the the other way around, or ??? I sold it a year after the rebuild....

I will be following this thread closely!!
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Old December 2nd, 2017, 09:27
trippled trippled is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

Quote:
Originally Posted by RCP Phx View Post
There no correlation what-so-ever. The crank end play is set by the thrust bearing and the torque converter is on a slip spline.
Not exactly. If the ballooning is enough, the TC can basically bottom against the front pump and exert significant pressure on the crank.
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Old December 2nd, 2017, 10:45
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Ecomike Ecomike is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

I have a related question, what all would cause the high pressure, and would it not cause a seal leak at some point?
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
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Old December 2nd, 2017, 11:03
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

Quote:
Originally Posted by trippled View Post
Not exactly. If the ballooning is enough, the TC can basically bottom against the front pump and exert significant pressure on the crank.
Isn't there about 1/4 to 1/8" of room on the spline, slop, before that happens on the 4.0-AW4 combo? I recall reading stories here where the TC was installed, not quite all the way on, or something???
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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Old December 2nd, 2017, 11:07
lawsoncl lawsoncl is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

Quote:
Originally Posted by Ecomike View Post
Isn't there about 1/4 to 1/8" of room on the spline, slop, before that happens on the 4.0-AW4 combo? I recall reading stories here where the TC was installed, not quite all the way on, or something???

When unbolting the TC from the flexplate, you can push the TC about 1/4" towards the tranny. OR vocee versa when bolting things up, you might have to slide the tc forward to get the bolts in.
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Old December 2nd, 2017, 18:07
BALTANAKT BALTANAKT is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

At this point I will keep the tranny in.

I am changing the engine, flex-plate & torque converter.

Still concerned the tranny may be the cause. Also unsure what is causing the tranny pressure to be so high. Maybe I will change the tranny filter, radiator & cooler lines in case they are clogged up.
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Old December 2nd, 2017, 18:14
lawsoncl lawsoncl is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

Quote:
Originally Posted by BALTANAKT View Post
At this point I will keep the tranny in.

I am changing the engine, flex-plate & torque converter.

Still concerned the tranny may be the cause. Also unsure what is causing the tranny pressure to be so high. Maybe I will change the tranny filter, radiator & cooler lines in case they are clogged up.

I didn't realize there was an adjustment for the pressure, unless the tech is just adjusting the cable to the throttlebody which affects the pressure (and hence shift firmness).
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Old December 2nd, 2017, 18:46
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Ecomike Ecomike is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

The peak(?) pressure is controlled by a kick down cable attached to the throttle body. It has an auto adjusting BUTTON on it you use to adjust it...

This is for the 91-01,Renix is reversed on the sides....

https://www.youtube.com/watch?v=gRBR43fhpA4

You should make sure that is adjusted after you swap everything, then test the pressure again I would think.

Quote:
Originally Posted by BALTANAKT View Post
At this point I will keep the tranny in.

I am changing the engine, flex-plate & torque converter.

Still concerned the tranny may be the cause. Also unsure what is causing the tranny pressure to be so high. Maybe I will change the tranny filter, radiator & cooler lines in case they are clogged up.
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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  #12  
Old December 2nd, 2017, 20:06
lawsoncl lawsoncl is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

Quote:
Originally Posted by lawsoncl View Post
I didn't realize there was an adjustment for the pressure, unless the tech is just adjusting the cable to the throttlebody which affects the pressure (and hence shift firmness).

I got curious and skimmed through the AW4 section in the 97 FSM. There is no pressure adjustment inside the transmission.

The FSM says:
61–to–70 psi in drive at idle
173–to–209 psi in drive at wide-open-throttle
75–to–90 psi in reverse
213–to–263 psi in reverse at wide open throttle

"If line pressure is not within specifications, adjust transmission throttle cable and repeat pressure test."
"If pressures in D and Reverse are higher than specified in test, check for the following:
• throttle cable loose, worn, binding or out of adjustment
• throttle valve, downshift plug, throttle cam, or primary regulator valve are sticking, worn or damaged"

If it's shifting fine, I doubt you have a transmission problem. If you had a pressure regulator problem, the idle pressures (which you didn't post) would be really high as well. I think the tech just corrected what was an overly tight throttle cable adjustment and your shifting might feel mushy or slower now.
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Old December 2nd, 2017, 20:09
lawsoncl lawsoncl is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

Quote:
Originally Posted by BALTANAKT View Post
Hi All,
Note: I have already ordered a new torque converter in case that had been balooning and making things even worse.
If the t/c is still intact and doesn't look deformed, I doubt it was "ballooning". It would have to expand a lot, and would probably take out the pump in the front of the trans first.
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Old December 3rd, 2017, 17:06
BALTANAKT BALTANAKT is offline
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

Quote:
Originally Posted by lawsoncl View Post
If the t/c is still intact and doesn't look deformed, I doubt it was "ballooning". It would have to expand a lot, and would probably take out the pump in the front of the trans first.
Maybe. There's just no obvious explanation why the engine developed crank walk, so I don't really have any choice but to replace everything that could be the culprit.
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Old December 3rd, 2017, 18:38
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Re: High Transmission Pressure & Crank Walk | Should I Replace Tranny?

FWIW, the AW4 tranny is pretty much an indestructible beast.

What tranny fluid was in it and what the fluid temp when he tested it?

Was his pressure calibrated???? I doubt it was!!!!!

How was the test run, with a bad engine crank attached to it?

Quote:
Originally Posted by BALTANAKT View Post
At this point I will keep the tranny in.

I am changing the engine, flex-plate & torque converter.

Still concerned the tranny may be the cause. Also unsure what is causing the tranny pressure to be so high. Maybe I will change the tranny filter, radiator & cooler lines in case they are clogged up.
__________________
Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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