Automatic transmission hesitation

[fairline38]

My 87 SA automatic transmission has an unusual symptom.

When in D (Drive) it will hesitate at low rpms from either start or coasting when making a turn, etc.

However, when accelerating from a stop position with the gearbox in 1st gear, it takes off like a rocket.

Any comments?

[richardw]

From Ashcroft Ttransmissions website - https://www.ashcroft-transmissions.co.u ... faq-s.html:

" I have a 4sp ZF, when I select "D" the vehicle won't move, when I select "1" the vehicle moves off. I can then select "D" and continue to drive normally. If I stop I have to start in first again. Why?

A sprag clutch has "inverted" and will need replacing. No further damage will occur if you continue to drive but you will need to select "1" every time to start moving. A rebuild is required to correct this."

Could this be the problem?

[fairline38]

I do not think this is my issue.

My car will move off in drive normally if I manipulate the accelerator.

It is almost as if when the revs are nil, low or drop while at low speed, the carbs are flooding, but as the car will strom off in first gear, I do not think it is a card problem.

[fueltheburn]

Sounds like a transmission fluid change is required.
If The fluid is old it allows too much slip before the clutches engage. Or you have lost fluid somewhere.

The other tell tale of requiring a fluid change can be the auto box holding onto one gear too long.

Transmission fluid change is by far the cheapest option in the rectification process. If it hasn't already been changed... my money is on that it comes out a disgusting colour.

[fairline38]

The auto box changes very smoothly.

I am pretty sure the transmission oil was recently changed.

[Lotus-e-Clan]

The auto box changes very smoothly.

I am pretty sure the transmission oil was recently changed.

Sounds like you have an air leak in the vacuum tubes (probably @ port 2) to your thermal air bleed valve (TABV) found at the front of the air box (only fitted to SA).


Have a look at the diagnostic table (Item 4) I compiled from the service notes in the following link (best download the PDF).

https://onedrive.live.com/embed?cid=752 ... ling="no">

[Hawaiis0]

My SA has the same sort of issue. Oil change and filter clean done with no effect. Old oil was pristine for the record with no sign of burning or blackening.

The thermal valve diagnostic is my next step.

One thing to listen for is whether your engine revs can be heard to change as the temp reaches operating temp, as this may indicate if the valves are working ok.

How is yours if you try to pull away up a steep incline from a standing start?

[fairline38]

Good news...

I have found the problem and resolved the issue.

It all relates to the engine idle rpm.

The auto transmission requires a steady rpm of at least 900 rpm when in gear. This means that the rpm in neutral needs to be at least 1100 rpm. This sounds high but this appears to be the situation.

I raised the neutral rpm to about 1100 and no more hesitation issues. Also, this has helped steady out the volt meter.

[Hawaiis0]

Good news...

I have found the problem and resolved the issue.

It all relates to the engine idle rpm.

The auto transmission requires a steady rpm of at least 900 rpm when in gear. This means that the rpm in neutral needs to be at least 1100 rpm. This sounds high but this appears to be the situation.

I raised the neutral rpm to about 1100 and no more hesitation issues. Also, this has helped steady out the volt meter.

Can you reference your idea of 1100 rpm in neutral to any document?

[NigelD]

I had to do the same thing but since I am not at home at the moment I cannot remember what I raised it to.

I have a feeling it was more than 1200 but will check when I return home in a couple of weeks.

Strangely mine only seemed to start doing this after I removed the ab14 etc. and replaced it with a pertronix dizzy and omex rev limiter.

Have run it like this for 18 months and all seems ok, so hope the same applies to your situation.

Sad to hear the oil change did not solve your issue Stu.

[fairline38]

More good news on the SA auto hesitation.

Having deduced that part of the problem may be related to the kick down, I found the topic "For all SA owners", which highlighted the issues of specific adjustments to the kick down cable on the auto transmission models. In less than one minute I adjusted the gap on the kick down cable to the required 5 mm spec. The transformation was amazing.

[Hawaiis0]

Interestingly, you have used 5 mm as the figure. This is what I would hope it to be, but my manual reads 0.5mm - which even with my bionic eyes cant read that

[DavidOliver]

I do not know which model of gearbox is fitted in the SA, the Elite/Eclat manual of 1976 refers to adjusting the throttle cable. There are 3 stages,
1. Ensure full throttle is obtained with full pedal.
2. At no throttle the cable needs a gap of 0.5 to 0.75MM between end of outer cable and crimped ferrule.
3. GEARBOX FLUID PRESSURE readings. Idle speed 850-900 rpm pressure needs 50-60 p.s.i.
Additional 500 r.p.m. should produce pressure increase of 15-20 p.s.i.

There is a pressure take off point at the centre rear of maincase (below tailshaft extension).

This may help, or not!

Dave the cog.

[richardw]

I do not know which model of gearbox is fitted in the SA, the Elite/Eclat manual of 1976 refers to adjusting the throttle cable. There are 3 stages,
1. Ensure full throttle is obtained with full pedal.
2. At no throttle the cable needs a gap of 0.5 to 0.75MM between end of outer cable and crimped ferrule.
3. GEARBOX FLUID PRESSURE readings. Idle speed 850-900 rpm pressure needs 50-60 p.s.i.
Additional 500 r.p.m. should produce pressure increase of 15-20 p.s.i.

There is a pressure take off point at the centre rear of maincase (below tailshaft extension).

This may help, or not!

Dave the cog.

The Elite/Eclat uses a Borg Warner type 35 (I think!) 3 speed gearbox and the Excel SA uses a ZF4HP22 4 speed box, so these adjustments don't apply.

ATB Richard

[fairline38]

Having now raised the idle rev to 1200 and adjusted the kick-down linkage to 5mm, she runs beautifully. Thanks for all the responses.