Reverse issues on 904 transmission
- Thread starter Ryansrt
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transman
Well-Known Member
After sitting for 24 years, you may need more than band adjustments. Try the band adjustments first, but after all that time sitting, the lip seals in the drums could need replacing. When you have in your case, a gear that doesn't work very well until warm, that is usually a sign that the lip seals are hard, and only soften when the oil warms up. As much as I hate to say it, a transmission overhaul could be in the near future.
Save time and money -> DO IT RIGHT - ONCE.
Save time and money -> DO IT RIGHT - ONCE.
Ryansrt
Active Member
Yep that’s what I was assuming. I know I might have a little too much transmission fluid in it too but that wouldn’t hurt it would it? If it needs overhauled then I don’t mind spending the cash on it.
My 67 with 273 904 and 7 1/4 rear does the exact same thing. Sometimes on first start of the day reverse feels like it is slipping. drive is 100%, subsequent reverses are fine. Trans was rebuilt ~20 -30 years ago and sat for 5 of those years, fluid has not been changed since I got it. (I know I know)
I also have the clunk. Not sure, but I attributed it to the diff being OLD (350,000 miles) and loose. grab your drive shaft with the car in neutral. (Wheels chocked and E brake on) and see ho much rotation you have. My guess is that when you park the pinion is still touching the face of the ring gear and when you put it into reverse it freewheels till the teeth make contact with the back side of the ring gear and clunk!
Admittedly I don't know all that much about the nuances of the 904 so maybe it is a trans issue causing the clunk.
I'm sure we both could use a rebuild!
But at least your not alone in clunking and slipping in reverse!
I also have the clunk. Not sure, but I attributed it to the diff being OLD (350,000 miles) and loose. grab your drive shaft with the car in neutral. (Wheels chocked and E brake on) and see ho much rotation you have. My guess is that when you park the pinion is still touching the face of the ring gear and when you put it into reverse it freewheels till the teeth make contact with the back side of the ring gear and clunk!
Admittedly I don't know all that much about the nuances of the 904 so maybe it is a trans issue causing the clunk.
I'm sure we both could use a rebuild!
But at least your not alone in clunking and slipping in reverse!
By the way love the tire sizes and the stance.
Ryansrt
Active Member
Thanks appreciate it I got another view of the car too I’ll post for ya! But Tomorrow I’ll check out the driveshaft to see if it has some play also! I know I changed the pinion seal in the differential and put new fluid in it ( the diff fluid was like Elmer’s glue from sitting) but no harm done to the differential!
What size are your rear tires?
I also like the painless - blackout look. kind of Back to the Future ish!
I also like the painless - blackout look. kind of Back to the Future ish!
Ryansrt
Active Member
I think they are 255/60s can’t remember, everyone said they would rub but I still have almost a inch till the fender and half inch till I hit the leaf springs. But they are almost 9 inches wide. Stripped her down for black paint but now I’m thinking silver looks good hahah so I can’t decide ....
Car looks bad *** the way it is. Clear it!
The torque converter drains back while sitting. Then the front pump doesn't run in park. Soooo, I start my 67 in park, let it run a minute then switch off, shift to neutral and start again. Torque convertor fills while engine warms. This is how I avoid that short delay followed by harsh reverse engage. I will ad this the drain back isn't nearly so bad if I drive the car consecutive days. I suppose some do drain back faster than others.
I don't know the internal workings of a trans or what part prevents/allows torque convertor drain. If I had to guess... One of those little balls in the valve body not seating just right. So long as I know how to make it function for me, I don't worry about.
I don't know the internal workings of a trans or what part prevents/allows torque convertor drain. If I had to guess... One of those little balls in the valve body not seating just right. So long as I know how to make it function for me, I don't worry about.
transman
Well-Known Member
Yes, the pump does run in park. It has to. The torque converter hub(or snout) is engaged to the inner pump gear, and the converter is connected to the engine. So, if the engine is running: the pump has to turn.
A trick I learned about torqueflites is this: Start it in park, but instead of putting in reverse immediately, put it in drive first. This will get the oil flowing throughout the trans. Wait a few seconds, then put into reverse. It worked for me in the past and with a harsh engagement in reverse, you'll bust the lugs on the reverse band eventually. Give it a try, you've got nothing to lose.
