sstrickstein

So I've adjusted the slack on my 84 928s Bowden cable and still my car is shifting to early and harsh. Manual shift works fine and no slip. What next? I can hear the kick down solenoid when I press the switch. I would be glad to hear suggestions. If a vacuum problem is present where do I look for the connection to the motor?

Landseer

Vac for trans originates at front center of spider. Look for a hex banjo bolt with a hardline coming off it.

That hard line runs across bell housing and switches to a hose, then back to hardline IIRC along top of torque tube, then goes rubber again to attach to modulator valve on left side of trans.

Raise car, put vac gauge of rubber line near modulator valve and check engine vac. IIRC you look for 20 inches or so of vac. If not, check closer to, or at, spider. If you find there is a break in line, repair or run a parallel replacement. Getting to the line connections to the hardline at top of TT can be a problem.


Take bright light and shine on mod valve rubber end cap ( or remove to inspect ). It is sometimes cracked.

When Bowden is correctly adjusted, and trans upsifts fast and hard, earlier shifting when under harder acceleration, fixing a vac deficiency has solved it for me. But I'm not an expert in these things, just giving you empirically what I've seen and done.

My 85, same trans, but takes vac source from 7 line vac junction, is upshifting fast on heavy accel, I think due to vac leaks where HVAC diaphragms are now all shot. Heavy accel means less vac to the auxiliary system. Like my old GMC with vac wipers, had to feather the gas to get wiping action.

Randy V

You can also adjust the shift modulator located on the side of the transmission.

dr bob

First to second shifts almost always seem to happen before redline even at full throttle, so the trans can change gears completely without tasking the rev limiter.

You can adjust the TV cable to keep A/T control pressure lower longer, therefore delaying upshifts some. The kickdown solenoid bleeds additional control pressure to do the same thing. Control pressure is also adjustable separately, but you --really-- want to do this with gauges attached. Make everything match stock pressure specs to start with, then only adjust as needed. Most folks start tweaking their trans pressures to compensate for some simple wear issues, and end up doing more damage than good. Mask one problem with a change, unmask a few others.

SMTCapeCod

So what would the simple wear issues and mitigation measures be, to avoid masking with coarse adjustments?

I've noted Gregg's comments on band adjustment- whats the process?

Jchiodi

I am having issue with harsh shifts at low throttle, 1-2. When I put mighty vac on line from engine, I get up to about 15-20psi, and it takes about 2-3 seconds to go to 0.

My problem is that on my car, I don't think I can get access to modulator at transmission. There is a heat shield right in the way. My exhaust is welded from headers on back. Have to drop the whole thing to gain access.

I would like to replace line, and adjust modulator pressure per instructions I've seen, but not sure how that would work without an exhaust connected?

jc

davek9

Did you (and how is) the Bowden cable adjusted, always do the mechanical adjustments first.

Dave

Tails

Carry out adjustment to bowden cable, cruise control and throttle as per WSM specifications.

If hash shifts continue then the Vacuum Modulator Valve requires adjustment. This can be done by a competent DIYer by placing the car on jack stands, get a small pressure/vacuum gauge and a nipple to fit the modulator valve test port as shown in WSM.

Remove the rubber cover off the modulating valve and pull out the small "T" adjustment key.
Remove the vacuum line from the modulating valve, start car and bring gear box and engine up to operating temperature, put gear box in drive and adjust modulating valve to specifications for the model gear box fitted to car (Refer to WSM). The RPMs can be adjusted to meet the low speed requirements as shown in WSM.

When pressure is correct button up modulating valve, remove pressure gauge and nipple and replace set bolt, reconnect the vacuum line and take the car for a drive and note the difference. I did this to my car and the gear changes are very smooth.

If the brake bands are worn, they can be adjusted by fitting a longer adjusting pin as described in the WSM. This is a more invasive procedure, however it is fully described in the WSM for the MY car.

Jchiodi

Bowden cable and throttle cable have been adjusted, cruise control not working. I've read the above procedure, just not sure how to do it given the limited amount of room, with exhaust in place?

Tails

It looks as though you may have to remove the exhaust pipe and then the heat shield to get initial access and the you may need to reinstall the exhaust pipe while you carry out adjustments as described in post 8.

WYAIT it would be a wise move to reset your starter Isolating Switch as described in the WSM to synchronise you auto gear change with you Auto Box Lever.

After you have finished you adjustments reinstate the heat shield.

The exhaust on my 90S4 has numerous joining flanges and no cats, which makes the removal of exhaust sections quite easy.