M. Requin

Took my wife out for a spin (her first) in the 928 last night. Heard a high-pitched whistle as we pulled out of the drive, and at the first intersection- no gears!
Limped home, got the Jag (oh, the shame...) and went off to dinner. Research here tells me it was the auto tranny vacuum line coming adrift, so my questions are:

diagnosis sound right?
any tips on fixing?- I'll start under the air cleaner box and work towards the less fun parts;
any chance I DIDN'T fry the tranny (drove about 1.5 miles to get home at <40)?

I'll be working on it tomorrow AM, and I REALLY REALLY REALLY want to make it to SITM- all advice appreciated!

joejoe

I believe if you lost the vacume the shift would be more harsh, but not positive.

Steve Cattaneo

NOT a vacuum problem. What do you mean by no Gears, NO movement in R- D -2-1. When the engine is running do you hear any noise from the transmission. Have you check transmission fluid level.

M. Requin

Sorry, that wasn't precise enough. I should have said it slips in all gears. And accordong to the WSM, one cause is "incorrect vacuum line routing or vacuum line disconnected." As for fluid level, it goes up on blocks tomorrow for a complete look-see, I just wanted to start collecting rennlist knowledge on what appears to be the most likely cause.

So what do you think? The whistle, I thought, was pretty diagnostic of a vacuum line going south. I can use any input you can give- thanks for the reply!

Steve Cattaneo

A disconnected vacuum modulator line on an A28/ 4speed transmission will cause harsh shifts, not slippage. The WSM is wrong on that diagnostic tip, and the only time when “incorrect vacuum line routing” would cause slippage, if vacuum were trapped in the (pinched) line and not respond to throttle opening.



Install a vacuum gauge directly to the modulator vacuum hose, with the engine running there should be a steady reading of manifold vacuum present 14” to 22”HG.

Check for vacuum responses, a quick opening and closing of the throttle should drop the vacuum to below 5’’If not, vacuum leak, plugged line or engine problem.

With the engine off vacuum should drop to “0” if you see a vacuum reading, the line is plugged or pinched = slippage when driving. If all is well…….



Install a pressure gauge and read working pressure. With the vacuum hose removed from the modulator and the car running at idle in drive hot, the pressure should read between 70 and 90 psi. Lower then 70 psi you could have a stuck pressure regulator valve (valve body) or a stuck modulating valve behind the modulator, defective modulator, plugged Trans filter, worn pump.

M. Requin

Steve, many thanks for the detailed procedure. I had a chance this AM to get the car up on stands and you were right, no leak in the vacuum line. But, as you suspected originally, very low on fluid, and signs of leakage all over. When I cleaned off the reservoir to look at the level I loosened the reservoir cap, just to see if it was possible - didn't look like enough clearnace for my fingers - and it came off OK. But when I tightened it back down I felt the threads slip, just as if the threaded neck were broken. Checked it out with a light and mirror, found no problem, scratched my head and took a close look at the cap. Ah-ha! Top of the cap reads, "USE FOMOCO BRAKE FLUID ONLY". Just some more PO pecker tracks. The cap can be tightened down enough to stay in place, but the mismatched threads hardly seal, ergo the ATF all over the place. Cap on the way, will drain and change ATF and filter tomorrow AM, and will also complete your suggested tests before I put it back on the road. Obviously I can't assume everything else is OK after finding this. I'll report any further stuff. Thanks again for your help!

RngTrtl

If memory serves, the cap must do more than "stay on" it must seal very tightly because when you put fluid in the resevoir the tranny is in gear and contain alot of the fluid. When you take it out of gear, the fluid runs back to the resevoir and up against the cap. If it is not sealed properly (i.e. tightly) it will leak profusely. At least that is my experience. Do a seach for filling the tranny. If you just fill the resevoir up with the engine off up to the full line, you will still be way low on fluid.

M. Requin

Yeah, this is exactly why, I think, it was loosing fluid - no seal = big leak. So this afternoon I'll bring the level up to where it should be and test drive it to see. If all is OK, then I just have to wait a few days for the new cap to get here, otherwise, continue the post mortem.