Builds boost when put in reverse?!?

[Fred 86 GN]

Really strange...

After driving around for a while and bringing the transmission up to normal operating temperatures, when I put it in reverse to back up, the rpms shoot up to 1500 or more and I hear the turbo start to spool! The ScanMaster shows LV8 values in the 80's It is like the car is power braking in reverse.

If I put the car in park, then into reverse it sometimes backs up normally -- 800rpm or so and normal load values (40 or less) for the engine.

Other than reverse boost thing, the transmission works great.

What could cause this weird behaviour? Could something be hanging up inside the transmission to make it act like a pseudo-transbrake?

 

[WE4]

Sure...

Sounds like the forward clutch is on still. I wonder if someone used a steel piston in an aluminum drum. Does it act funny in park or "N" ? Lazy at all? Rolled sprag is a possibility too. This would cause that. I wonder...



Later on:

You know sitting here thinking , it sounds more like a crossleak in center support from Rev to Forward passages in the od center support.
Any crossleak between Rev feed and Forward feed would give you this symptom. Not to mention, in Reverse, Pressure is boosted so more likely for a leak to occur anywhere in the system, be it at vb or case or center support itself. I would say 2 or 3 out of 10 crossleaked to some extent when new. But if yours is enough to "bleed" then this is definitly a consideration.


Bruce
WE4

 

[quickt]

Steel piston in proper drum. Rolled sprag would cause other problems as well and the trans does not have any of those other problems. Not a cross leak as it Bruces drum and center support and have not seen one leak yet. Fred does it do this with out depressing the pedal or what?

 

[WE4]

Lonnie...

This is one of ours Lonnie? One you put togther? Hrmm....We ck them thoroughly, so I doubt that then. Lonnie call me to discuss this when you can. Man... Odd one....but Forward has to be trying to apply for some reason. Hrmm. A stumper this one is....

 

[Fred 86 GN]

Found one item that just about fixed it!

One of the transmission cooling lines was up against the crossover pipe. I have moved them both away from the pipe and this seems to have cured the problem some of the time. It did build just a little bit at the strip recently. Not nearly as bad though.

Could lots of heat in the tranny fluid make it act this way?

 

[WE4]

Whatever works...

I find it hard to believe but whatever works.

 

[Fred 86 GN]

Still does it...

Well, after driving around more, the boost-building in reverse seems to happen sporatically. Last time it started to do it, I put the transmission into neutral for a few seconds, then back into reverse and it behaved normally.

Weird...

Maybe I'll take it to Lonnie after the season winds down, or if I blow the car up, whichever comes first!