During full throttle 1-2 shifts it feels like the shift hangs there for .4 of a second and then goes into second gear. this is on a new build for a friend, it was fine for the first 9 runs @ the track and maybe 300 street miles. last time at the track he felt it on the fourth and fith run and it also shows up on the data log. last night was the was the same thing. part throttle shifts are normal. anyone have a suggestion where to look first ? thanks, dave
set up is transgo 1-2 kit,valve body has the 1-2 accumulator valve with one spring(for firmest shift) on the inside.the manual control mod,using the transgo vb plate. the high pressure pump spring, govener is modified to shift @5300. alto reds and kolene steels,6 disc direct,no wave plates. rear thrust roller setup(from your post on nasty z28). no transbrake or manual vb. thats all i can remember right now, if you need more specific info let me know.thanks dave
Were the heavy direct springs from the Transgo kit installed or was there a bleed hole drilled in the direct drum? It may be getting centrifugal apply in low gear of the direct clutches.
yes the heavy springs were installed, also has a 34 element sprag(forgot to mention that). the car is left in drive and shifts @5300 with modified govener. it was perfect the first nine runs(two different days). this is a big block car w/ 550hp&tq,3840weight. he also said it felt like the 2-3 shift got harder since this happened. thanks, dave
I would put a pressure gauge on it to see what may be happening. MY guess at this point is an issue with an accumulator piston or seal.
pulled the pan on saturday and there was a light coat of clutch dust on the bottom of the pan. is this normal for 300miles and 10 runs at the track ? i will be putting a pressure gauge on it wednesday. what should i be looking for? if it is a problem with the accumulator piston or seal will it show up on the pressure gauge? on the data log the rpm just hangs @ shift rpm for .4 of a second. if 2nd gear was slipping would the rpm flare up ? thanks, dave
ok, put a pressure gauge on it and went for a ride. the 1-2 shift hangs for a half second then shifts. doesn't feel like its slipping. pressure readings. w/ vacuum with out/vacuum park 120 170 reverse 180 300 n 120 165 drive 120 145 2nd 160 150 1st 160 160 reverse went up to 350 w/no vacuum stalled against the converter. cruising @55mph light throttle 80psi,when kicked down(3-2)jumps to 120. when kicked down to 1st starts @150 then gradually drops to 120 when it gets to 1-2 shift. when put in manual low has 180 while driving, when manual shifting 1-2 has 180 in both gears,still has the hang up but doesn't feel as long. any opinions or thoughts appreciated, thanks, dave
Odd that the pressure drops in 2nd with no vacuum. I would check the rear servo assembly for cracked piston or damaged seal, and while you have the pan and VB off, check the 1-2 shift valve and valve body/case casting passages.
thanks Jake, i will check that out. my friend was talking to the owner of a local trans shop, and he suggested it could be the sprag slipping.(one important detail i forgot to mention to you, was shiney flecks in the trans pan) his feeling was the flecks could be the sprag race. what are your thoughts ? thanks again, dave
pulled the trans out and the second gear clutches are burnt bad. forward and direct are perfect. hot spots on all the steels and the backing plate. there are small chunks missing from the clutches and they are black. some of the clutches are black toward the inside of the clutch with somewhat ok looking toward the outside.accumulator piston is fine and the sealing rings look good. what would cause the intermediates to burn up like this ? thanks, dave
Pressure leak in the int circuit somewhere, look at the lip seals on the intermediate piston. The 2nd gear circuit is also the outermost circuit around the edge of the VB. If there is a burr on the front edge of the VB, it can cause a severe pressure loss in only second gear. ( I learned this the hard way using a vendor supplied VB).
the only thing i can find is the rear accumulator bore is worn 008. when you put the piston in the bore it doesn't feel like there is much drag. looking at the flow path it doesn't seem like this would be enough to burn the 2nd gear out. what do you think ? thanks, dave
If it is crossleaking from the 1st gear circuit to the 2nd circuit while in low gear it will burn the clutches. I've seen it happen when there is a gouge in that bore. IIRC there is a sleeve kit to fix the bore.
so the intermediates would be partially applied in first gear ? where would i find the sleeve kit ? when the 1-2 shift valve moves is it a gradual movement or does it slam over ? thanks, dave
I looked in my catalog and it's a front servo sleeve, not rear. Put a steel sealing ring on it that will expand to fit tighter.
there was a metal sealing ring(hook type) on it. i think thats what ate the case bore. what about sealing rings from a 4L80e. i think they are teflon or rubber ? thanks, dave
4L80E are rubber but I don't know if they'll take up the oversize. The steel rings do eat the bore. I should have some extra 4L80 stuff. I'll try to remember to look.
its back together. i used teflon rings on the 1-2 accumulator peston and shimed the pump spring with one shim.installed a four disc clutch in the intermediates. the pressures in 1st and 2nd are now 150. were before it started at 150 and dropped to 120 before the 1-2 shift. the pressure does drop to 120 at the 3rd gear shift, is this normal ? what are normal pressures (part throttle and full throttle)on a road test? it feels good, going to the track tommorow to beat on it. hopefully it holds up this time. thanks, dave
The pressure drops in 3rd gear on a stock TH400 due to the modulator system. Sounds good. Pressures are a bit low if that is with the modulator unhooked. I like to see 160-180 with the rpm around 1000 and no vacuum in gear. However, the TH400 will handle around 1000 HP with 160 psi fixed line.
