tranny trouble

[derbyman78x]

Hi all & happy New Year!
I rebuilt my 727 a year ago and it works fine untell it warms up then drive well go away. It's like you put it in neutral but when you give it a little gas it well hold again . Any of you had this problem?
I put the TCI rebuilt kit in it with shift kit.

[John Kunkel]

Does reverse work OK?
If so, it sounds like a problem with the rear clutch, worn/broken sealing rings or a leaking piston seal that gets worse when the fluid warms up and thins out.

[Jkat]

To John.Kunkel

i have a similar problem with my 904tf, when it heats up or when theirs a lot of weight in the car, it feels like it's in neutral at the lights and when i go it takes a second to grab properly, even when i stall it, my reverse works good. I also have a problem where the tranny doesn't hold second for more than a split second, unless your on wot, where it holds alll the gears well to redline. It's happened since my last valve body reco, but everything seemed ok when we looked recently. Anyway is it a similar problem , because iv'e had it for awhile now even though it's annoying i hope it's not doing any damage.

Thanks for any help

[John Kunkel]

Sounds like rear a clutch problem. The rear clutch is the basic component used in all forward gears. If there are fluid leaks in the circuit that feeds the clutch, the clutch will release at idle when the line pressure is low and reengage when the throttle is opened and the fluid pressure rises.
Removing the valve body and performing an air check (see the service manual) will usually identify this problem.

[Jkat]

Thanks for your knowlegeable reply john.

I've had this problem for a year now since my last reco and no one could give me an answer as to what it could be, but what you expalained makes total sense. Do you think it could also be related to the 2-3 shift valve circuit as it doesn't hold second at all unless at wot. But apart from that it pulls hard under wot with no slip and holds all the gears well, except for takeoff , where theirs a slight jolt as the clutch engages when the cars moving.

P.s. I'm from melb australia and we have problems with braking drive plates and chewing converter bolts and converter necks on our 904's behind our hemi 265's , do you have similar problems with the 904 318's or slants, and what do you guys do to remedy them, apart from aligning trans and engine. Which i think solves most of the problems but the standard driveplates still fail.

[derbyman78x]

well mine holds first & second but lose's it in drive.
All seals rings bands are new still slips or gos to neutral
but ouly when you try to hold a stady speed.

[John Kunkel]

There's a difference in terminology, "drive" to me is forward while to derbyman it means third or high gear.
Now that that's out of the way, slippage or loss of third gear is a front clutch fault. Either the rubber seals or sealing rings are failing to hold pressure when the fluid warms up and thins out. It could also be caused by a failed front pump-to-case gasket. This can be confirmed by pulling the valve body and performing an air check per the service manual.

Jkat's problems may all be the result of fluid leakage in the rear clutch circuit, leakage anywhere in the system tends to affect the whole system. The fluid pressure and volume are higher at WOT and the system can better tolerate the leakage.

Flex plate breakage can sometimes be prevented by putting more "flex" in the flexplate. If the flexplate is the type that has a triangular opening by each converter bolt hole, cutting clear through one of the "spokes" at each opening with a hacksaw will allow the plate to flex more and still have sufficient strength to do the job. This is an often recommended procedure but I've never tried it myself.

[Jkat]

John.K if i remove the valve body can i seel off the outlet ports some how and pump air pressure in to see if there is a leak or should i do it while it'still in the car from the pan. That's an interesting idea about the flex plate never heard of it, and yes it's the type with two spokes per bolt, iv'e been thinking about flexplates for a while, whether more or less flex is better, wouldn't a weeker more giving flex plate alow the converter to move wherever it wants and then begin to wobble, where as if everything is perfectly alligned a stiffer driveplate would be harder to break and wouldn't need to flex. One thing that just came to mind is that when the converter is bolted to the crank should the converter bush push all the way in and sit up tight against the crank or should it be loose, as if it's loose it's move in and out and slowly cause damage , i think? maybe thats my problem.

[derbyman78x]

thanks john I well try that

[John Kunkel]

Jkat,
Once the valve body is removed you will see a series of holes in the main case through which fluid flows from the valve body to the case. You'll need a service manual (or website) to identify the clutch feed port.
By using a rubber tipped air blow gun, you pressurize these ports and listen for escaping air to determine the amount of leakage. This is the air check I spoke of.
The hub at the front of the converter should be a snug fit in the pilot register at the crank flange. This way the converter held centered on the crank and the flex plate only has to deal with the slight "wobble" caused by minor misalignment.

[Jkat]

When i pull the valvebody i'll perform that test to the rear clutch feed port on the trans case, and hopefully i can hear how much leakage their is , i could imagine it being not totally sealed, but as to how much of a leak is bad, well have to see. Do you also perform a test to the valbody body part of the rear clutch circuit.

Thanks from me too John.k , you have given some very interesting and knowledgeable answers.