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Pretty self explainatory. Reverse not even engaging. Tore down the tranny and replaced the clutches and reverse piston seals. Still I got nothing. Sunshell looked good. Not cracked or broken. Usually that part goes bad. With the tranny on the ground apply air to the system and the reverse piston engages. Installed I got no reverse. Tranny is a stock 99 model so it is better than the earlier versions. Does anybody know what I missed. I am going to remove the valve body again to make sure nothing is clogged but forward gears are working fine. Really fustrated at this point. $400 dollars in parts and 2 weeks of wrenching and still no reverse.

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What does it do in reverse?

When you rev it up does it act like it is in neutral or does it act like a trans-brake?

 

There are two sets of clutches used in reverse, the low/reverse clutch pack in the back of the case, and the reverse input clutches in the drum just behind the pump. Which seals/clutches did you replace?

 

Do you have engine braking in 1st gear manual?

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In reverse it acts as neutral. 1st gear braking? How to make sure of that. I replaced all the seals and soft pads inside the case. There is also a rubbing sound that is going on. Almost sounds as if it is coming from the oil pump. If I were to guess the vanes inside the oil pump. I am baffled. I have done a couple of these transmissions thru the years as friends needed help and this one has got me stumped...

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Check for 1st gear engine braking by shifting the trans into 1st gear as you are traveling at a reasonable speed in 2nd. Say 15-20 mph downshift to low and you should feel the downshift ,the engine rpm go up, and the car should decelerate. If if just "freewheels" without any engine braking you have a problem in the low reverse clutch.

 

The rubbing sounds could be the sun shell rubbing the case. The sun shell tangs get spread out from being driven by the reverse input drum. IF they are spread out the sun shell needs to be replaced. I ALWAYS replace the sun shell with a "Beast" sun shell on a 700 or 4L60E build. It's a $45 part and well worth the peace of mind. It could also be a torrington bearing.

Does it increase with the engine rpm or with the gear changes?

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Yes it is the same trans that a 95 PU would use, however ALL ranges must have a functioning pump to drive, an auto trans functions off of hydraulic pressure and without it the trans will not engage any gear.

 

You either misunderstood your trans builder or he 1. doesn't know how they operate, or 2. was filling you full of BS.

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It could also be a torrington bearing.

Does it increase with the engine rpm or with the gear changes?

 

I will have to go back thru the manual to find where this torrington bearing is...The sun shell looked good. It had the casting numbers from the replacement version used later by chevy and not the earlier version that split apart at the weld.

 

The sounds starts to dissapate with engine speed increasing. Can still here it but at lower speeds you can really notice it. Not a grinding dry sound but something is not right. I have the same transmission in my Suburban and never heard this before.

 

I am really leaning towards the oil pump but then again drive is working so hesitant to wrench it out of there again. If I do not have 1st gear then it is definitly a sun shell right?

 

 

 

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No,

If you do not have 1st gear engine braking or reverse, you have an issue with the low/reverse clutch pack.

This clutch pack can be totally omitted from the transmission and the feed hole plugged and you would still have 1st gear forward range, you just would not have any engine braking in 1st gear.

I omit this clutch pack on some applications like a Bonneville Salt Flats car where reverse isn't needed or wanted and it lessens parasitic drag at 200+ mph.

The low sprag is the holding element that allows 1st gear.

 

The sun shell, no matter what GM design it is, can spread the tangs out that mate to the revers einput drum. The common failure if the sun shell is the splines stripping on the sun gear. When this happens you have no 2nd gear, 4th gear, or reverse. Some people don't realize they don't have 2nd, the trans will shift from 1st to 3rd at a late rpm with an odd slide-bump shift.

 

If you do take this trans back apart, and I suspect you will be, replace the sun shell with the upgraded aftermarket "Beast sun shell".

 

I suspect you have an issue with one of clutches that holds in reverse, the reverse input or the low/reverse pack.

 

I would suggest getting a pressure guage on the trans to diagnose from this point, but if it is making noise, I would try to pinpoint that first. There are several torrington bearings throughout the trans.

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Thanks for all the replies. I took the car out for another test run today. Doing the engine brake tests I found that I do not have 1st or 4th. Also reverse is not engaging. I am starting to think that the sunshell is the problem. That is if I am ready the above posts correctly. If someone could verify my thoughts or continue to point me in the right direction.

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If the pump is bad, you would have slipping in all ranges.

You COULD have an issue with the reverse boost valve and not have reverse or slipping in reverse.

However that wouldnt have any affect on low or 4th.

 

You need to pinpoint what area of the trans the noise is coming from first. You need to ensure the trans is properly filled with fluid, the TV cable adjustment and geometry are correct, and then diagnose what gears you do and do not have for sure.

 

Then it will probably be getting removed for repair. It might be helpful to hook up a pressure guage and check pressures before you remove it to help diagnose it completely.

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