I got this tip from a transmission builder who worked in the cold part of the country.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Yer both right
>If the engine is running, the pump is too and its making pressure
>The difference is, in park most of the pressure is dumped by the manual valve and line pressure could be between 5 and 30 psi, depending on rpm,etc
>But in neutral the leak does not exist, so pressure will be whatever you have it adjusted to, usually about 55 psi
>But here's the biggest deal;
when you put it into reverse all line pressure regulation is bypassed and the servo gets whatever the pump is putting out, usually between 230 and 260psi....... and BAM! The hi-drum is supposed to be a shock absorber for that circuit, but if the idle is too high, it can only do so much
> I think from 67 and on there is no longer a drain-back check-ball. Instead we have a TC control valve. It sits up front beside the regulator valve. It has a multi-function.While the engine is running ,it regulates the lube pressure, and connects the TC to the pump...And when not running, the spring in there pushes the valve forward. This does two things simultaneously. It closes the door between the TC and the lube circuit, and it closes the door to the pump, effectively isolating the TC and thus it becomes the anti-drainback.
However; the hi-drum gets it's lube from the TC...... and I suppose , that's where the leakdown can occur, especially as the trans ages
>And to further cloud the issue, I have seen a couple of different L/R servo cushion springs .
> Oh I better mention that as the line pressure rises, so does the TC pressure, so that's a double whammy to the band. The faster the engine is idling, the higher the pressures will rise to. So, the way I see it;
The simplest solution,IMO, is to slow the idle down for the reverse engagement.Or to increase the L/R cushion, or to install a restriction orifice in the circuit; to slow the apply.
As to the clunk in the back;
I'm guessing
about 90% of the time this is caused by the spiders moving back and forth. Maybe 8% of the time, it's tired U-joints, and, the other 2% of the time it will be the spider-pin slamming around in its "wallered out"(thx RRR) saddles. The first is easily fixed by installing additional pinion washers, or additional side-gear washers or some combination depending on what you have laying around,lol.. The later will require specialized equipment to repair, or replacement of the case. The U-joints are a regular maintenance item.
If after adding the extra pinion washers, the rear-end becomes noisy while turning, then all those 4 gears are probably worn out, and in need of replacement; they are either very tired or someone has been peg-legging it.
>If the engine is running, the pump is too and its making pressure
>The difference is, in park most of the pressure is dumped by the manual valve and line pressure could be between 5 and 30 psi, depending on rpm,etc
>But in neutral the leak does not exist, so pressure will be whatever you have it adjusted to, usually about 55 psi
>But here's the biggest deal;
when you put it into reverse all line pressure regulation is bypassed and the servo gets whatever the pump is putting out, usually between 230 and 260psi....... and BAM! The hi-drum is supposed to be a shock absorber for that circuit, but if the idle is too high, it can only do so much
> I think from 67 and on there is no longer a drain-back check-ball. Instead we have a TC control valve. It sits up front beside the regulator valve. It has a multi-function.While the engine is running ,it regulates the lube pressure, and connects the TC to the pump...And when not running, the spring in there pushes the valve forward. This does two things simultaneously. It closes the door between the TC and the lube circuit, and it closes the door to the pump, effectively isolating the TC and thus it becomes the anti-drainback.
However; the hi-drum gets it's lube from the TC...... and I suppose , that's where the leakdown can occur, especially as the trans ages
>And to further cloud the issue, I have seen a couple of different L/R servo cushion springs .
> Oh I better mention that as the line pressure rises, so does the TC pressure, so that's a double whammy to the band. The faster the engine is idling, the higher the pressures will rise to. So, the way I see it;
The simplest solution,IMO, is to slow the idle down for the reverse engagement.Or to increase the L/R cushion, or to install a restriction orifice in the circuit; to slow the apply.
As to the clunk in the back;
I'm guessing
about 90% of the time this is caused by the spiders moving back and forth. Maybe 8% of the time, it's tired U-joints, and, the other 2% of the time it will be the spider-pin slamming around in its "wallered out"(thx RRR) saddles. The first is easily fixed by installing additional pinion washers, or additional side-gear washers or some combination depending on what you have laying around,lol.. The later will require specialized equipment to repair, or replacement of the case. The U-joints are a regular maintenance item.
If after adding the extra pinion washers, the rear-end becomes noisy while turning, then all those 4 gears are probably worn out, and in need of replacement; they are either very tired or someone has been peg-legging it.
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