gjjcvette

My 78 L48 shifts hard from Park to Reverse and to Drive as well. Like it kicks in with a slam. This happens equally when cold as well as when fully warmed up. My idle in Park is around 900-1000 RPM and this happens even on any flat surface. Sounds quite embarrassing. I am afraid I might be damaging something. The transmission and differentials where fixed and this has always been like this since I bought the car about 18 months ago. I already changed the transmission and motor mounts as well as the from differential "snubber" support-bushings (that long 2 bushing bolt at the front of the differential. Also, the 2 wheel axles have been changed and the drive shaft u joints are good. Any ideas on what the issue might be? Took the car to 3 shops and they really don't know. Some say the diff, others the transmission, others the mounts (which have al been changed). Thanks in advance.

REELAV8R

Probably need a rear differential snubber replaced.


https://www.ecklerscorvette.com/1963...gaAtrcEALw_wcB

Peterbuilt

resdoggie

Is there a modulator(?) valve on that transmission? I had a Powerglide tranny long ago that clunked going into gear because that valve was faulty.

interpon

Trailing arm bushings will do that…
https://www.corvetteforum.com/forums...nd-advice.html

Fly skids up!

900-1000 idle speed? That's way too high bro. 600 is a good speed for a stocker.

interpon

What is cold and hot idle rpm? Are you using tachometer or tach timing light?
what is cold / hot in park and drive rpm?
assume at cold higher idle it is worse than hot assumed lower idle?
Did you double check fluid level? Last time chaged?
Are engine mounts tight?
someone videoing the engine movement and drivetrain when gear selection may help diagnose.

70s

^^^^^ This. Way too high of an idle speed so of course it will slam when shifting from idle to a driving gear. Fix that first.

interpon

Op states hot or cold same?
assume even on high cold idle (12-1500?) going into gear should not be as traumatic as described, let alone 900 rpm stated..i think it is another issue.

doorgunner

Is it possible someone installed a "shift kit" in thr transmission which would cause the shifts to be harder?
IF you remove the transmission pan take a couple pics of any residue that may have settled in th bottom of the pan. This will help members advise you.

Lakeside49

The snubber bushing fixed mine. It is a well known maintenance part requirement. If yours is anywhere near to being original it is toast and needs to be replaced. Every C3 parts supplier partner sells then. I got mine from Willcox. But, whatever you do, do NOT install a polyurethane snubber. Ensure that this uniquely located/designed part is rubber as noted by several C3 brethren here at the forum - and, not to mention the prominent "Warning" label to this effect that Willcox Corvette includes with the snubber replacement instructions at their website. A poly snubber will risk serious breakage of driveline affixment structures due to their less-yielding material design.

Good luck -

Dave