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SIV pops out of 4th gear under acceleration

C

Chasedan

Donation Time
Hi all,
I've been working on my Series IV (B9400037) transmission. It is the original tranny that came with the car. I currently have the tranny apart and on the bench and am trying to determine the cause of the transmission slipping out of 4th gear and into neutral while under acceleration. I thought that there may be a problem with the linkages and the problem would be apparent when I opened up the tranny on the bench. Nothing jumps out as the obvious problem. Shifting is smooth. The Layshaft Cluster shows a little wear. The roller bearings and race surfaces at the point where the primary shaft and main (output) shaft meet are a little rough. The first gear sprocket has some wear, not bad though. The fourth gear sprocket and syncro look good.
Has anyone encountered this problem before? What did you have to do to resolve it?
Thanks
Chasedan
 
jumpinjan

jumpinjan

Bronze Level Sponsor
Well, they usually don't pop out of 4th. I would check your crankshaft pilot bushing. If worn badly, it will allow the input shaft to wiggle (and throw the clutch plate off center and introduce a lot of vibration). Make sure it good first. Secondly, the detent ball in the 3rd/4th shifter fork and the condition of the fork. Those races shouldn't be rough. What do mean by rough, pitting? You should mic the diameters & needles.
Jan
 
nickraymond

nickraymond

Donation Time
It's not an automatic.

If it was it would have BW on the end of the serial and wouldn't have a fourth gear.

It is possibly the clutch, my Dad had the same problem on his Alpine but jumping out of third in a series V. I think he changed the clutch... (I think that's right) but I remember him being suprised it wasn't the gearbox.

(My main point was that it's not automatic!)
 
C

Chasedan

Donation Time
The shifter fork detent ball was in place, before I took it apart. The shifting operation was smooth and worked well on the bench. I can mic the outer diameter of the output shaft and will get back to you. The inner diameter of the input shaft might be a little more difficult to get. I don't have calipers long enough to reach inside the race. The race surfaces are pitted and scratched up.

I'm not sure what the crankshaft pilot bushing is. Do you mean the throw-out bearing (AKA release bearing as refered to in the manual) or the primary main bearing?

Also when driving the car there did not seem to be any excess vibration coming from the drive train. If I held the shifter lever down in 4th while accelerating or climbing a hill it would easily stay in gear. As soon as I let go of the shifter, it would pop into neutral.

Chasedan
 
C

Chasedan

Donation Time
Hello again,
The secondary shaft end race is 0.75" od. A random sampling of the roller bearings diameter is 0.09375".
thanks

chasedan
 
George Coleman

George Coleman

Gold Level Sponsor
In all my years of Alpine ownership that problem has always been the sycro rings were worn and needed to be replaced, it could be that simple!:cool:
 
C

Chasedan

Donation Time
The measurement of the diameter of the inside race on the primary shaft is 121/128" or 0.9453".
A typical roller measured 12/128" or 0.09375".
The outside diameter of the secondary (output) shaft measured 96/128" or 0.75".
Two roller diameters plus the outside diameter of the secondary (output) shaft is
(12+12+96)/128 " or 120/128". That leaves 1/128" or 0.0078125" of play or slop in the bearing. My question: Is that good or bad?

Thanks
Chasedan
 
M

maceropa

Donation Time
Jan, my SV pops out of 2nd, 4th and reverse under acceleration. The simple weight of my hand is enough to keep it in gear. I have the trans apart and see minor wear on the lay shaft and first gear sycro. Also the main gland nut (that's supposed by torqued to 80 ft lbs) by first gear was finger loose but the staked area was holding it on. The balls and springs seem good as do the forks. I'm not sure if the layshaft wear is enough to cause the poping out or the syncros because it can pop out of reverse as well.

What has been your experience? and the best place to order parts.

Thank Pmac
 
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